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Synthesis, characterisation and study of mercury(II) bromide complexes with triphenylphosphine and heterocyclic thiones. The crystal structures of [bis(triphenylphosphine) dibromo mercury(II)] and [dibromo (pyrimidine-2-thionato) (triphenylphosphine) mercury(II)]. Extended intra-molecular linkages via NH⋯Br and CH⋯Br interactions
Polyhedron 20 (2001) 2179– 2185 www.elsevier.com/locate/poly
Synthesis, characterisation and study of mercury(II) bromide complexes with triphenylphosphine and heterocyclic thiones. The crystal structures of [bis(triphenylphosphine) dibromo mercury(II)] and [dibromo (pyrimidine-2-thionato) (triphenylphosphine) mercury(II)]. Extended intra-molecular linkages via NH···Br and CH···Br interactions M. Kubicki a, S.K. Hadjikakou b,*, M.N. Xanthopoulou b b
a Department of Chemistry, A. Mickiewicz Uni6ersity, ul. Grunwaldzka 6, 60 -780 Poznan, Poland Section of Inorganic and Analytical Chemistry, Department of Chemistry, Uni6ersity of Ioannina, 45110 Ioannina, Greece
Received 26 February 2001; accepted 24 April 2001 Dedicated to Professor Petros Karagiannidis
Abstract Fractional crystallisation of the mixture, resulting from the direct reaction of mercury(II) bromide with triphenylphosphine (PPh3) and pyrimidine-2-thione (pmtH), gives crystals of [HgBr2(PPh3)2] (1) and [HgBr2(PPh3)(pmtH)] (2). The complexes have been characterised by their elemental analyses, melting points and their FT-IR, far-IR, and UV– Vis spectroscopic data. The crystal structures of both [bis(triphenylphosphine) dibromo mercury(II)] (1) and [dibromo (pyrimidine-2-thionato)(triphenylphosphine) mercury(II)] (2) complexes have been established by single crystal X-ray crystallography at room temperature. Molecule 1 is monomeric with tetrahedral geometry around the metal ion. Two bromide atoms are co-ordinated to the mercury(II) ion [Hg(1)Br(1)=2.627(2) and Hg(1)Br(2)=2.6368(14) A, ] while two triphenylphosphine molecules are also co-ordinated to the metal ion via their phosphorus atoms with Hg(1)P(1) and Hg(1)P(2) bond distances of 2.550(4) and 2.491(5) A, , respectively. The complex is covalent in the solid state. The unit cell of 2 consists of a molecule with tetrahedral geometry around the mercury(II) ion. A triphenylphosphine ligand and a pyrimidine-2-thione molecule are co-ordinated to the metal ion through their phosphorus and sulfur atoms with Hg(1)P(1) and Hg(1)S(2) bond lengths of 2.450(2) and 2.4795(19) A, , respectively. Two bromide atoms are also co-ordinated to the mercury ion [Hg(1)Br(1)= 2.7065(10) and Hg(1)Br(2)= 2.6997(11) A, ]. The entire complex is covalent in the solid state. Extended intra-molecular linkages via NH···Br interactions lead to a polymeric structure. Extended CH···Br contacts link the alternate parallel chains forming a supramolecular assembly. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Mercury(II) complexes; Triphenylphosphine; Pyrimidine-2-thione; Crystal structures
1. Introduction Although mercury has been used as a constituent of drugs such as bactericides, diuretics, antiseptics, skin ointments and laxatives [1,2], recently mercurials have been replaced by more specific drugs. Nevertheless, the * Corresponding author. Tel.: + 30-651-98-374. E-mail address: [email protected] (S.K. Hadjikakou).
toxicity of mercury and its compounds to living systems is well known [3]. The only significant antidotes to the toxicity of mercury and its compounds of clinical importance are monothiols or dithioles [3]. Therefore, there is an increasing interest in the study of the co-ordination and structural chemistry of mercury(II) complexes with sulfur-containing ligands like thiones or thioles, not only for the clarification of the mercury poisoning mechanism but for the development of new
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 1 ) 0 0 8 2 7 - 0
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antidotes as well [4– 16]. On the other hand, the multiformity of the structural types which are formed from mercury(II) halides or pseudo-halides with aryl-phosphine ligands provides an area of continual interest [17 – 29]. However, there are very few reports on the structural characterisation of mixed ligand mercury(II) complexes with heterocyclic thiones and triaryl-phosphine ligands [30,31]. Searching for the factors which govern the formation of a particular geometry around the mercury ions in its complexes, we report herewith the structural and spectroscopic characterisation of mercury(II) complexes [HgBr2(PPh3)2] (1) and [HgBr2(PPh3)(pmtH)] (2) derived from the reaction of HgBr2 with triphenylphosphine and pyrimidine-2-thione (I, C4H4N2S).
1: 0.050 g; The purity of the sample was established by m.p., elemental analysis and important far-IR data which are identical to those described earlier [32,33]. IR (cm − 1): 3047w, 1481s, 1436vs, 1202s, 1172s, 1072vs, 1100s, 802s, 774s, 748vs, 711s, 690vs, 633s, 516vs, 508vs, 493s. UV–Vis (umax nm (log m)): (CHCl3); 256 nm (4.442); (CH3CN); 252.5 nm (4.278), 205.5 nm (4.539). 2: 0.055 g; m.p. 189–191 °C. Anal. Found: C, 36.13; H, 2.66; N, 3.49; S, 4.94. Calc. for C22H19Br2HgN2PS: C, 35.96; H, 2.60; N, 3.81; S, 4.36%. IR (cm − 1): 3155m, 2925w, 2864w, 1600s, 1577s, 1491s, 1435s, 1433vs, 1320vs, 1173s, 1099s, 983s, 793s, 753vs, 741vs, 694vs, 524vs, 503s, 490s. Far-IR (cm − 1): 279s, 249m, 224m, 196s, 179s, 169m, 153s, 138vs, 128vs, 121vs, 106vs. UV –Vis (umax nm (log m)): (CHCl3); 354 nm (3.121), 281.5 nm (4.190), 242 nm (4.321); (CH3CN); 365 nm (3.057), 281 nm (4.260), 251.5 nm (4.227), 207.5 nm (4.551).
2.3. X-ray data collection and reduction of the intensity data of the complexes 2. Experimental
2.1. Materials and instruments All solvents used were reagent grade. Mercury(II) bromide, triphenylphosphine (Merck) and pyrimidine2-thione (Aldrich) were used with no other purification prior to use. Elemental analyses for C, H, N, and S were carried out with a Carlo Erba EA MODEL 1108. Melting points were measured in open tubes with a STUART scientific apparatus and are uncorrected. IR spectra in the region of 4000– 370 cm − 1 were obtained as KBr discs while far-IR spectra in the region of 400–50 cm − 1 were obtain as polyethylene discs, with a Perkin –Elmer Spectrum GX FT-IR spectrometer. A Jasco UV/Vis/NIR V 570 series spectrophotometer was used to obtain the electronic absorption spectra.
2.2. Synthesis and crystallisation of [HgBr2(PPh3)2] (1) and [HgBr2(PPh3)(pmtH)] (2) complexes A mixture of mercury(II) bromide (0.180 g, 0.5 mmol), triphenylphosphine (0.132 g, 0.5 mmol) and pyrimidine-2-thione (0.112 g, 1 mmol) was suspended in a 20 ml solution of methanol– acetonitrile 1:1 and stirred to clearness. Afterwards, the solution was filtered off to remove any solid still suspended and the clear solution was kept in darkness at room temperature. After 24 h pale-yellow colorless crystals of the complex (1), suitable for single crystal analysis by crystallography, were filtered off and the new clear solution was kept for two more days to give orange crystals of the complex 2, again suitable for single crystal analysis by crystallography.
