Versatility of Thiosemicarbazones in the Construction of Monomers

Nov 5, 2007 - Tarlok S. Lobana,*,† Sonia Khanna,† Rekha Sharma,† Geeta Hundal,† Razia Sultana,†. Manisha Chaudhary,† R. J. Butcher,‡ and...
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CRYSTAL GROWTH & DESIGN

Versatility of Thiosemicarbazones in the Construction of Monomers, Dimers and Hydrogen-Bonded Networks of Silver(I) Complexes

2008 VOL. 8, NO. 4 1203–1212

Tarlok S. Lobana,*,† Sonia Khanna,† Rekha Sharma,† Geeta Hundal,† Razia Sultana,† Manisha Chaudhary,† R. J. Butcher,‡ and A. Castineirasξ Department of Chemistry, Guru Nanak DeV UniVersity, Amritsar - 143 005, India, Department of Chemistry, Howard UniVersity, Washington, D.C. 20059, and Departamento De Quimica Inorganica, Facultad de Farmacia, UniVersidad de Santiago, 15782 Santiago, Spain ReceiVed July 20, 2007; ReVised Manuscript ReceiVed NoVember 5, 2007

ABSTRACT: Reactions of thiosemicarbazones {R1R2C2dN3-N2(H)-C1(dS)-N1H2}, a multidonor class of ligands, with silver(I) halides in the presence of PPh3 have yielded a variety of compounds, viz.: (i) halogen-bridged dimers, [Ag2(µ-X)2(η1-S-Haptsc)2(PPh3)2] (R1 ) Ph, R2 ) Me, Haptsc, X ) Cl (1); Br (2)), [Ag2(µ-Br)2(η1-S-Hbtsc)2(PPh3)2] (R1 ) Ph, R2 ) H, Hbtsc (3)), [Ag2(µ-Br)2(η1S-Hactsc)2(PPh3)2] (R1 ) R2 ) Me, Hactsc (4)); (ii) sulfur-bridged dimers, [Ag2Br2(µ-S-Hptsc)2(PPh3)2] · 2H2O (R1 ) pyrrole, R2 ) H, Hptsc (5)), and [Ag2Cl2(µ-S-Httsc)2(PPh3)2] · 2CH3CN (R1 ) thiophene, R2 ) H, Httsc (6)), and (iii) monomers, [AgX(η1S-Hpytsc)(PPh3)2] · CH3CN (R1 ) pyridine, R2 ) H, Hpytsc, X ) Br (7); Cl (8)). In contrast, silver(I) nitrate has formed only sulfur-bridged dimers, [Ag2(η1-N-µ-S-Hftsc)2(Ph3P)2](NO3)2 (9) (R1 ) furan, R2 ) H, Hftsc), and [Ag2(η1-S-Hptsc)2(µ-SHptsc)2(Ph3P)2](NO3)2 · 2CHCl3 (10) (R1 ) pyrrole, R2 ) H, Hptsc) (Hpytsc ) pyridine-2-carbaldehyde thiosemicarbazone, Hptsc ) pyrrole-2-carbaldehyde thiosemicarbazone, Httsc ) thiophene-2-carbaldehyde thiosemicarbazone, Hftsc ) furan-2-carbaldehyde thiosemicarbazone, Hbtsc ) benzaldehyde thiosemicarbazone, Hactsc ) acetone thiosemicarbazone, and Haptsc ) acetophenone thiosemicarbazone). Complexes 1-10 are the first examples exhibiting new bonding modes (η1-S, µ-S, and µ-S-η1-N3) in silver(I)thiosemicarbazone chemistry. The substituents at C2 carbon appear to have significant influence on the nature of bonding in the complexes. The intermolecular interactions such as, NH · · · X (X ) S, Br, Cl, O), CH · · · π and CH · · · X (X ) S, Cl) have led to the formation of one- and two-dimensional (1D and 2D) networks. Interestingly, a novel feature is that some of the 2D networks encapsulate organic molecules in the voids. Introduction Thiosemicarbazones constitute an important class of N,Sdonors with their propensity to react with a wide range of metals,1 and thus can bind to a metal center via a variety of coordination modes in their neutral and anionic forms (I, II).2 As neutral ligands, they exhibit modes A and B (binding through an S donor atom) as well as modes C, D (binding through N, S donor atoms). Further, as anionic ligands they bind to metals via modes A-G (Chart 1).2 The interest in thiosemicarbazone stems not only from bonding and structure considerations, but also due to their ion-sensing ability,3 and pharmacological properties such as anticancer, antibacterial, antifungal, etc.4 Coordination chemistry of coinage metals with thiosemicarbazones is relatively much less investigated, and only recently, a systematic investigation of copper(I) halides with a series of thiosemicarbazones has been reported from this laboratory.5 In the case of silver(I), a few compounds of silver(I) salts with thiosemicarbazones have been synthesized,2o but except for a hexanuclear complex [Ag6(Hstsc)6] (Hstsc ) anion of salicylaldehyde thiosemicarbazone),2m there are no structurally characterized compounds of thiosemicarbazones with silver(I) salts. In the literature, coordination of silver(I) with various N, S-donors other than thiosemicarbazones is known.6–17 In this paper, novel one- and two-dimensional (1D and 2D) hydrogenbonded supramolecular networks of monomeric and dimeric complexes of silver(I) salts are reported using a series of thiosemicarbazones (Chart 2). The study of supramolecular networks have importance in the context of their possible * Corresponding author. E-mail: [email protected]. Fax: 91-1832-258820. † Guru Nanak Dev University. ‡ Howard University. ξ Universidad de Santiago.

