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The template synthesis and X-ray characterization of pyrrole-derived hexadentate uranyl(VI) Schiff-base macrocyclic complexes
ELSEVIER
Inorganica
Chimica Acta 246 (1996) 23-30
The template synthesis and X-ray characterization of pyrrole-derived hexadentate uranyl(V1) Schiff-base macrocyclic complexes Jonathan L. Sesslera,*, Tarak D. Modyb.1,Maria T. Dulay cy2,Roberto Espinozaa, Vincent Lyncha aDepartment
of
Chemistry and Biochemistry, Universify of Texas at Austin, Austin, TX 78712, USA bPharmacyclics Inc., Sunnyvale, CA, USA CDepartment of Chemistry, Stanford University, Stacford, CA, USA
Abstract The template condensation of 3,4-diethyl-2,5-dicarbaldehyde with ethylenediamine and 13-propanediamine in the presence of UO,(NO& gave neutral complexes of formulae U0+24Hs2Ne) ([UOz(bi-pyen)], 2) and U02(C&HseN6) ([UO,(bi-pytmd)], 3), respectively. X-Ray diffraction quality single crystals were obtained from chloroform/methanol. In the case of 2, these were monoclinic, space group C2/c, with a = 30.549(5), b = 8.251(l), c = 21.969(4)& /I = 114.47(l)“, V= 5040( 1) A3, Z= 8, pcatc = 1.78 g cmT3. Crystals of 3 were also monoclinic, space group Cut, with a = 26.946(7), b = 9.436(2), c = 10.862(2) A, /I = 105.04(2)‘, V= 2667(l) A3, Z= 4, pcalc = 1.75 g cme3. In the X-ray structure of 3, the complex lies on a crystallographic twofold axis. For 2, the final R = 0.0335, WR = 0.0371 for 297 parameters and 4475 reflections [F 14(a(F,,))], while for 3, the final R = 0.0223, WR = 0.0265 for 213 parameters and 2810 reflections [F 24 (u(F,))]. In each complex, the uranyl(V1) cation is bound to all six nitrogen atoms such that the metal center, with its two apical oxygen atoms, lies in a distorted hexagonal bipyramidal environment. The change in overall macrocycle size that results in going from 2 to 3 does not affect the U-N bond lengths. Rather, the principal difference between 2 and 3 is the extent of the twist between the two nearly planar halves of the macrocycle. In 2, the imine-pyrrole-imine dihedral angle is 17.5(l)” while in 3 it is 35.7(l)“. On the other hand, it is near 0” in an earlier reported complex, 1, derived from o-phenylenediamine [J.L. Sessler, T.D. Mody and V. Lynch, Inorg. Chem., 31 (1992) 5311. Complex 1 displays two reversible oxidations at +0.82 V and +1.09 V versus FJF,+ in CH,Cl, containing TBAPF6, while complexes 2 and 3 display irreversible oxidation waves at +1.22 V, +1.46 V and +1.22 V and +1.47 V versus FclFc+, respectively. Complexes 1, 2, and 3 also display quasi-reversible uranyl-centered reductions at -0.85 V, -1.02 V, and -0.96 V versus F,jFc+, respectively. Keywords: Template condensation; Uranyl(V1) complexes; Pyrrole-derived; Schiff base complexes
1. Introduction In the past several years, there has been considerable interest in designing stable, well-characterized chelands for the complexation of the uranyl cation [l-5]. Recently, we reported the synthesis and structural characterization of the first hexadentate pyrrole-derived uranyl(V1) Schiffbase complex 1 [6]. Solid state evidence revealed that the
* Corresponding author. ’ Pharmacyclics lnc, Sunnyvale, CA, USA. 2 Stanford university, Department of Chemistry,
Stanford,
USA.
0 1996 Elsevier Science S.A. All rights reserved 0020-1693/96/$15.00 PII SOO20-1693(96)05046-8
uranyl cation is coordinated to all six nitrogen atoms in a planar fashion. These results led us to prepare other analogous systems (i.e. U02(bi-pyen) 2 and UO,(bipytmd) 3) with a view to determining whether the planarity observed for complex 1 is due primarily to the rigidity of the phenylene diamine rings or whether it is inherent to the hexagonal bipyramidal chelating geometry of the macrocycle-bound uranyl ion. Thus, in this paper, we wish to report the uranyl nitrate template synthesis and structural characterization of two new pyrrole-derived uranyl(V1) macrocyclic Schiff base complexes 2 and 3. From this study, we are able to conclude that the rigidity of the phenylene diamine rings in complex 1, does con-
24
J.L. Seder
et al. I Inorganica Chimica Acta 246 (1996) 23-30
strain the overall ligand to a planar conformation. On the other hand, in all three crystal structures a local hexagonal bipyramidal arrangement around the uranyl(V1) cation is found. Such a finding is not inconsistent with earlier conclusions derived from the study of a range of very different (i.e. unrelated) ligand systems [7].
H
J-4 ‘\
0
E
H
+
WWWJH,
0
4
5 6
n=* n=3
2. Experimental
2.1. General information Proton and 13C NMR spectra were obtained in CDC13 on a General Electric QE-300 (300 MHz) using Me& as an internal standard. Electronic spectra were recorded on a Beckman DU-7 spectrophotometer in CHC13. Infrared spectra were recorded, as KBr pellets, from 4000 to 800 cm-* on a Nicolet 510P FT-IR spectrophotometer. Low and high resolution fast atom bombardment mass spectrometry (FAB MS) were performed using FinniganMAT TSQ-70 and VG ZAB-2E instruments, respectively. A nitrobenzyl alcohol (NBA) matrix was used with CHC13 as the co-solvent. Elemental analyses were performed by Atlantic Microlabs Inc.
2.2. Synthesis All reagents were of reagent grade quality, purchased commercially, and used as received. All solvents were spectroscopic grade and used as received. Tetra-n-butylammonium hexafluorophosphate (TBAPFs) used for electrochemical studies was recrystallized from hot ethyl acetate. 2.2.1. Uranyl complex of 9,10,19,20-tetraethyl3,6,13,16,21,22-hexaazapentacyclo[l6.2.l.l8~~1.~~s. 014~1S]docosa-2,4,6,8,10,12,16,18,20-octaene ([UOz(bipyenU 2) The uranyl complex 2 was prepared by combining a mixture of 3,4-diethylpyrrole-2,5-dicarbaldehyde (4) [6] (300 mg, 1.68 mmol), ethylenediamine (5) (101 mg,
1.68 mmol) and uranyl nitrate (355 mg, 0.90 mmol) in 60 ml of absolute ethanol at reflux. After 5 h, the fine orange powder was filtered off, washed several times with methanol, and dried in vacua to yield 490 mg (88%) of the crude product. Dissolving this crude material in CHC13 and layering with methanol then yielded orange X-ray quality crystals. For [UOz(bi-pyen)]: iH NMR (CDC13) 6: 1.26 (t, 12H, CH,CH3), 2.82 (q, 8H, CH2CH3), 4.57 (s, 8H, CHJ, 9.25 (s, 4H, CHN). 13C NMR (CDC13) 6: 17.6, 18.3, 62.2, 131.4, 142.6, 161.2. UV/vis: (CHC13) Amax (log E): 379.5 (4.41). IR (Kbr, cm-‘, selected peaks): v 1609 (C=N), 1599 (C=N), 897 (OUO); FAB MS, m/z (rel. intensity) 674 (100); HRMS (M+) 674.3082 (talc. for CZ4H3zN602U: 674.3095). Anal. Calc. for C24H32N602U: C, 42.73; H, 4.78; N, 12.46. Found: C, 42.84; H, 4.80; N, 12.40%. This compound was further characterized by X-ray crystallography (see below). 2.2.2. Uranyl complex of 10,11,21,22-tetraethyl3,7,13,18,23,24-hexaazapentacyclo[l8.2.l.l9~~2.~~s. 015~16]tetracosa-2,7,9,11,13,18,20,22-octaene ([U02(bipytmd)l, 3) The uranyl complex 3 was prepared by combining a mixture of 4 (200 mg, 1.12 mmol), 1,3-propanediamine (6) (83 mg, 1.12 mmol) and uranyl nitrate (230 mg, 0.58 mmol) in 60 ml of absolute ethanol at reflux. After 4 h, the scarlet red crystalline product was filtered off, rinsed with methanol, and dried in vacua for several hours to afford 235 mg (60%). Dissolving this crude material in CHCl, and layering with methanol then yielded scarlet red X-ray quality crystals. For 3: ‘H NMR (CDC13) 6: 1.35 (t, 12H, CH,CHs), 2.37 (p, 4H, CH2CH2CH2), 2.84 (q, 8H, CH2CH3), 4.3 1 (t, 8H, CH2CH2CH2), 9.25 (s, 4H, CHN). i3C NMR (CDC13) 6: 17.6, 18.3, 30.3, 55.1, 130.4, 142.2, 160.6. UV/vis: (CHCls) &,,, (log E): 370.5 (4.45). IR (KBr, cm-‘, selected peaks): v 1605 (C=N), 1595 (C=N), 897 (OUO); FAB MS, m/z (rel. intensity) 703(100); HRMS (M + H) 703.3489 (talc. for C26H37Ns02U: 703.3486). Anal. Calc. for C2sH3sNs0&J: C, 44.44; H, 5.16; N, 11.96. Found: C, 44.44; H, 5.16; N, 11.88%. This compound was further characterized by Xray crystallography (see below). 2.3. Electrochemical measurements Cyclic voltammetric measurements of uranyl(V1) complexes 1, 2, and 3 (1 X 10m3 M) were performed under a nitrogen atmosphere at 23 + 2°C with a conventional three-electrode system using a Bioanalytical System (BAS) 100. A platinum button (area ca. 0.03 cm2) was used as the working electrode and a platinum wire was used as a counter electrode. An Ag/AgCl electrode was used as reference and was separated from the bulk solution (which contained anhydrous CH2C12 and 0.1 M TBAPF, as the supporting electrolyte) by a fritted glass
J.L. Seder
et al. I Inorganica Chimica Actu 246 (I 996) 23-30
bridge. All potentials, at a scan rate of 100 mV s-l, were recorded against Ag/AgCl in CHQ containing 0.1 M TBAPF,. The ferrocene/ferrocenium (F,IF,+) couple was recorded at +0.68 V versus Ag/AgCl under similar electrochemical conditions. For the sake of consistency, all redox potentials (Ein) in this paper are reported versus FJF,+. 2.4. Stability studies
Complex stability was determined kinetically by monitoring the change in the Soret-like absorbance at 450 nm, 379.5 nm, and 370.5 nm for complexes 1,2, and 3, respectively, as a function of time using a Beckman DU-7 spectrophotometer. This was done for a period of 24 h using starting concentrations of 1 X 10Y5M and two different solvent systems, namely (1) 9:l (v/v) CHCls/HOAc and (2) 12:6: 1: 1 (v/v/v/v) CHClJMeOW HOAc/H20. 2.5. X-Ray crystallography Crystals were grown as described above. Crystals of 2 grew as well-formed plates while those of 3 were generTable 1 Crystallographic
data” for (C24H32Nb)U02
(2) and (C26H36N6)U02
(3) 2
Cd-!&U%
Formula Pw (1 (A) b (A) c (A) B (“) v (A3) Z F(OO0) Space group Radiation pcalc, P
(g cme3)
(cm-‘)
Transmission factorb range Crystal size (mm) WIc Rw(F) Reflections
used,
674.58 30.549(S) 8.251(l) 2 I .969(4) I 14.47( 1) 5040( 1) 8 2608 C2/c (no. 15) Graphite monochromated, (h = 0.71073W) 1.78 61.38 0.09942-0.4692 0.13 x 0.40 x 0.46 0.0335 0.037 1 4475
3
C26H36N6U02 702.64 26.946(7) 9.436(2) 10.862(2) 105.04(2) 2667( 1) 4 1368 C2/c (no. 1.5) MoKa 1.75 58.02 0.2264-0.3855 0.17 x 0.28 x 0.31 0.0223 0.0265 2810
Ft, > 4(W,)) ‘Data for both samples were collected on a Nicolet P3 diffractometer. Data for 3 were collected at -90°C while using a Nicolet LT-2 lowtemperature delivery system. Lattice parameters were obtained from the least-squares refinement of 37 reflections with 16.3 rc 20 < 21.5” for 2 and 39 reflections with 12.1 < 20 < 20.5” for 3. bAbsorption correction was based on measured crystal faces. ‘The function Zw(lF,I - IF,$ was minimized, and where w = I/(u(F,,)~ + (0.02F)2). R(F) = T(IF,,I - IFelEIFoI; R,(F) = [Zw(lF,I - lFcD2/ Pw(lF 0 l)2]“2.