Although the crystallographic data for the unit cell of the complex 1 have been reported earlier [25] the full X-ray analysis of this complex was prevented because of the poor quality of the crystals. Here we report the full X-ray analysis of complexes 1 and 2. X-ray diffraction data were collected on a KUMA KM4CCD k-geometry diffractometer with CCD detector [34], using graphite-filtered Mo Ka radiation (u=0.71073 A, ). The unit cell dimensions were calculated from the leastsquares fit of the most intense reflections from the whole experiment [35]. We used 1150 and 3937 reflections (q angles ranged from 3 to 25°) for complexes 1 and 2, respectively. Relevant crystallographic data together with data collection and structure refinement details for both complexes 1 and 2 are listed in Table 1. The measurements were performed in six separate runs, four runs consisted of 133 frames, and two of 125 frames ( width of each frame was 0.75°). The q, s and angles for the runs were chosen in such a way as to cover the appropriate part of the Ewald sphere. Two reference frames were measured after every 50 frames of experiment; neither the geometry nor the intensity of the reflections in these frames changed significantly during the data collection. Intensity data were corrected for Lorentz and polarization effects [35] and converted into F2’s. These data were corrected for absorption and averaged with respect to the point group symmetry with the SORTAV program [36]. The structures were solved with the SHELXS-97 program [37]. Full-matrix leastsquares refinement was done with the SHELXL-93 program [38]. Scattering factors incorporated in SHELXL-93 were used. The function w( Fo 2 − Fc 2)2 was minimized, with w − 1 = [| 2(Fo)2 + 0.02P 2 + 0.8P] (where
M. Kubicki et al. / Polyhedron 20 (2001) 2179–2185
P =[max(F 2o,0)+2F 2c ]/3). The non-hydrogen atoms were refined anisotropically, hydrogen atoms were placed in calculated positions and refined as ‘riding Table 1 Crystal data and structure refinement parameters for complexes 1 and 2
Empirical formula Formula weight Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) V (A, 3) Z Dcalc (g cm−3) v (mm−1) Crystal size (mm) 2[ Range (°) Index ranges
1
2
C36H30Br2HgP2 884.95 orthorhombic Pna21
C22H19Br2HgN2PS 734.83 orthorhombic Pna21
17.901(3) 10.181(2) 18.509(4) 3373.3(8) 4 1.74 7.05 0.1×0.15×0.2 1–50 05h521, 05k512, −225l522 Reflections collected 24 415 Independent reflections 5841 [Rint = 0.10] Parameters 370 R(F) [I\2|(I)] 0.066 wR(F 2) [I\2|(I)] 0.092 Goodness-of-fit on F 2 1.08 Largest difference peak and 0.78 and −0.75 hole (e A, −3)
19.3460(15) 7.8909(5) 15.6364(11) 2387.0(5) 4 2.045 9.96 0.1×0.1×0.4 1–52 05h523, 05k59, −195l519 17 641 4638 [Rint = 0.06] 262 0.038 0.068 1.32 0.85 and −0.76
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Table 3 Selected bond lengths (A, ) and bond angles (°) for molecule 2 with e.s.d.s in parentheses Bond lengths Hg(1)P(1) Hg(1)Br(2) N(1)C(6) N(1)C(2) C(2)N(3) C(2)S(2) P(1)C(11)
2.450(2) 2.6997(11) 1.326(12) 1.334(11) 1.369(11) 1.704(10) 1.814(9)
P(1)C(31) P(1)C(21) Hg(1)S(2) Hg(1)Br(1) N(3)C(4) C(4)C(5) C(5)C(6)
1.824(8) 1.825(9) 2.4795(19) 2.7065(10) 1.336(13) 1.376(15) 1.377(14)
Bond angles P(1)Hg(1)S(2) P(1)Hg(1)Br(2) S(2)Hg(1)Br(2) C(2)S(2)Hg(1) C(31)P(1)Hg(1) C(6)N(1)C(2) N(1)C(2)N(3) N(1)C(2)S(2) N(3)C(2)S(2) C(11)P(1)C(31) C(11)P(1)C(21) C(31)P(1)C(21) C(12)C(11)P(1) C(16)C(11)P(1)
103.96(6) 95.18(9) 101.9(3) 114.0(3) 118.8(8) 119.3(8) 123.8(7) 116.9(7) 106.5(4) 109.7(4) 106.2(4) 118.6(8) 121.5(7) 119.6(7)
C(26)C(21)P(1) C(22)C(21)P(1) P(1)Hg(1)Br(1) S(2)Hg(1)Br(1) Br(2)Hg(1)Br(1) C(11)P(1)Hg(1) C(21)P(1)Hg(1) C(4)N(3)C(2) N(3)C(4)C(5) C(4)C(5)C(6) N(1)C(6)C(5) C(32)C(31)P(1) C(36)C(31)P(1)
115.6(7) 122.8(6) 108.49(6) 104.11(6) 103.28(5) 112.0(3) 108.2(3) 122.6(9) 118.5(10) 117.1(10) 123.7(10) 119.6(7) 119.7(7)
Table 2 Selected bond lengths (A, ) and bond angles (°) for molecule 1 with e.s.d.s in parentheses Bond lengths Hg(1)P(2) Hg(1)P(1) P(1)C(111) P(1)C(121) P(1)C(131)
2.491(5) 2.550(4) 1.835(14) 1.845(17) 1.802(15)
Hg(1)Br(1) Hg(1)Br(2) P(2)C(211) P(2)C(221) P(2)C(231)
2.627(2) 2.6368(14) 1.769(16) 1.788(13) 1.794(13)
Bond angles P(2)Hg(1)P(1) P(2)Hg(1)Br(1) P(1)Hg(1)Br(1) C(111)P(1)Hg(1) C(131)P(1)Hg(1) C(121)P(1)Hg(1) C(111)P(1)C(121) C(111)P(1)C(131) C(121)P(1)C(131) C(112)C(111)P(1) C(116)C(111)P(1) C(122)C(121)P(1) C(126)C(121)P(1) C(132)C(131)P(1) C(136)C(131)P(1)
113.01(14) 113.12(10) 105.12(10) 109.9(4) 115.8(5) 110.7(5) 107.6(7) 107.6(7) 104.8(7) 122.5(12) 115.5(12) 116.6(15) 118.6(13) 121.4(13) 119.4(14)
P(2)Hg(1)Br(2) P(1)Hg(1)Br(2) Br(1)Hg(1)Br(2) C(211)P(2)Hg(1) C(221)P(2)Hg(1) C(231)P(2)Hg(1) C(211)P(2)C(221) C(211)P(2)C(231) C(221)P(2)C(231) C(212)C(211)P(2) C(216)C(211)P(2) C(222)C(221)P(2) C(226C(221)P(2) C(232)C(231)P(2) C(236)C(231)P(2)
114.23(12) 103.37(9) 107.12(8) 106.0(6) 117.9(5) 111.9(5) 102.5(7) 110.7(7) 107.3(6) 117.3(13) 125.0(14) 120.9(11) 122.2(11) 119.0(10) 124.2(12)
Fig. 1. Thermal ellipsoid representations of 1 together with atomic numbering schemes.
mode’, i.e. they followed the movements of their carrier atoms. The isotropic displacement parameters for hydrogen atoms were calculated as 1.2 times the equivalent displacement parameters for the respective non-hydrogen carrier atoms. Due to the relatively poor quality of the crystals of complex 1 some restraints had to be applied to the anisotropic displacement parameters of the carbon atoms; these restraints were supposed to ensure the more or less proper shape of the ellipsoids (ISOR, [38]). The bond lengths and angles for complexes 1 and 2 are given in Tables 2 and 3, respectively, while the displacement ellipsoid representation of complexes 1 and 2 is shown in Figs. 1 and 2, respectively.
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2.4. Computational details Extended Huckel calculations were performed using the CACAO program [39]. The calculations were carried out using crystallographic data of the studied molecules. The EHT parameters for Hg, were those established in the literature.