Chart 1

applications such as carriers to transport drugs in biological systems, as mass and potentiometric sensors, and as probes to detect trace metals.18–21 Experimental Section Materials and Methods. Pyridine-2-carbaldehyde, pyrrole-2-carbaldehyde, furan-2-carbaldehyde, thiophene-2-carbaldehyde, acetophenone, benzaldehyde, acetone, triphenylphosphine, and silver nitrate were procured from Aldrich Sigma Ltd. The ligands pyridine-2-carbaldehyde thiosemicarbazone (Hpytsc), pyrrole-2-carbaldehyde thiosemicarbazone (Hptsc), thiophene-2-carbaldehyde thiosemicarbazone (Httsc), furan2-carbaldehyde thiosemicarbazone (Hftsc), benzaldehyde thiosemicarbazone (Hbtsc), acetone thiosemicarbazone (Hactsc), and acetophenone thiosemicarbazone (Haptsc) were prepared by the reported methods.22,23 Silver(I) halides (Br, Cl) were prepared by mixing a methanolic solution

10.1021/cg700672e CCC: $40.75  2008 American Chemical Society Published on Web 03/05/2008

1204 Crystal Growth & Design, Vol. 8, No. 4, 2008 Chart 2

of silver(I) nitrate with a solution of sodium bromide/chloride in distilled water. The C, H, N analyses were obtained with a Carlo-Erba 1108 microanalyser from University of Santiago, Spain, and a Thermoelectron FLASHEA1112 CHNS analyzer from Department of Chemistry, Guru Nanak Dev University. The melting points were determined with a Gallenkamp electrically heated apparatus. Infrared (IR) spectra were recorded using KBr pellets on a Pye Unicam SP-3-300 and FTIR NICOLET 320 Fourier transform infrared spectophotometer in the 4000-400 cm-1 range. The 1H NMR spectra of the complexes were recorded on an AL-300 FT JEOL spectrometer operating at a frequency of 300 MHz in CDCl3 with TMS as the internal reference. The 31P NMR spectra were recorded on a Bruker ACP-300 spectrometer operating at a frequency of 121.5 MHz with (CH3O)3P as the external reference set at zero value. Synthesis. Synthesis of [Ag2(µ-Cl)2(η1-S-Haptsc)2(PPh3)2] (1). To AgCl (0.025 g, 0.174 mmol) suspended in acetonitrile (15 mL) was added solid PPh3 (0.045 g, 0.174 mmol), and the contents were stirred for 24 h. The white solid formed was filtered and dried in vacuo. The analytical data of this white solid supported the formation of [AgCl(PPh3)]. To this solid (0.050 g, 0.123 mmol), suspended in chloroform, was added Haptsc ligand (0.024 g, 0.123 mmol), and the contents were stirred until a clear solution was obtained, which was allowed to evaporate slowly at room temperature. The solid mass obtained was dissolved in CH2Cl2 (5 mL) in a culture tube, and a layer of CH3CN (1 mL) was spread over it. The slow evaporation of this solution resulted in the colorless crystals. Yield, 60.1%, 0.06 g, m.p. 200 – 202 °C. Anal. Calcd. for C54H52Ag2Cl2N6P2S2: C, 54.15, H, 4.34, N, 7.02; Found: C, 53.89, H, 4.83, N, 7.28. IR data (KBr, cm-1): ν(N-H) 3425(s), 3310(m), 3360(m) (-NH2-) 3150(s), 3100(s) (-NH-); ν(CdN) + δNH2 + ν(CdC) 1591(m), 1512(s), 1488(s); ν(CdS) 839(s); ν(C-N) 1000(s); ν(P-CPh) 1093(s). 1H NMR (CDCl3, δ ppm): 2.49s (CH3), 7.33–7.49 m (N1H2 + Ph + PPh3), 9.98s (-N2H). 31P NMR (CDCl3, δ ppm): -99.5 ppm, ∆δ(δcomplex - δ ligand) ) 13.7 ppm. This complex is soluble in CHCl3 but poorly soluble in CH3CN and CH3OH. Complexes 2–4 were prepared by the same method. Synthesis of [Ag2(µ-Br)2(η1-S-Haptsc)2(PPh3)2] (2). Yield, 0.05 g, 55%, m.p. 205-207 °C. Anal. Calcd. for C54H52Ag2Br2N6P2S2: C, 50.35, H, 4.04, N, 6.52; Found: C, 50.38, H, 4.02, N, 6.59. IR data (KBr, cm-1): ν(N-H) 3414(s), 3236(m) (-NH2-), 3140(m) (-NH-); ν(CdN) + δNH2 + ν(CdC) 1579(m), 1512(s), 1489(s); ν(CdS) 838(s); ν(C-N) 1072(s); ν(P-CPh) 1091(s). 1H NMR (CDCl3, δ ppm) 2.44s (CH3), 7.75b, 8.46s (-N1H2), 7.32–7.68m (Ph + PPh3), 10.25 s (-N2H). 31P NMR (CDCl3, δ ppm): -100.4 ppm, ∆δ(δcomplex - δ ligand) ) 12.3 ppm. This complex is partially soluble in CHCl3 but poorly soluble in CH3CN and CH3OH. Synthesis of [Ag2(µ-Br)2(η1-S-Hbtsc)2(PPh3)2] (3). Yield, 0.07 g, 80%, m.p. 220–222 °C. Anal. Calcd. for C52H48Ag2Br2N6P2S2: C, 49.58, H, 3.81, N, 6.67; Found: C, 49.87, H, 3.82, N, 7.16. Main IR peaks (KBr, cm-1): ν(N-H) 3421(s), 3248(m) (-NH2-), 3190(b), 3150(m) (-NH-); ν(CdN) + δNH2 + ν(CdC) 1581(s), 1523(s), 1434(s); ν(CdS) 817(s); ν(C-N) 1045(s); ν(P-CPh) 1095(s). 1H NMR (CDCl3, δ ppm), 6.40s (-N1H2), 7.33–7.48 (Ph + PPh3), 8.42s (-C2H), 11.49s (-N2H). 31P NMR (CDCl3, δ ppm): -100.9 ppm, ∆δ (δcomplex - δ ligand) ) 12.2 ppm. This complex is soluble in CHCl3 but poorly soluble in CH3CN. Synthesis of [Ag2(µ-Br)2(η1-S-Hactsc)2(PPh3)2] (4). Yield, 0.04 g, 66%, m.p. 178-180 °C. Anal. Calcd. for C44H48Ag2Br2N6P2S2: C, 45.42,

