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Reactivity of [ReOX3(AsPh3)2] (X=Cl, Br) complexes towards gaseous nitric oxide.
Polyhedron 21 (2002) 2617 /2629 www.elsevier.com/locate/poly
Reactivity of [ReOX3(AsPh3)2] (X Cl, Br) complexes towards gaseous nitric oxide. Crystal, molecular and electronic structure of [ReBr3(NO)(OAsPh3)2], [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2], [ReCl4(OAsPh3)2] and [ReBr3(NO)(AsPh3)2] /
B. Machura a, J.O. Dzie˛gielewski a,*, S. Michalik a, T.J. Bartczak b,*, R. Kruszynski b, J. Kusz c a
Department of Inorganic and Radiation Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland b X-Ray Crystallography Laboratory, Institute of General and Ecological Chemistry, Technical University of Lo´dz´, ˙ eromski St., 90-924 Lo´dz´, Poland 116 Z c Institute of Physics, University of Silesia, 4th Uniwersytecka St., 40-006 Katowice, Poland Received 4 July 2002; accepted 2 September 2002
Abstract The reactions of the complexes [ReOX3(AsPh3)2] (X/Cl, Br) with gaseous nitric oxide and the reactions of the compounds [NBu4]2[ReX5(NO)] (X/Cl, Br) with an excess of triphenylarsine have been examined. [ReOBr3(AsPh3)2] reacts with nitric oxide to give mer ,cis -[ReBr3(NO)(OAsPh3)2] (1), whereas the reaction of the chlorine oxocomplex with NO leads to three products: [ReCl3(NO)(OAsPh3)2] (2), mer ,trans -[ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2] (3) and cis -[ReCl4(OAsPh3)2] (4). The compounds [NBu4]2[ReX5(NO)] (X /Cl, Br) react with an excess of AsPh3 to give 3 and mer ,trans -[ReBr3(NO)(AsPh3)2] (5), respectively. The complexes obtained in these reactions have been characterised by IR, UV /Vis and magnetical measurements. Crystal and molecular structures have been determined for complexes 1 and 3 /5. EPR spectra have been recorded for compounds 1 and 5. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Rhenium; Nitrosyl; X-ray structures; Electronic structures; Nitric oxide
1. Introduction Nitric oxide is known to play key roles in human cardiovascular and nervous systems and in immune response to pathogen invasion. These discoveries have stimulated much interest in nitrosyl complexes of transition metals */compounds that could deliver NO
* Corresponding authors. Tel.: /48-32-258-2441; fax: /48-32-2599978 E-mail addresses: [email protected] (J.O. Dzie˛gielewski), [email protected] (T.J. Bartczak).
to biological targets upon demand either by thermal reactions or by photochemical excitation [1 /4]. The chemistry of nitrosyl rhenium complexes arouses particular interest among these compounds, as the favourable nuclear properties of 186Re and 188Re nuclides make the radioisotopes useful for diagnostic nuclear medicine and applications in radioimmunotheraphy [5,6]. In our previous papers we reported on the structural and spectroscopic characterisation of the nitrosyl rhenium complexes obtained in the reactions between the complexes [ReOX3(PPh3)2] (X /Cl, Br) and gaseous nitric oxide [7 /16].
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 2 5 4 - 8
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Now we are extending our studies to the reactivity of the compounds [ReOX3(AsPh3)2] (X /Cl, Br) towards NO and here we present our results of the synthesis, spectroscopic and structural characterisation of the following complexes: [ReBr3(NO)(OAsPh3)2] (1), [ReCl3(NO)(OAsPh3)2] (2), [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2] (3) and [ReCl4(OAsPh3)2] (4). We have also carried out the reactions of [NBu4]2[ReX5(NO)] (X /Cl, Br) with an excess of triphenylarsine, which lead to [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2] (3) and [ReBr3(NO)(AsPh3)2] (5), respectively. Considering that AsPh3 and OAsPh3 molecules are replaced more readily than P- and N-donor ligands, these complexes are predicted to be very useful starting material in the synthesis of new rhenium nitrosyls [17 / 22].
2. Experimental Triphenylarsine and NH4ReO4 were purchased from Aldrich Chemical Co. and used without further purification. The [ReOX3(AsPh3)2] and [NBu4]2[ReX5(NO)] (X /Cl, Br) complexes were synthesised according to the literature methods [23,24]. Gaseous NO, obtained in the reaction: 2NaNO2 3H2 SO4 2FeSO4 0 2NO/ /2NaHSO Fe (SO ) 2H O; was purified by passing 4 2 4 3 2 through washers with concentrated KOH solution and over solid NaOH. Solvents were dried and deoxygenated prior to use in the usual way. The reaction, all preparations and the recrystallisation were performed under argon atmosphere. 2.1. Synthesis of 1 NO was passed through a vigorously stirred and refluxing solution of [ReOBr3(AsPh3)2] (1.05 g, 1 mmol) in CH2Cl2, tetrahydrofurane or C6H6 (40 cm3). The reaction was carried out for 4 /5 h. The colour changed gradually from bright green to dark green. Then the resulting solution was evaporated to the volume of 10 cm3. The green precipitate was formed by an addition of 40 cm3 of EtOH and after 15 min it was filtered off. The product was washed with cold ether and dried in vacuo. The yield of 1 does not depend on sort of solution and it equals to 0.88 g (0.80 mmol). Anal . Calc. for C36H30As2Br3O3NRe (1): C, 39.29; H, 2.75; N, 1.27. Found: C, 39.24; H, 2.72; N, 1.29%.
recrystallisation. At room temperature complex 3 does not dissolve in MeCN but 2 and 4 compounds dissolve in CH3CN readily and 4 precipitates from the solution first. Compound 3 was recrystallised from CH2Cl2. The yield of 2, 3 and 4 depends on the kind of the reaction solution; in CH2Cl2 and tetrahydrofurane */2 (75%), 3 and 4 (3%); in C6H6 */2 (70%), 3 and 4 (5%). Anal . Calc. for C36H30As2Cl3O3NRe (2): C, 44.71; H, 3.13; N, 1.45. Found: C, 44.64; H, 3.16; N, 1.41%. Calc. for C72H60As4Cl7ONRe2 (3): C, 46.11; H, 3.22; N, 0.75. Found: C, 46.24; H, 3.25; N, 0.87%. Calc. for C36H30As2Cl4O2Re (4): C, 44.46; H, 3.11. Found: C, 44.57; H, 3.15%. 2.3. Synthesis of 3 A mixture of [NBu4]2[Re(NO)Cl5] (1 g, 1.14 mmol) and AsPh3 (5 g, 0.016 mol) in EtOH (30 cm3) was refluxed for 6 h. The formed dark red precipitate was filtered and washed with ether. Yield: 65%. 2.4. Synthesis of 5 A mixture of [NBu4]2[Re(NO)Br5] (1 g, 0.91 mmol) and AsPh3 (5 g, 0.016 mol) in EtOH (30 cm3) was refluxed for 6 h. The formed dark red precipitate was filtered and washed with ether. Yield: 70%. Anal . Calc. for C36H30As2Br3ONRe (5): C, 40.47; H, 2.83; N, 1.31. Found: C, 40.41; H, 2.87; N, 1.34%. 2.5. Physical measurements Infrared spectra were recorded on a Nicolet Magna 560 spectrophotometer in the spectral range 4000 /400 cm 1 with the samples in the form of potassium bromide pellets. Electronic spectra were measured on a Beckman 5240 spectrophotometer in the range 800/220 nm in deoxygenated CH2Cl2 solution. EPR spectra in the X-band (n :/9.5 GHz) at T /295 K have been recorded for CH2Cl2 solutions of complexes 1 and 5 and for 5 in the solid state, using a Bruker EMX spectrometer. About 10 3 M solutions of 1 and 5 in CH2Cl2 were used. Magnetic susceptibilities were measured at 296 K by the Faraday method. Elemental analyses (C H N) were performed on a Perkin/Elmer CHN-2400 analyzer. 2.6. Crystal structure determination and refinement
2.2. Synthesis of 2, 3 and 4 The reaction of gaseous NO with [ReOCl3(AsPh3)2] (0.92 g, 1 mmol) in a CH2Cl2, tetrahydrofurane or C6H6 solution (40 cm3) was carried out in the same manner as for 1, but a mixture of the three products was isolated and the complexes 2, 3 and 4 were separated by
The crystals of 1, 3 /5 suitable for X-ray structure determination were obtained by slow evaporation from MeCN solutions. The X-ray intensity data were collected on a Kuma KM-4 diffractometer (compounds 3 and 5) with v /2u scan mode and on a KM-4-CCD automatic diffractometer equipped with CCD detector
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Table 1 Crystal data and structure refinement for 1, 3, 4 and 5
Empirical formula Formula weight Temperature (K) Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) Volume (A Z Dcalc (Mg m 3) Absolute coefficient (mm 1) F (000) Crystal dimensions (mm) u Range for data collection (8) Index ranges
Reflections collected Independent reflections Data/restraints/ parameters Goodness-of-fit on F2 Final R indices [I 2s (I )] R indices (all data) Largest difference peak ˚ 3) and hole (e A
1
3
4
5
C36H30As2Br3O3NRe 1100.38 293(2) monoclinic P 21/n
C36H30As2Cl3.33O0.67N0.67Re 936.81 293(2) triclinic ¯/ /P1
C36H30As2Cl4O2Re 972.44 293(2) monoclinic C 2/c
C36H30As2Br3ONRe 1068.38 293(2) monoclinic C 2/c
10.2800(3) 20.8840(8) 17.3947(6) 90 93.559(3) 90 3727.2(2) 4 1.961 8.273 2092 0.25 0.09 0.09 3.15 /25.05
12.077(3) 14.143(3) 16.605(3) 65.56(2) 83.34(2) 87.88(2) 2564.5(10) 3 1.820 5.763 1361 0.11 0.32 0.45 1.36 /25.05
14.077(3) 13.271(3) 19.376(4) 90 95.00(3) 90 3606.0(13) 4 1.791 5.519 1884 0.17 0.11 0.04 3.44 /28.83
25.044(5) 9.664(5) 16.225(8) 90 116.77(5) 90 3506(3) 4 2.024 8.788 2028 0.08 0.20 0.20 1.82 /25.05
12 5 h 5 12, 05 k 5 24, 20 5 l 5 0 6587 6587 (Rint 0.00) 6587/0/445
145 h 5 14, 05 k 5 15, 185 l 5 18 8833 8535 (Rint 0.0207) 8535/1/593
195 h 5 19, 05 k 5 17, 05 l 5 25 4435 4435 (Rint 0.00) 4435/0/205
185 h 5 29, 25 k 5 11, 185 l 5 19 3906 3059 (Rint 0.0394) 3059/0/202
1.061 R1 0.0348 wR2 0.0874 R1 0.0464 wR2 0.0946 0.841 and 0.936
1.152 R1 0.0512 wR2 0.1081 R1 0.0750 wR2 0.1200 2.109 and 1.448
1.148 R1 0.0684 wR2 0.1064 R1 0.0883 wR2 0.1152 2.017 and 1.567
1.134 R1 0.0416 wR2 0.0948 R1 0.0619 wR2 0.1085 1.328 and 0.870
(compounds 1 and 4), with v scan mode, 30 s exposure time was used and a half of the Ewald sphere was collected. The unit cell parameters were determined from least-squares refinement of the setting angles from a number of the strongest reflections. Details concerning crystal data and refinement are given in Table 1. Lorentz, polarization, empirical absorption corrections (compounds 3 and 5) and numerical absorption corrections [25] (compounds 1 and 4) were applied. The structures were solved by means of the Patterson and direct methods and subsequently completed by difference Fourier recycling. All the non-hydrogen atoms were refined anisotropically using full-matrix, leastsquares technique. The hydrogen atoms of the phenyl rings were treated as ‘riding’ on their parent carbon ˚ ] and assigned isotropic tematoms [d (C /H) /0.96 A perature factors equal to 1.2 times the value of the equivalent temperature factor of the parent carbon atom. SHELXS-97 [26a], SHELXL-97 [26b] and SHELXTL [27] programs were used for all the calculations. Atomic
scattering factors were those incorporated in the computer programs.