3. Results and discussion
3.1. General aspects Crystals of complexes 1 and 2 have been prepared by slow evaporation of the solution remaining, after the filtration of the initial solution, from the reaction of 0.5 mmol HgBr2 with 0.5 mmol triphenylphosphine and 1 mmol pyrimidine-2-thione, in methanol– acetonitrile solution. After one day 0.060 mmol pale-yellow colorless crystals, of complex 1 were filtered off and after two further days the new clear solution gave 0.075 mmol orange crystals of complex 2. The formulae of the complexes were firstly deduced from their elemental analysis, m.p. and spectroscopic data. The crystals of the complexes are air stable when stored in darkness at room temperature. Searching for the factors that govern the formation of a particular geometry around the mercury ions in mixed ligands complexes, we have reported previously the synthesis and structural characterisation of the [(benzothiazole-2-thionato) (benzothiazole-2-thione) (bis-triphenylphosphine) chloro mercury(II)] (3) and the [(m2 -dichloro){(bis-pyrimidine-2-thionato)mercury(II)}{(bis-triphenylphosphine) mercury(II)}] (4) complexes, derived from the reaction between HgCl2, triphenylphosphine and benzothiazole-2-thione or pyrimidine-2thione [31]:
In these complexes, 3 and 4, thione ligands have been deprotonated upon co-ordination, contrary to complex 2 where pyrimidine-2-thione is co-ordinated in its neutral form. Thus, the relatively higher covalent character of the HgBr bond in case of 2 compared to the more ionic HgCl bond in case of 3 and 4 leaves pyrimidine2-thione unchanged upon co-ordination.
3.2. UV –Vis spectroscopy The UV spectrum of complex 1 in chloroform is dominated by one main absorption band at umax =256 nm (log m= 4.442) which is ascribed to the intra-ligand transitions of triphenylphosphine (umax = 263 nm, log m=4.076), since umax of this absorption band exhibits no significance shift from either the corresponding umax of the band of the free ligand or from the corresponding umax of the band of complex 1 in acetonitrile (umax = 252.5 nm, log m= 4.278) [40]. The UV–Vis spectrum of complex 2 in chloroform is dominated by absorption bands with umax (log m) values 354 nm (3.121), 281.5 nm (4.190) and 242 nm (4.321). The first band is attributed to a charge transfer band since it occurs with a shift of 26 nm to lower wavelengths in respect of the corresponding band of free thione and a shift of 11 nm from the corresponding absorption band of the complex in acetonitrile, while the second band is ascribed to the intra-ligand transitions of pyrimidine-2thione [40]. The spectrum of free thione in chloroform consist of absorption bands at 380.5 and 291.5 nm having log m values 3.193 and 4.129, respectively.
3.3. IR spectroscopy
Fig. 2. Thermal ellipsoid representations of 2 together with atomic numbering schemes.
The IR spectrum of complex 1 shows bands at 690, 516, 508 and 493 cm − 1 which have been attributed to the vibrations of the CP bond. No significant change has been observed between the IR spectrum of complex 1 and the corresponding spectrum of triphenylphosphine. The IR spectrum of complex 2 shows distinct vibrational bands at 1577 and 1320 cm − 1 which have been assigned to vibrations of the CN bond (thioamide I and II bands) and at 983 and 793 cm − 1 which were attributed to the CS bond vibrations (thioamide III and IV bands). The corresponding thioamide bands of free pyrimidine-2-thione ligand are at 1561, 1320, 982 and 791 cm − 1, respectively [41]. The bands at 694, 524, 503 and 490 cm − 1 have been attributed to the vibrations of the CP bond. Further information about the complexes was obtained from
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Fig. 3. Far-IR spectra of complexes 1 and 2.
the study of far-IR spectra. Fig. 3 shows the far-IR spectra of complexes 1 and 2. The new band at 151 cm − 1 (vs) in the far-IR spectrum of complex 1 has been assigned to the vibrations of the HgBr bond [9,17,32,33,42] while the band appearing at 120 cm − 1 (vs) has been attributed to the vibration of the HgP bond [19,27,32,43]. The far-IR spectrum of complex 2 shows a band at 153 cm − 1 (s) which is assigned as vibrations of the HgBr bond with a band at 121 cm − 1 (vs) which is ascribed to the HgP bond vibrations. The band at 196 cm − 1 is attributed to the vibration of the HgS bond [42,44].
3.4. Structures of [HgBr2(PPh3)2] (1) and [HgBr2(PPh3)(pmtH)] (2) complexes Although the crystallographic data for the unit cell along with some initial data of complex 1 have been reported earlier, the structure was not fully solved [25]. Views of molecules 1 and 2 are shown in Figs. 1 and 2, respectively, while selected bond lengths and angles for molecules 1 and 2 are given in Tables 2 and 3, respectively. The two complexes are covalent in the solid state. The geometry around the mercury(II) ion, in both complexes, is tetrahedral. Molecule 1 is a monomer in the solid state with two phosphorus and two bromide atoms around the mercury atom. A triphenylphosphine ligand, a pyrimidine-2-thione molecule and two bromide atoms are co-ordinated to the metal ion in complex 2. The Hg(1)Br(1) and Hg(1)Br(2) bond distances are 2.627(2) and 2.6368(14) A, , respectively, in complex 1 and are in accordance with those found by Nowell et al. [25] (HgBr1 =2.633(6) and HgBr2 = 2.627(8) A, ), while the corresponding Hg(1)Br(2) and Hg(1)Br(1) bond distances measured for complex 2 are
2.6997(11) and 2.7065(10) A, , respectively. The HgBr bond distances found in [Hg(Ph2PCHCHPPh2)Br2] are HgBr(1)terminal = 2.545(2) and HgBr(2)terminal = 2.560(2) A, [26] while in [Pr3PHgBr2]2 they are HgBr(1)terminal = 2.507(2) and HgBr(2)bridging = 2.667(2) A, [20], in [(PPh3)HgBr2]2 they are Hg(1)Br(1)terminal = 2.499(7) and Hg(2)Br(2)terminal = 2.505(7) A, , Hg(1)Br(4)bridging = 2.721(7), Hg(2)Br(3)bridging = 2.704(7) A, [19] and in [DMPPHgBr2] they are Hg(1)Br(2)terminal = 2.6129(6) and Hg(1)Br(1)bridging = 2.6272(6) A, ) [17]. The HgBr bond lengths of complexes 1 and 2 are relatively longer than those found in bonds with terminal bromide atoms and closer to those with bridging bromide atoms, indicating an intra- or inter- HgBr···X interactions for both complexes studied. Extended intra-molecular linkages via NH···Br interactions lead to a polymeric structure for complex 2. The H(3)a[N(3)a]···Br(1) distance is 2.4448 A, with a N(3)a···Br(1) distance of 3.2938 A, (symmetry operations used: x, − 1+y, z) [45]. Extended CH···Br contacts link the alternate parallel chains forming a supramolecular assembly. The H(4)b[C(4)b]···Br(2) distance is 2.8529 A, with a C(4)b···Br(2) distance of 3.7518 A, (symmetry operations used (−x, 2− y, − 1/2 + z) [45]. Fig. 4 shows the intra-molecular linkages via NH···Br and the CH···Br interactions in complex 2. A Br(1)···H(125)a[C(125)a] interaction in case of complex 1 is also detected by the inter-atomic distance of 2.9773 A, (symmetry operations used: x, 1+ y, z) [45]. The two Hg(1)P(2) and Hg(1)P(1) bond lengths in complex 1 are 2.491(5) and 2.550(4) A, , respectively, and are similar to the corresponding values found in [Hg(Ph2PCHCHPPh2)2Br2] (HgP = 2.572(2) A, ) [26], in [Pr3PHgBr2]2 (HgP = 2.408(4) A, ) [20], in [(PPh3)HgBr2]2 (Hg(1)P(1) =