Lobana et al. H, 4.13, N, 7.22; Found: C, 45.76, H, 4.68, N, 6.98. IR data (KBr, cm-1): ν(N-H) 3458(s), 3338(m), 3260(s) (-NH2-), 3178(m) (-NH-); ν(CdN) + δNH2 + ν(CdC) 1643(s), 1618(s), 1569(s); ν(CdS) 800(s); ν(C-N) 999(s); ν(P-CPh) 1095(s). 1H NMR (CDCl3, δ ppm): 7.29–7.48m (Ph + PPh3 + N1H2), 9.46s (-N2H), 2.00s, 2.09s (CH3). 31 P NMR (CDCl3, δ ppm): -100.50 ppm, ∆ δ(δcomplex - δ ligand) ) 12.65 ppm. This complex is soluble in CHCl3. Synthesis of [Ag2Br2(µ-S-Hptsc)2(Ph3P)2] · 2H2O (5). To AgBr (0.025 g, 0.133 mmol) suspended in acetonitrile (15 mL), was added ligand Hptsc (0.022 g, 0.133 mmol), and stirring was continued for 24 h. To the white solid formed was added solid PPh3 (0.035 g, 0.133 mmol), resulting in a clear solution, which was kept for crystallization. Slow evaporation of this solution resulted in the colorless crystals. Yield, 0.06 g, 70%, m.p. 142 -146 °C. Anal. Calcd. for C48H46Ag2Br2N8P2S2 · 2H2O: C, 46.60; H, 3.72; N, 9.06; Found: C, 46.60; H, 3.75; N, 9.06. IR data (KBr, cm-1): ν(N-H), 3430(m), 3340(m) 3230(m) (-NH2 group), 3175(m) (-NH-); ν(C-H), 3051(m); (δNH2+ ν(CdN) +ν(C-C) 1610(s), 1571(s), 1529(s); ν(CdS) 825(s); ν (C-N) 1070(s), 1029(s); ν (P-CPh), 1093(s). 1H NMR (CDCl3, δ ppm): 11.47s (-N4H), 10.97s (-N2H), 8.28sb, 7.98 sb (-N1H2), 8.05 s (-C2H), 7.38–7.69 m (PPh3), 6.87d (-C4H), 6.17dd (-C5H). 31P NMR (CDCl3, δ ppm): -78.4, -99.8 ppm, ∆ δ(δcomplex - δ ligand) ) 34.7, 13.4 ppm. Complex is partially soluble in CHCl3 and CH3CN. Complexes 6–8 were prepared by a similar method. Synthesis of [Ag2Cl2(µ-S-Httsc)2(Ph3P)2] · 2CH3CN (6). Yield, 0.16 g, 72%, m.p. 110-112 °C. Anal. Calcd. for C52H50Ag2Cl2N8S4P2: C, 49.42, H, 3.96, N, 8.87; Found: C, 49.75, H, 4.36, N, 8.94. IR data (KBr, cm-1): ν(N-H) 3431(s), 3248(m) (-NH2-), 3190(b), 3150(m) (-NH-); ν(CdN) + δNH2 + ν (CdC) 1581(s), 1523(s), 1434(s); ν (CdS) 817(s); ν (C-N) 1029(s), 1045(s), 1070(s); ν (P-CPh) 1095(s). 1 H NMR (CDCl3, δ ppm): 11.49s (-N2H), 8.42s (-C2H), 7.33–7.48 m (Ph + PPh3), 6.40s (-N1H2). 31P NMR (CDCl3, δ ppm): -100.9 ppm, ∆δ (δcomplex - δ ligand) ) 12.2 ppm. This complex is soluble in CHCl3 and partially soluble in CH3CN. Synthesis of [AgBr(η1-S-Hpytsc)(Ph3P)2] · CH3CN (7). Yield, 0.09 g, 75%, m.p. 145–150 °C. Anal. Calcd. for C45H41AgBrN5P2S, C, 57.90, H, 4.40, N, 7.50; Found: C, 58.40, H, 4.90, N, 7.28. IR data (KBr, cm-1): ν(N-H) 3330(m), 3300(m) (-NH2-), 3051(b) (-NH-); ν(CdN) + δNH2 + ν(CdC) 1600(s), 1529(s); ν(CdS) 912(s); ν(C-N) 1047(s); ν(P-CPh) 1093(s). 