3. Results and discussion It is known that reactions of high oxidation state metal halides with gaseous nitric oxide usually lead to low-valent nitrosyl complexes and it is accompanied with the elimination of nitrosyl halides [28,29]. The reaction of [ReOCl3(AsPh3)2] with NO leads to the complex 2 (the main product) and two by-products (3 and 4), whereas only one compound (complex 1) was isolated in the reaction of the bromine oxocomplex with nitric oxide. The difference in the course of the reactions [ReOX3(AsPh3)2] (X /Cl, Br) with NO depending on the kind of halogen in the starting oxocomplex can be explained considering that NOX are relatively unstable
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gaseous compounds under normal conditions and that NOBr is much less stable than NOCl. The suggested course of the main (2) and minor (3 and 4) product formation is given in the following scheme: [ReOCl3 (AsPh3 )2 ]3NO 0[ReCl3 (NO)(OAsPh3 )2 ] N2 O
(1)
[ReOCl3 (AsPh3 )2 ]4NO 0[ReCl2 (NO)2 (AsPh3 )2 ] NOClNO2
(2) (3)
2[ReOCl3 (AsPh3 )2 ]NOCl 0[ReCl3 (NO)(AsPh3 )2 ] [ReCl4 (AsPh3 )2 ]O2
[NBu4 ]2 [ReBr5 (NO)]2AsPh3 0[ReBr3 (NO)(AsPh3 )2 ] 2[NBu4 ]Br whereas the reaction of [NBu4]2[ReCl5(NO)] with triphenylarsine goes as follows:
[ReCl2 (NO)2 (AsPh3 )2 ]2NOCl 0[ReCl4 (OAsPh3 )2 ] 2N2 O
As in the reaction of [ReOBr3(AsPh3)2] with NO only one product has been isolated */[ReBr3(NO)(OAsPh3)2] (1)*/it can be assumed that the unstable NOBr is not formed and the reactions similar to Eqs. (2) /(4) do not occur. The reaction equation explains the formation of complex 5:
(4)
The [ReCl2(NO)2(AsPh3)2] compound has not been isolated, but the analogous dinitrosyl [ReCl2(NO)2(PPh3)2], obtained in the reaction of [ReOCl3(PPh3)2] with nitric oxide, has been characterised [7]. The proposed above mechanism of the reaction of [ReOCl3(AsPh3)2] with NO can be confirmed by the higher yields of by-products in benzene solution than in CH2Cl2 or THF. Due to the formation of the ClNO ×/C6H6 complex, the concentration of nitrosyl chloride in benzene is much higher than in dichloromethane or tetrahydrofurane, where ClNO ×/CH2Cl2 and ClNO ×/THF are not formed [30,31].
2[NBu4 ]2 [ReCl5 (NO)]4AsPh3 0[ReCl3 (NO)(AsPh3 )2 ] [ReCl4 (AsPh3 )2 ]NOCl2[NBu4 ]Cl The yield of the product in the reactions of [NBu4]2[ReX5(NO)] with AsPh3 depends on: / mass ratio of [NBu4]2[ReX5(NO)] to triphenylarsine and it is the highest when it is equal to 1:5. / reaction time; the yield drops considerably when the reaction is carried out for a time shorter than 6 h. The complex 1 crystallises in the monoclinic space group P 21/n and its structure consists of discrete and well-separated monomers. Fig. 1 shows the molecular structure of this compound. The rhenium atom is in a distorted octahedral environment with a linear N /O group trans to one of the OAsPh3 ligands, two mutually
Fig. 1. The molecular structure of 1. The thermal ellipsoids are drawn at the 50% probability level.
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Fig. 2. The molecular structure of 3.
cis OAsPh3 molecules and three bromine ligands in meridional geometry. The major distortion in the geometry, which is an increase in the N(1) /Re(1) / O(1) angle, is caused by the presence of a multiply bonding ligand (Re /NO) and sizeable steric interactions of two mutually cis OAsPh3 molecules. The asymmetric unit of 3, which crystallises in the ¯ consists of one molecule */ triclinic space group P1; [ReCl3(NO)(AsPh3)2]*/with all atoms in general positions and half the [ReCl4(AsPh3)2] molecule with the rhenium atom on a centre of symmetry. Due to the requirements of the symmetry, the atoms Re(1), Cl(1), Cl(2) and the symmetry equivalents of the two chlorine atoms of the [ReCl4(AsPh3)2] complex lie in one plane and the coordination around the central atom is a square bipyramid extended along the Re /As bonds. Three mutually meridional chlorine atoms, two AsPh3 ligands trans to each other and the linear nitrosyl group octahedrally surround the rhenium atom in the [ReCl3(NO)(AsPh3)2] complex. The departure from the ideal octahedron */the angles between cis -ligands vary between 85.318 and 95.388, and the trans -angles are between 175.178 and 178.318*/appears to be due to the electronic factors and steric interactions with the NO ligand and it is commonly observed in octahedral complexes containing a multiply bonding ligand [32 / 34]. The relative orientation of the [ReCl4(AsPh3)2] and [ReCl3(NO)(AsPh3)2] molecules is depicted in Fig. 2. The complex 4 belongs to the C 2/c space group and the molecular structure of 4 is shown in Fig. 3. The
rhenium atom in 4 occupies a special position e of the space group C 2/c with multiplicity 4 and site symmetry 2. Atom O(1) shows signs of disorder with a particularly high value of one of the displacement parameters, but all attempts to model the disorder failed. It can be suggested that the disorder is dynamical in character. The atom Cl(2) shows multipositional disorder, but invoking this model did not improve the quality of refinement, therefore the model was not applied. The chlorine atoms Cl(2) and its symmetry equivalent Cl(2A) and two cis -oxo atoms of OAsPh3 molecules, O(1) and O(1A) hold the equatorial positions. The Cl(1) and its symmetry equivalent Cl(1A) ions occupy the apical positions. The deviations from an ideal octahedron (the angles between cis -ligands vary between 84.18 and 95.068, and the trans -angles are between 171.338 and 178.48) are caused by steric interactions of two mutually cis OAsPh3 molecules. The structure of 5 consists of discrete and wellseparated monomers. The numbering scheme of 5 is shown in Fig. 4. The complex has pseudooctahedral geometry with trans arsine ligands, meridional bromo ligands and a linear nitrosyl group. The rhenium, NO and bromine species are sited on a crystallographic twofold axis, therefore only half of the molecule is independently located in the asymmetric unit. The three mutually perpendicular coordination planes are well defined and there are no significant intermolecular contacts. The angles between cis -ligands vary between 87.838 and 92.148 (Table 2), and the trans -angles are between 177.888 and 1808.
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Fig. 3. The molecular structure of 4.
Fig. 4. The molecular structure of 5.
The complex 5 is isomorphous with [ReX3(NO)(PPh3)2] (X /Cl and Br) [14,16], [ReOCl3(PPh3)2] [35] and several similar ruthenium nitrosyl compounds [36,37]. The packing of the two bulky triphenylarsine or triphenylphosphine ligands, which are trans to each other, seems to govern the solid-state structure of these
complexes. In fact, the C 2/c space group with four formula units per unit cell is the preferred one for such neutral pseudooctahedral bis(triphenylphosphine) or bis(triphenylarsine) complexes when the co-ordination plane perpendicular to the P /P or As /As vector contains three or four ligands of low steric bulk, which will not cause unusual intermolecular interactions. The trans -arrangement of the two bulky triphenylarsine molecules in 3 and 5 complexes, connected with sterically demanding nature of the arsine ligands, causes the cis -location of the nitrosyl group, with respect to the AsPh3 molecules (p-acid ligands). This is also supported by the electronic influence of the multiply bonded ligand, which forces the metal nonbonding d electrons to lie in the plane perpendicular to the M /NO bond axis. This general rule appears to hold for isonitrile, carbonyl, olefin, acetylene, thioether and often phosphine ligands [38 /40]. Table 1 presents crystal data and structural refinement for compounds 1, 3, 4 and 5. The most important bond lengths and angles for compounds 1, 3, 4 and 5 are reported in Table 2. The Re /NO and N/O bond lengths and the values of Re /N /O angles for complexes 1, 3 and 5, summarised in Table 3, confirm the linear coordination of the nitrosyl group and are comparable with values previously found by others (Table 3). For nitrosyl complexes containing two trans triphenylarsine molecules, elongation of the Re /halogen bond trans to the linear nitrosyl group is observed: the Re /Br(2) bond ˚ in 5 is longer than Re /Br(1) by length at 2.5578(19) A ˚ and in [ReCl3(NO)(AsPh3)2] the Re /Cl(3) about 0.05 A
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Table 2 ˚ ) and angles (8) for 1, 3, 4 and 5 Selected bond lengths (A 1
3
4
5
Bond lengths Re(1) N(1) Re(1) O(1) Re(1) O(2) Re(1) Br(2) Re(1) Br(1) Re(1) Br(3) N(1) O(3) O(1) As(1) O(2) As(2)
1.749(5) 2.050(4) 2.059(4) 2.5117(7) 2.5180(7) 2.5263(7) 1.156(6) 1.680(4) 1.662(4)
Re(1) Cl(2) Re(1) Cl(1) Re(1) As(1) Re(2) N(1) Re(2) Cl(5) Re(2) Cl(4) Re(2) Cl(3) Re(2) As(2) Re(2) As(3) N(1) O(1)
2.329(3) 2.358(3) 2.6023(10) 1.816(10) 2.338(3) 2.339(2) 2.376(2) 2.6060(11) 2.6186(11) 1.092(2)
Re(1) O(1) Re(1) Cl(2) Re(1) Cl(1) As(1) O(1)
2.000(7) 2.292(7) 2.370(2) 1.640(7)
Re(1) N(1) Re(1) Br(1) Re(1) Br(2) Re(1) As(1) N(1) O(1)
1.740(11) 2.5034(19) 2.5578(19) 2.5946(9) 1.177(13)
Bond angles N(1) Re(1) O(1) N(1) Re(1) O(2) O(1) Re(1) O(2) N(1) Re(1) Br(2) O(1) Re(1) Br(2) O(2) Re(1) Br(2) N(1) Re(1) Br(1) O(1) Re(1) Br(1) O(2) Re(1) Br(1) Br(2) Re(1) Br(1) N(1) Re(1) Br(3) O(1) Re(1) Br(3) O(2) Re(1) Br(3) Br(2) Re(1) Br(3) Br(1) Re(1) Br(3) O(3) N(1) Re(1) As(1) O(1) Re(1) O(1) As(1) C(13) O(1) As(1) C(7) C(13) As(1) C(7) O(1) As(1) C(1) C(13) As(1) C(1) C(7) As(1) C(1)