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2.40(2) A, ) [19] and in [DMPPHgBr2] (HgP = 2.4490(2) A, ) [17]. Moreover, the HgP bond lengths of complex 1 are also in accordance with those measured in mixed ligand mercury(II) complexes as in [Hg(PPh3)(bzthztH)(bzthzt)Cl] (HgP =2.453(2) A, ) [31], in [Hg2Cl2(PPh3)2(pmt)2] (HgP =2.4826(9) A, ) [31] and in [Hg(PPh3)2(SCN4Ph)2] (HgP =2.500(3) A, ) [30]. The Hg(1)P(1) bond length in complex 2 is 2.450(2) A, and is in the range of the corresponding bond distances measured in [Hg(PPh3)(bzthztH)(bzthzt)Cl] (Hg(1) P(1) =2.453(2) A, ) [31], in [Hg2Cl2(PPh3)2(pmt)2] (HgP = 2.4826(9) A, ) [31] and in [Hg(PPh3)2(SCN4Ph)2] (HgP = 2.500(3) A, ) [30]. The Hg(1)S(2) bond length in complex 2 is 2.4795(19) A, , while the HgS bond distances measured in [Hg(PPh3)(bzthztH)(bzthzt)Cl] are Hg(1)S(2)thionato =2.453(2) A, , Hg(1)S(2A)thione =
2.726(2) A, [31] and in [Hg2Cl2(PPh3)2(pmt)2] it is Hg(2)S(42) = 2.3513(11) A, [31]. The S(2)C(2) and C(2)N(3) bond lengths in complex 2 are 1.704(10) and 1.369(11) A, , respectively, and are in accordance with the corresponding bond distances found for bzthztH in [Hg(PPh3)(bzthztH)(bzthzt)Cl] (S(2A)C(2A) =1.690(9) A, and C(2A)N(3A) = 1.320(11) A, ) [31]. The P(1)Hg(1)P(2) angle measured in complex 1 is 113.01(14)° and is in accordance to the corresponding angle found in [Hg2Cl2(PPh3)2(pmt)2] (P(1)Hg(1) P1)i = 116.32(4)° [31] but smaller than those measured in ([Hg(PPh3)2(SCN4Ph)2] (P1HgP2 = 125.6(1)°) [30], in [HgCl2(PPh3)2] (P1HgP2 = 134.1(1)°) [25] and in [HgCl2((thienyl)3P)2] (P(1)HgP(2) = 128.6(1)°) [24]. The increasing value of the PHgP% angle observed, on going from complex 1 to [HgCl2((thienyl)3P)2] [24] or [HgCl2(PPh3)2] [25] complexes follows the increasing electronegativity between bromide and chlorine halogens, as expected. The Br(1)Hg(1)Br(2) angle in complex 1 is 107.12(8),° similar to the corresponding angle found in [Hg(Ph2PCHCHPPh2)2Br2] (Br(1)Hg Br(2)=112.7(1)°) [26]. The Br(2)Hg(1)Br(1) bond angle in complex 2 is 103.28(5)° and is slightly smaller than the corresponding angle measured for complex 1 (Br(1)Hg(1)Br(2) =107.12(8)o). The S(2)Hg(1) Br(1) angle is 103.96(6)° and is higher than the value of the S(2a)Hg(1)Cl(1) angle (99.10(7)°) in [Hg(PPh3)(bzthztH)(bzthzt)Cl] [31] where the amide hydrogen atom takes part in an inter-molecular hydrogen bond. The S(2)Hg(1)Br(2) bond angle is 95.18(9)°.
3.5. Computational study
Fig. 4. Intra-molecular linkages via NH···Br and CH···Br interactions in complex 2.
The differences in co-ordination mode of the mixed ligand mercury(II) complexes with thione and phosphine prompted us to undertake a computational study in order to verify the factors leading the formation of the different types of complex. The energy of the lowest unoccupied molecular orbital (LUMO) of complex 1 lies 3.768 eV higher than the energy of its highest occupied molecular orbital (HOMO), while the LUMO’s energy is 3.094 eV nearer the HOMO’s energy in case of the complex 2. The calculated overlap populations, in case of complex 1, for the Hg(1)Br(1) and Hg(1)Br(2) bonds are 0.418e and 0.412e, respectively, while the overlap populations calculated for the Hg(1)P(1) and Hg(1)P(2) bonds are 0.600e and 0.625e, respectively. The calculated overlap populations for the two Hg(1)Br(1) and Hg(1)Br(2) bonds are 0.363e and 0.348e, respectively in case of complex 2 indicating a smaller covalent bond strength compared to the corresponding bonds in complex 1, due to the strong intra-molecular interactions. The overlap population for the HgS bond is 0.528e.
M. Kubicki et al. / Polyhedron 20 (2001) 2179–2185
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 158018 and 158017 for compounds 1 and 2, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336033; e-mail: [email protected]. ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements S.K.H. wishes to thank Professor N. Hadjiliadis (Coordinator of the graduate program — E.P.E.A.E.K. — in Bioinorganic Chemistry) for the instrumental support in vibrational spectroscopy.
References [1] A.K. Das, S. Setb, J. Inorg. Biochem. 65 (1997) 207. [2] J.J. Vostal, R.W. Clarkson, J. Occup. Med. 15 (1973) 649. [3] L. Magos, in: H.G. Seiler, H. Sigel, A. Sigel (Eds.), Handbook on Toxicity of Inorganic Compounds, Marcel Dekker, New York, 1988, pp. 419 –436 (chap. 35). [4] N.A. Bell, W. Clegg, J.R. Creighton, E.S. Raper, Inorg. Chim. Acta 303 (2000) 12. [5] Z. Popovic, G. Pavlovic, D. Matkovic-Calogovic, Z. Soldin, M. Rajic, D. Vikic-Topic, D. Kovacek, Inorg. Chim. Acta 306 (2000) 142. [6] T.S. Lobana, S. Paul, A. Castineiras, J. Chem. Soc., Dalton Trans. (1999) 1819. [7] E.S. Raper, J.R. Creighton, N.A. Bell, W. Clegg, L. CucurullSanchez, Inorg. Chim. Acta 277 (1998) 14. [8] R. Baggio, M.T. Garland, M. Perec, J. Chem. Soc., Dalton Trans. (1995) 987. [9] J. Dai, M. Munakata, G. Bian, Q. Xu, T. Kuroda-Sowa, M. Maekawa, Polyhedron 17 (1998) 2267. [10] G. Fleissner, P.M. Kozlowski, M. Vargek, J.W. Bryson, T.V. O’Halloran, T.G. Spiro, Inorg. Chem. 38 (1999) 3523. [11] C.M.V. Stalhandske, I. Persson, M. Sandstrom, M. Aberg, Inorg. Chem. 36 (1997) 4945. [12] D.T. Jiang, S.M. Heald, T.K. Sham, M.J. Stillman, J. Am. Chem. Soc. 116 (1994) 11004. [13] P. Barbaro, F. Cecconi, C.A. Ghilardi, S. Midollini, A. Orlandini, A. Vacca, Inorg. Chem. 33 (1994) 6163. [14] T. Alsina, W. Clegg, K.A. Fraser, J. Sola, J. Chem. Soc., Chem. Commun. (1992) 1010. [15] R.A. Santos, E.S. Gruff, S.A. Koch, G.S. Harbinson, J. Am. Chem. Soc. 113 (1991) 469.