1H NMR (CDCl3, δ ppm): 12.41s (-N2H), 7.34d (-N1H2), 8.24s (-C2H), 8.07d (-C4H), 6.75t (-C5H), 8.37dt (-C6H), 8.84d (C7H), 7.29–7.81m (PPh3). 31P NMR (CDCl3, δ ppm): -102.9, ∆δ (δcomplex - δ ligand) ) 10.2 ppm. This complex is poorly soluble in CHCl3 and CH3CN. Synthesis of [AgCl(η1-S-Hpytsc)(Ph3P)2] · CH3CN (8). Yield, 0.09 g, 69%, m.p. 145-148 °C. Anal. Calcd. for C45H41AgClN5P2S · CH3CN: C, 60.73; H, 4.61; N, 7.87; Found: C, 60.99; H, 4.59; N, 7.05. IR data (KBr, cm-1): ν(N-H), 3335(m), 3285(m) (-NH2 group), 3125(m) (-NH-); ν(C-H), 3068(m), 3051(m); (δNH2 + ν(CdN) + ν(C-C) 1630(s), 1537(s); ν(CdS) 822(s); ν(C-N) 1070(s), 1029(s); ν(P-CPh), 1094(s). 1H NMR (CDCl3, δ ppm): 12.30s (-N2H), 8.73s (-C2H), 8.61d (-C6H), 8.36 d (-C7H), 7.93d (-N1H2), 7.85d (-C4H), 7.78td (-C5H), 7.30–7.56m (PPh3 + N1H2). 31P NMR (CDCl3, δ ppm): –78.2, –98.3, ∆δ (δcomplex - δ ligand) ) 34.9, 14.9 ppm. Synthesis of [Ag2(µ3-N,S-Hftsc)2(Ph3P)2](NO3)2 (9). To AgNO3 (0.025 g, 0.147 mmol) suspended in 20 mL of hot CHCl3 (50 °C) for 1 h was added solid Hftsc ligand (0.024 g, 0.147 mmol). To the white compound formed during stirring (24 h) was added Ph3P (0.038 g, 0.147 mmol), and the contents were stirred further for 1 h. The clear solution formed was filtered and kept for crystallization for 2–3 days when yellow crystals were formed. Yield, 0.06 g, 72%, m.p. 156–162 °C. Anal. Calcd. for C48H44Ag2N8O8P2S2: C, 47.92; H, 3.66; N, 9.31; Found: C, 47.55; H, 3.57; N, 9.36. IR data (KBr, cm-1): ν(N-H), 3445(m), 3350(m); 3160(m) (-NH-), ν(C-H), 3000(m); (NH2 + ν(CdN) + ν(C-C), 1610(s), 1556(s), 1525(s); ν (CdS) 828(s); ν (C-N) 1070(m); (ν(P-CPh), 1094(s). This complex is partially soluble in CHCl3 and CH3CN. Synthesis of [Ag2(µ-S-Hptsc)2(η1-S-Hptsc)2(Ph3P)2](NO3)2 · 2CHCl3 (10). To AgNO3 (0.025 g, 0.147 mmol) suspended in 20 mL of hot CHCl3 (50 °C) for 1 h was added solid Hptsc ligand (0.017 g, 0.147 mmol). To the white compound formed during stirring (24 h) was added Ph3P (0.077 g, 0.294 mmol), and the contents were stirred further for 1 h. The clear solution formed was filtered and kept for crystallization for 2–3 days. Needle-shaped crystals were formed. Yield, 0.08 g, 65%, m.p. 155–160 °C. Anal. Calcd. for C31H32AgCl3N9O3PS2:

Thiosemicarbazones in Networks of Silver(I) Complexes C, 41.89; H, 3.60; N 14.20; Found: C, 42.4; H, 3.64; N 14.35. IR data (KBr, cm-1): ν(N-H), 3433m, 3240m (-NH2 group), 3165m (-NH-); ν(C-H), 3072(m), 3053(m), 3002(w); (δNH2 + ν(CdN) + ν(C-C) 1620(s), 1602(s), 1556(s), 1523(s); ν(CdS) 829(s); ν(C-N) 1080(s); 1034(s); ν(P-CPh), 1095(s). This complex is partially soluble in CHCl3 and CH3CN. Crystal Structure Determination. Prismatic crystals of complexes 1–3, 5, and 8–10 were mounted on an automatic Enraf-Nonius CAD-4 diffractometer equipped with a graphite monochromator, and Mo KR radiation (λ ) 0.71073 Å). The unit cell dimensions and intensity data were measured at 103 K for 9 and 10, 273 K for 3, 296 K for 1, 295 K for 2, 293 K for 8, and 93 K for 5. The structures were solved by the direct methods and refined by full matrix least-squares based on F2 with anisotropic thermal parameters for non-hydrogen atoms using XCAD-49 (data reduction) and SHELXL (absorption correction, structure solution refinement and molecular graphics).24 A colorless prismatic crystal of 4 was mounted on a Bruker SMART CCD 1000 diffractometer equipped with graphite monochromated Mo KR radiation (λ ) 0.71073 Å). The unit cell dimensions and intensity data were measured at 103 K. The data were processed with SAINT25a and corrected for absorption using SADABS (transmissions factors: 0.724 - 0.515).25b The structure was solved by direct methods using the program SHELXS-9725c and refined by full-matrix least-squares techniques against F2 using SHELXL-97.25d Positional and anisotropic atomic displacement parameters were refined for all non-hydrogen atoms. Hydrogen atoms bonded to carbon were placed geometrically and the N-H hydrogen atoms were initially positioned at sites determined from difference maps, but the positional parameters of all H atoms were included as fixed contributions riding on attached atoms with isotropic thermal parameters 1.2 times those of their carrier atoms. Criteria of a satisfactory complete analysis were the ratios of rms shift to standard deviation less than 0.001 and no significant features in final difference maps. The data for 6 and 7 were collected at 293 K, on a Siemens P4 diffractometer using XSCANS.25e The θ-2θ technique was used to measure the intensities, up to a maximum of 2θ ) 50°, with graphite monochromatized Mo KR radiator (λ ) 0.71073 Å). The data were corrected for Lorentz and polarization factors. An empirical psi absorption correction was applied. The structures were solved by direct methods and refined by full matrix least-squares methods based on F2. The solvent molecule acetonitrile showed disorder in both 6 and 7 in terms of high thermal parameters and unusual bond distances. This disorder could be resolved in 7 but not in 6. In 6, the solvent was refined anisotropically with restraints over bond lengths involving the atoms of the solvent molecule, with C(sp3)-C(sp) 1.436(3), C(sp)-N (triple bond) as 1.137(3) Å and nonbonding C · · · N distance as 2.600(3) Å. In 7, this disorder was resolved by splitting each atom of the acetonitrile into two components with total site occupancy as one. These were also refined with above-mentioned restraints on the bond lengths. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were fixed geometrically and were not refined. Scattering factors from the International Tables for X-ray Crystallography were used.26 Data reduction, structure solution, refinement, and molecular graphics were performed using SHELXTL-PC27a and WinGX.27b