100.6(2) 175.98(19) 83.24(16) 93.30(17) 86.59(12) 88.06(12) 89.90(16) 169.43(11) 86.27(12) 91.76(3) 92.22(17) 88.03(12) 86.73(12) 172.92(2) 92.68(2) 176.8(5) 132.9(2) 116.7(2) 107.2(2) 105.9(3) 107.2(2) 109.1(3) 110.6(3)
Cl(2)#1 Re(1) Cl(2) Cl(2)#1 Re(1) Cl(1) Cl(2) Re(1) Cl(1) Cl(1) Re(1) Cl(1)#1 Cl(2) Re(1) As(1)#1 Cl(1) Re(1) As(1)#1 Cl(2) Re(1) As(1) Cl(1) Re(1) As(1) As(1)#1 Re(1) As(1) N(1) Re(2) Cl(5) N(1) Re(2) Cl(4) Cl(5) Re(2) Cl(4) N(1) Re(2) Cl(3) Cl(5) Re(2) Cl(3) Cl(4) Re(2) Cl(3) N(1) Re(2) As(2) Cl(5) Re(2) As(2) Cl(4) Re(2) As(2) Cl(3) Re(2) As(2) N(1) Re(2) As(3) Cl(5) Re(2) As(3) Cl(4) Re(2) As(3) Cl(3) Re(2) As(3) As(2) Re(2) As(3) O(1) N(1) Re(2) C(7) As(1) C(13) C(7) As(1) C(1) C(13) As(1) C(1) C(7) As(1) Re(1) C(13) As(1) Re(1) C(1) As(1) Re(1)
180.0 91.08(11) 88.92(11) 180.0 92.40(8) 87.10(8) 87.60(8) 92.90(8) 180.0 93.9(3) 90.8(3) 175.17(9) 178.2(3) 87.90(9) 87.34(9) 89.5(3) 85.49(7) 93.71(7) 90.29(7) 91.9(3) 95.38(7) 85.31(7) 88.29(7) 178.31(3) 176.0(9) 103.9(4) 103.7(4) 102.2(4) 114.1(3) 114.6(3) 116.8(3)
O(1)#2 Re(1) O(1) O(1)#2 Re(1) Cl(2) O(1) Re(1) Cl(2) Cl(2) Re(1) Cl(2)#2 O(1)#2 Re(1) Cl(1) O(1) Re(1) Cl(1) Cl(2) Re(1) Cl(1) Cl(2)#2 Re(1) Cl(1) Cl(1) Re(1) Cl(1)#2 O(1) As(1) C(1) O(1) As(1) C(13) C(1) As(1) C(13) O(1) As(1) C(7) C(1) As(1) C(7) C(13) As(1) C(7) As(1) O(1) Re(1)
84.8(7) 178.4(4) 93.8(4) 87.6(4) 84.1(2) 89.5(2) 95.06(14) 91.20(13) 171.33(12) 104.0(4) 110.8(5) 110.7(4) 115.8(4) 107.4(4) 108.1(4) 147.5(4)
N(1) Re(1) Br(1) Br(1) Re(1) Br(1)#3 N(1) Re(1) Br(2) Br(1) Re(1) Br(2) N(1) Re(1) As(1) Br(1) Re(1) As(1) Br(1)#3 Re(1) As(1) Br(2) Re(1) As(1) As(1) Re(1) As(1)#3 O(1) N(1) Re(1) C(7) As(1) C(1) C(7) As(1) C(13) C(1) As(1) C(13) C(7) As(1) Re(1) C(1) As(1) Re(1) C(13) As(1) Re(1)
90.88(2) 178.25(5) 180.000(1) 89.12(2) 91.07(2) 87.82(6) 92.15(6) 88.93(2) 177.87(4) 180.000(2) 106.4(4) 100.3(3) 104.3(3) 119.9(3) 107.2(2) 117.3(3)
Table 3 Relevant structural data for selected rhenium nitrosyl complexes Complex
˚) Re NO bond length (A
˚) N O bond length (A
Re N O angle (8)
[ReBr3(NO)(AsPh3)2] [ReCl3(NO)(AsPh3)2] [ReBr3(NO)(OAsPh3)2] [ReCl3(NO)(OPPh3)2] [13] [ReCl3(NO)(PPh3)2] [14] [ReBr3(NO)(OPPh3)2] [16] [ReBr3(NO)(PPh3)2] [16] [NEt4][ReBr4(NO)(MeCN)] [41] [NEt4][ReBr4(NO)(EtOH)] [41] [ReCl3(NO)(NPPh3)(OPPh3)] [42]
1.740(11) 1.816(10) 1.749(5) 1.72(3) 1.765(9) 1.757(12) 1.769(12) 1.771(11) 1.723(15) 1.734(10)
1.177(13) 1.092(2) 1.156(6) 1.21(3) 1.200(11) 1.261(13) 1.12(2) 0.99(2) 1.19(2) 1.183(13)
180.000(2) 176.0(9) 176.8(5) 172.0(4) 180.000(2) 172.6(13) 180.000(2) 178.0(6) 169.0(3) 174.1(9)
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629
2624
Table 4 Band position (cm 1) in IR range for complexes 1 /5 1
2
3
1733 1483 1439 1085 1023 893 837 739 688 628 480
1721 1481 1439 1085 1024 888 850 739 689 625 481
1738 1482 1435 1077 1024
741 692
4
1482 1436 1080 1024 890 840 740 690
471
˚ is longer than Re /Cl(4) and bond length at 2.376(2) A ˚ Re /Cl(5) by about 0.04 A. A similar trend is observed in [ReX3(NO)(PPh3)2] (X /Cl, Br) complexes [14,16]. ˚ The Re /As distances 2.6023(10) A in ˚ in [ReCl4(AsPh3)2], 2.6060(11) and 2.6186(11) A ˚ in 5 are consider[ReCl3(NO)(AsPh3)2] and 2.5946(9) A able longer than those found in the rhenium complexes with a cis arrangement of arsine ligands: 2.557(2) and ˚ in [ReO2(dadpe)2] and 2.532(1), 2.552(1), 2.541(2)A ˚ in [ReN(dpae)2Cl] [43]. 2.541(1) and 2.546(1) A The Re /OAsPh3 and the As /O bond lengths in complexes 1 and 4 (Table 2) are in good agreement with values found for [ReOBr3(AsPh3)(OAsPh3)] (Re / ˚ ) and [ReOCl3O /2.010(7), As /O /1.675(7) A (AsPh3)(OAsPh3)] (Re /O /2.019(8), As /O /1.643(9) ˚ [44]). In complex 4, the Re /Cl(2) distance at 2.292(7) A ˚ as a result of ˚ is shorter than Re /Cl(1) by about 0.08 A A its trans position to the OAsPh3 molecule. The bond valences were computed as nij /exp[(Rij / dij )/0.37] [47 /49], where Rij is the bond-valence parameter (in the formal sense Rij is the single-bond length between i and j atoms) [50]. The RReO, RReN, RReBr, RReCl values were taken as 1.97, 2.06, 2.45 and 2.23 [47], respectively. The computed bond valences of rhenium in compound 1 are nReO /0.79, 0.80, nReBr /0.80, 0.81, 0.85; nReN /2.32 v.u. (valence units), in compound 3 are nReAs /0.81, 0.84, nReCl / 0.67, 0.71, 0.75, 0.74, 0.76, 0.81, 0.85; nReN /1.93 v.u., in compound 4 are nReO /0.92, nReCl /0.68, 1.04 v.u. and in compound 5 are nReAs /0.86, nReBr /0.74, 0.86; nReN /2.37 v.u. The weakest bonds are Re /Cl bonds in compound 3 and the strongest are Re /N bonds (formally these bonds can be considered as double bonds). The molecules of 1 are linked to form dimers via C(10) /H(10A) Br(2#/x , /y/2, /z/1) intermolecular weak hydrogen bonds [51] (D A distance equals ˚ and D /H A angle 137.48). One more 3.603(8) A C(26) /H(26A) O(2) weak intramolecular hydrogen ˚ and D /H A bond (D A distance equals 2.992(8) A
5
Assignment
1773 1481 1435 1076 1034
n (NO) d (C CH in the plane) n (As C6H5) d (C H in the plane) d (C H in the plane) n (As O) n (As O) d (C C out of the plane) d (C C in the plane) d (C C in the plane) n (Re N)
737 691 474
angle 112.98) exists in the molecule, which provides additional conformational stabilisation. The conformations of molecules of compound 3 are stabilised by six C /H Cl weak intramolecular hydrogen bonds (D A ˚ and D/H A distances vary from 3.31(1) to 3.67(1) A angles vary from 112.98 to 149.98) and one C(38) / H(38A) N(1) weak intramolecular hydrogen bond ˚ and D /H A angle (D A distance equals 3.34(1) A 127.28). The molecules of 4 are assembled via C(11) / H(11A) Cl(1/x/1/2, /y/1/2, /z/1) weak intermolecular hydrogen bonds (D A distance equal to ˚ and D /H A angle 145.98) to give an infinite 3.59(1) A hydrogen bonded chain created by perpendicular rings in a spiro arrangement. Only one weak intramolecular hydrogen bond, C(8) /H(8A) Br(1/x , y , /z/1/2) ˚ and D/ with a D A distance equal to 3.507(9) A H A angle 133.18, can be found in compound 5, providing slight stabilisation to the molecule. Table 4 contains assignments of characteristic bands in the IR range for 1/5 compounds. For [ReX3(NO)L2] complexes with an identical ligand L, the NO stretching frequency of the chloro-compounds is lower than that of the corresponding bromo-complexes, which is in accordance with the greater p-acceptor character of the bromo ion than the chloro one. A neutral group, L, also causes a variation in the NO stretching frequency. The higher frequencies are found for complexes containing AsPh3 than OAsPh3. The difference between nNO of bromo- and chloronitrosyl is much higher for complexes containing arsines (3 and 5) than for complexes containing arsine oxides (1 and 2), which results from the different ligands’ arrangement around the rhenium atom in these complexes. The presence of two strong bands at about 890 and 840 cm 1 in the IR spectra of complexes 1, 2 and 4 confirms the cis geometry of the two coordinated OAsPh3 molecules. Complexes 1, 2, 4 and 5 are paramagnetic compounds with a magnetic moment corresponding to one unpaired electron.
Table 5 Band positions, molar absorption coefficients and assignments for complexes 1 /5 [ReCl3(NO)(OAsPh3)2] (2)
[ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2] (3)
[ReCl4(OAsPh3)2] (4)
Band position (cm 1)
Band position (cm1)
o
Band position (cm 1)
o
Band position (cm1)
o
14 150 23 000
30 dxy 0 dxz 410 dyz 0 dx2y2
18 800 25 850
320 dxy 0 dyz 280 dxy 0 dxz
15 100 25 300
13 dxy 0 dyz 300 dxy 0 dxz
25 125
960 poOAs 0 dxz
36 100
14 925 23 900 27 740
31 850 36 900 37 900 43 300
o
Assignment
150 dxy 0 dxz 2050 dxz 0 dx2y2, dyz 0 p* OAs 4800 dxy 0 p* NO, dyz 0 dx2y2 2400 dxy 0 p* OAs 14 500 dxy 0 dx2y2, poBr 0 p* NO 17 000 pbReBr 0 dxz 75 000 pbC6H5 0 4dAs
29 750 36 900 37 900 43 300
Assignment
1390 dxy 0 p* NO 6400 dxy 0 dx2y2, dxy 0 p* OAs 6850 pbReCl 0 dxz 43 000 pbC6H5 0 4dAs
42 920
Assignment
5180 dxy 0 dx2y2, pbReCl 0 dxz , (dxy 0 p* NO) 7400 pbC6H5 0 4dAs
34 000
[ReBr3(NO)(AsPh3)2] (5) Assignment
6400 dxy 0 dx2y2, dxy 0 p* OAs
Band position (cm 1)
o
Assignment
14 700 15 550
200 dxz 0 p* 270 dyz 0 p*
17 850
2050 dxy 0 dxz
NO NO
a
43 700
47 000 pbC6H5 0 4dAs
21 600 35 200 38 750 42 900
15 090 poBr 0 dxz 16 080 dxy 0 dx2y2, dxy 0 p* NO 17 640 pbReBr 0 dxz 17 930 pbC6H5 0 4dAs
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629
[ReBr3(NO)(OAsPh3)2] (1)
o molar absorption coefficient (dm3 mol 1 cm 1). a Covered by pbReCl 0 dxz transition.
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2626
Table 6 Values of ligand field parameters for 1, 2, 4 and 5 Complex
[ReBr3(NO)(OAsPh3)2] [ReCl3(NO)(OAsPh3)2] [ReCl4(OAsPh3)2] [ReBr3(NO)(AsPh3)2]
Ligand field parameter Dq (cm1)
Ds (cm1)
Dt (cm1)
3690 3690 3400 3521
3741 5104 5272 5952
449 111 143 1
The positions and molar absorption coefficients of electronic bands for complexes 1 /5 and the electronic transitions assigned to the bands are shown in Table 5. Based on the data of Table 5, the values of the ligand field parameters Dq, Ds and Dt have been defined and the energies of molecular orbitals for the complexes have been estimated. The values of ligand field parameters are listed in Table 6, and simplified MO diagrams for complexes 1, 2, 4 and 5 are presented in Fig. 5. Intensities of pbC6H5 0/4dAs transitions in complexes containing arsine oxides are significantly higher in
Fig. 5. The simplified molecular orbitals diagrams for 1, 2, 4 and 5.