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[16] L. Carlton, D. White, Polyhedron 9 (1990) 2717. [17] N.A. Bell, S.J. Coles, M.B. Hursthouse, M.E. Light, K. Abdul Malik, R. Mansor, Polyhedron 19 (2000) 1719. [18] A. Knoepfler-Muhlecker, B. Scheffter, H. Kopacka, K. Wurst, P. Peringer, J. Chem. Soc., Dalton Trans. (1999) 2525. [19] G.A. Bowmaker, H.J. Clase, N.W. Alcock, J.M. Kessler, J.H. Nelson, J.S. Frye, Inorg. Chim. Acta 210 (1993) 107. [20] N.A. Bell, L.A. March, I.W. Nowell, Inorg. Chim. Acta 162 (1989) 57. [21] T.S. Lobana, M.K. Sandhu, D.C. Povey, G.W Smith, V. Ramdas, J. Chem. Soc., Dalton Trans. (1989) 2339. [22] N.A. Bell, L.A. March, I.W Nowell, Inorg. Chim. Acta 156 (1989) 201. [23] T. Allman, R.E. Lenkinski, Inorg. Chem. 25 (1986) 3202. [24] D.W Allen, N.A. Bell, S.T. Fong, L.A. March, L.W. Nowell, Inorg. Chim. Acta 99 (1985) 157. [25] N.A. Bell, T.D. Dee, M. Goldstein, P.J. McKenna, I.W. Nowell, Inorg. Chim. Acta 71 (1983) 135. [26] H.B. Buergi, E. Fischer, R.W. Kunz, M. Parvez, P.S. Pregosin, Inorg. Chem. 21 (1982) 1246. [27] N.A. Bell, M. Goldstein, T. Jones, L.A. March, I.W. Nowell, Inorg. Chim. Acta 61 (1982) 83. [28] N.A. Bell, M. Goldstein, T. Jones, I.W. Nowell, Inorg. Chim. Acta 48 (1981) 185. [29] N.A. Bell, M. Goldstein, T. Jones, I.W. Nowell, Inorg. Chim. Acta 43 (1980) 87. [30] H. Noth, W. Beck, K. Burger, Eur. J. Inorg. Chem. (1998) 93. [31] S.K. Hadjikakou, M. Kubicki, Polyhedron 19 (2000) 2231. [32] T. Allman, R.G. Goel, P. Pilon, Spectrochim. Acta 35A (1979) 923. [33] N.A. Bell, T.D. Dee, P.L. Goggin, M. Goldstein, R.J. Goodfellow, T. Jones, K. Kessler, D.M. McEwan, I.W. Nowell, J. Chem. Res. (S) (1981) 2. [34] KUMA KM-4CCD user manual, KUMA Diffraction, Wroclaw, Poland, 1999. [35] CrysAlis: Program for Reduction of the Data from KUMA CCD diffractometer, KUMA Diffraction, Wroclaw, Poland, 1999. [36] R.H. Blessing, J. Appl. Crystallogr. 22 (1989) 396. [37] G.M. Sheldrick, Programs for Crystal Structure Analysis (Release 97-2), Institut fu¨ r Anorganische Chemie der Universita¨ t, Tammanstrasse 4, D-3400 Go¨ ttingen, Germany, 1998. [38] G.M. Sheldick, SHELXL-93: Program for the Refinement of Crystal Structures, University of Go¨ ttingen, Go¨ ttingen, Germany, 1993. [39] C. Mealli, D. Proserpio, J. Chem. Educ. 67 (1990) 399 (CACAO: Computer Aided Composition of Atomic Orbitals, PC Ver. 4.0). [40] P. Karagiannidis, S.K. Hadjikakou, P. Aslanidis, A. Hountas, Inorg. Chim. Acta 128 (1990) 27. [41] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Wiley, New York, 1966. [42] M. Cannas, F.A. Devillanova, G. Marongiu, G. Verani, J. Nucl. Chem. 43 (1981) 2383. [43] G.B. Deacon, J.H. Green, Chem. Commun. (1966) 629. [44] E.S. Raper, Coord. Chem. Rev. 61 (1985) 115. [45] A.L. Spek, Acta Crystallogr., Sect. A 46 (1990) C-34 (PLATON).
Synthesis, characterisation and study of mercury(II) bromide complexes with triphenylphosphine and heterocyclic thiones. The crystal structures of [bis(triphenylphosphine) dibromo mercury(II)] and [dibromo (pyrimidine-2-thionato) (triphenylphosphine) mercury(II)]. Extended intra-molecular linkages via NH···Br and CH···Br interactions M. Kubicki a, S.K. Hadjikakou b,*, M.N. Xanthopoulou b b
a Department of Chemistry, A. Mickiewicz Uni6ersity, ul. Grunwaldzka 6, 60 -780 Poznan, Poland Section of Inorganic and Analytical Chemistry, Department of Chemistry, Uni6ersity of Ioannina, 45110 Ioannina, Greece
Received 26 February 2001; accepted 24 April 2001 Dedicated to Professor Petros Karagiannidis
Abstract Fractional crystallisation of the mixture, resulting from the direct reaction of mercury(II) bromide with triphenylphosphine (PPh3) and pyrimidine-2-thione (pmtH), gives crystals of [HgBr2(PPh3)2] (1) and [HgBr2(PPh3)(pmtH)] (2). The complexes have been characterised by their elemental analyses, melting points and their FT-IR, far-IR, and UV– Vis spectroscopic data. The crystal structures of both [bis(triphenylphosphine) dibromo mercury(II)] (1) and [dibromo (pyrimidine-2-thionato)(triphenylphosphine) mercury(II)] (2) complexes have been established by single crystal X-ray crystallography at room temperature. Molecule 1 is monomeric with tetrahedral geometry around the metal ion. Two bromide atoms are co-ordinated to the mercury(II) ion [Hg(1)Br(1)=2.627(2) and Hg(1)Br(2)=2.6368(14) A, ] while two triphenylphosphine molecules are also co-ordinated to the metal ion via their phosphorus atoms with Hg(1)P(1) and Hg(1)P(2) bond distances of 2.550(4) and 2.491(5) A, , respectively. The complex is covalent in the solid state. The unit cell of 2 consists of a molecule with tetrahedral geometry around the mercury(II) ion. A triphenylphosphine ligand and a pyrimidine-2-thione molecule are co-ordinated to the metal ion through their phosphorus and sulfur atoms with Hg(1)P(1) and Hg(1)S(2) bond lengths of 2.450(2) and 2.4795(19) A, , respectively. Two bromide atoms are also co-ordinated to the mercury ion [Hg(1)Br(1)= 2.7065(10) and Hg(1)Br(2)= 2.6997(11) A, ]. The entire complex is covalent in the solid state. Extended intra-molecular linkages via NH···Br interactions lead to a polymeric structure. Extended CH···Br contacts link the alternate parallel chains forming a supramolecular assembly. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Mercury(II) complexes; Triphenylphosphine; Pyrimidine-2-thione; Crystal structures
1. Introduction Although mercury has been used as a constituent of drugs such as bactericides, diuretics, antiseptics, skin ointments and laxatives [1,2], recently mercurials have been replaced by more specific drugs. Nevertheless, the * Corresponding author. Tel.: + 30-651-98-374. E-mail address: [email protected] (S.K. Hadjikakou).
toxicity of mercury and its compounds to living systems is well known [3]. The only significant antidotes to the toxicity of mercury and its compounds of clinical importance are monothiols or dithioles [3]. Therefore, there is an increasing interest in the study of the co-ordination and structural chemistry of mercury(II) complexes with sulfur-containing ligands like thiones or thioles, not only for the clarification of the mercury poisoning mechanism but for the development of new
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 1 ) 0 0 8 2 7 - 0
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antidotes as well [4– 16]. On the other hand, the multiformity of the structural types which are formed from mercury(II) halides or pseudo-halides with aryl-phosphine ligands provides an area of continual interest [17 – 29]. However, there are very few reports on the structural characterisation of mixed ligand mercury(II) complexes with heterocyclic thiones and triaryl-phosphine ligands [30,31]. Searching for the factors which govern the formation of a particular geometry around the mercury ions in its complexes, we report herewith the structural and spectroscopic characterisation of mercury(II) complexes [HgBr2(PPh3)2] (1) and [HgBr2(PPh3)(pmtH)] (2) derived from the reaction of HgBr2 with triphenylphosphine and pyrimidine-2-thione (I, C4H4N2S).