Results and Discussion Synthesis. The stoichiometry of complexes of silver(I) halides and nitrate (AgX, X ) Cl, Br, NO3) with a series of thiosemicarbazones is represented in Chart 3. Three synthetic routes were adopted for the synthesis of the complexes. In the first method, a silver(I) halide was reacted with PPh3 ligand in CH3CN to form a silver(I)-phosphine complex of composition, [AgX(PPh3)] (X ) Cl,28a Br28b) as confirmed by analysis, which was then suspended in CHCl3 followed by the addition of a thiosemicarbazone (Htsc) ligand {route i}. In the second method, silver(I) halide was reacted with a thiosemicarbazone in CH3CN followed by the addition of PPh3 in the same solvent (route ii). In the third method (route iii}, silver(I) nitrate was reacted with Htsc ligand in CHCl3 followed by the addition of PPh3 in the same solvent. The analytical data supported stoichiometry {AgX(Htsc)(PPh3)} for complexes, 1-6, and 9, and stoichi-

Crystal Growth & Design, Vol. 8, No. 4, 2008 1205 Chart 3

ometry {Ag(Htsc)2(PPh3)(NO3)} for complex 10. Direct reaction of silver(I) chloride/bromide with Hpytsc in CH3CN in the presence of 2 mol of PPh3 formed monomers 7 and 8. IR Spectroscopy. The infrared spectra of complexes 1-10 have shown the presence of ν(N-H) and ν(C-H) in the regions, 3490-3225 cm-1 (due to the -N1H2 group), and 3100-3190 cm-1 (due to the -N2H- and -N4H- groups), and 3000–3055 cm-1 (-C-H of Htsc rings and PPh3), supporting interaction of thiosemicarbazones with silver(I), probably, via sulfur or via N, S-donor atoms. Thioamide bands of complexes, namely, ν(CdS) and ν(C-N), appear in the ranges, 817-960 cm-1 and 1000–1070 cm-1, respectively, exhibiting small shifts relative to the free ligands {ν(CdS), 815–865 cm-1; ν(C-N), 963–1124 cm-1}. Complexes showed medium to broad peaks in the region, 1434–1643 cm-1 corresponding to δNH2 + ν(CdN) + ν(CdC) vibrational modes, which are at slightly low energy regions vis-à-vis those of free ligands.22 The ν(P-C) bands at 1091-1095 cm-1, support the presence of Ph3P ligands in the complexes. To establish the structures of the complexes, single crystal X-ray crystallography has been used for all the complexes reported in this paper. Bonding and Structures. Complexes 1–3, 5, 6, and 10, crystallized in the triclinic crystal system with space group P1j, while complexes 4, 7-9 crystallized in the monoclinic crystal system (Table 1) with space groups P21/n, P21/c, P21/c, and P21/n, respectively. Table 2 gives the important bond distances and angles. Chart 4 depicts a structural representation of complexes. Complexes 1–6, 9, and 10, probably dimerize, via halogen or sulfur bridging, and the nitrate anion is noncoordinating. The different bonding trends in the complexes can be correlated with the nature of substituents at the C2 carbon of the thiosemicarbazones as well as with the nature of the anion. It can be seen that for R1 ) Ph, R2 ) CH3, or H, and X ) Cl, Br, only halogen-bridged dimers (1-4), for R1 ) pyrrole, furan, and thiophene, R2 ) H, and X ) Cl, Br, and NO3, only sulfurbridged dimers (5, 6, 9, 10), and for R1 ) py, R2 ) H, and X ) Cl, Br, only monomers (7, 8) were formed. Thiosemicarbazones have exhibited variable bonding modes, namely, η1-S mode in complexes 1-4, 7, 8; µ-S mode in compounds 5 and 6; N3, µ-S-η1-N mode in compound 9, and finally both η1-S and µ-S modes in complex 10. Halogen-Bridged Dimers. A complex of silver(I) chloride with acetophenone thiosemicarbazone is a chloride-bridged dimer, [Ag2(µ-Cl)2(η1-S-Haptsc)2(PPh3)2] (1), in which two PPh3 and two Haptsc ligands occupy trans positions across the central Ag(µ-Cl)2Ag core with a Ag · · · Ag distance of 3.356(1) Å, which is less than twice the sum of van der Waals radius of

C31H32AgCl3N9 O3PS2 887.97 triclinic P1j 11.4344(13) 13.2875(16) 13.4041(16) 77.031(2) 68.163(2) 89.655(2) 1835.4(4) 2 1.607 0.972 1.026 0.0662, 0.1241 0.1008, 0.1382 C24H22AgN4 O4PS 601.36 monoclinic P21/n 10.9879(15) 21.673(3) 21.338(3) 90 96.839(3) 90 5045.3(12) 8 1.583 0.983 0.985 0.0442, 0.0847 0.1052, 0.1017 C45H41AgCl N5P2S 889.15 monoclinic P21/c 14.5563(14) 12.6222(11) 22.355(2) 90 97.489(2) 90 4072.3(7) 4 1.450 0.730 0.956 0.0352, 0.0772 0.0619, 0.0827 MW crystal system space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z Dc (Mg m-3) µ (mm-1) GOF on F2 R1, wR2 [I > 2σ(I)] R1, wR2 (all data)

empirical formula

C54H52Ag2Cl2 N6P2S2 1197.72 triclinic P1j 11.1986(1) 11.4853(1) 12.2358(1) 70.008(1) 63.327(1) 73.889(1) 1307.05(2) 1 1.522 8.608 1.069 0.0321, 0.0760 0.0377, 0.0789

C54H52Ag2Br2 N6P2S2 1286.64 triclinic P1j 11.3791(1) 11.5287(1) 12.1816(1) 69.712(1) 63.759(1) 73.459(1) 1327.95(2) 1 1.609 9.310 1.090 0.0219, 0.0550 0.0277, 0.0555

C52H48Ag2Br2 N6P2S2 1258.58 triclinic P1j 11.0968(5) 11.5110(5) 12.0889(6) 94.506(1) 116.180(1) 107.346(1) 1282.3(2) 1 1.630 2.507 1.036 0.0287, 0.0652 0.0401, 0.0694

C44H48Ag2Br2 N6P2S2 1162.50 monoclinic P21/n 9.200(2) 17.859(3) 13.990(3) 90 93.331(9) 90 2294.7(8) 2 1.682 2.794 1.076 0.0382, 0.0779 0.0677, 0.0890

C48H50Ag2Br2 N8O2P2S2 1272.58 triclinic P1j 9.9684(11) 10.0974(10) 13.5138(14) 102.664(2) 100.139(2) 98.179(2) 1283.0(2) 2 1.647 2.510 1.006 0.0348, 0.0894 0.0495, 0.0930

C52H52Ag2Cl2 N8S2P2 663.89 triclinic P1j 8.992(5) 12.263(5) 13.955(5) 105.030(5) 100.170(5) 101.760(5) 1411.5(11) 2 1.562 1.093 1.122 0.0692, 0.2001 0.0964, 0.2777

C45H37AgBr N5P2S 929.58 monoclinic P21/c 14.683(5) 12.940(5) 23.583(5) 90 96.960(5) 90 4448(2) 4 1.388 1.506 1.084 0.0565, 0.1343 0.1062, 0.1735