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629
comparison with complexes containing arsines, which is connected to: / As [/O electron density transfer, / lack of a Re 0/As transition, which leads to an increase in As acceptor ability towards pC6H5 electrons. Significant intensities of bands: / / / /
at at at at
23 900, 27 740, 36 900 and 37 900 cm 1 in 1, 36 900 cm 1 in 2 36 100 cm 1 in 3 34 000 cm 1 in 4
result from a superposition of charge transfer transitions and d 0/d transitions. The lower intensity of the dxy 0/p* NO transition in complexes containing arsine oxides in comparison with complexes containing arsines results from the presence of an O /As acceptor group in the xy plane, which is competitive towards NO. That is why in complexes containing an O /As group, the N /O bond is shorter and the Re /N bond is longer than in complexes containing AsPh3. High electron density on oxygen atoms from the O /As group also results in an effective sReO bonding and simultaneously an increase in electron density on the ReII ion. The last fact increases its p-donor ability towards Br(1), resulting in a shortening of the Re /Br(1) bond in comparison with the Re / Br(3) bond. The comparatively high intensity of the bands attributed to the dxy 0/p* NO transition proves the linear NO coordination (lack of electron density in p* NO). The low intensity of the dyz 0/p* NO and dxz 0/p* NO transition is caused by the symmetry of these orbitals and NO to each other. Based on the presented simplified
2627
MO diagrams and absorption band analysis, one can conclude that complexes 1, 2 and 5 have electron configurations (dxy )2(dyz )2(dxz )1, and complex 4*/ (dxy )2(dyz )1. In 3 both these configurations exist simultaneously. The Dq parameter for the [ReBr3(NO)(AsPh3)2] complex is slightly higher (by 2638 cm1) than Dq for the [ReBr3(NO)(PPh3)2] complex. This increase in its value is connected with the increase in the degree of covalency of the Re /As bonds (higher p-acceptor ability of As compared to P) and Re /N bonds. The higher pacceptor ability of As manifests also in an increase in molar extinction coefficient of the band resulting from pbC6 H5 0 4dAs and in consequence in an elongation of C / C bonds in AsPh3 compared to PPh3. The small ˚) elongation of the Re /As bond (by only 0.054 A compared to the Re /P bond, in spite of the fact that ˚ ) also proves the higher acceptor rAs3 is longer (by 0.1 A ability of As in comparison to P. The decrease in electron density at the rhenium atom, connected with 5dxz ,yz 0/4dAs electron transitions, increases the probability of charge transfer from Br to 5dRe (the band at 21 598 cm 1; other authors observed the Br 0/Re transition at 23 830 cm 1) [45,46]. Therefore, it leads to an increase in the probability of the dxy 0 p+NO electron transition and causes an abridgement of the ˚ ) and an elongation of the N /O Re /N bond (by 0.015 A ˚ bond (by 0.057 A) in the [ReBr3(NO)(AsPh3)2] complex compared to the [ReBr3(NO)(PPh3)2] complex. Replacing PPh3 with AsPh3 in nitrosyl Re(II) complexes causes a change in charge distribution in complex molecules. Spectroscopic data confirm EPR signals in the solid phase of 5 and in methylene chloride solutions of 1 and 5 (Figs. 6 /8). The solid phase signal clearly confirms the axial symmetry of complex 5, characterised by g /
Fig. 6. Experimental X-band EPR spectrum of 5 in the solid phase at T/295 K.
2628
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629
Fig. 7. Experimental X-band EPR spectrum of 3 in CH2Cl2 at T /295 K.
Fig. 8. Experimental X-band EPR spectrum of 5 in CH2Cl2 at T /295 K.
2.4057, g /2.0412 and gav /2.1624 values. EPR signals of methylene chloride solutions of 1 and 5 also have axial symmetry. Complex 5 is characterised by gav /2.1942 and Aav /31.3 mT values, and complex 1 */by gav /2.2192 and Aav /26.7 mT values. These facts confirm an interaction of an unpaired electron (dxz )1 with the axial ligands. If the unpaired electron was on the dxy orbital, the values of gav in complexes 1 and 5 would be in reverse relation. The higher gav value in 1 results from a higher spin-orbital contribution of axial Br ligands (lBr /2460 cm 1) into gjj, compared to AsPh3 ligands with significantly lower lAs value. The lower Aav value of complex 1 results from covalency of the Re /Br bond, confirmed by rReBr /0.251 nm. The Re /Br distance is shorter than the sum of the ion radii 2 rRe /rBr by 0.041 nm. The sextet signal of complexes 1 and 5, resulting from an interaction of the unpaired electron with the nuclear spins of 185Re and 187Re, indicates a small delocalisation of this electron towards the ligands. Quadruple moments of 14N, 75As, 79Br, 81Br, 185Re and 187Re, broadening the signals, cause superposition of hyperfine structure components.
Acknowledgements
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 188153 /56 for compounds [ReBr3(NO)(AsPh3)2], [ReCl3(NO)(AsPh3)2][ReCl4(OAsPh3)2], [ReBr3(NO)[ReCl4(AsPh3)2], (OAsPh3)2]. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: /44-1223336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
We wish to express our thanks to Danuta Kwapulin´ska for recording EPR spectra. X-ray crystallography of compounds 1 and 4 was financed by statutory funds allocated by the State Committee for Scientific Research to the Institute of General and Ecological Chemistry, Technical University of Lo´dz´.
References [1] R.M.J. Palmer, A.G. Ferrige, S. Moncada, Nature 327 (1987) 524. [2] S. Moncada, R.M.J. Palmer, E.A. Higgs, Pharmacol. Rev. 43 (1991) 109. [3] P.L. Feldman, O.W. Griffith, D.J. Stuehr, Chem. Eng. News 71 (1993) 26. [4] M. Feeelish, J.S. Stamler (Eds.), Methods in Nitric Oxide Research, Wiley, Chichester, England, 1996. [5] W. Volkert, W.F. Goeckeler, G.J. Ehrhardt, A.R. Ketring, J. Nucl. Med. 32 (1991) 174. [6] E.A. Deutsch, K. Libson, J.L. Vanderheyden, Technetium and Rhenium in Chemistry and Nuclear Medicine, Raven Press, New York, 1990. [7] J.O. Dzie˛gielewski, K. Filipek, B. Machura, Polyhedron 14 (1995) 555. [8] J.O. Dzie˛gielewski, B. Machura, T. Kupka, in: J.C. Merlin, S. Turrell, J.P. Huvenne (Eds.), Spectroscopy of Biological Molecules, Kluver Academic Publishers, Dordrecht, 1995, p. 589. [9] J.O. Dzie˛gielewski, B. Machura, J. Marek, Polyhedron 15 (1996) 3713. [10] J.O. Dzie˛gielewski, B. Machura, T.J. Bartczak, Polyhedron 15 (1996) 2813. [11] T.J. Bartczak, W. Czurak, J.O. Dzie˛gielewski, B. Machura, Polish J. Chem. 72 (1998) 633. [12] J.O. Dzie˛gielewski, B. Machura, T. Kupka, T.J. Bartczak, W. Czurak, Polish J. Chem. 72 (1998) 1009. [13] J.O. Dzie˛gielewski, B. Machura, T.J. Bartczak, W. Czurak, J. Kusz, J. Warczewski, J. Coord. Chem. 48 (1999) 125. [14] T.J. Bartczak, W. Czurak, J.O. Dzie˛gielewski, B. Machura, A. Jankowska, J. Kusz, J. Warczewski, Polyhedron 18 (1999) 2313. [15] T.J. Bartczak, W. Czurak, J.O. Dzie˛gielewski, B. Machura, J. Kusz, J. Warczewski, Polish J. Chem. 74 (2000) 265.
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629 [16] T.J. Bartczak, W. Czurak, J.O. Dzie˛gielewski, B. Machura, A. Jankowska, J. Kusz, J. Warczewski, J. Coord. Chem. 52 (2001) 361. [17] S.G. Fonta´n, A. Marchi, L. Marvelli, R. Rossi, S. Antoniutti, G. Albertin, J. Chem. Soc., Dalton Trans. (1996) 2779. [18] C. Bolzati, F. Tisato, F. Refosco, G. Bandali, A. Dolmella, Inorg. Chem. 35 (1996) 6221. [19] F. Connac, Y. Lucchese, M. Dartiguenave, A.L. Beauchamp, Inorg. Chem. 36 (1997) 256. [20] R.G. Cavell, R.W. Hilts, H. Luo, R. McDonald, Inorg. Chem. 38 (1999) 897. [21] R. Rossi, A. Marchi, A. Duatti, L. Magon, U. Casellato, R. Graziani, J. Chem. Soc., Dalton Trans. (1998) 1857. [22] M.F.N.N. Carvalho, A.J.L. Pombeiro, D.L. Hughes, R.L. Richards, J. Organomet. Chem. 335 (1987) C23. [23] N.P. Johnson, C.J.L. Lock, G. Wilkinson, J. Chem. Soc. (1964) 1054. [24] D. Giusto, G. Cova, Gazz. Chem. Ital. 102 (1972) 265. [25] STOE & Cie (1999). X-RED. Version 1.18. STOE & Cie GmbH, Darmstadt, Germany. [26] (a) G.M. Sheldrick, Acta Crystallgr., Sect. A 46 (1990) 467 /473; (b) G.M. Sheldrick, SHELXL-97, Program for the Solution and Refinement of Crystal Structures, University of Go¨ttingen, Germany, 1997. [27] G.M. Sheldrick, SHELXTL: release 4.1 for Siemens Crystallographic Research Systems, 1990. [28] W.B. Hughes, E.A. Zeuch, Inorg. Chem. 12 (1973) 471. [29] L. Bencze, J. Kohan, Inorg. Chim. Acta 65 (1982) L17. [30] D.L.H. Williams, Nitrosation, Cambridge University Press, New York, 1988. [31] R.P. Mueller, S. Murata, J.R. Huber, Chem. Phys. 66 (1982) 237. [32] P.W.R. Corfield, R.J. Doedens, J.A. Ibers, Inorg. Chem. 6 (1967) 197.
2629
[33] G. La Monica, S. Cenini, J. Chem. Soc., Dalton Trans. (1980) 1145. [34] D.C. Bradley, M.B. Hursthouse, K.M.A. Malik, A.J. Nielson, R.L. Short, J. Chem. Soc., Dalton Trans. (1983) 2651. [35] A.M. Lebuis, A.L. Beauchamp, Can. J. Chem. 71 (1993) 441. [36] D. Bright, J.A. Ibers, Inorg. Chem. 8 (1969) 1078. [37] D.H.F. Souza, G. Oliva, A. Teixeira, A.A. Batista, Polyhedron 14 (1995) 1031. [38] T. Lis, Acta Crystallogr., Sect. B 33 (1977) 944. [39] V.S. Sergienko, M.A. Porai-Koshits, V.E. Mistryukov, K.V. Kotegov, Koord. Khim. 8 (1982) 230. [40] J.M. Mayer, D.L. Thorn, T.H. Tulip, J. Am. Chem. Soc. 107 (1985) 7454. [41] G. Ciani, D. Giusto, M. Manassero, M. Sansoni, J. Chem. Soc., Dalton Trans. (1975) 2156. [42] N. Mronga, F. Weller, K. Dehnicke, Z. Anorg. Allg. Chem. 502 (1983) 35. [43] M.T. Castello, P.E. Farwick, M.A. Green, R.A. Walton, Inorg. Chem. 30 (1991) 861. [44] J.O. Dzie˛gielewski, B. Machura, T.J. Bartczak, J. Kusz, J. Warczewski, submitted to J. Coord. Chem. [45] A.P. Mortala, J.W. Moskowitz, N. Rooch, C.D. Cousman, H.B. Gray, Chem. Phys. Lett. 32 (1975) 283. [46] F.A. Cotton, E.P. Edersen, J. Am. Chem. Soc. 97 (1975) 303. [47] I.D. Brown, Acta Crystallogr., Sect. B 48 (1992) 553. [48] I.D. Brown, Acta Crystallogr., Sect. B 53 (1997) 381. [49] M. O’Keeffe, N.E. Brese, J. Am. Chem. Soc. 113 (1991) 3226. [50] L. Sieron, M. Bukowska-Strzyzewska, Acta Crystallogr., Sect. C 55 (1999) 1230. [51] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond in Structural Chemistry and Biology, Oxford University Press, Oxford, 1999.