1: 0.050 g; The purity of the sample was established by m.p., elemental analysis and important far-IR data which are identical to those described earlier [32,33]. IR (cm − 1): 3047w, 1481s, 1436vs, 1202s, 1172s, 1072vs, 1100s, 802s, 774s, 748vs, 711s, 690vs, 633s, 516vs, 508vs, 493s. UV–Vis (umax nm (log m)): (CHCl3); 256 nm (4.442); (CH3CN); 252.5 nm (4.278), 205.5 nm (4.539). 2: 0.055 g; m.p. 189–191 °C. Anal. Found: C, 36.13; H, 2.66; N, 3.49; S, 4.94. Calc. for C22H19Br2HgN2PS: C, 35.96; H, 2.60; N, 3.81; S, 4.36%. IR (cm − 1): 3155m, 2925w, 2864w, 1600s, 1577s, 1491s, 1435s, 1433vs, 1320vs, 1173s, 1099s, 983s, 793s, 753vs, 741vs, 694vs, 524vs, 503s, 490s. Far-IR (cm − 1): 279s, 249m, 224m, 196s, 179s, 169m, 153s, 138vs, 128vs, 121vs, 106vs. UV –Vis (umax nm (log m)): (CHCl3); 354 nm (3.121), 281.5 nm (4.190), 242 nm (4.321); (CH3CN); 365 nm (3.057), 281 nm (4.260), 251.5 nm (4.227), 207.5 nm (4.551).
2.3. X-ray data collection and reduction of the intensity data of the complexes 2. Experimental
2.1. Materials and instruments All solvents used were reagent grade. Mercury(II) bromide, triphenylphosphine (Merck) and pyrimidine2-thione (Aldrich) were used with no other purification prior to use. Elemental analyses for C, H, N, and S were carried out with a Carlo Erba EA MODEL 1108. Melting points were measured in open tubes with a STUART scientific apparatus and are uncorrected. IR spectra in the region of 4000– 370 cm − 1 were obtained as KBr discs while far-IR spectra in the region of 400–50 cm − 1 were obtain as polyethylene discs, with a Perkin –Elmer Spectrum GX FT-IR spectrometer. A Jasco UV/Vis/NIR V 570 series spectrophotometer was used to obtain the electronic absorption spectra.
2.2. Synthesis and crystallisation of [HgBr2(PPh3)2] (1) and [HgBr2(PPh3)(pmtH)] (2) complexes A mixture of mercury(II) bromide (0.180 g, 0.5 mmol), triphenylphosphine (0.132 g, 0.5 mmol) and pyrimidine-2-thione (0.112 g, 1 mmol) was suspended in a 20 ml solution of methanol– acetonitrile 1:1 and stirred to clearness. Afterwards, the solution was filtered off to remove any solid still suspended and the clear solution was kept in darkness at room temperature. After 24 h pale-yellow colorless crystals of the complex (1), suitable for single crystal analysis by crystallography, were filtered off and the new clear solution was kept for two more days to give orange crystals of the complex 2, again suitable for single crystal analysis by crystallography.
Although the crystallographic data for the unit cell of the complex 1 have been reported earlier [25] the full X-ray analysis of this complex was prevented because of the poor quality of the crystals. Here we report the full X-ray analysis of complexes 1 and 2. X-ray diffraction data were collected on a KUMA KM4CCD k-geometry diffractometer with CCD detector [34], using graphite-filtered Mo Ka radiation (u=0.71073 A, ). The unit cell dimensions were calculated from the leastsquares fit of the most intense reflections from the whole experiment [35]. We used 1150 and 3937 reflections (q angles ranged from 3 to 25°) for complexes 1 and 2, respectively. Relevant crystallographic data together with data collection and structure refinement details for both complexes 1 and 2 are listed in Table 1. The measurements were performed in six separate runs, four runs consisted of 133 frames, and two of 125 frames ( width of each frame was 0.75°). The q, s and angles for the runs were chosen in such a way as to cover the appropriate part of the Ewald sphere. Two reference frames were measured after every 50 frames of experiment; neither the geometry nor the intensity of the reflections in these frames changed significantly during the data collection. Intensity data were corrected for Lorentz and polarization effects [35] and converted into F2’s. These data were corrected for absorption and averaged with respect to the point group symmetry with the SORTAV program [36]. The structures were solved with the SHELXS-97 program [37]. Full-matrix leastsquares refinement was done with the SHELXL-93 program [38]. Scattering factors incorporated in SHELXL-93 were used. The function w( Fo 2 − Fc 2)2 was minimized, with w − 1 = [| 2(Fo)2 + 0.02P 2 + 0.8P] (where
M. Kubicki et al. / Polyhedron 20 (2001) 2179–2185
P =[max(F 2o,0)+2F 2c ]/3). The non-hydrogen atoms were refined anisotropically, hydrogen atoms were placed in calculated positions and refined as ‘riding Table 1 Crystal data and structure refinement parameters for complexes 1 and 2
Empirical formula Formula weight Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) V (A, 3) Z Dcalc (g cm−3) v (mm−1) Crystal size (mm) 2[ Range (°) Index ranges
1
2
C36H30Br2HgP2 884.95 orthorhombic Pna21
C22H19Br2HgN2PS 734.83 orthorhombic Pna21
17.901(3) 10.181(2) 18.509(4) 3373.3(8) 4 1.74 7.05 0.1×0.15×0.2 1–50 05h521, 05k512, −225l522 Reflections collected 24 415 Independent reflections 5841 [Rint = 0.10] Parameters 370 R(F) [I\2|(I)] 0.066 wR(F 2) [I\2|(I)] 0.092 Goodness-of-fit on F 2 1.08 Largest difference peak and 0.78 and −0.75 hole (e A, −3)
19.3460(15) 7.8909(5) 15.6364(11) 2387.0(5) 4 2.045 9.96 0.1×0.1×0.4 1–52 05h523, 05k59, −195l519 17 641 4638 [Rint = 0.06] 262 0.038 0.068 1.32 0.85 and −0.76
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Table 3 Selected bond lengths (A, ) and bond angles (°) for molecule 2 with e.s.d.s in parentheses Bond lengths Hg(1)P(1) Hg(1)Br(2) N(1)C(6) N(1)C(2) C(2)N(3) C(2)S(2) P(1)C(11)
2.450(2) 2.6997(11) 1.326(12) 1.334(11) 1.369(11) 1.704(10) 1.814(9)
P(1)C(31) P(1)C(21) Hg(1)S(2) Hg(1)Br(1) N(3)C(4) C(4)C(5) C(5)C(6)
1.824(8) 1.825(9) 2.4795(19) 2.7065(10) 1.336(13) 1.376(15) 1.377(14)
Bond angles P(1)Hg(1)S(2) P(1)Hg(1)Br(2) S(2)Hg(1)Br(2) C(2)S(2)Hg(1) C(31)P(1)Hg(1) C(6)N(1)C(2) N(1)C(2)N(3) N(1)C(2)S(2) N(3)C(2)S(2) C(11)P(1)C(31) C(11)P(1)C(21) C(31)P(1)C(21) C(12)C(11)P(1) C(16)C(11)P(1)
103.96(6) 95.18(9) 101.9(3) 114.0(3) 118.8(8) 119.3(8) 123.8(7) 116.9(7) 106.5(4) 109.7(4) 106.2(4) 118.6(8) 121.5(7) 119.6(7)
C(26)C(21)P(1) C(22)C(21)P(1) P(1)Hg(1)Br(1) S(2)Hg(1)Br(1) Br(2)Hg(1)Br(1) C(11)P(1)Hg(1) C(21)P(1)Hg(1) C(4)N(3)C(2) N(3)C(4)C(5) C(4)C(5)C(6) N(1)C(6)C(5) C(32)C(31)P(1) C(36)C(31)P(1)
115.6(7) 122.8(6) 108.49(6) 104.11(6) 103.28(5) 112.0(3) 108.2(3) 122.6(9) 118.5(10) 117.1(10) 123.7(10) 119.6(7) 119.7(7)
Table 2 Selected bond lengths (A, ) and bond angles (°) for molecule 1 with e.s.d.s in parentheses Bond lengths Hg(1)P(2) Hg(1)P(1) P(1)C(111) P(1)C(121) P(1)C(131)
2.491(5) 2.550(4) 1.835(14) 1.845(17) 1.802(15)
Hg(1)Br(1) Hg(1)Br(2) P(2)C(211) P(2)C(221) P(2)C(231)
2.627(2) 2.6368(14) 1.769(16) 1.788(13) 1.794(13)
Bond angles P(2)Hg(1)P(1) P(2)Hg(1)Br(1) P(1)Hg(1)Br(1) C(111)P(1)Hg(1) C(131)P(1)Hg(1) C(121)P(1)Hg(1) C(111)P(1)C(121) C(111)P(1)C(131) C(121)P(1)C(131) C(112)C(111)P(1) C(116)C(111)P(1) C(122)C(121)P(1) C(126)C(121)P(1) C(132)C(131)P(1) C(136)C(131)P(1)
113.01(14) 113.12(10) 105.12(10) 109.9(4) 115.8(5) 110.7(5) 107.6(7) 107.6(7) 104.8(7) 122.5(12) 115.5(12) 116.6(15) 118.6(13) 121.4(13) 119.4(14)
P(2)Hg(1)Br(2) P(1)Hg(1)Br(2) Br(1)Hg(1)Br(2) C(211)P(2)Hg(1) C(221)P(2)Hg(1) C(231)P(2)Hg(1) C(211)P(2)C(221) C(211)P(2)C(231) C(221)P(2)C(231) C(212)C(211)P(2) C(216)C(211)P(2) C(222)C(221)P(2) C(226C(221)P(2) C(232)C(231)P(2) C(236)C(231)P(2)
114.23(12) 103.37(9) 107.12(8) 106.0(6) 117.9(5) 111.9(5) 102.5(7) 110.7(7) 107.3(6) 117.3(13) 125.0(14) 120.9(11) 122.2(11) 119.0(10) 124.2(12)
Fig. 1. Thermal ellipsoid representations of 1 together with atomic numbering schemes.