9 6 5 4 3 2 1

Table 1. Crystallographic Data for Complexes 1–10

7

8

10

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Ag+ (3.40 Å)29 (Figure 1). In this complex, each silver(I) is bonded to one S {Ag-S, 2.5851(8) Å}, one P {Ag-P, 2.4422(8) Å}, and two chlorine atoms with unequal Ag-Cl bond distances{Ag-Cl, 2.6254(8), 2.7056(8) Å}, and this central core forms a parallelogram. Other halogen-bridged dimers, [Ag2(µ-Br)2(η1-S-Haptsc)2(PPh3)2] (2), [Ag2(µ-Br)2(η1S-Hbtsc)2(PPh3)2] (3), and [Ag2(µ-Br)2(η1-S-Hactsc)2(PPh3)2] (4), are similar to 1, with Ag-Ag contacts in the range, 3.202–3.609 Å. The core bond distances, Ag-P, 2.428–2.453; Ag-S, 2.508–2.593; Ag-Br, 2.647–2.726, 2.791–2.838 Å (Table 2), are similar to those (Ag-P, 2.4390(7), Ag-S, 2.5548(9), Ag-Br, 2.7350(6), 2.8241(5) Å) in the analogous compound [Ag2(µ-Br)2(pymSH)2(Ph3P)2] (pymSH ) pyrimidine-2-thione).30 The X-Ag-X and Ag-X-Ag angles of central core, Ag(µ-X)Ag, of complexes 1–4, lie in the ranges ca. 98–110° and 70-82°, respectively, while P-Ag-S angles are in a close range 118-121°, and are largest. The core angles vary in the inverse fashion in the analogous complex, [Ag2(µBr)2(pym2SH)2(Ph3P)2] {Br-Ag-Br, 95.17(2)°, Ag-Br-Ag, 84.83(2)°}.30 The geometry around each Ag atom in complexes 1-4 may be formally labeled as distorted tetrahedral. Sulfur-Bridged Dimers. In compound 5, the PPh3 and bromine atom occupy trans positions across the central sulfurbridged Ag(µ-S)2Ag core. Each silver(I) atom is bonded to one bromine (Ag-Br, 2.6857(4) Å), one PPh3 (Ag-P, 2.4394(9) Å), and two S-donor atoms of thiosemicarbazone ligands with the unequal Ag-S distances {2.6070(9), 2.6851(9) Å}, resulting in a parallelogram of central core (Figure 2). These Ag-S distances are slightly longer than 2.507–2.592 Å found in the halogen-bridged dimers 1-4. The ligand Httsc formed a similar sulfur-bridged dimer, [Ag2Cl2(µ-S-Httsc)2(PPh3)2] · 2CH3CN (6). Two solvent molecules of CH3CN appear in the crystal lattice and were confirmed by the respective analytical data. The bond parameters, viz. Ag-P, 2.428(18) Å; Ag-S, 2.611(2), 2.876(2) Å; Ag-Cl, 2.520(2) Å (Table 2), are comparable to those of the sulfur-bridged dimer 5. Figure 2 shows the molecular structure of [Ag2Cl2(µ-S-Httsc)2(PPh3)2] · 2CH3CN (6). Compounds [Ag2(η1-N-µ-S-Hftsc)2(Ph3P)2](NO3)2 (9) and [Ag2(η1-S-Hptsc)(µ2-S-Hptsc)2(Ph3P)2](NO3)2 · CHCl3 (10) exhibit different bonding modes with different thiosemicarbazones in 9 (Figure 3) and 10 (Figure 4). The presence of CHCl3 is confirmed by the elemental analysis, and it appears in the crystal lattice of 10. Both these complexes have similar core distances (Ag-P, 2.40–2.43; Ag-S, 2.54–2.58, 2.65–2.66 Å). The central core, Ag(µ-S)2Ag of complexes 5-6, 9, and 10, have S-Ag-S, and Ag-S-Ag bond angles in the ranges of ca. 97–116° and ca. 68–83°, respectively. The P-Ag-S and S-Ag-S bond angles vary in the ranges of ca.105–127° and 97–111°, respectively. The Ag-S distances, are smaller than 2.744 Å in a related compound [Ag2(µ-S-pySH)(PPh3)2(MoS4)] (pySH ) pyridine-2-thione),31 having only one ligand with its sulfur donor atom bridging two silver(I) atoms. The Ag · · · Ag contacts are in the range of 3.09–3.50 Å, and it may be interesting to note here that in compound 6, with chlorine as the terminal group, and in complexes 9 and 10, with the nitrate outside the coordination sphere, short Ag · · · Ag contacts are observed, leading to the enhanced argentophilicity. Mononuclear Complexes. Silver(I) bromide/chloride with pyridine-2-carbaldehyde thiosemicarbazone (Hpytsc) in the presence of PPh3 has formed mononuclear complexes [AgBr(η1S-Hpytsc)(Ph3P)2] · CH3CN (7) and [AgCl(η1-S-Hpytsc)(Ph3P)2] · CH3CN (8). Compound 7 was prepared from the reaction of AgBr with Hpytsc and PPh3 in CH3CN, and compound 8 was prepared similarly. Compounds 7 and 8 both

Thiosemicarbazones in Networks of Silver(I) Complexes

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Table 2. Important Bond Distances (Å) and Bond Angles (°) for Complexes 1–10