Reactivity of [ReOX3(AsPh3)2] (X Cl, Br) complexes towards gaseous nitric oxide. Crystal, molecular and electronic structure of [ReBr3(NO)(OAsPh3)2], [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2], [ReCl4(OAsPh3)2] and [ReBr3(NO)(AsPh3)2] /
B. Machura a, J.O. Dzie˛gielewski a,*, S. Michalik a, T.J. Bartczak b,*, R. Kruszynski b, J. Kusz c a
Department of Inorganic and Radiation Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland b X-Ray Crystallography Laboratory, Institute of General and Ecological Chemistry, Technical University of Lo´dz´, ˙ eromski St., 90-924 Lo´dz´, Poland 116 Z c Institute of Physics, University of Silesia, 4th Uniwersytecka St., 40-006 Katowice, Poland Received 4 July 2002; accepted 2 September 2002
Abstract The reactions of the complexes [ReOX3(AsPh3)2] (X/Cl, Br) with gaseous nitric oxide and the reactions of the compounds [NBu4]2[ReX5(NO)] (X/Cl, Br) with an excess of triphenylarsine have been examined. [ReOBr3(AsPh3)2] reacts with nitric oxide to give mer ,cis -[ReBr3(NO)(OAsPh3)2] (1), whereas the reaction of the chlorine oxocomplex with NO leads to three products: [ReCl3(NO)(OAsPh3)2] (2), mer ,trans -[ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2] (3) and cis -[ReCl4(OAsPh3)2] (4). The compounds [NBu4]2[ReX5(NO)] (X /Cl, Br) react with an excess of AsPh3 to give 3 and mer ,trans -[ReBr3(NO)(AsPh3)2] (5), respectively. The complexes obtained in these reactions have been characterised by IR, UV /Vis and magnetical measurements. Crystal and molecular structures have been determined for complexes 1 and 3 /5. EPR spectra have been recorded for compounds 1 and 5. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Rhenium; Nitrosyl; X-ray structures; Electronic structures; Nitric oxide
1. Introduction Nitric oxide is known to play key roles in human cardiovascular and nervous systems and in immune response to pathogen invasion. These discoveries have stimulated much interest in nitrosyl complexes of transition metals */compounds that could deliver NO
* Corresponding authors. Tel.: /48-32-258-2441; fax: /48-32-2599978 E-mail addresses: [email protected] (J.O. Dzie˛gielewski), [email protected] (T.J. Bartczak).
to biological targets upon demand either by thermal reactions or by photochemical excitation [1 /4]. The chemistry of nitrosyl rhenium complexes arouses particular interest among these compounds, as the favourable nuclear properties of 186Re and 188Re nuclides make the radioisotopes useful for diagnostic nuclear medicine and applications in radioimmunotheraphy [5,6]. In our previous papers we reported on the structural and spectroscopic characterisation of the nitrosyl rhenium complexes obtained in the reactions between the complexes [ReOX3(PPh3)2] (X /Cl, Br) and gaseous nitric oxide [7 /16].
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 2 5 4 - 8
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Now we are extending our studies to the reactivity of the compounds [ReOX3(AsPh3)2] (X /Cl, Br) towards NO and here we present our results of the synthesis, spectroscopic and structural characterisation of the following complexes: [ReBr3(NO)(OAsPh3)2] (1), [ReCl3(NO)(OAsPh3)2] (2), [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2] (3) and [ReCl4(OAsPh3)2] (4). We have also carried out the reactions of [NBu4]2[ReX5(NO)] (X /Cl, Br) with an excess of triphenylarsine, which lead to [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2] (3) and [ReBr3(NO)(AsPh3)2] (5), respectively. Considering that AsPh3 and OAsPh3 molecules are replaced more readily than P- and N-donor ligands, these complexes are predicted to be very useful starting material in the synthesis of new rhenium nitrosyls [17 / 22].
2. Experimental Triphenylarsine and NH4ReO4 were purchased from Aldrich Chemical Co. and used without further purification. The [ReOX3(AsPh3)2] and [NBu4]2[ReX5(NO)] (X /Cl, Br) complexes were synthesised according to the literature methods [23,24]. Gaseous NO, obtained in the reaction: 2NaNO2 3H2 SO4 2FeSO4 0 2NO/ /2NaHSO Fe (SO ) 2H O; was purified by passing 4 2 4 3 2 through washers with concentrated KOH solution and over solid NaOH. Solvents were dried and deoxygenated prior to use in the usual way. The reaction, all preparations and the recrystallisation were performed under argon atmosphere. 2.1. Synthesis of 1 NO was passed through a vigorously stirred and refluxing solution of [ReOBr3(AsPh3)2] (1.05 g, 1 mmol) in CH2Cl2, tetrahydrofurane or C6H6 (40 cm3). The reaction was carried out for 4 /5 h. The colour changed gradually from bright green to dark green. Then the resulting solution was evaporated to the volume of 10 cm3. The green precipitate was formed by an addition of 40 cm3 of EtOH and after 15 min it was filtered off. The product was washed with cold ether and dried in vacuo. The yield of 1 does not depend on sort of solution and it equals to 0.88 g (0.80 mmol). Anal . Calc. for C36H30As2Br3O3NRe (1): C, 39.29; H, 2.75; N, 1.27. Found: C, 39.24; H, 2.72; N, 1.29%.
recrystallisation. At room temperature complex 3 does not dissolve in MeCN but 2 and 4 compounds dissolve in CH3CN readily and 4 precipitates from the solution first. Compound 3 was recrystallised from CH2Cl2. The yield of 2, 3 and 4 depends on the kind of the reaction solution; in CH2Cl2 and tetrahydrofurane */2 (75%), 3 and 4 (3%); in C6H6 */2 (70%), 3 and 4 (5%). Anal . Calc. for C36H30As2Cl3O3NRe (2): C, 44.71; H, 3.13; N, 1.45. Found: C, 44.64; H, 3.16; N, 1.41%. Calc. for C72H60As4Cl7ONRe2 (3): C, 46.11; H, 3.22; N, 0.75. Found: C, 46.24; H, 3.25; N, 0.87%. Calc. for C36H30As2Cl4O2Re (4): C, 44.46; H, 3.11. Found: C, 44.57; H, 3.15%. 2.3. Synthesis of 3 A mixture of [NBu4]2[Re(NO)Cl5] (1 g, 1.14 mmol) and AsPh3 (5 g, 0.016 mol) in EtOH (30 cm3) was refluxed for 6 h. The formed dark red precipitate was filtered and washed with ether. Yield: 65%. 2.4. Synthesis of 5 A mixture of [NBu4]2[Re(NO)Br5] (1 g, 0.91 mmol) and AsPh3 (5 g, 0.016 mol) in EtOH (30 cm3) was refluxed for 6 h. The formed dark red precipitate was filtered and washed with ether. Yield: 70%. Anal . Calc. for C36H30As2Br3ONRe (5): C, 40.47; H, 2.83; N, 1.31. Found: C, 40.41; H, 2.87; N, 1.34%. 2.5. Physical measurements Infrared spectra were recorded on a Nicolet Magna 560 spectrophotometer in the spectral range 4000 /400 cm 1 with the samples in the form of potassium bromide pellets. Electronic spectra were measured on a Beckman 5240 spectrophotometer in the range 800/220 nm in deoxygenated CH2Cl2 solution. EPR spectra in the X-band (n :/9.5 GHz) at T /295 K have been recorded for CH2Cl2 solutions of complexes 1 and 5 and for 5 in the solid state, using a Bruker EMX spectrometer. About 10 3 M solutions of 1 and 5 in CH2Cl2 were used. Magnetic susceptibilities were measured at 296 K by the Faraday method. Elemental analyses (C H N) were performed on a Perkin/Elmer CHN-2400 analyzer. 2.6. Crystal structure determination and refinement
2.2. Synthesis of 2, 3 and 4 The reaction of gaseous NO with [ReOCl3(AsPh3)2] (0.92 g, 1 mmol) in a CH2Cl2, tetrahydrofurane or C6H6 solution (40 cm3) was carried out in the same manner as for 1, but a mixture of the three products was isolated and the complexes 2, 3 and 4 were separated by
The crystals of 1, 3 /5 suitable for X-ray structure determination were obtained by slow evaporation from MeCN solutions. The X-ray intensity data were collected on a Kuma KM-4 diffractometer (compounds 3 and 5) with v /2u scan mode and on a KM-4-CCD automatic diffractometer equipped with CCD detector
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Table 1 Crystal data and structure refinement for 1, 3, 4 and 5
Empirical formula Formula weight Temperature (K) Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) Volume (A Z Dcalc (Mg m 3) Absolute coefficient (mm 1) F (000) Crystal dimensions (mm) u Range for data collection (8) Index ranges
Reflections collected Independent reflections Data/restraints/ parameters Goodness-of-fit on F2 Final R indices [I 2s (I )] R indices (all data) Largest difference peak ˚ 3) and hole (e A
1
3
4
5
C36H30As2Br3O3NRe 1100.38 293(2) monoclinic P 21/n
C36H30As2Cl3.33O0.67N0.67Re 936.81 293(2) triclinic ¯/ /P1
C36H30As2Cl4O2Re 972.44 293(2) monoclinic C 2/c
C36H30As2Br3ONRe 1068.38 293(2) monoclinic C 2/c
10.2800(3) 20.8840(8) 17.3947(6) 90 93.559(3) 90 3727.2(2) 4 1.961 8.273 2092 0.25 0.09 0.09 3.15 /25.05
12.077(3) 14.143(3) 16.605(3) 65.56(2) 83.34(2) 87.88(2) 2564.5(10) 3 1.820 5.763 1361 0.11 0.32 0.45 1.36 /25.05
14.077(3) 13.271(3) 19.376(4) 90 95.00(3) 90 3606.0(13) 4 1.791 5.519 1884 0.17 0.11 0.04 3.44 /28.83
25.044(5) 9.664(5) 16.225(8) 90 116.77(5) 90 3506(3) 4 2.024 8.788 2028 0.08 0.20 0.20 1.82 /25.05
12 5 h 5 12, 05 k 5 24, 20 5 l 5 0 6587 6587 (Rint 0.00) 6587/0/445
145 h 5 14, 05 k 5 15, 185 l 5 18 8833 8535 (Rint 0.0207) 8535/1/593
195 h 5 19, 05 k 5 17, 05 l 5 25 4435 4435 (Rint 0.00) 4435/0/205
185 h 5 29, 25 k 5 11, 185 l 5 19 3906 3059 (Rint 0.0394) 3059/0/202
1.061 R1 0.0348 wR2 0.0874 R1 0.0464 wR2 0.0946 0.841 and 0.936
1.152 R1 0.0512 wR2 0.1081 R1 0.0750 wR2 0.1200 2.109 and 1.448
1.148 R1 0.0684 wR2 0.1064 R1 0.0883 wR2 0.1152 2.017 and 1.567
1.134 R1 0.0416 wR2 0.0948 R1 0.0619 wR2 0.1085 1.328 and 0.870
(compounds 1 and 4), with v scan mode, 30 s exposure time was used and a half of the Ewald sphere was collected. The unit cell parameters were determined from least-squares refinement of the setting angles from a number of the strongest reflections. Details concerning crystal data and refinement are given in Table 1. Lorentz, polarization, empirical absorption corrections (compounds 3 and 5) and numerical absorption corrections [25] (compounds 1 and 4) were applied. The structures were solved by means of the Patterson and direct methods and subsequently completed by difference Fourier recycling. All the non-hydrogen atoms were refined anisotropically using full-matrix, leastsquares technique. The hydrogen atoms of the phenyl rings were treated as ‘riding’ on their parent carbon ˚ ] and assigned isotropic tematoms [d (C /H) /0.96 A perature factors equal to 1.2 times the value of the equivalent temperature factor of the parent carbon atom. SHELXS-97 [26a], SHELXL-97 [26b] and SHELXTL [27] programs were used for all the calculations. Atomic
scattering factors were those incorporated in the computer programs.