mode’, i.e. they followed the movements of their carrier atoms. The isotropic displacement parameters for hydrogen atoms were calculated as 1.2 times the equivalent displacement parameters for the respective non-hydrogen carrier atoms. Due to the relatively poor quality of the crystals of complex 1 some restraints had to be applied to the anisotropic displacement parameters of the carbon atoms; these restraints were supposed to ensure the more or less proper shape of the ellipsoids (ISOR, [38]). The bond lengths and angles for complexes 1 and 2 are given in Tables 2 and 3, respectively, while the displacement ellipsoid representation of complexes 1 and 2 is shown in Figs. 1 and 2, respectively.
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2.4. Computational details Extended Huckel calculations were performed using the CACAO program [39]. The calculations were carried out using crystallographic data of the studied molecules. The EHT parameters for Hg, were those established in the literature.
3. Results and discussion
3.1. General aspects Crystals of complexes 1 and 2 have been prepared by slow evaporation of the solution remaining, after the filtration of the initial solution, from the reaction of 0.5 mmol HgBr2 with 0.5 mmol triphenylphosphine and 1 mmol pyrimidine-2-thione, in methanol– acetonitrile solution. After one day 0.060 mmol pale-yellow colorless crystals, of complex 1 were filtered off and after two further days the new clear solution gave 0.075 mmol orange crystals of complex 2. The formulae of the complexes were firstly deduced from their elemental analysis, m.p. and spectroscopic data. The crystals of the complexes are air stable when stored in darkness at room temperature. Searching for the factors that govern the formation of a particular geometry around the mercury ions in mixed ligands complexes, we have reported previously the synthesis and structural characterisation of the [(benzothiazole-2-thionato) (benzothiazole-2-thione) (bis-triphenylphosphine) chloro mercury(II)] (3) and the [(m2 -dichloro){(bis-pyrimidine-2-thionato)mercury(II)}{(bis-triphenylphosphine) mercury(II)}] (4) complexes, derived from the reaction between HgCl2, triphenylphosphine and benzothiazole-2-thione or pyrimidine-2thione [31]:
In these complexes, 3 and 4, thione ligands have been deprotonated upon co-ordination, contrary to complex 2 where pyrimidine-2-thione is co-ordinated in its neutral form. Thus, the relatively higher covalent character of the HgBr bond in case of 2 compared to the more ionic HgCl bond in case of 3 and 4 leaves pyrimidine2-thione unchanged upon co-ordination.
3.2. UV –Vis spectroscopy The UV spectrum of complex 1 in chloroform is dominated by one main absorption band at umax =256 nm (log m= 4.442) which is ascribed to the intra-ligand transitions of triphenylphosphine (umax = 263 nm, log m=4.076), since umax of this absorption band exhibits no significance shift from either the corresponding umax of the band of the free ligand or from the corresponding umax of the band of complex 1 in acetonitrile (umax = 252.5 nm, log m= 4.278) [40]. The UV–Vis spectrum of complex 2 in chloroform is dominated by absorption bands with umax (log m) values 354 nm (3.121), 281.5 nm (4.190) and 242 nm (4.321). The first band is attributed to a charge transfer band since it occurs with a shift of 26 nm to lower wavelengths in respect of the corresponding band of free thione and a shift of 11 nm from the corresponding absorption band of the complex in acetonitrile, while the second band is ascribed to the intra-ligand transitions of pyrimidine-2thione [40]. The spectrum of free thione in chloroform consist of absorption bands at 380.5 and 291.5 nm having log m values 3.193 and 4.129, respectively.
3.3. IR spectroscopy
Fig. 2. Thermal ellipsoid representations of 2 together with atomic numbering schemes.
The IR spectrum of complex 1 shows bands at 690, 516, 508 and 493 cm − 1 which have been attributed to the vibrations of the CP bond. No significant change has been observed between the IR spectrum of complex 1 and the corresponding spectrum of triphenylphosphine. The IR spectrum of complex 2 shows distinct vibrational bands at 1577 and 1320 cm − 1 which have been assigned to vibrations of the CN bond (thioamide I and II bands) and at 983 and 793 cm − 1 which were attributed to the CS bond vibrations (thioamide III and IV bands). The corresponding thioamide bands of free pyrimidine-2-thione ligand are at 1561, 1320, 982 and 791 cm − 1, respectively [41]. The bands at 694, 524, 503 and 490 cm − 1 have been attributed to the vibrations of the CP bond. Further information about the complexes was obtained from
M. Kubicki et al. / Polyhedron 20 (2001) 2179–2185
2183
Fig. 3. Far-IR spectra of complexes 1 and 2.
the study of far-IR spectra. Fig. 3 shows the far-IR spectra of complexes 1 and 2. The new band at 151 cm − 1 (vs) in the far-IR spectrum of complex 1 has been assigned to the vibrations of the HgBr bond [9,17,32,33,42] while the band appearing at 120 cm − 1 (vs) has been attributed to the vibration of the HgP bond [19,27,32,43]. The far-IR spectrum of complex 2 shows a band at 153 cm − 1 (s) which is assigned as vibrations of the HgBr bond with a band at 121 cm − 1 (vs) which is ascribed to the HgP bond vibrations. The band at 196 cm − 1 is attributed to the vibration of the HgS bond [42,44].