25
ally thicker and more block-like in appearance. Data were collected on a Nicolet P3 diffractometer with a graphite monochromator and using MoKa radiation (A = 0.71073 A). Crystallographic details are listed in Table 1. Data were collected using the w scan technique, with a 1.2” scan range and a variable scan rate (5-10” min-l for 2 and 4, 8” min-’ for 3). Data were collected to 55” in 28. Two symmetry equivalent sets of data were collected for each sample. 12 354 reflections were collected for 2, of which 5838 were unique with an R for averaging symmetry equivalent data, Rint= 0.028. For 3, 6527 reflections were collected, yielding 3269 unique data points with an Rint= 0.033. Systematically absent reflections indicated the space group could be Cc or C2lc for both 2 and 3. The assignment of C2/c was justified by the refinement results. Data reduction and decay correction were performed using the SHELXTL-Plus software package [8]. The structures were solved by direct methods and refined by full-matrix least-squares [8] with anisotropic thermal parameters for the non-H atoms. In the X-ray structure of 3, the complex lies on a crystallographic twofold axis that passes through the U02 moiety. For 2, two ethyl carbon atoms, C24 and C28, were disordered about two orientations. The site-occupancy factors for C24 and C28 refined to 47(2)% and 65(3)%, respectively. These atoms were refined isotropically. Except for the disordered atoms for which no hydrogen atoms were included, the hydrogen atoms for 2 were calculated in ideal positions (C-H 0.96 A) with Uiso fixed at 1.2 X Ueq of the attached atom. For 3, most hydrogens were obtained from a AF map and refined with isotropic thermal parameters. The hydrogen atoms of one ethyl group of 3, carbons C 15 and C16, did not refine well and were calculated in ideal positions with LIisofixed at 1.2 X Ueq of the attached atom. The function, Cw(lF,I - lFJ)2, was minimized, where w = I/(o(F,))~ and o(F,,) = (0.5W’” [(ao2 + (0.02J)2]1’2}. The intensity, I, is given by (Ipeak - Ibackground) X (scan rate); where 0.02 is a factor to downweight intense reflections and to account for instrument instability and k is the correction due to Lp effects, absorption and decay. The absorption correction was based on measured crystal dimensions. a(Z) was estimated from counting statistics; a(l) = [(Zpeak + X (scan rate)]. The data were corrected Ibackground)‘” for secondary extinction effects. The correction is of the form: F,,,, = F,l[( 1 + X X Fe2/sin 28)“.25], where X = 3.2(2) X low7 for 2 and 3.7(3) X 10v6 for 3. Neutral atom scattering factors for the non-H atoms were taken from Cromer and Mann [9], with the anomalous-dispersion corrections taken from the work of Cromer and Liberman [lo]. The scattering factors for the H atoms were obtained from Stewart et al. [ 111. Values used to calculate the linear absorption coefficient are from the International Tables for X-ray Crystallography (1974) [ 121. All figures were generated using SHELXTL-Plus [8]. Other computer programs used in this work are listed elsewhere u31.
J.L. Seder et al. I Inorganica Chimica Acta 246 (1996) 23-30
26
3. Results and discussion
Uranyl(V1) tetraimine complexes 2 and 3 were prepared in the presence of many1 nitrate via a metal template [2 + 21 condensation between 3,4-diethyl-2,5-dicarbaldehyde (4) [6,14] and ethylenediamine (5) or 1,3propanediamine (6), respectively [6,15]. Complexes 2 and 3 proved highly soluble (to the ca. 40 mg/ml level) in chloroform and dichloromethane but practically insoluble in more polar solvents such as HzO, MeOH, and EtOH. Nonetheless, they were obtained in good yields (88 and 60%, respectively) and were fully characterized by spectroscopic and structural methods as discussed below. Both complexes 2 and 3 display iH and i3C NMR of remarkable simplicity (cf. e.g. Fig. 1). This simplicity is due to their symmetrical structure. In addition, the IR spectra of complexes 2 and 3 proved simple to interpret. For instance, these complexes displayed an identical single sharp absorption at 897 cm-i for the asymmetric vibration of the uranyl ion and lacked vibrations that could be assigned to either pyrrole NH residual groups or adventitious coordinating anions. Thus, as seen for the uranyl complex 1 [6], the spectral data of complexes 2 and 3 are completely consistent with a neutral complex in which the uranyl ion is coordinated to all six ring nitrogen atoms [6]. 3.2. Structural features Single crystals suitable for X-ray diffraction were obtained for both complexes 2 and 3 by dissolving the
complex in chloroform and layering with methanol (see Figs. 2 and 3, respectively). As in the case of complex 1 (Fig. 4) the uranyl(V1) cation in complexes 2 and 3 is bound to all six of the core nitrogen atoms, however in a non-planar fashion. Although the ring size of the macrocycle in 3 is larger than that in 2, the nitrogen-uranium bond lengths for 2 and 3 are nearly identical. In addition, as is observed in the analogous complex 1, the U-Npyrrole bond lengths are substantially shorter than the lJ_Nihne bond lengths. For 2, the U-Npyrrolebond lengths average 2.456(3) 8, while the U-NtGne bond lengths average 2.656(3) A. For 3, the U-Npyrr,,te bond length is 2.444(3) %, and the U-Nimine bond lengths average 2.660(2) A. By comparison, for 1, the U-Nihne bonds are slightly longer (2.740(5) A) and the U-Npynole bonds are slightly shorter (2.418(7) A) than those found in 2 and 3 (see Figs. 2-4 and Tables IA). One of the critical findings to emerge from the X-ray structural studies is that while macrocycles in 2 and 3 are non-planar (in marked contrast to l), they are composed of two nearly planar parts comprised of the pyrrole ring and the adjacent imine moieties. Although the size of the C-C bridges in 2 and 1 (i.e. C17-Cl8 and C7-C12, respectively) are very similar in length, the sp3 versus sp2 hybridization induces twist on the adjacent imines for 2 that can only be relieved by a twist of the entire half molecule. In the case of complex 3, this twist is even greater than complex 2 due the larger propylene bridging group. As a result the dihedral angle is near 0” in complex 1, while it increases to 17.5” and 35.7”, respectively, for the ethylene and propylene bridged systems 2 and 3. In complex 1 the two o-phenylene groups fused to the imine moieties considerably reduce the flexibility of the macrocycle compared to the more conformationally mobile
-- _j_
a
-1
b
,:I l.T, -
_I
J.
I
r
’
I
7,
a
( 6
4
2
0 PPM
1
PPM
Fig. 1. (a) ‘H NMR spectrum of uranyl(V1) chelate 2 in CDCI, with (CH&Si as reference. (b) ‘H NMR spectrum of uranyl(VI) chelate 3 in CDC13 with (CH&Si as reference.