3. Results and discussion It is known that reactions of high oxidation state metal halides with gaseous nitric oxide usually lead to low-valent nitrosyl complexes and it is accompanied with the elimination of nitrosyl halides [28,29]. The reaction of [ReOCl3(AsPh3)2] with NO leads to the complex 2 (the main product) and two by-products (3 and 4), whereas only one compound (complex 1) was isolated in the reaction of the bromine oxocomplex with nitric oxide. The difference in the course of the reactions [ReOX3(AsPh3)2] (X /Cl, Br) with NO depending on the kind of halogen in the starting oxocomplex can be explained considering that NOX are relatively unstable
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gaseous compounds under normal conditions and that NOBr is much less stable than NOCl. The suggested course of the main (2) and minor (3 and 4) product formation is given in the following scheme: [ReOCl3 (AsPh3 )2 ]3NO 0[ReCl3 (NO)(OAsPh3 )2 ] N2 O
(1)
[ReOCl3 (AsPh3 )2 ]4NO 0[ReCl2 (NO)2 (AsPh3 )2 ] NOClNO2
(2) (3)
2[ReOCl3 (AsPh3 )2 ]NOCl 0[ReCl3 (NO)(AsPh3 )2 ] [ReCl4 (AsPh3 )2 ]O2
[NBu4 ]2 [ReBr5 (NO)]2AsPh3 0[ReBr3 (NO)(AsPh3 )2 ] 2[NBu4 ]Br whereas the reaction of [NBu4]2[ReCl5(NO)] with triphenylarsine goes as follows:
[ReCl2 (NO)2 (AsPh3 )2 ]2NOCl 0[ReCl4 (OAsPh3 )2 ] 2N2 O
As in the reaction of [ReOBr3(AsPh3)2] with NO only one product has been isolated */[ReBr3(NO)(OAsPh3)2] (1)*/it can be assumed that the unstable NOBr is not formed and the reactions similar to Eqs. (2) /(4) do not occur. The reaction equation explains the formation of complex 5:
(4)
The [ReCl2(NO)2(AsPh3)2] compound has not been isolated, but the analogous dinitrosyl [ReCl2(NO)2(PPh3)2], obtained in the reaction of [ReOCl3(PPh3)2] with nitric oxide, has been characterised [7]. The proposed above mechanism of the reaction of [ReOCl3(AsPh3)2] with NO can be confirmed by the higher yields of by-products in benzene solution than in CH2Cl2 or THF. Due to the formation of the ClNO ×/C6H6 complex, the concentration of nitrosyl chloride in benzene is much higher than in dichloromethane or tetrahydrofurane, where ClNO ×/CH2Cl2 and ClNO ×/THF are not formed [30,31].
2[NBu4 ]2 [ReCl5 (NO)]4AsPh3 0[ReCl3 (NO)(AsPh3 )2 ] [ReCl4 (AsPh3 )2 ]NOCl2[NBu4 ]Cl The yield of the product in the reactions of [NBu4]2[ReX5(NO)] with AsPh3 depends on: / mass ratio of [NBu4]2[ReX5(NO)] to triphenylarsine and it is the highest when it is equal to 1:5. / reaction time; the yield drops considerably when the reaction is carried out for a time shorter than 6 h. The complex 1 crystallises in the monoclinic space group P 21/n and its structure consists of discrete and well-separated monomers. Fig. 1 shows the molecular structure of this compound. The rhenium atom is in a distorted octahedral environment with a linear N /O group trans to one of the OAsPh3 ligands, two mutually
Fig. 1. The molecular structure of 1. The thermal ellipsoids are drawn at the 50% probability level.
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Fig. 2. The molecular structure of 3.
cis OAsPh3 molecules and three bromine ligands in meridional geometry. The major distortion in the geometry, which is an increase in the N(1) /Re(1) / O(1) angle, is caused by the presence of a multiply bonding ligand (Re /NO) and sizeable steric interactions of two mutually cis OAsPh3 molecules. The asymmetric unit of 3, which crystallises in the ¯ consists of one molecule */ triclinic space group P1; [ReCl3(NO)(AsPh3)2]*/with all atoms in general positions and half the [ReCl4(AsPh3)2] molecule with the rhenium atom on a centre of symmetry. Due to the requirements of the symmetry, the atoms Re(1), Cl(1), Cl(2) and the symmetry equivalents of the two chlorine atoms of the [ReCl4(AsPh3)2] complex lie in one plane and the coordination around the central atom is a square bipyramid extended along the Re /As bonds. Three mutually meridional chlorine atoms, two AsPh3 ligands trans to each other and the linear nitrosyl group octahedrally surround the rhenium atom in the [ReCl3(NO)(AsPh3)2] complex. The departure from the ideal octahedron */the angles between cis -ligands vary between 85.318 and 95.388, and the trans -angles are between 175.178 and 178.318*/appears to be due to the electronic factors and steric interactions with the NO ligand and it is commonly observed in octahedral complexes containing a multiply bonding ligand [32 / 34]. The relative orientation of the [ReCl4(AsPh3)2] and [ReCl3(NO)(AsPh3)2] molecules is depicted in Fig. 2. The complex 4 belongs to the C 2/c space group and the molecular structure of 4 is shown in Fig. 3. The
rhenium atom in 4 occupies a special position e of the space group C 2/c with multiplicity 4 and site symmetry 2. Atom O(1) shows signs of disorder with a particularly high value of one of the displacement parameters, but all attempts to model the disorder failed. It can be suggested that the disorder is dynamical in character. The atom Cl(2) shows multipositional disorder, but invoking this model did not improve the quality of refinement, therefore the model was not applied. The chlorine atoms Cl(2) and its symmetry equivalent Cl(2A) and two cis -oxo atoms of OAsPh3 molecules, O(1) and O(1A) hold the equatorial positions. The Cl(1) and its symmetry equivalent Cl(1A) ions occupy the apical positions. The deviations from an ideal octahedron (the angles between cis -ligands vary between 84.18 and 95.068, and the trans -angles are between 171.338 and 178.48) are caused by steric interactions of two mutually cis OAsPh3 molecules. The structure of 5 consists of discrete and wellseparated monomers. The numbering scheme of 5 is shown in Fig. 4. The complex has pseudooctahedral geometry with trans arsine ligands, meridional bromo ligands and a linear nitrosyl group. The rhenium, NO and bromine species are sited on a crystallographic twofold axis, therefore only half of the molecule is independently located in the asymmetric unit. The three mutually perpendicular coordination planes are well defined and there are no significant intermolecular contacts. The angles between cis -ligands vary between 87.838 and 92.148 (Table 2), and the trans -angles are between 177.888 and 1808.
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Fig. 3. The molecular structure of 4.
Fig. 4. The molecular structure of 5.
The complex 5 is isomorphous with [ReX3(NO)(PPh3)2] (X /Cl and Br) [14,16], [ReOCl3(PPh3)2] [35] and several similar ruthenium nitrosyl compounds [36,37]. The packing of the two bulky triphenylarsine or triphenylphosphine ligands, which are trans to each other, seems to govern the solid-state structure of these
complexes. In fact, the C 2/c space group with four formula units per unit cell is the preferred one for such neutral pseudooctahedral bis(triphenylphosphine) or bis(triphenylarsine) complexes when the co-ordination plane perpendicular to the P /P or As /As vector contains three or four ligands of low steric bulk, which will not cause unusual intermolecular interactions. The trans -arrangement of the two bulky triphenylarsine molecules in 3 and 5 complexes, connected with sterically demanding nature of the arsine ligands, causes the cis -location of the nitrosyl group, with respect to the AsPh3 molecules (p-acid ligands). This is also supported by the electronic influence of the multiply bonded ligand, which forces the metal nonbonding d electrons to lie in the plane perpendicular to the M /NO bond axis. This general rule appears to hold for isonitrile, carbonyl, olefin, acetylene, thioether and often phosphine ligands [38 /40]. Table 1 presents crystal data and structural refinement for compounds 1, 3, 4 and 5. The most important bond lengths and angles for compounds 1, 3, 4 and 5 are reported in Table 2. The Re /NO and N/O bond lengths and the values of Re /N /O angles for complexes 1, 3 and 5, summarised in Table 3, confirm the linear coordination of the nitrosyl group and are comparable with values previously found by others (Table 3). For nitrosyl complexes containing two trans triphenylarsine molecules, elongation of the Re /halogen bond trans to the linear nitrosyl group is observed: the Re /Br(2) bond ˚ in 5 is longer than Re /Br(1) by length at 2.5578(19) A ˚ and in [ReCl3(NO)(AsPh3)2] the Re /Cl(3) about 0.05 A
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Table 2 ˚ ) and angles (8) for 1, 3, 4 and 5 Selected bond lengths (A 1
3
4
5
Bond lengths Re(1) N(1) Re(1) O(1) Re(1) O(2) Re(1) Br(2) Re(1) Br(1) Re(1) Br(3) N(1) O(3) O(1) As(1) O(2) As(2)
1.749(5) 2.050(4) 2.059(4) 2.5117(7) 2.5180(7) 2.5263(7) 1.156(6) 1.680(4) 1.662(4)
Re(1) Cl(2) Re(1) Cl(1) Re(1) As(1) Re(2) N(1) Re(2) Cl(5) Re(2) Cl(4) Re(2) Cl(3) Re(2) As(2) Re(2) As(3) N(1) O(1)
2.329(3) 2.358(3) 2.6023(10) 1.816(10) 2.338(3) 2.339(2) 2.376(2) 2.6060(11) 2.6186(11) 1.092(2)
Re(1) O(1) Re(1) Cl(2) Re(1) Cl(1) As(1) O(1)
2.000(7) 2.292(7) 2.370(2) 1.640(7)
Re(1) N(1) Re(1) Br(1) Re(1) Br(2) Re(1) As(1) N(1) O(1)
1.740(11) 2.5034(19) 2.5578(19) 2.5946(9) 1.177(13)
Bond angles N(1) Re(1) O(1) N(1) Re(1) O(2) O(1) Re(1) O(2) N(1) Re(1) Br(2) O(1) Re(1) Br(2) O(2) Re(1) Br(2) N(1) Re(1) Br(1) O(1) Re(1) Br(1) O(2) Re(1) Br(1) Br(2) Re(1) Br(1) N(1) Re(1) Br(3) O(1) Re(1) Br(3) O(2) Re(1) Br(3) Br(2) Re(1) Br(3) Br(1) Re(1) Br(3) O(3) N(1) Re(1) As(1) O(1) Re(1) O(1) As(1) C(13) O(1) As(1) C(7) C(13) As(1) C(7) O(1) As(1) C(1) C(13) As(1) C(1) C(7) As(1) C(1)