3.4. Structures of [HgBr2(PPh3)2] (1) and [HgBr2(PPh3)(pmtH)] (2) complexes Although the crystallographic data for the unit cell along with some initial data of complex 1 have been reported earlier, the structure was not fully solved [25]. Views of molecules 1 and 2 are shown in Figs. 1 and 2, respectively, while selected bond lengths and angles for molecules 1 and 2 are given in Tables 2 and 3, respectively. The two complexes are covalent in the solid state. The geometry around the mercury(II) ion, in both complexes, is tetrahedral. Molecule 1 is a monomer in the solid state with two phosphorus and two bromide atoms around the mercury atom. A triphenylphosphine ligand, a pyrimidine-2-thione molecule and two bromide atoms are co-ordinated to the metal ion in complex 2. The Hg(1)Br(1) and Hg(1)Br(2) bond distances are 2.627(2) and 2.6368(14) A, , respectively, in complex 1 and are in accordance with those found by Nowell et al. [25] (HgBr1 =2.633(6) and HgBr2 = 2.627(8) A, ), while the corresponding Hg(1)Br(2) and Hg(1)Br(1) bond distances measured for complex 2 are
2.6997(11) and 2.7065(10) A, , respectively. The HgBr bond distances found in [Hg(Ph2PCHCHPPh2)Br2] are HgBr(1)terminal = 2.545(2) and HgBr(2)terminal = 2.560(2) A, [26] while in [Pr3PHgBr2]2 they are HgBr(1)terminal = 2.507(2) and HgBr(2)bridging = 2.667(2) A, [20], in [(PPh3)HgBr2]2 they are Hg(1)Br(1)terminal = 2.499(7) and Hg(2)Br(2)terminal = 2.505(7) A, , Hg(1)Br(4)bridging = 2.721(7), Hg(2)Br(3)bridging = 2.704(7) A, [19] and in [DMPPHgBr2] they are Hg(1)Br(2)terminal = 2.6129(6) and Hg(1)Br(1)bridging = 2.6272(6) A, ) [17]. The HgBr bond lengths of complexes 1 and 2 are relatively longer than those found in bonds with terminal bromide atoms and closer to those with bridging bromide atoms, indicating an intra- or inter- HgBr···X interactions for both complexes studied. Extended intra-molecular linkages via NH···Br interactions lead to a polymeric structure for complex 2. The H(3)a[N(3)a]···Br(1) distance is 2.4448 A, with a N(3)a···Br(1) distance of 3.2938 A, (symmetry operations used: x, − 1+y, z) [45]. Extended CH···Br contacts link the alternate parallel chains forming a supramolecular assembly. The H(4)b[C(4)b]···Br(2) distance is 2.8529 A, with a C(4)b···Br(2) distance of 3.7518 A, (symmetry operations used (−x, 2− y, − 1/2 + z) [45]. Fig. 4 shows the intra-molecular linkages via NH···Br and the CH···Br interactions in complex 2. A Br(1)···H(125)a[C(125)a] interaction in case of complex 1 is also detected by the inter-atomic distance of 2.9773 A, (symmetry operations used: x, 1+ y, z) [45]. The two Hg(1)P(2) and Hg(1)P(1) bond lengths in complex 1 are 2.491(5) and 2.550(4) A, , respectively, and are similar to the corresponding values found in [Hg(Ph2PCHCHPPh2)2Br2] (HgP = 2.572(2) A, ) [26], in [Pr3PHgBr2]2 (HgP = 2.408(4) A, ) [20], in [(PPh3)HgBr2]2 (Hg(1)P(1) =
2184
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2.40(2) A, ) [19] and in [DMPPHgBr2] (HgP = 2.4490(2) A, ) [17]. Moreover, the HgP bond lengths of complex 1 are also in accordance with those measured in mixed ligand mercury(II) complexes as in [Hg(PPh3)(bzthztH)(bzthzt)Cl] (HgP =2.453(2) A, ) [31], in [Hg2Cl2(PPh3)2(pmt)2] (HgP =2.4826(9) A, ) [31] and in [Hg(PPh3)2(SCN4Ph)2] (HgP =2.500(3) A, ) [30]. The Hg(1)P(1) bond length in complex 2 is 2.450(2) A, and is in the range of the corresponding bond distances measured in [Hg(PPh3)(bzthztH)(bzthzt)Cl] (Hg(1) P(1) =2.453(2) A, ) [31], in [Hg2Cl2(PPh3)2(pmt)2] (HgP = 2.4826(9) A, ) [31] and in [Hg(PPh3)2(SCN4Ph)2] (HgP = 2.500(3) A, ) [30]. The Hg(1)S(2) bond length in complex 2 is 2.4795(19) A, , while the HgS bond distances measured in [Hg(PPh3)(bzthztH)(bzthzt)Cl] are Hg(1)S(2)thionato =2.453(2) A, , Hg(1)S(2A)thione =
2.726(2) A, [31] and in [Hg2Cl2(PPh3)2(pmt)2] it is Hg(2)S(42) = 2.3513(11) A, [31]. The S(2)C(2) and C(2)N(3) bond lengths in complex 2 are 1.704(10) and 1.369(11) A, , respectively, and are in accordance with the corresponding bond distances found for bzthztH in [Hg(PPh3)(bzthztH)(bzthzt)Cl] (S(2A)C(2A) =1.690(9) A, and C(2A)N(3A) = 1.320(11) A, ) [31]. The P(1)Hg(1)P(2) angle measured in complex 1 is 113.01(14)° and is in accordance to the corresponding angle found in [Hg2Cl2(PPh3)2(pmt)2] (P(1)Hg(1) P1)i = 116.32(4)° [31] but smaller than those measured in ([Hg(PPh3)2(SCN4Ph)2] (P1HgP2 = 125.6(1)°) [30], in [HgCl2(PPh3)2] (P1HgP2 = 134.1(1)°) [25] and in [HgCl2((thienyl)3P)2] (P(1)HgP(2) = 128.6(1)°) [24]. The increasing value of the PHgP% angle observed, on going from complex 1 to [HgCl2((thienyl)3P)2] [24] or [HgCl2(PPh3)2] [25] complexes follows the increasing electronegativity between bromide and chlorine halogens, as expected. The Br(1)Hg(1)Br(2) angle in complex 1 is 107.12(8),° similar to the corresponding angle found in [Hg(Ph2PCHCHPPh2)2Br2] (Br(1)Hg Br(2)=112.7(1)°) [26]. The Br(2)Hg(1)Br(1) bond angle in complex 2 is 103.28(5)° and is slightly smaller than the corresponding angle measured for complex 1 (Br(1)Hg(1)Br(2) =107.12(8)o). The S(2)Hg(1) Br(1) angle is 103.96(6)° and is higher than the value of the S(2a)Hg(1)Cl(1) angle (99.10(7)°) in [Hg(PPh3)(bzthztH)(bzthzt)Cl] [31] where the amide hydrogen atom takes part in an inter-molecular hydrogen bond. The S(2)Hg(1)Br(2) bond angle is 95.18(9)°.
3.5. Computational study
Fig. 4. Intra-molecular linkages via NH···Br and CH···Br interactions in complex 2.
The differences in co-ordination mode of the mixed ligand mercury(II) complexes with thione and phosphine prompted us to undertake a computational study in order to verify the factors leading the formation of the different types of complex. The energy of the lowest unoccupied molecular orbital (LUMO) of complex 1 lies 3.768 eV higher than the energy of its highest occupied molecular orbital (HOMO), while the LUMO’s energy is 3.094 eV nearer the HOMO’s energy in case of the complex 2. The calculated overlap populations, in case of complex 1, for the Hg(1)Br(1) and Hg(1)Br(2) bonds are 0.418e and 0.412e, respectively, while the overlap populations calculated for the Hg(1)P(1) and Hg(1)P(2) bonds are 0.600e and 0.625e, respectively. The calculated overlap populations for the two Hg(1)Br(1) and Hg(1)Br(2) bonds are 0.363e and 0.348e, respectively in case of complex 2 indicating a smaller covalent bond strength compared to the corresponding bonds in complex 1, due to the strong intra-molecular interactions. The overlap population for the HgS bond is 0.528e.
M. Kubicki et al. / Polyhedron 20 (2001) 2179–2185
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 158018 and 158017 for compounds 1 and 2, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336033; e-mail: [email protected]. ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements S.K.H. wishes to thank Professor N. Hadjiliadis (Coordinator of the graduate program — E.P.E.A.E.K. — in Bioinorganic Chemistry) for the instrumental support in vibrational spectroscopy.
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