J.L. Seder
et al. I Inorganica Chimica Acta 246 (1996) 23-30
21
at substantially varying angles of approach. As a consequence, changes in the overall macrocycle size are found to have little effect on the actual uranium(V1) inner coordination sphere, even though, as discussed above, they can have a dramatic effect on the overall, generalized complex geometry. This conclusion is consistent with earlier reports in the literature (made using very different ligands) [7], and helps account, in a qualitative way, for the differences in reactivity discussed immediately below. C
3.3. Stability studies Although complexes 2 and 3 are essentially insoluble in polar solvents (i.e. H20, MeOH, EtOH, etc.), basic stability studies of these complexes could be made by using a 9:1 (v/v) mixture of CHCls and glacial HOAc. In this solvent system, it was determined that the uranyl(V1) complex 3 (at an initial 1 X low5 M concentration) has a half-life for decomposition of 12 h at room temperature, as evidenced by a bleaching of the Soret-like absorption band at 370.5 nm. Furthermore, in a water-containing solvent mixture consisting of 12:6:1:1 (v/v/v/v) CHCls/ MeOI-I/HOAc/H20, this same complex displayed a halflife for decomposition of 1 h at room temperature. HowFig. 2. Thermal ellipsoid view of 2 scaled to the 30% probability level showing partial atom labelling scheme. The complex is composed of two planar portions separated by the ethylene bridges. The dihedral angle between planes is 17.5(l)“. Top: view approximately perpendicular to the mean plane of the six nitrogen atoms. Bottom: side view of the complex.
complexes 2 and 3, in which the =N-(CHz),-N= (i.e. n = 2 or 3) groups function as adjustable hinges. Similarly, the linear uranyl cation is inclined at angles of 81.3” and 72.2” relative to the planar portion of the macrocycle in the case of 2 and 3, respectively, whereas it is nearorthogonal in 1. As a consequence, even though there is no significant difference in the nitrogen-uranium bond lengths in 2 and 3 (relative either to each other or 1) the N-U-N angles are seen to be affected strongly by an increase in the number of bridging atoms in the macrocycle. In particular, the average N-U-N angles involving adjacent nitrogens are found to be 60.0(l)“, 60.55(6)“, and 62.48(5)’ in the case of complexes 1, 2, and 3, respectively. Since an angle of 60” is expected for an ideal hexagonal arrangement, the deviation observed in the case of 3 provides yet a further indication of overall complex non-planarity. In spite of the above subtleties, it is important to appreciate that in all three uranyl complexes, the basic coordination geometry about the uranyl cation remains approximately hexagonal bipyramidal. In fact, the U-N bond distances in both 2 and 3 are essentially the same, a finding that serves to substantiate the fact that the bonding orbitals of the uranium(V1) cation are quite diffuse and can bind with equal strength to nitrogen atoms even
Fig. 3. View of 3 showing atom labelling scheme. The thermal ellipsoids are scaled to the 30% probability level. The complex lies on a crystallographic two-fold axis passing through the UO2 cation. As in 2, the ligand has two planar portions separated by an alkyl bridge. However, the dihedral angle between planar portions of the molecule is more than double and is 35.7(l)‘. Top: view approximately perpendicular to the mean plane of the six nitrogen atoms. Bottom: side view of the complex.
28
J.L. Sessler et al. I Inorganica Chimica Acta 246 (1996) 23-30
supporting electrolyte are shown in Fig. 6 (parts b and c, respectively). Two oxidation waves at +I.22 V and + 1.46 V versus F,IF,+ are obtained for complex 2. Similarly, two oxidation waves are also obtained for 3 at + 1.22 V and + 1.47 V versus FJFC+. The CVs also reveal reduction waves, which are slightly negatively shifted with no significant change in peak shape (as compared to l), at -1.02 V and -0.96 V versus F,IF,+ for 2 and 3, respectively. For complexes 2 and 3, the anodic oxidation processes are irreversible, while the cathodic potential scans show similar quasi-reversible reduction processes as compared to 1. The degree of cathodic reversibility for 2 and 3 is less pronounced than for 1.For 2 and 3, the quasi-reversible reductions are characterized by IE, iJiC = 0.3 EJ = 350 mV, and IE, - EJ = 470 mV, i& = 0.2, respectively.
Table 2 Fractional coordinates and equivalent isotropic for the non-hydrogen atoms of (C24f&Ne)U02
Fig. 4. View of 1 with a partial atom labelling scheme. Thermal ellipsoids are scaled to the 50% probability level. The U atom lies on a crystallographic inversion center and the ligand is planar. The UO2 cation is inclined at an angle of 86.2” to the N6 plane. Top: view approximately perpendicular to the plane through the six nitrogen atoms of the ligand. Bottom: side view of the complex.
ever, under similar conditions complexes 1 and 2 appear to be quite stable, undergoing no apparent decomposition or demetallation over a 24 h period (see Fig. 5). This difference in stability suggests that even though complexes 1, 2, and 3 share many spectroscopic and structural features in common, they differ substantially in terms of their reactivity. 3.4. Electrochemistry The effects of changes in macrocycle type for congeners l-3 were also probed using cyclic voltammetry. Representative cyclic voltammograms (CVs) are shown in Fig. 6 and key results are summarized in Table 5. In the case of complex 1 in CHpC12 containing 0.1 M TBAPF6 as the supporting electrolyte, the CV shows two nearly reversible l-electron oxidations as illustrated in Fig. 6a. For the first oxidation at +0.82 V versus FCIFC+, IE,E,I = 67 mV, i,/i, = 1.1 at a scan rate of 100 mV s-l and for the second oxidation at +1.09 V versus FJFC+, IE, E,I = 61 mV, i,/i, = 0.8 at 100 mV s-i. Under identical conditions, however, a cathodic potential scan characterized by a peak potential at -0.85 V versus F,IF,+ shows a quasi-reversible process with IE, - E,I = 300 mV, iJiC = 1.4. The CVs of 2 and 3 in CH2C12 with TBAPF6 as the
Atom
x
Y
U 01 02 Cl c2 c3 c4 C.5 N6 Cl C8 N9 Cl0 Cl1 Cl2 Cl3 Cl4 Cl5 N16 Cl7 Cl8 N19 c20 N21 N22 C23 C24 C24A C25 C26 C27 C28 C28A C29 c30
0.247620(10) 0.24078( 14) 0.25447( 14) 0.3654(2) 0.3981(2) 0.3724(2) 0.3253(2) 0.2819(2) 0.2435(2) 0.1980(2) 0.1604(2) 0.1630(2) 0.1245(2) 0.1277(2) 0.0946(2) 0.1223(2) 0.1705(2) 0.215X(2) 0.2539(2) 0.3006(2) 0.3306(2) 0.3294(2) 0.3675(2) 0.3217(2) 0.1735(2) 0.4486(3) 0.4875(9) 0.4858( 11) 0.3908(3) 0.4068(4) 0.0418(3) 0.0151(7) 0.0140(10) 0.1047(3) 0.0999(4)
0.46971(3) 0.2562(5) 0.6827(4) 0.3884(7) 0.3597(8) 0.3896(7) 0.4332(7) 0.4639(7) 0.4793(6) 0.5087(7) 0.4126(8) 0.4494(6) 0.4587(S) 0.4883(7) 0.4966(7) 0.5219(7) 0.5250(7) 0.5372(7) 0.5222(5) 0.5367(g) 0.4009(8) 0.4102(6) 0.3775(7) 0.4324(5) 0.5034(4) 0.3033(9) 0.430(3) 0.455(4) 0.3784(8) 0.5392111) 0.4812(11) 0.651(2) 0.632(4) 0.5382(9) 0.7128(10)
thermal parameters (2)
Z
0.123030( 10) 0.1138(2) 0.1326(2) 0.2277(3) 0.2940(3) 0.3336(3) 0.2884(3) 0.2950(3) 0.2416(2) 0.2467(3) 0.1932(3) 0.1299(2) 0.0770(3) 0.0150(3) -0.0524(3) -0.0893(3) -0.0424(3) -0.0463(3) 0.0078(2) 0.0044(3) 0.0459(3) 0.1119(2) 0.1639(3) 0.2247(2) 0.0205(3) 0.3170(4) 0.3458( 13) 0.3250( 14) 0.4086(3) O&36(4) -0.0783(4) -0.0903(9) -0.0665( 13) -0.1642(3) -0.1866(4)
(A’)
(I
0.02735(8) 0.040(2) 0.044(2) 0.038(2) 0.047(2) 0.044(2) 0.039(2) 0.039(2) 0.038(2) 0.045(3) 0.045(2) 0.039(2) 0.042(2) 0.039(2) 0.046(3) 0.043(2) 0.039(2) 0.037(2) 0.035(2) 0.039(2) 0.046(3) 0.038(2) 0.040(2) 0.@35(2) 0.033(2) 0.064(3) 0.081(7) 0.109(9) 0.056(3) 0.091(5) 0.070(3) 0.100(6) 0.068(7) 0.054(3) 0.097(5)
For anisotropic atoms, the LI value is CIcq calculated as (leq = 113 E&j Vu ai*aj*Ao where Au is the dot product of the ith and jth direct space unit cell vectors.
J.L. Sessler ef al. I Inorgunica Chimica Acta 246 (1996) 23-30
29
Table 3 Fractional
coordinates
for the non-hydrogen
and equivalent
isotropic
atoms of (C2,jH3,jNrj)U02
thermal parameters
(A*)
(3)
‘.”
A 1 at 450.0 nm 1.8
9 ??
Atom
x
Y
Z
u
U 01 02 Cl c2 c3 c4 CS N6 C7 C8 c9 NlO Cl1 N12 Cl3 Cl4 Cl5 Cl6
0.5 0.5 0.5 0.37183(13) 0.33257( 13) 0.3567(2) 0.4088(2) 0.4548(2) 0.49823( 12) 0.54446(14) 0.5773(2) 0.5808(2) 0.58439(11) 0.62658( 13) 0.41743(11) 0.2771(2) 0.2421(2) 0.3323(2) 0.3347(2)
0.22284(2) 0.4113(4) 0.0347(3) 0.1868(4) 0.1972(4) 0.2508(4) 0.2654(4) 0.3029(3) 0.2878(3) 0.3377(4) 0.2124(4) 0.0959(4) 0.1537(3) 0.1401(3) 0.2274(3) 0.1582(5) 0.2823(7) 0.2812(5) 0.4360(6)
0.25 0.25 0.25 0.2273(3) 0.2914(3) 0.4140(3) 0.4171(3) 0.5135(3) 0.4871(3) 0.5801(3) 0.6440(3) 0.551 l(3) 0.4288(2) 0.3967(3) 0.3041(3) 0.2383(4) 0.1887(g) 0.5209(4) 0.5602(5)
0.01715(6) 0.0304(12) 0.0251(11) 0.0258(10) 0.0273( 11) 0.0280( 12) 0.0257( 11) 0.0257( 11) 0.0220(g) 0.0276( 11) 0.0295( 12) 0.0266( 11) 0.0242(9) 0.0246( 10) 0.0230(g) 0.0360(13) 0.059(2) 0.0389( 13) 0.066(2)
2 at 379.5 nm 3 at 370.5 nm
1.6 -
0.8 -
0.6 -
“_?I
I
0
2
I
I
4
6
t
I
8
10
12
00
Fig. 5. Kinetics of decomposition of uranyl(V1) complexes: Plot of the change in absorbance at the Soret maximum (450.0 nm, 379.5 nm, and 370.5 nm, for 1, 2, and 3, respectively) as a function of time (h) for 1 X low5 M solutions of l-3 in 9:l (v/v) CHCl$HOAc.