100.6(2) 175.98(19) 83.24(16) 93.30(17) 86.59(12) 88.06(12) 89.90(16) 169.43(11) 86.27(12) 91.76(3) 92.22(17) 88.03(12) 86.73(12) 172.92(2) 92.68(2) 176.8(5) 132.9(2) 116.7(2) 107.2(2) 105.9(3) 107.2(2) 109.1(3) 110.6(3)
Cl(2)#1 Re(1) Cl(2) Cl(2)#1 Re(1) Cl(1) Cl(2) Re(1) Cl(1) Cl(1) Re(1) Cl(1)#1 Cl(2) Re(1) As(1)#1 Cl(1) Re(1) As(1)#1 Cl(2) Re(1) As(1) Cl(1) Re(1) As(1) As(1)#1 Re(1) As(1) N(1) Re(2) Cl(5) N(1) Re(2) Cl(4) Cl(5) Re(2) Cl(4) N(1) Re(2) Cl(3) Cl(5) Re(2) Cl(3) Cl(4) Re(2) Cl(3) N(1) Re(2) As(2) Cl(5) Re(2) As(2) Cl(4) Re(2) As(2) Cl(3) Re(2) As(2) N(1) Re(2) As(3) Cl(5) Re(2) As(3) Cl(4) Re(2) As(3) Cl(3) Re(2) As(3) As(2) Re(2) As(3) O(1) N(1) Re(2) C(7) As(1) C(13) C(7) As(1) C(1) C(13) As(1) C(1) C(7) As(1) Re(1) C(13) As(1) Re(1) C(1) As(1) Re(1)
180.0 91.08(11) 88.92(11) 180.0 92.40(8) 87.10(8) 87.60(8) 92.90(8) 180.0 93.9(3) 90.8(3) 175.17(9) 178.2(3) 87.90(9) 87.34(9) 89.5(3) 85.49(7) 93.71(7) 90.29(7) 91.9(3) 95.38(7) 85.31(7) 88.29(7) 178.31(3) 176.0(9) 103.9(4) 103.7(4) 102.2(4) 114.1(3) 114.6(3) 116.8(3)
O(1)#2 Re(1) O(1) O(1)#2 Re(1) Cl(2) O(1) Re(1) Cl(2) Cl(2) Re(1) Cl(2)#2 O(1)#2 Re(1) Cl(1) O(1) Re(1) Cl(1) Cl(2) Re(1) Cl(1) Cl(2)#2 Re(1) Cl(1) Cl(1) Re(1) Cl(1)#2 O(1) As(1) C(1) O(1) As(1) C(13) C(1) As(1) C(13) O(1) As(1) C(7) C(1) As(1) C(7) C(13) As(1) C(7) As(1) O(1) Re(1)
84.8(7) 178.4(4) 93.8(4) 87.6(4) 84.1(2) 89.5(2) 95.06(14) 91.20(13) 171.33(12) 104.0(4) 110.8(5) 110.7(4) 115.8(4) 107.4(4) 108.1(4) 147.5(4)
N(1) Re(1) Br(1) Br(1) Re(1) Br(1)#3 N(1) Re(1) Br(2) Br(1) Re(1) Br(2) N(1) Re(1) As(1) Br(1) Re(1) As(1) Br(1)#3 Re(1) As(1) Br(2) Re(1) As(1) As(1) Re(1) As(1)#3 O(1) N(1) Re(1) C(7) As(1) C(1) C(7) As(1) C(13) C(1) As(1) C(13) C(7) As(1) Re(1) C(1) As(1) Re(1) C(13) As(1) Re(1)
90.88(2) 178.25(5) 180.000(1) 89.12(2) 91.07(2) 87.82(6) 92.15(6) 88.93(2) 177.87(4) 180.000(2) 106.4(4) 100.3(3) 104.3(3) 119.9(3) 107.2(2) 117.3(3)
Table 3 Relevant structural data for selected rhenium nitrosyl complexes Complex
˚) Re NO bond length (A
˚) N O bond length (A
Re N O angle (8)
[ReBr3(NO)(AsPh3)2] [ReCl3(NO)(AsPh3)2] [ReBr3(NO)(OAsPh3)2] [ReCl3(NO)(OPPh3)2] [13] [ReCl3(NO)(PPh3)2] [14] [ReBr3(NO)(OPPh3)2] [16] [ReBr3(NO)(PPh3)2] [16] [NEt4][ReBr4(NO)(MeCN)] [41] [NEt4][ReBr4(NO)(EtOH)] [41] [ReCl3(NO)(NPPh3)(OPPh3)] [42]
1.740(11) 1.816(10) 1.749(5) 1.72(3) 1.765(9) 1.757(12) 1.769(12) 1.771(11) 1.723(15) 1.734(10)
1.177(13) 1.092(2) 1.156(6) 1.21(3) 1.200(11) 1.261(13) 1.12(2) 0.99(2) 1.19(2) 1.183(13)
180.000(2) 176.0(9) 176.8(5) 172.0(4) 180.000(2) 172.6(13) 180.000(2) 178.0(6) 169.0(3) 174.1(9)
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Table 4 Band position (cm 1) in IR range for complexes 1 /5 1
2
3
1733 1483 1439 1085 1023 893 837 739 688 628 480
1721 1481 1439 1085 1024 888 850 739 689 625 481
1738 1482 1435 1077 1024
741 692
4
1482 1436 1080 1024 890 840 740 690
471
˚ is longer than Re /Cl(4) and bond length at 2.376(2) A ˚ Re /Cl(5) by about 0.04 A. A similar trend is observed in [ReX3(NO)(PPh3)2] (X /Cl, Br) complexes [14,16]. ˚ The Re /As distances 2.6023(10) A in ˚ in [ReCl4(AsPh3)2], 2.6060(11) and 2.6186(11) A ˚ in 5 are consider[ReCl3(NO)(AsPh3)2] and 2.5946(9) A able longer than those found in the rhenium complexes with a cis arrangement of arsine ligands: 2.557(2) and ˚ in [ReO2(dadpe)2] and 2.532(1), 2.552(1), 2.541(2)A ˚ in [ReN(dpae)2Cl] [43]. 2.541(1) and 2.546(1) A The Re /OAsPh3 and the As /O bond lengths in complexes 1 and 4 (Table 2) are in good agreement with values found for [ReOBr3(AsPh3)(OAsPh3)] (Re / ˚ ) and [ReOCl3O /2.010(7), As /O /1.675(7) A (AsPh3)(OAsPh3)] (Re /O /2.019(8), As /O /1.643(9) ˚ [44]). In complex 4, the Re /Cl(2) distance at 2.292(7) A ˚ as a result of ˚ is shorter than Re /Cl(1) by about 0.08 A A its trans position to the OAsPh3 molecule. The bond valences were computed as nij /exp[(Rij / dij )/0.37] [47 /49], where Rij is the bond-valence parameter (in the formal sense Rij is the single-bond length between i and j atoms) [50]. The RReO, RReN, RReBr, RReCl values were taken as 1.97, 2.06, 2.45 and 2.23 [47], respectively. The computed bond valences of rhenium in compound 1 are nReO /0.79, 0.80, nReBr /0.80, 0.81, 0.85; nReN /2.32 v.u. (valence units), in compound 3 are nReAs /0.81, 0.84, nReCl / 0.67, 0.71, 0.75, 0.74, 0.76, 0.81, 0.85; nReN /1.93 v.u., in compound 4 are nReO /0.92, nReCl /0.68, 1.04 v.u. and in compound 5 are nReAs /0.86, nReBr /0.74, 0.86; nReN /2.37 v.u. The weakest bonds are Re /Cl bonds in compound 3 and the strongest are Re /N bonds (formally these bonds can be considered as double bonds). The molecules of 1 are linked to form dimers via C(10) /H(10A) Br(2#/x , /y/2, /z/1) intermolecular weak hydrogen bonds [51] (D A distance equals ˚ and D /H A angle 137.48). One more 3.603(8) A C(26) /H(26A) O(2) weak intramolecular hydrogen ˚ and D /H A bond (D A distance equals 2.992(8) A
5
Assignment
1773 1481 1435 1076 1034
n (NO) d (C CH in the plane) n (As C6H5) d (C H in the plane) d (C H in the plane) n (As O) n (As O) d (C C out of the plane) d (C C in the plane) d (C C in the plane) n (Re N)
737 691 474
angle 112.98) exists in the molecule, which provides additional conformational stabilisation. The conformations of molecules of compound 3 are stabilised by six C /H Cl weak intramolecular hydrogen bonds (D A ˚ and D/H A distances vary from 3.31(1) to 3.67(1) A angles vary from 112.98 to 149.98) and one C(38) / H(38A) N(1) weak intramolecular hydrogen bond ˚ and D /H A angle (D A distance equals 3.34(1) A 127.28). The molecules of 4 are assembled via C(11) / H(11A) Cl(1/x/1/2, /y/1/2, /z/1) weak intermolecular hydrogen bonds (D A distance equal to ˚ and D /H A angle 145.98) to give an infinite 3.59(1) A hydrogen bonded chain created by perpendicular rings in a spiro arrangement. Only one weak intramolecular hydrogen bond, C(8) /H(8A) Br(1/x , y , /z/1/2) ˚ and D/ with a D A distance equal to 3.507(9) A H A angle 133.18, can be found in compound 5, providing slight stabilisation to the molecule. Table 4 contains assignments of characteristic bands in the IR range for 1/5 compounds. For [ReX3(NO)L2] complexes with an identical ligand L, the NO stretching frequency of the chloro-compounds is lower than that of the corresponding bromo-complexes, which is in accordance with the greater p-acceptor character of the bromo ion than the chloro one. A neutral group, L, also causes a variation in the NO stretching frequency. The higher frequencies are found for complexes containing AsPh3 than OAsPh3. The difference between nNO of bromo- and chloronitrosyl is much higher for complexes containing arsines (3 and 5) than for complexes containing arsine oxides (1 and 2), which results from the different ligands’ arrangement around the rhenium atom in these complexes. The presence of two strong bands at about 890 and 840 cm 1 in the IR spectra of complexes 1, 2 and 4 confirms the cis geometry of the two coordinated OAsPh3 molecules. Complexes 1, 2, 4 and 5 are paramagnetic compounds with a magnetic moment corresponding to one unpaired electron.
Table 5 Band positions, molar absorption coefficients and assignments for complexes 1 /5 [ReCl3(NO)(OAsPh3)2] (2)
[ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2] (3)
[ReCl4(OAsPh3)2] (4)
Band position (cm 1)
Band position (cm1)
o
Band position (cm 1)
o
Band position (cm1)
o
14 150 23 000
30 dxy 0 dxz 410 dyz 0 dx2y2
18 800 25 850
320 dxy 0 dyz 280 dxy 0 dxz
15 100 25 300
13 dxy 0 dyz 300 dxy 0 dxz
25 125
960 poOAs 0 dxz
36 100
14 925 23 900 27 740
31 850 36 900 37 900 43 300
o
Assignment
150 dxy 0 dxz 2050 dxz 0 dx2y2, dyz 0 p* OAs 4800 dxy 0 p* NO, dyz 0 dx2y2 2400 dxy 0 p* OAs 14 500 dxy 0 dx2y2, poBr 0 p* NO 17 000 pbReBr 0 dxz 75 000 pbC6H5 0 4dAs
29 750 36 900 37 900 43 300
Assignment
1390 dxy 0 p* NO 6400 dxy 0 dx2y2, dxy 0 p* OAs 6850 pbReCl 0 dxz 43 000 pbC6H5 0 4dAs
42 920
Assignment
5180 dxy 0 dx2y2, pbReCl 0 dxz , (dxy 0 p* NO) 7400 pbC6H5 0 4dAs
34 000
[ReBr3(NO)(AsPh3)2] (5) Assignment
6400 dxy 0 dx2y2, dxy 0 p* OAs
Band position (cm 1)
o
Assignment
14 700 15 550
200 dxz 0 p* 270 dyz 0 p*
17 850
2050 dxy 0 dxz
NO NO
a
43 700
47 000 pbC6H5 0 4dAs
21 600 35 200 38 750 42 900
15 090 poBr 0 dxz 16 080 dxy 0 dx2y2, dxy 0 p* NO 17 640 pbReBr 0 dxz 17 930 pbC6H5 0 4dAs
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629
[ReBr3(NO)(OAsPh3)2] (1)
o molar absorption coefficient (dm3 mol 1 cm 1). a Covered by pbReCl 0 dxz transition.
2625
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629
2626
Table 6 Values of ligand field parameters for 1, 2, 4 and 5 Complex
[ReBr3(NO)(OAsPh3)2] [ReCl3(NO)(OAsPh3)2] [ReCl4(OAsPh3)2] [ReBr3(NO)(AsPh3)2]
Ligand field parameter Dq (cm1)
Ds (cm1)
Dt (cm1)
3690 3690 3400 3521
3741 5104 5272 5952
449 111 143 1
The positions and molar absorption coefficients of electronic bands for complexes 1 /5 and the electronic transitions assigned to the bands are shown in Table 5. Based on the data of Table 5, the values of the ligand field parameters Dq, Ds and Dt have been defined and the energies of molecular orbitals for the complexes have been estimated. The values of ligand field parameters are listed in Table 6, and simplified MO diagrams for complexes 1, 2, 4 and 5 are presented in Fig. 5. Intensities of pbC6H5 0/4dAs transitions in complexes containing arsine oxides are significantly higher in
Fig. 5. The simplified molecular orbitals diagrams for 1, 2, 4 and 5.