For anisotropic atoms, the U value is Ueq calculated as Ueq = 1/3X,~j Uu ai*nj*Aij where Ad is the dot product of the ith and jth direct space unit cell vectors.
The anodic oxidation waves seen in the CVs for all complexes are presumed to be ligand-based oxidations. In contrast, the cathodic reduction waves for complexes 1, 2, and 3 are presumed to involve reduction of the uranyl(V1) cation [i.e. U(V1) to U(V)], in accordance with the treatise by van Doorn et al. [I], who found that the uranyl(V1) cation bound to a variety of Schiff-base derived hosts undergoes a one electron reduction in the range -0.94 V to -1.08 V versus Ag/AgCl in CH$N. Imine reductions occur at much more negative potentials and therefore do not contribute to the reduction processes observed electrochemically [ 16-l 81.
I
-
64
k
1
+I 4
+I”
+ooJ
0.0
a5
-12
Table 4 Selected bond lengths (A), angles (“) and intramolecular 1 U-Npyrro’e U-%nine u-o N-U-Navg ’ Ni-U-Ni Ni-U-Np N.‘-Ni, b N...Ni ” C = N’ C-CpyrroleC
2.418(7) 2.740(5) 1.770(6) 60.0( 1) 57.7(2) 61.1(l) 2.638(7) 2.647(9) 1.296(7) 1.415(7)
2 2.456(3) 2.656(3) 1.774(3) 60.55(6) 60.1(l) 60.8( 1) 2.592(4) 2.662(4) 1.274(3)
1.409(4)
contacts (A) 3 2.444(3) 2.660(2) 1.777(2) 62.48(5) 64.94(9) 61.24(6) 2.608(3) 2.857(4) 1.281(4) 1.409(3)
“N-U-N angles include only those for adjacent nitrogen atoms. bi and p refer to the imine and pyrrole nitrogen atoms, respectively. ‘Values listed are average bond lengths for the pyrrole rings.
Fig. 6. Cyclic voltammograms of uranyl(V1) complexes (a) 1, (b) 2, (c) 3 recorded under nitrogen in CH2C12 containing 0.1 M TBAPF6 at a scan rate of 100 mV s-’ The potential axis is calibrated with respect to Ag/AgCl.
30
J.L.. Sessler et al. I Inorganica Chimica Acta 246 (1996) 23-30
Table 5 Redox potentials (E~Q, V versus Fe/Fe+) for uranyl(V1) complexes 1,2, 3
Complex
1 2 3
E&
(V versus FdFc+)b
1st oxidation
2nd oxidation
1st reduction
+0.82 +1.22 +I.22
+1.09 +1.46 +1.47
-0.85 -1.02 -0.96
aO.l M TBAPF6 in CH$&. scan rate = 100 mV s-l. bThe observed potentials were referenced to a ferrocene internal standard. The ferrocene/ferrocenium (Fc/Fc+) couple was recorded at +0.68 V versus Ag/AgCl.
The near-reversibility of the oxidation waves for complex 1 as compared to complexes 2 and 3 can be rationalized in terms of complex stability under electrochemical oxidations. The presence of four electrondonating methoxy substituents on the macrocyclic periphery, as well as, the n-conjugation of the ligand may impart stability to complex 1. For both complexes 2 and 3, the non-planar geometry, macrocyclic flexibility, and lack of a delocalization pathway, destabilizes them towards oxidation. Thus, these electrochemical measurements reveal a degree of increased chemical reactivity in both of these newer complexes (i.e. 2 and 3) that is not present in the parent system 1. As such, they serve to highlight the importance of considering the details of both inner, metalcentered geometric factors and overall macrocyclic structural effects when assessing the stability, reactivity, and properties of new, ostensibly similar macrocyclic ligand complexes. 4. Supplementary
material
Tables of anisotropic thermal parameters, hydrogen positional parameters, bond distances and angles, and unit-cell packing diagrams for uranyl(V1) complexes 2 and 3 (20 pages); listing of observed and calculated structure factor amplitudes for 2 and 3 (35 pages). Acknowledgements
This work was supported by grants to J.L.S. from the National Institute of Health (AI 28845), National Science Foundation (CHE 9122161), and Pharmacyclics, Inc. T.D.M. and M.T.D. wish to thank also the UT Austin Department of Chemistry and Biochemistry for Texaco Foundation and Department of Education Fellowships, respectively. References [I] Uranyl complexes of Schiff base macrocyclic ligands. see: A.R. van Doom, M. Bos, S. Harkema, J. van Eerden, W. Verboom and D.N. Reinhoudt, J. Org. Chem., 56 (1991) 2371 and references therein; W. Nijenhuis, A.R. van Doom, A.M. Reichwein, F. de
Jong and D.N. Reinhoudt, J. Am. Chem. Sot., I13 (1991) 3607; R. Chandra, Synrh. React. Inorg. Met.-Org. Chem., 20 (1990) 645 and references therein; U. Casellato, P. Guerriero, S. Tamburini, P.A. Vigato and R. Graziani, J. Chem. Sot., Dalton Trans., (1990) 1533; F. Benetollo, G. Bombieri, L. De Cola, A. Polo, D.L. Smailes and L.M. Vallarino, Inorg. Chem., 28 (1989) 3447; F.A. El-Saied, fnorg. Chim. Acta., 165 (1989) 147; F. Bullita, P. Guerriero, S. Tamburini and P.A. Vigato, J. Less Common Mef., 153 (1989) 211; C.J. van Staveren, D.E. Fenton, D.N. Reinhoudt, J. van Eerden and S. Harkema, J. Am. Chem. Sot., 109 (1987) 3456. PI For overviews of macrocyclic Schiff base complexes of lanthanides and actinides, see: V. Alexander, Chem. Rev,, 95 (1995) 273; D.E. Fenton and P.A. Vigato, Chem. Sot. Rev., I7 (1988) 69; G. Bombieri, Inorg. Chim. Acta, 139 (1987) 21; L.M. Vallarino, in, K.A. Gschneider, Jr. and L. Eyring (eds.), Handbook on the Physics and Chemistry of Rare Earths, Vol. 15, Ch. 4, Elsevier, Amsterdam, 1991. [31 Uranyl(V1) superpthalocyanine, see: V.W. Day, T.J. Marks and W.A. Wachter, J. Am. Chem. Sot., 97 (1975) 4519; T.J. Marks and D.R. Stojakovic, J. Am. Chem. Sot., IO0 (1978) 1695; E.A. Cuellar, D.R. Stojakovic and T.J. Marks, Inorg. Synrh., 20 (1980) 97; E.A. Cuellar and T.J. Marks, Inorg. Chem., 20 (1981) 3766; T.J. Marks and D.R. Stojakovic, J. Chem. Sot., Chem. Commun., (1975) 28.
[41 A.K. Burrell, G. Hemmi, V. Lynch and J.L. Sessler, J. Am. Chem. Sot., 113 (1991) 4690.
r51 A.K. Burrell, M.J. Cyr, V. Lynch and J.L. Sessler, J. Chem. Sot., Chem. Commun., (1991) 1710. PI J.L. Sessler, T.D. Mody and V. Lynch, Inorg. Chem., 31 (1992) 531; T.D. Mody, Ph.D. Dissertation, University of Texas at Austin, 1993. 171 G. Marangoni, S. Degetto, R. Graziani, G. Bombieri and E. Forsellini, J. Inorg. Nucl. Chem., 36 (1974) 1787; G. Paolucci, G. Marangoni, G. Bandoli and D.A. Clemente, J. Chem. Sot., Dalton Trans., (1980) 459; R. Graziani, U. Casellato, P.A. Vigato, S. Tamburini and M. Vidali, J. Chem. Sot., Dalton Trans., (1983) 697; N.W. Alcock, D.J. Flanders and D. Brown J. Chem. Sot., Dalton Trans., (1985) 1001; A. Cousson, J. Proust and E.N. Rizkalla, Acra Crysrallogr. C., 47 (1991) 2065. PI G.M. Sheldrick, SHELXTL-Plus, Siemens Analytical X-Ray Instruments Inc., Madison, WI, USA, 1987. t91 D.T. Cromer and J.B. Mann, Acta Crystallogr., A24 (1968) 321. DOI D.T. Cromer and D. Liberman, J. Chem. Phys., 53 (1970) 189 1. [111 R.F. Stewart, E.R. Davidson and W.T. Simpson, .J. Phys. Chem., 42 (1965) 3175. WI International Tables for X-Ray Crystallography, Vol. IV, Kynoch Press, Birmingham, UK, 1974, p 55. [I31 S.M. Gadol and R.E. Davis, Organomerallics, 1 (1982) 1607. u41 The preparation of 3,4-diethylpyrrole-2,5_dicarbaldehyde, 4, has also been reported by E. Vogel, N. Jux, E. Rodriguez-Val, J. Lex and H. Schmicker, Angew. Chem. Int. Ed. Engl., 29 (1990) 1387, see also Ref. [6]. t151 Well prior to this work, Fenton et al. prepared a series of macrocycles derived from alkyl-free pyrrole-2,5_dicarbaldehyde, and used these to chelate Cu(I1) and other cations of the transition series, see: D.E. Fenton and R. Moody, J. Chem. Sot., Dalton Trans., (1987) 219; H. Adams, N.A. Bailey, D.E. Fenton, S. Moss, C.O. Rodriguez de Barbarin and G. Jones, J. Chem. Sot., Dalton Trans., (1986) 693; H. Adams, N.A. Bailey, D.E. Fenton, S. Moss and G. Jones, Inorg. Chim. Acta, 83 (1984) L79. [I61 A.J. Bard (ed.). Encyclopedia of Electrochemistry of the Elements. Organic Section; Vol. XV, Marcel Dekker, New York, 1984. P71 Any imine reductions could not be observed because reduction potentials greater than ca. -1.6 V versus Ag/AgCl are well outside the electrochemical range of the solvent (i.e. +1.8 V to -1.6 V versus Ag/AgCl), see also Ref. [18]. H81 A.J. Bard, Electrochemical Methods Fundamentals and Applicarions, Wiley, New York, 1980.
Inorganica
Chimica Acta 246 (1996) 23-30
The template synthesis and X-ray characterization of pyrrole-derived hexadentate uranyl(V1) Schiff-base macrocyclic complexes Jonathan L. Sesslera,*, Tarak D. Modyb.1,Maria T. Dulay cy2,Roberto Espinozaa, Vincent Lyncha aDepartment
of
Chemistry and Biochemistry, Universify of Texas at Austin, Austin, TX 78712, USA bPharmacyclics Inc., Sunnyvale, CA, USA CDepartment of Chemistry, Stanford University, Stacford, CA, USA
Abstract The template condensation of 3,4-diethyl-2,5-dicarbaldehyde with ethylenediamine and 13-propanediamine in the presence of UO,(NO& gave neutral complexes of formulae U0+24Hs2Ne) ([UOz(bi-pyen)], 2) and U02(C&HseN6) ([UO,(bi-pytmd)], 3), respectively. X-Ray diffraction quality single crystals were obtained from chloroform/methanol. In the case of 2, these were monoclinic, space group C2/c, with a = 30.549(5), b = 8.251(l), c = 21.969(4)& /I = 114.47(l)“, V= 5040( 1) A3, Z= 8, pcatc = 1.78 g cmT3. Crystals of 3 were also monoclinic, space group Cut, with a = 26.946(7), b = 9.436(2), c = 10.862(2) A, /I = 105.04(2)‘, V= 2667(l) A3, Z= 4, pcalc = 1.75 g cme3. In the X-ray structure of 3, the complex lies on a crystallographic twofold axis. For 2, the final R = 0.0335, WR = 0.0371 for 297 parameters and 4475 reflections [F 14(a(F,,))], while for 3, the final R = 0.0223, WR = 0.0265 for 213 parameters and 2810 reflections [F 24 (u(F,))]. In each complex, the uranyl(V1) cation is bound to all six nitrogen atoms such that the metal center, with its two apical oxygen atoms, lies in a distorted hexagonal bipyramidal environment. The change in overall macrocycle size that results in going from 2 to 3 does not affect the U-N bond lengths. Rather, the principal difference between 2 and 3 is the extent of the twist between the two nearly planar halves of the macrocycle. In 2, the imine-pyrrole-imine dihedral angle is 17.5(l)” while in 3 it is 35.7(l)“. On the other hand, it is near 0” in an earlier reported complex, 1, derived from o-phenylenediamine [J.L. Sessler, T.D. Mody and V. Lynch, Inorg. Chem., 31 (1992) 5311. Complex 1 displays two reversible oxidations at +0.82 V and +1.09 V versus FJF,+ in CH,Cl, containing TBAPF6, while complexes 2 and 3 display irreversible oxidation waves at +1.22 V, +1.46 V and +1.22 V and +1.47 V versus FclFc+, respectively. Complexes 1, 2, and 3 also display quasi-reversible uranyl-centered reductions at -0.85 V, -1.02 V, and -0.96 V versus F,jFc+, respectively. Keywords: Template condensation; Uranyl(V1) complexes; Pyrrole-derived; Schiff base complexes
1. Introduction In the past several years, there has been considerable interest in designing stable, well-characterized chelands for the complexation of the uranyl cation [l-5]. Recently, we reported the synthesis and structural characterization of the first hexadentate pyrrole-derived uranyl(V1) Schiffbase complex 1 [6]. Solid state evidence revealed that the
* Corresponding author. ’ Pharmacyclics lnc, Sunnyvale, CA, USA. 2 Stanford university, Department of Chemistry,
Stanford,
USA.
0 1996 Elsevier Science S.A. All rights reserved 0020-1693/96/$15.00 PII SOO20-1693(96)05046-8
uranyl cation is coordinated to all six nitrogen atoms in a planar fashion. These results led us to prepare other analogous systems (i.e. U02(bi-pyen) 2 and UO,(bipytmd) 3) with a view to determining whether the planarity observed for complex 1 is due primarily to the rigidity of the phenylene diamine rings or whether it is inherent to the hexagonal bipyramidal chelating geometry of the macrocycle-bound uranyl ion. Thus, in this paper, we wish to report the uranyl nitrate template synthesis and structural characterization of two new pyrrole-derived uranyl(V1) macrocyclic Schiff base complexes 2 and 3. From this study, we are able to conclude that the rigidity of the phenylene diamine rings in complex 1, does con-
24
J.L. Seder
et al. I Inorganica Chimica Acta 246 (1996) 23-30
strain the overall ligand to a planar conformation. On the other hand, in all three crystal structures a local hexagonal bipyramidal arrangement around the uranyl(V1) cation is found. Such a finding is not inconsistent with earlier conclusions derived from the study of a range of very different (i.e. unrelated) ligand systems [7].
H
J-4 ‘\
0
E
H
+
WWWJH,
0
4
5 6
n=* n=3
2. Experimental
2.1. General information Proton and 13C NMR spectra were obtained in CDC13 on a General Electric QE-300 (300 MHz) using Me& as an internal standard. Electronic spectra were recorded on a Beckman DU-7 spectrophotometer in CHC13. Infrared spectra were recorded, as KBr pellets, from 4000 to 800 cm-* on a Nicolet 510P FT-IR spectrophotometer. Low and high resolution fast atom bombardment mass spectrometry (FAB MS) were performed using FinniganMAT TSQ-70 and VG ZAB-2E instruments, respectively. A nitrobenzyl alcohol (NBA) matrix was used with CHC13 as the co-solvent. Elemental analyses were performed by Atlantic Microlabs Inc.
2.2. Synthesis All reagents were of reagent grade quality, purchased commercially, and used as received. All solvents were spectroscopic grade and used as received. Tetra-n-butylammonium hexafluorophosphate (TBAPFs) used for electrochemical studies was recrystallized from hot ethyl acetate. 2.2.1. Uranyl complex of 9,10,19,20-tetraethyl3,6,13,16,21,22-hexaazapentacyclo[l6.2.l.l8~~1.~~s. 014~1S]docosa-2,4,6,8,10,12,16,18,20-octaene ([UOz(bipyenU 2) The uranyl complex 2 was prepared by combining a mixture of 3,4-diethylpyrrole-2,5-dicarbaldehyde (4) [6] (300 mg, 1.68 mmol), ethylenediamine (5) (101 mg,
1.68 mmol) and uranyl nitrate (355 mg, 0.90 mmol) in 60 ml of absolute ethanol at reflux. After 5 h, the fine orange powder was filtered off, washed several times with methanol, and dried in vacua to yield 490 mg (88%) of the crude product. Dissolving this crude material in CHC13 and layering with methanol then yielded orange X-ray quality crystals. For [UOz(bi-pyen)]: iH NMR (CDC13) 6: 1.26 (t, 12H, CH,CH3), 2.82 (q, 8H, CH2CH3), 4.57 (s, 8H, CHJ, 9.25 (s, 4H, CHN). 13C NMR (CDC13) 6: 17.6, 18.3, 62.2, 131.4, 142.6, 161.2. UV/vis: (CHC13) Amax (log E): 379.5 (4.41). IR (Kbr, cm-‘, selected peaks): v 1609 (C=N), 1599 (C=N), 897 (OUO); FAB MS, m/z (rel. intensity) 674 (100); HRMS (M+) 674.3082 (talc. for CZ4H3zN602U: 674.3095). Anal. Calc. for C24H32N602U: C, 42.73; H, 4.78; N, 12.46. Found: C, 42.84; H, 4.80; N, 12.40%. This compound was further characterized by X-ray crystallography (see below). 2.2.2. Uranyl complex of 10,11,21,22-tetraethyl3,7,13,18,23,24-hexaazapentacyclo[l8.2.l.l9~~2.~~s. 015~16]tetracosa-2,7,9,11,13,18,20,22-octaene ([U02(bipytmd)l, 3) The uranyl complex 3 was prepared by combining a mixture of 4 (200 mg, 1.12 mmol), 1,3-propanediamine (6) (83 mg, 1.12 mmol) and uranyl nitrate (230 mg, 0.58 mmol) in 60 ml of absolute ethanol at reflux. After 4 h, the scarlet red crystalline product was filtered off, rinsed with methanol, and dried in vacua for several hours to afford 235 mg (60%). Dissolving this crude material in CHCl, and layering with methanol then yielded scarlet red X-ray quality crystals. For 3: ‘H NMR (CDC13) 6: 1.35 (t, 12H, CH,CHs), 2.37 (p, 4H, CH2CH2CH2), 2.84 (q, 8H, CH2CH3), 4.3 1 (t, 8H, CH2CH2CH2), 9.25 (s, 4H, CHN). i3C NMR (CDC13) 6: 17.6, 18.3, 30.3, 55.1, 130.4, 142.2, 160.6. UV/vis: (CHCls) &,,, (log E): 370.5 (4.45). IR (KBr, cm-‘, selected peaks): v 1605 (C=N), 1595 (C=N), 897 (OUO); FAB MS, m/z (rel. intensity) 703(100); HRMS (M + H) 703.3489 (talc. for C26H37Ns02U: 703.3486). Anal. Calc. for C2sH3sNs0&J: C, 44.44; H, 5.16; N, 11.96. Found: C, 44.44; H, 5.16; N, 11.88%. This compound was further characterized by Xray crystallography (see below). 2.3. Electrochemical measurements Cyclic voltammetric measurements of uranyl(V1) complexes 1, 2, and 3 (1 X 10m3 M) were performed under a nitrogen atmosphere at 23 + 2°C with a conventional three-electrode system using a Bioanalytical System (BAS) 100. A platinum button (area ca. 0.03 cm2) was used as the working electrode and a platinum wire was used as a counter electrode. An Ag/AgCl electrode was used as reference and was separated from the bulk solution (which contained anhydrous CH2C12 and 0.1 M TBAPF, as the supporting electrolyte) by a fritted glass
J.L. Seder
et al. I Inorganica Chimica Actu 246 (I 996) 23-30
bridge. All potentials, at a scan rate of 100 mV s-l, were recorded against Ag/AgCl in CHQ containing 0.1 M TBAPF,. The ferrocene/ferrocenium (F,IF,+) couple was recorded at +0.68 V versus Ag/AgCl under similar electrochemical conditions. For the sake of consistency, all redox potentials (Ein) in this paper are reported versus FJF,+. 2.4. Stability studies
Complex stability was determined kinetically by monitoring the change in the Soret-like absorbance at 450 nm, 379.5 nm, and 370.5 nm for complexes 1,2, and 3, respectively, as a function of time using a Beckman DU-7 spectrophotometer. This was done for a period of 24 h using starting concentrations of 1 X 10Y5M and two different solvent systems, namely (1) 9:l (v/v) CHCls/HOAc and (2) 12:6: 1: 1 (v/v/v/v) CHClJMeOW HOAc/H20. 2.5. X-Ray crystallography Crystals were grown as described above. Crystals of 2 grew as well-formed plates while those of 3 were generTable 1 Crystallographic
data” for (C24H32Nb)U02
(2) and (C26H36N6)U02
(3) 2
Cd-!&U%
Formula Pw (1 (A) b (A) c (A) B (“) v (A3) Z F(OO0) Space group Radiation pcalc, P
(g cme3)
(cm-‘)
Transmission factorb range Crystal size (mm) WIc Rw(F) Reflections
used,
674.58 30.549(S) 8.251(l) 2 I .969(4) I 14.47( 1) 5040( 1) 8 2608 C2/c (no. 15) Graphite monochromated, (h = 0.71073W) 1.78 61.38 0.09942-0.4692 0.13 x 0.40 x 0.46 0.0335 0.037 1 4475
3
C26H36N6U02 702.64 26.946(7) 9.436(2) 10.862(2) 105.04(2) 2667( 1) 4 1368 C2/c (no. 1.5) MoKa 1.75 58.02 0.2264-0.3855 0.17 x 0.28 x 0.31 0.0223 0.0265 2810
Ft, > 4(W,)) ‘Data for both samples were collected on a Nicolet P3 diffractometer. Data for 3 were collected at -90°C while using a Nicolet LT-2 lowtemperature delivery system. Lattice parameters were obtained from the least-squares refinement of 37 reflections with 16.3 rc 20 < 21.5” for 2 and 39 reflections with 12.1 < 20 < 20.5” for 3. bAbsorption correction was based on measured crystal faces. ‘The function Zw(lF,I - IF,$ was minimized, and where w = I/(u(F,,)~ + (0.02F)2). R(F) = T(IF,,I - IFelEIFoI; R,(F) = [Zw(lF,I - lFcD2/ Pw(lF 0 l)2]“2.