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629
comparison with complexes containing arsines, which is connected to: / As [/O electron density transfer, / lack of a Re 0/As transition, which leads to an increase in As acceptor ability towards pC6H5 electrons. Significant intensities of bands: / / / /
at at at at
23 900, 27 740, 36 900 and 37 900 cm 1 in 1, 36 900 cm 1 in 2 36 100 cm 1 in 3 34 000 cm 1 in 4
result from a superposition of charge transfer transitions and d 0/d transitions. The lower intensity of the dxy 0/p* NO transition in complexes containing arsine oxides in comparison with complexes containing arsines results from the presence of an O /As acceptor group in the xy plane, which is competitive towards NO. That is why in complexes containing an O /As group, the N /O bond is shorter and the Re /N bond is longer than in complexes containing AsPh3. High electron density on oxygen atoms from the O /As group also results in an effective sReO bonding and simultaneously an increase in electron density on the ReII ion. The last fact increases its p-donor ability towards Br(1), resulting in a shortening of the Re /Br(1) bond in comparison with the Re / Br(3) bond. The comparatively high intensity of the bands attributed to the dxy 0/p* NO transition proves the linear NO coordination (lack of electron density in p* NO). The low intensity of the dyz 0/p* NO and dxz 0/p* NO transition is caused by the symmetry of these orbitals and NO to each other. Based on the presented simplified
2627
MO diagrams and absorption band analysis, one can conclude that complexes 1, 2 and 5 have electron configurations (dxy )2(dyz )2(dxz )1, and complex 4*/ (dxy )2(dyz )1. In 3 both these configurations exist simultaneously. The Dq parameter for the [ReBr3(NO)(AsPh3)2] complex is slightly higher (by 2638 cm1) than Dq for the [ReBr3(NO)(PPh3)2] complex. This increase in its value is connected with the increase in the degree of covalency of the Re /As bonds (higher p-acceptor ability of As compared to P) and Re /N bonds. The higher pacceptor ability of As manifests also in an increase in molar extinction coefficient of the band resulting from pbC6 H5 0 4dAs and in consequence in an elongation of C / C bonds in AsPh3 compared to PPh3. The small ˚) elongation of the Re /As bond (by only 0.054 A compared to the Re /P bond, in spite of the fact that ˚ ) also proves the higher acceptor rAs3 is longer (by 0.1 A ability of As in comparison to P. The decrease in electron density at the rhenium atom, connected with 5dxz ,yz 0/4dAs electron transitions, increases the probability of charge transfer from Br to 5dRe (the band at 21 598 cm 1; other authors observed the Br 0/Re transition at 23 830 cm 1) [45,46]. Therefore, it leads to an increase in the probability of the dxy 0 p+NO electron transition and causes an abridgement of the ˚ ) and an elongation of the N /O Re /N bond (by 0.015 A ˚ bond (by 0.057 A) in the [ReBr3(NO)(AsPh3)2] complex compared to the [ReBr3(NO)(PPh3)2] complex. Replacing PPh3 with AsPh3 in nitrosyl Re(II) complexes causes a change in charge distribution in complex molecules. Spectroscopic data confirm EPR signals in the solid phase of 5 and in methylene chloride solutions of 1 and 5 (Figs. 6 /8). The solid phase signal clearly confirms the axial symmetry of complex 5, characterised by g /
Fig. 6. Experimental X-band EPR spectrum of 5 in the solid phase at T/295 K.
2628
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629
Fig. 7. Experimental X-band EPR spectrum of 3 in CH2Cl2 at T /295 K.
Fig. 8. Experimental X-band EPR spectrum of 5 in CH2Cl2 at T /295 K.
2.4057, g /2.0412 and gav /2.1624 values. EPR signals of methylene chloride solutions of 1 and 5 also have axial symmetry. Complex 5 is characterised by gav /2.1942 and Aav /31.3 mT values, and complex 1 */by gav /2.2192 and Aav /26.7 mT values. These facts confirm an interaction of an unpaired electron (dxz )1 with the axial ligands. If the unpaired electron was on the dxy orbital, the values of gav in complexes 1 and 5 would be in reverse relation. The higher gav value in 1 results from a higher spin-orbital contribution of axial Br ligands (lBr /2460 cm 1) into gjj, compared to AsPh3 ligands with significantly lower lAs value. The lower Aav value of complex 1 results from covalency of the Re /Br bond, confirmed by rReBr /0.251 nm. The Re /Br distance is shorter than the sum of the ion radii 2 rRe /rBr by 0.041 nm. The sextet signal of complexes 1 and 5, resulting from an interaction of the unpaired electron with the nuclear spins of 185Re and 187Re, indicates a small delocalisation of this electron towards the ligands. Quadruple moments of 14N, 75As, 79Br, 81Br, 185Re and 187Re, broadening the signals, cause superposition of hyperfine structure components.
Acknowledgements
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 188153 /56 for compounds [ReBr3(NO)(AsPh3)2], [ReCl3(NO)(AsPh3)2][ReCl4(OAsPh3)2], [ReBr3(NO)[ReCl4(AsPh3)2], (OAsPh3)2]. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: /44-1223336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
We wish to express our thanks to Danuta Kwapulin´ska for recording EPR spectra. X-ray crystallography of compounds 1 and 4 was financed by statutory funds allocated by the State Committee for Scientific Research to the Institute of General and Ecological Chemistry, Technical University of Lo´dz´.
References [1] R.M.J. Palmer, A.G. Ferrige, S. Moncada, Nature 327 (1987) 524. [2] S. Moncada, R.M.J. Palmer, E.A. Higgs, Pharmacol. Rev. 43 (1991) 109. [3] P.L. Feldman, O.W. Griffith, D.J. Stuehr, Chem. Eng. News 71 (1993) 26. [4] M. Feeelish, J.S. Stamler (Eds.), Methods in Nitric Oxide Research, Wiley, Chichester, England, 1996. [5] W. Volkert, W.F. Goeckeler, G.J. Ehrhardt, A.R. Ketring, J. Nucl. Med. 32 (1991) 174. [6] E.A. Deutsch, K. Libson, J.L. Vanderheyden, Technetium and Rhenium in Chemistry and Nuclear Medicine, Raven Press, New York, 1990. [7] J.O. Dzie˛gielewski, K. Filipek, B. Machura, Polyhedron 14 (1995) 555. [8] J.O. Dzie˛gielewski, B. Machura, T. Kupka, in: J.C. Merlin, S. Turrell, J.P. Huvenne (Eds.), Spectroscopy of Biological Molecules, Kluver Academic Publishers, Dordrecht, 1995, p. 589. [9] J.O. Dzie˛gielewski, B. Machura, J. Marek, Polyhedron 15 (1996) 3713. [10] J.O. Dzie˛gielewski, B. Machura, T.J. Bartczak, Polyhedron 15 (1996) 2813. [11] T.J. Bartczak, W. Czurak, J.O. Dzie˛gielewski, B. Machura, Polish J. Chem. 72 (1998) 633. [12] J.O. Dzie˛gielewski, B. Machura, T. Kupka, T.J. Bartczak, W. Czurak, Polish J. Chem. 72 (1998) 1009. [13] J.O. Dzie˛gielewski, B. Machura, T.J. Bartczak, W. Czurak, J. Kusz, J. Warczewski, J. Coord. Chem. 48 (1999) 125. [14] T.J. Bartczak, W. Czurak, J.O. Dzie˛gielewski, B. Machura, A. Jankowska, J. Kusz, J. Warczewski, Polyhedron 18 (1999) 2313. [15] T.J. Bartczak, W. Czurak, J.O. Dzie˛gielewski, B. Machura, J. Kusz, J. Warczewski, Polish J. Chem. 74 (2000) 265.
B. Machura et al. / Polyhedron 21 (2002) 2617 /2629 [16] T.J. Bartczak, W. Czurak, J.O. Dzie˛gielewski, B. Machura, A. Jankowska, J. Kusz, J. Warczewski, J. Coord. Chem. 52 (2001) 361. [17] S.G. Fonta´n, A. Marchi, L. Marvelli, R. Rossi, S. Antoniutti, G. Albertin, J. Chem. Soc., Dalton Trans. (1996) 2779. [18] C. Bolzati, F. Tisato, F. Refosco, G. Bandali, A. Dolmella, Inorg. Chem. 35 (1996) 6221. [19] F. Connac, Y. Lucchese, M. Dartiguenave, A.L. Beauchamp, Inorg. Chem. 36 (1997) 256. [20] R.G. Cavell, R.W. Hilts, H. Luo, R. McDonald, Inorg. Chem. 38 (1999) 897. [21] R. Rossi, A. Marchi, A. Duatti, L. Magon, U. Casellato, R. Graziani, J. Chem. Soc., Dalton Trans. (1998) 1857. [22] M.F.N.N. Carvalho, A.J.L. Pombeiro, D.L. Hughes, R.L. Richards, J. Organomet. Chem. 335 (1987) C23. [23] N.P. Johnson, C.J.L. Lock, G. Wilkinson, J. Chem. Soc. (1964) 1054. [24] D. Giusto, G. Cova, Gazz. Chem. Ital. 102 (1972) 265. [25] STOE & Cie (1999). X-RED. Version 1.18. STOE & Cie GmbH, Darmstadt, Germany. [26] (a) G.M. Sheldrick, Acta Crystallgr., Sect. A 46 (1990) 467 /473; (b) G.M. Sheldrick, SHELXL-97, Program for the Solution and Refinement of Crystal Structures, University of Go¨ttingen, Germany, 1997. [27] G.M. Sheldrick, SHELXTL: release 4.1 for Siemens Crystallographic Research Systems, 1990. [28] W.B. Hughes, E.A. Zeuch, Inorg. Chem. 12 (1973) 471. [29] L. Bencze, J. Kohan, Inorg. Chim. Acta 65 (1982) L17. [30] D.L.H. Williams, Nitrosation, Cambridge University Press, New York, 1988. [31] R.P. Mueller, S. Murata, J.R. Huber, Chem. Phys. 66 (1982) 237. [32] P.W.R. Corfield, R.J. Doedens, J.A. Ibers, Inorg. Chem. 6 (1967) 197.
2629
[33] G. La Monica, S. Cenini, J. Chem. Soc., Dalton Trans. (1980) 1145. [34] D.C. Bradley, M.B. Hursthouse, K.M.A. Malik, A.J. Nielson, R.L. Short, J. Chem. Soc., Dalton Trans. (1983) 2651. [35] A.M. Lebuis, A.L. Beauchamp, Can. J. Chem. 71 (1993) 441. [36] D. Bright, J.A. Ibers, Inorg. Chem. 8 (1969) 1078. [37] D.H.F. Souza, G. Oliva, A. Teixeira, A.A. Batista, Polyhedron 14 (1995) 1031. [38] T. Lis, Acta Crystallogr., Sect. B 33 (1977) 944. [39] V.S. Sergienko, M.A. Porai-Koshits, V.E. Mistryukov, K.V. Kotegov, Koord. Khim. 8 (1982) 230. [40] J.M. Mayer, D.L. Thorn, T.H. Tulip, J. Am. Chem. Soc. 107 (1985) 7454. [41] G. Ciani, D. Giusto, M. Manassero, M. Sansoni, J. Chem. Soc., Dalton Trans. (1975) 2156. [42] N. Mronga, F. Weller, K. Dehnicke, Z. Anorg. Allg. Chem. 502 (1983) 35. [43] M.T. Castello, P.E. Farwick, M.A. Green, R.A. Walton, Inorg. Chem. 30 (1991) 861. [44] J.O. Dzie˛gielewski, B. Machura, T.J. Bartczak, J. Kusz, J. Warczewski, submitted to J. Coord. Chem. [45] A.P. Mortala, J.W. Moskowitz, N. Rooch, C.D. Cousman, H.B. Gray, Chem. Phys. Lett. 32 (1975) 283. [46] F.A. Cotton, E.P. Edersen, J. Am. Chem. Soc. 97 (1975) 303. [47] I.D. Brown, Acta Crystallogr., Sect. B 48 (1992) 553. [48] I.D. Brown, Acta Crystallogr., Sect. B 53 (1997) 381. [49] M. O’Keeffe, N.E. Brese, J. Am. Chem. Soc. 113 (1991) 3226. [50] L. Sieron, M. Bukowska-Strzyzewska, Acta Crystallogr., Sect. C 55 (1999) 1230. [51] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond in Structural Chemistry and Biology, Oxford University Press, Oxford, 1999.