25
ally thicker and more block-like in appearance. Data were collected on a Nicolet P3 diffractometer with a graphite monochromator and using MoKa radiation (A = 0.71073 A). Crystallographic details are listed in Table 1. Data were collected using the w scan technique, with a 1.2” scan range and a variable scan rate (5-10” min-l for 2 and 4, 8” min-’ for 3). Data were collected to 55” in 28. Two symmetry equivalent sets of data were collected for each sample. 12 354 reflections were collected for 2, of which 5838 were unique with an R for averaging symmetry equivalent data, Rint= 0.028. For 3, 6527 reflections were collected, yielding 3269 unique data points with an Rint= 0.033. Systematically absent reflections indicated the space group could be Cc or C2lc for both 2 and 3. The assignment of C2/c was justified by the refinement results. Data reduction and decay correction were performed using the SHELXTL-Plus software package [8]. The structures were solved by direct methods and refined by full-matrix least-squares [8] with anisotropic thermal parameters for the non-H atoms. In the X-ray structure of 3, the complex lies on a crystallographic twofold axis that passes through the U02 moiety. For 2, two ethyl carbon atoms, C24 and C28, were disordered about two orientations. The site-occupancy factors for C24 and C28 refined to 47(2)% and 65(3)%, respectively. These atoms were refined isotropically. Except for the disordered atoms for which no hydrogen atoms were included, the hydrogen atoms for 2 were calculated in ideal positions (C-H 0.96 A) with Uiso fixed at 1.2 X Ueq of the attached atom. For 3, most hydrogens were obtained from a AF map and refined with isotropic thermal parameters. The hydrogen atoms of one ethyl group of 3, carbons C 15 and C16, did not refine well and were calculated in ideal positions with LIisofixed at 1.2 X Ueq of the attached atom. The function, Cw(lF,I - lFJ)2, was minimized, where w = I/(o(F,))~ and o(F,,) = (0.5W’” [(ao2 + (0.02J)2]1’2}. The intensity, I, is given by (Ipeak - Ibackground) X (scan rate); where 0.02 is a factor to downweight intense reflections and to account for instrument instability and k is the correction due to Lp effects, absorption and decay. The absorption correction was based on measured crystal dimensions. a(Z) was estimated from counting statistics; a(l) = [(Zpeak + X (scan rate)]. The data were corrected Ibackground)‘” for secondary extinction effects. The correction is of the form: F,,,, = F,l[( 1 + X X Fe2/sin 28)“.25], where X = 3.2(2) X low7 for 2 and 3.7(3) X 10v6 for 3. Neutral atom scattering factors for the non-H atoms were taken from Cromer and Mann [9], with the anomalous-dispersion corrections taken from the work of Cromer and Liberman [lo]. The scattering factors for the H atoms were obtained from Stewart et al. [ 111. Values used to calculate the linear absorption coefficient are from the International Tables for X-ray Crystallography (1974) [ 121. All figures were generated using SHELXTL-Plus [8]. Other computer programs used in this work are listed elsewhere u31.
J.L. Seder et al. I Inorganica Chimica Acta 246 (1996) 23-30
26
3. Results and discussion
Uranyl(V1) tetraimine complexes 2 and 3 were prepared in the presence of many1 nitrate via a metal template [2 + 21 condensation between 3,4-diethyl-2,5-dicarbaldehyde (4) [6,14] and ethylenediamine (5) or 1,3propanediamine (6), respectively [6,15]. Complexes 2 and 3 proved highly soluble (to the ca. 40 mg/ml level) in chloroform and dichloromethane but practically insoluble in more polar solvents such as HzO, MeOH, and EtOH. Nonetheless, they were obtained in good yields (88 and 60%, respectively) and were fully characterized by spectroscopic and structural methods as discussed below. Both complexes 2 and 3 display iH and i3C NMR of remarkable simplicity (cf. e.g. Fig. 1). This simplicity is due to their symmetrical structure. In addition, the IR spectra of complexes 2 and 3 proved simple to interpret. For instance, these complexes displayed an identical single sharp absorption at 897 cm-i for the asymmetric vibration of the uranyl ion and lacked vibrations that could be assigned to either pyrrole NH residual groups or adventitious coordinating anions. Thus, as seen for the uranyl complex 1 [6], the spectral data of complexes 2 and 3 are completely consistent with a neutral complex in which the uranyl ion is coordinated to all six ring nitrogen atoms [6]. 3.2. Structural features Single crystals suitable for X-ray diffraction were obtained for both complexes 2 and 3 by dissolving the
complex in chloroform and layering with methanol (see Figs. 2 and 3, respectively). As in the case of complex 1 (Fig. 4) the uranyl(V1) cation in complexes 2 and 3 is bound to all six of the core nitrogen atoms, however in a non-planar fashion. Although the ring size of the macrocycle in 3 is larger than that in 2, the nitrogen-uranium bond lengths for 2 and 3 are nearly identical. In addition, as is observed in the analogous complex 1, the U-Npyrrole bond lengths are substantially shorter than the lJ_Nihne bond lengths. For 2, the U-Npyrrolebond lengths average 2.456(3) 8, while the U-NtGne bond lengths average 2.656(3) A. For 3, the U-Npyrr,,te bond length is 2.444(3) %, and the U-Nimine bond lengths average 2.660(2) A. By comparison, for 1, the U-Nihne bonds are slightly longer (2.740(5) A) and the U-Npynole bonds are slightly shorter (2.418(7) A) than those found in 2 and 3 (see Figs. 2-4 and Tables IA). One of the critical findings to emerge from the X-ray structural studies is that while macrocycles in 2 and 3 are non-planar (in marked contrast to l), they are composed of two nearly planar parts comprised of the pyrrole ring and the adjacent imine moieties. Although the size of the C-C bridges in 2 and 1 (i.e. C17-Cl8 and C7-C12, respectively) are very similar in length, the sp3 versus sp2 hybridization induces twist on the adjacent imines for 2 that can only be relieved by a twist of the entire half molecule. In the case of complex 3, this twist is even greater than complex 2 due the larger propylene bridging group. As a result the dihedral angle is near 0” in complex 1, while it increases to 17.5” and 35.7”, respectively, for the ethylene and propylene bridged systems 2 and 3. In complex 1 the two o-phenylene groups fused to the imine moieties considerably reduce the flexibility of the macrocycle compared to the more conformationally mobile
-- _j_
a
-1
b
,:I l.T, -
_I
J.
I
r
’
I
7,
a
( 6
4
2
0 PPM
1
PPM
Fig. 1. (a) ‘H NMR spectrum of uranyl(V1) chelate 2 in CDCI, with (CH&Si as reference. (b) ‘H NMR spectrum of uranyl(VI) chelate 3 in CDC13 with (CH&Si as reference.
J.L. Seder
et al. I Inorganica Chimica Acta 246 (1996) 23-30
21
at substantially varying angles of approach. As a consequence, changes in the overall macrocycle size are found to have little effect on the actual uranium(V1) inner coordination sphere, even though, as discussed above, they can have a dramatic effect on the overall, generalized complex geometry. This conclusion is consistent with earlier reports in the literature (made using very different ligands) [7], and helps account, in a qualitative way, for the differences in reactivity discussed immediately below. C
3.3. Stability studies Although complexes 2 and 3 are essentially insoluble in polar solvents (i.e. H20, MeOH, EtOH, etc.), basic stability studies of these complexes could be made by using a 9:1 (v/v) mixture of CHCls and glacial HOAc. In this solvent system, it was determined that the uranyl(V1) complex 3 (at an initial 1 X low5 M concentration) has a half-life for decomposition of 12 h at room temperature, as evidenced by a bleaching of the Soret-like absorption band at 370.5 nm. Furthermore, in a water-containing solvent mixture consisting of 12:6:1:1 (v/v/v/v) CHCls/ MeOI-I/HOAc/H20, this same complex displayed a halflife for decomposition of 1 h at room temperature. HowFig. 2. Thermal ellipsoid view of 2 scaled to the 30% probability level showing partial atom labelling scheme. The complex is composed of two planar portions separated by the ethylene bridges. The dihedral angle between planes is 17.5(l)“. Top: view approximately perpendicular to the mean plane of the six nitrogen atoms. Bottom: side view of the complex.
complexes 2 and 3, in which the =N-(CHz),-N= (i.e. n = 2 or 3) groups function as adjustable hinges. Similarly, the linear uranyl cation is inclined at angles of 81.3” and 72.2” relative to the planar portion of the macrocycle in the case of 2 and 3, respectively, whereas it is nearorthogonal in 1. As a consequence, even though there is no significant difference in the nitrogen-uranium bond lengths in 2 and 3 (relative either to each other or 1) the N-U-N angles are seen to be affected strongly by an increase in the number of bridging atoms in the macrocycle. In particular, the average N-U-N angles involving adjacent nitrogens are found to be 60.0(l)“, 60.55(6)“, and 62.48(5)’ in the case of complexes 1, 2, and 3, respectively. Since an angle of 60” is expected for an ideal hexagonal arrangement, the deviation observed in the case of 3 provides yet a further indication of overall complex non-planarity. In spite of the above subtleties, it is important to appreciate that in all three uranyl complexes, the basic coordination geometry about the uranyl cation remains approximately hexagonal bipyramidal. In fact, the U-N bond distances in both 2 and 3 are essentially the same, a finding that serves to substantiate the fact that the bonding orbitals of the uranium(V1) cation are quite diffuse and can bind with equal strength to nitrogen atoms even
Fig. 3. View of 3 showing atom labelling scheme. The thermal ellipsoids are scaled to the 30% probability level. The complex lies on a crystallographic two-fold axis passing through the UO2 cation. As in 2, the ligand has two planar portions separated by an alkyl bridge. However, the dihedral angle between planar portions of the molecule is more than double and is 35.7(l)‘. Top: view approximately perpendicular to the mean plane of the six nitrogen atoms. Bottom: side view of the complex.
28
J.L. Sessler et al. I Inorganica Chimica Acta 246 (1996) 23-30
supporting electrolyte are shown in Fig. 6 (parts b and c, respectively). Two oxidation waves at +I.22 V and + 1.46 V versus F,IF,+ are obtained for complex 2. Similarly, two oxidation waves are also obtained for 3 at + 1.22 V and + 1.47 V versus FJFC+. The CVs also reveal reduction waves, which are slightly negatively shifted with no significant change in peak shape (as compared to l), at -1.02 V and -0.96 V versus F,IF,+ for 2 and 3, respectively. For complexes 2 and 3, the anodic oxidation processes are irreversible, while the cathodic potential scans show similar quasi-reversible reduction processes as compared to 1. The degree of cathodic reversibility for 2 and 3 is less pronounced than for 1.For 2 and 3, the quasi-reversible reductions are characterized by IE, iJiC = 0.3 EJ = 350 mV, and IE, - EJ = 470 mV, i& = 0.2, respectively.
Table 2 Fractional coordinates and equivalent isotropic for the non-hydrogen atoms of (C24f&Ne)U02
Fig. 4. View of 1 with a partial atom labelling scheme. Thermal ellipsoids are scaled to the 50% probability level. The U atom lies on a crystallographic inversion center and the ligand is planar. The UO2 cation is inclined at an angle of 86.2” to the N6 plane. Top: view approximately perpendicular to the plane through the six nitrogen atoms of the ligand. Bottom: side view of the complex.
ever, under similar conditions complexes 1 and 2 appear to be quite stable, undergoing no apparent decomposition or demetallation over a 24 h period (see Fig. 5). This difference in stability suggests that even though complexes 1, 2, and 3 share many spectroscopic and structural features in common, they differ substantially in terms of their reactivity. 3.4. Electrochemistry The effects of changes in macrocycle type for congeners l-3 were also probed using cyclic voltammetry. Representative cyclic voltammograms (CVs) are shown in Fig. 6 and key results are summarized in Table 5. In the case of complex 1 in CHpC12 containing 0.1 M TBAPF6 as the supporting electrolyte, the CV shows two nearly reversible l-electron oxidations as illustrated in Fig. 6a. For the first oxidation at +0.82 V versus FCIFC+, IE,E,I = 67 mV, i,/i, = 1.1 at a scan rate of 100 mV s-l and for the second oxidation at +1.09 V versus FJFC+, IE, E,I = 61 mV, i,/i, = 0.8 at 100 mV s-i. Under identical conditions, however, a cathodic potential scan characterized by a peak potential at -0.85 V versus F,IF,+ shows a quasi-reversible process with IE, - E,I = 300 mV, iJiC = 1.4. The CVs of 2 and 3 in CH2C12 with TBAPF6 as the
Atom
x
Y
U 01 02 Cl c2 c3 c4 C.5 N6 Cl C8 N9 Cl0 Cl1 Cl2 Cl3 Cl4 Cl5 N16 Cl7 Cl8 N19 c20 N21 N22 C23 C24 C24A C25 C26 C27 C28 C28A C29 c30
0.247620(10) 0.24078( 14) 0.25447( 14) 0.3654(2) 0.3981(2) 0.3724(2) 0.3253(2) 0.2819(2) 0.2435(2) 0.1980(2) 0.1604(2) 0.1630(2) 0.1245(2) 0.1277(2) 0.0946(2) 0.1223(2) 0.1705(2) 0.215X(2) 0.2539(2) 0.3006(2) 0.3306(2) 0.3294(2) 0.3675(2) 0.3217(2) 0.1735(2) 0.4486(3) 0.4875(9) 0.4858( 11) 0.3908(3) 0.4068(4) 0.0418(3) 0.0151(7) 0.0140(10) 0.1047(3) 0.0999(4)
0.46971(3) 0.2562(5) 0.6827(4) 0.3884(7) 0.3597(8) 0.3896(7) 0.4332(7) 0.4639(7) 0.4793(6) 0.5087(7) 0.4126(8) 0.4494(6) 0.4587(S) 0.4883(7) 0.4966(7) 0.5219(7) 0.5250(7) 0.5372(7) 0.5222(5) 0.5367(g) 0.4009(8) 0.4102(6) 0.3775(7) 0.4324(5) 0.5034(4) 0.3033(9) 0.430(3) 0.455(4) 0.3784(8) 0.5392111) 0.4812(11) 0.651(2) 0.632(4) 0.5382(9) 0.7128(10)
thermal parameters (2)
Z
0.123030( 10) 0.1138(2) 0.1326(2) 0.2277(3) 0.2940(3) 0.3336(3) 0.2884(3) 0.2950(3) 0.2416(2) 0.2467(3) 0.1932(3) 0.1299(2) 0.0770(3) 0.0150(3) -0.0524(3) -0.0893(3) -0.0424(3) -0.0463(3) 0.0078(2) 0.0044(3) 0.0459(3) 0.1119(2) 0.1639(3) 0.2247(2) 0.0205(3) 0.3170(4) 0.3458( 13) 0.3250( 14) 0.4086(3) O&36(4) -0.0783(4) -0.0903(9) -0.0665( 13) -0.1642(3) -0.1866(4)
(A’)
(I
0.02735(8) 0.040(2) 0.044(2) 0.038(2) 0.047(2) 0.044(2) 0.039(2) 0.039(2) 0.038(2) 0.045(3) 0.045(2) 0.039(2) 0.042(2) 0.039(2) 0.046(3) 0.043(2) 0.039(2) 0.037(2) 0.035(2) 0.039(2) 0.046(3) 0.038(2) 0.040(2) 0.@35(2) 0.033(2) 0.064(3) 0.081(7) 0.109(9) 0.056(3) 0.091(5) 0.070(3) 0.100(6) 0.068(7) 0.054(3) 0.097(5)
For anisotropic atoms, the LI value is CIcq calculated as (leq = 113 E&j Vu ai*aj*Ao where Au is the dot product of the ith and jth direct space unit cell vectors.
J.L. Sessler ef al. I Inorgunica Chimica Acta 246 (1996) 23-30
29
Table 3 Fractional
coordinates
for the non-hydrogen
and equivalent
isotropic
atoms of (C2,jH3,jNrj)U02
thermal parameters
(A*)
(3)
‘.”
A 1 at 450.0 nm 1.8
9 ??
Atom
x
Y
Z
u
U 01 02 Cl c2 c3 c4 CS N6 C7 C8 c9 NlO Cl1 N12 Cl3 Cl4 Cl5 Cl6
0.5 0.5 0.5 0.37183(13) 0.33257( 13) 0.3567(2) 0.4088(2) 0.4548(2) 0.49823( 12) 0.54446(14) 0.5773(2) 0.5808(2) 0.58439(11) 0.62658( 13) 0.41743(11) 0.2771(2) 0.2421(2) 0.3323(2) 0.3347(2)
0.22284(2) 0.4113(4) 0.0347(3) 0.1868(4) 0.1972(4) 0.2508(4) 0.2654(4) 0.3029(3) 0.2878(3) 0.3377(4) 0.2124(4) 0.0959(4) 0.1537(3) 0.1401(3) 0.2274(3) 0.1582(5) 0.2823(7) 0.2812(5) 0.4360(6)
0.25 0.25 0.25 0.2273(3) 0.2914(3) 0.4140(3) 0.4171(3) 0.5135(3) 0.4871(3) 0.5801(3) 0.6440(3) 0.551 l(3) 0.4288(2) 0.3967(3) 0.3041(3) 0.2383(4) 0.1887(g) 0.5209(4) 0.5602(5)
0.01715(6) 0.0304(12) 0.0251(11) 0.0258(10) 0.0273( 11) 0.0280( 12) 0.0257( 11) 0.0257( 11) 0.0220(g) 0.0276( 11) 0.0295( 12) 0.0266( 11) 0.0242(9) 0.0246( 10) 0.0230(g) 0.0360(13) 0.059(2) 0.0389( 13) 0.066(2)
2 at 379.5 nm 3 at 370.5 nm
1.6 -
0.8 -
0.6 -
“_?I
I
0
2
I
I
4
6
t
I
8
10
12
00
Fig. 5. Kinetics of decomposition of uranyl(V1) complexes: Plot of the change in absorbance at the Soret maximum (450.0 nm, 379.5 nm, and 370.5 nm, for 1, 2, and 3, respectively) as a function of time (h) for 1 X low5 M solutions of l-3 in 9:l (v/v) CHCl$HOAc.
For anisotropic atoms, the U value is Ueq calculated as Ueq = 1/3X,~j Uu ai*nj*Aij where Ad is the dot product of the ith and jth direct space unit cell vectors.
The anodic oxidation waves seen in the CVs for all complexes are presumed to be ligand-based oxidations. In contrast, the cathodic reduction waves for complexes 1, 2, and 3 are presumed to involve reduction of the uranyl(V1) cation [i.e. U(V1) to U(V)], in accordance with the treatise by van Doorn et al. [I], who found that the uranyl(V1) cation bound to a variety of Schiff-base derived hosts undergoes a one electron reduction in the range -0.94 V to -1.08 V versus Ag/AgCl in CH$N. Imine reductions occur at much more negative potentials and therefore do not contribute to the reduction processes observed electrochemically [ 16-l 81.
I
-
64
k
1
+I 4
+I”
+ooJ
0.0
a5
-12
Table 4 Selected bond lengths (A), angles (“) and intramolecular 1 U-Npyrro’e U-%nine u-o N-U-Navg ’ Ni-U-Ni Ni-U-Np N.‘-Ni, b N...Ni ” C = N’ C-CpyrroleC
2.418(7) 2.740(5) 1.770(6) 60.0( 1) 57.7(2) 61.1(l) 2.638(7) 2.647(9) 1.296(7) 1.415(7)
2 2.456(3) 2.656(3) 1.774(3) 60.55(6) 60.1(l) 60.8( 1) 2.592(4) 2.662(4) 1.274(3)
1.409(4)
contacts (A) 3 2.444(3) 2.660(2) 1.777(2) 62.48(5) 64.94(9) 61.24(6) 2.608(3) 2.857(4) 1.281(4) 1.409(3)
“N-U-N angles include only those for adjacent nitrogen atoms. bi and p refer to the imine and pyrrole nitrogen atoms, respectively. ‘Values listed are average bond lengths for the pyrrole rings.
Fig. 6. Cyclic voltammograms of uranyl(V1) complexes (a) 1, (b) 2, (c) 3 recorded under nitrogen in CH2C12 containing 0.1 M TBAPF6 at a scan rate of 100 mV s-’ The potential axis is calibrated with respect to Ag/AgCl.
30
J.L.. Sessler et al. I Inorganica Chimica Acta 246 (1996) 23-30
Table 5 Redox potentials (E~Q, V versus Fe/Fe+) for uranyl(V1) complexes 1,2, 3
Complex
1 2 3
E&
(V versus FdFc+)b
1st oxidation
2nd oxidation
1st reduction
+0.82 +1.22 +I.22
+1.09 +1.46 +1.47
-0.85 -1.02 -0.96
aO.l M TBAPF6 in CH$&. scan rate = 100 mV s-l. bThe observed potentials were referenced to a ferrocene internal standard. The ferrocene/ferrocenium (Fc/Fc+) couple was recorded at +0.68 V versus Ag/AgCl.
The near-reversibility of the oxidation waves for complex 1 as compared to complexes 2 and 3 can be rationalized in terms of complex stability under electrochemical oxidations. The presence of four electrondonating methoxy substituents on the macrocyclic periphery, as well as, the n-conjugation of the ligand may impart stability to complex 1. For both complexes 2 and 3, the non-planar geometry, macrocyclic flexibility, and lack of a delocalization pathway, destabilizes them towards oxidation. Thus, these electrochemical measurements reveal a degree of increased chemical reactivity in both of these newer complexes (i.e. 2 and 3) that is not present in the parent system 1. As such, they serve to highlight the importance of considering the details of both inner, metalcentered geometric factors and overall macrocyclic structural effects when assessing the stability, reactivity, and properties of new, ostensibly similar macrocyclic ligand complexes. 4. Supplementary
material
Tables of anisotropic thermal parameters, hydrogen positional parameters, bond distances and angles, and unit-cell packing diagrams for uranyl(V1) complexes 2 and 3 (20 pages); listing of observed and calculated structure factor amplitudes for 2 and 3 (35 pages). Acknowledgements
This work was supported by grants to J.L.S. from the National Institute of Health (AI 28845), National Science Foundation (CHE 9122161), and Pharmacyclics, Inc. T.D.M. and M.T.D. wish to thank also the UT Austin Department of Chemistry and Biochemistry for Texaco Foundation and Department of Education Fellowships, respectively. References [I] Uranyl complexes of Schiff base macrocyclic ligands. see: A.R. van Doom, M. Bos, S. Harkema, J. van Eerden, W. Verboom and D.N. Reinhoudt, J. Org. Chem., 56 (1991) 2371 and references therein; W. Nijenhuis, A.R. van Doom, A.M. Reichwein, F. de
Jong and D.N. Reinhoudt, J. Am. Chem. Sot., I13 (1991) 3607; R. Chandra, Synrh. React. Inorg. Met.-Org. Chem., 20 (1990) 645 and references therein; U. Casellato, P. Guerriero, S. Tamburini, P.A. Vigato and R. Graziani, J. Chem. Sot., Dalton Trans., (1990) 1533; F. Benetollo, G. Bombieri, L. De Cola, A. Polo, D.L. Smailes and L.M. Vallarino, Inorg. Chem., 28 (1989) 3447; F.A. El-Saied, fnorg. Chim. Acta., 165 (1989) 147; F. Bullita, P. Guerriero, S. Tamburini and P.A. Vigato, J. Less Common Mef., 153 (1989) 211; C.J. van Staveren, D.E. Fenton, D.N. Reinhoudt, J. van Eerden and S. Harkema, J. Am. Chem. Sot., 109 (1987) 3456. PI For overviews of macrocyclic Schiff base complexes of lanthanides and actinides, see: V. Alexander, Chem. Rev,, 95 (1995) 273; D.E. Fenton and P.A. Vigato, Chem. Sot. Rev., I7 (1988) 69; G. Bombieri, Inorg. Chim. Acta, 139 (1987) 21; L.M. Vallarino, in, K.A. Gschneider, Jr. and L. Eyring (eds.), Handbook on the Physics and Chemistry of Rare Earths, Vol. 15, Ch. 4, Elsevier, Amsterdam, 1991. [31 Uranyl(V1) superpthalocyanine, see: V.W. Day, T.J. Marks and W.A. Wachter, J. Am. Chem. Sot., 97 (1975) 4519; T.J. Marks and D.R. Stojakovic, J. Am. Chem. Sot., IO0 (1978) 1695; E.A. Cuellar, D.R. Stojakovic and T.J. Marks, Inorg. Synrh., 20 (1980) 97; E.A. Cuellar and T.J. Marks, Inorg. Chem., 20 (1981) 3766; T.J. Marks and D.R. Stojakovic, J. Chem. Sot., Chem. Commun., (1975) 28.
[41 A.K. Burrell, G. Hemmi, V. Lynch and J.L. Sessler, J. Am. Chem. Sot., 113 (1991) 4690.
r51 A.K. Burrell, M.J. Cyr, V. Lynch and J.L. Sessler, J. Chem. Sot., Chem. Commun., (1991) 1710. PI J.L. Sessler, T.D. Mody and V. Lynch, Inorg. Chem., 31 (1992) 531; T.D. Mody, Ph.D. Dissertation, University of Texas at Austin, 1993. 171 G. Marangoni, S. Degetto, R. Graziani, G. Bombieri and E. Forsellini, J. Inorg. Nucl. Chem., 36 (1974) 1787; G. Paolucci, G. Marangoni, G. Bandoli and D.A. Clemente, J. Chem. Sot., Dalton Trans., (1980) 459; R. Graziani, U. Casellato, P.A. Vigato, S. Tamburini and M. Vidali, J. Chem. Sot., Dalton Trans., (1983) 697; N.W. Alcock, D.J. Flanders and D. Brown J. Chem. Sot., Dalton Trans., (1985) 1001; A. Cousson, J. Proust and E.N. Rizkalla, Acra Crysrallogr. C., 47 (1991) 2065. PI G.M. Sheldrick, SHELXTL-Plus, Siemens Analytical X-Ray Instruments Inc., Madison, WI, USA, 1987. t91 D.T. Cromer and J.B. Mann, Acta Crystallogr., A24 (1968) 321. DOI D.T. Cromer and D. Liberman, J. Chem. Phys., 53 (1970) 189 1. [111 R.F. Stewart, E.R. Davidson and W.T. Simpson, .J. Phys. Chem., 42 (1965) 3175. WI International Tables for X-Ray Crystallography, Vol. IV, Kynoch Press, Birmingham, UK, 1974, p 55. [I31 S.M. Gadol and R.E. Davis, Organomerallics, 1 (1982) 1607. u41 The preparation of 3,4-diethylpyrrole-2,5_dicarbaldehyde, 4, has also been reported by E. Vogel, N. Jux, E. Rodriguez-Val, J. Lex and H. Schmicker, Angew. Chem. Int. Ed. Engl., 29 (1990) 1387, see also Ref. [6]. t151 Well prior to this work, Fenton et al. prepared a series of macrocycles derived from alkyl-free pyrrole-2,5_dicarbaldehyde, and used these to chelate Cu(I1) and other cations of the transition series, see: D.E. Fenton and R. Moody, J. Chem. Sot., Dalton Trans., (1987) 219; H. Adams, N.A. Bailey, D.E. Fenton, S. Moss, C.O. Rodriguez de Barbarin and G. Jones, J. Chem. Sot., Dalton Trans., (1986) 693; H. Adams, N.A. Bailey, D.E. Fenton, S. Moss and G. Jones, Inorg. Chim. Acta, 83 (1984) L79. [I61 A.J. Bard (ed.). Encyclopedia of Electrochemistry of the Elements. Organic Section; Vol. XV, Marcel Dekker, New York, 1984. P71 Any imine reductions could not be observed because reduction potentials greater than ca. -1.6 V versus Ag/AgCl are well outside the electrochemical range of the solvent (i.e. +1.8 V to -1.6 V versus Ag/AgCl), see also Ref. [18]. H81 A.J. Bard, Electrochemical Methods Fundamentals and Applicarions, Wiley, New York, 1980.