Chart 4

contain CH3CN as a solvent of crystallization (the latter crystallized from CH2Cl2-CH3CN mixture). Figure 5 shows the molecular structure of [AgBr(η1-S-Hpytsc)(Ph3P)2] · CH3CN (7). Both the compounds have distorted tetrahedral structures as the bond angles around the silver atom vary from ca. 103–122° in 7 and 8 with P-Ag-P being the largest angle. The Ag-S, Ag-P, and Ag-X distances of 2.6284(7)–2.6405(19), 2.44–2.49,

and 2.64–2.73 Å, respectively, are comparable with those of dimeric complexes discussed above. Hydrogen-Bonded Polymeric Networks. Chart 5 depicts participation of amino and imino hydrogen atoms of monomers

Figure 1. Structure of [Ag2(µ-Cl)2(η1-S-Haptsc)2(PPh3)2] (1), with numbering scheme. (Complexes 2–4 have similar molecular structures.)

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Figure 2. Structure of [Ag2Br2(µ-S-Httsc)2(Ph3P)2] · 2CH3CN (6) with numbering scheme. (Complex 5 has similar molecular structure.)

Figure 4. Structure of Ag2(η1-S-Hptsc)2(µ2-S-Hptsc)2(Ph3P)2](NO3)2 · · · CHCl3 (10) with partial numbering scheme.

Figure 3. Structure of [Ag2(η1-N3-µ-S-Hftsc)2(Ph3P)2](NO3)2 (9) with numbering scheme.

Chart 5

Figure 5. Structure of [AgBr((η1-S-Hpytsc)(Ph3P)2] · CH3CN (7) with numbering scheme. (Compound 8 has similar structure.)

and dimers in the intramolecular hydrogen bonding with the bridging halogen atoms (1–4), terminal halogen atoms (5–8), and terminal or bridging S atoms (10). Compound 9 does not have similar intramolecular interactions. The formation of polymeric networks occurs via a variety of interactions and is briefly delineated below. Silver(I) Halide Complexes. Dimer 1 with a methyl and a phenyl group at C2 carbon of Haptsc ligand shows intramo-

lecular hydrogen bonding via one of the amino hydrogen with chlorine atom (-HN1H · · · Cl). Two dimer units are further linked to each other via intermolecular hydrogen bonding by one hydrogen atom of the methyl group at C2 carbon with sulfur atom of the second molecule (H2C-H · · · S) as well as via -N2H · · · S interactions, forming a linear polymeric chain (Figure 6). Dimer 2 also displays similar intramolecular hydrogen bonding (-HN1H · · · Br) as well as intermolecular hydrogen bonding (-N2H · · · S, H2C-H · · · S) except the latter dimer has additional methyl-bromine hydrogen bonding (H2C-H · · · Br). This may be due to the size difference of halogen atom. These interactions lead to the formation of hydrogen-bonded chains running in the ac plane (Figure 7). Dimer 3 with a hydrogen substituent at the C2 carbon in place of a methyl group also has similar intramolecular hydrogen

Thiosemicarbazones in Networks of Silver(I) Complexes

Figure 6. Hydrogen-bonded 1D polymeric chains of [Ag2(µ-Cl)2(η1S-Haptsc)2(PPh3)2] (1).

bonding (-HN1H · · · Br). The intermolecular interactions between dimer units via imino hydrogen and sulfur atoms (N2H · · · S) form a polymeric chain running parallel to the a axis. The interchain interactions between C-H proton of phenyl ring of PPh3 of one chain with π-elelctrons of another phenyl ring of another chain (C-H · · · π interactions, (3.97, 4.09 Å) form a 2D network along the ab plane (Figure 8). This C-H · · · π interaction appears to have become possible due to different steric requirements of substituents at C2 carbon in this dimer (R1 ) Ph, R2 ) H) versus dimers 1 and 2 (R1 ) Ph, R2 ) Me). In dimer 4, the presence of two methyl groups at the C2 carbon of acetone thiosemicarbazone (Hactsc) changes the intramolecular hydrogen-bonding behavior from amino-halogen (-HN1H · · · X) to imino-halogen (-N2H · · · Br) forming a sixmembered ring. This makes a change in orientation of the methyl groups at the C2 carbon, drawing them closer to the phenyl rings of PPh3, making them unavailable to interact with S or bromine atoms as in 1 and 2. Thus, in the dimer units of 4 are linked to each other via amino-bromine intermolecular hydrogen bonding (HN1H · · · Br) forming linear chains. Introduction of a pyrrole group at the C2 carbon in dimer 5 results in sulfur bridging instead of halogen bridging as in 1-4, and this makes the hydrogen-bonding characteristics of the former different from those of the latter. This dimer also has intramolecular amino-bromine hydrogen bonding (-HN1H · Br). The same bromine is intermolecularly linked to the pyrrole hydrogen of the second dimer (Br · · · Hpyrrole) along the a axis leading to the formation of a 1D network. The chains are further interconnected by the water molecules via bromine-water (Br · · · HO, 3.255(3) Å) and imino-water hydrogen-bonding interactions (N2H · · · O, 2.872(1) Å), and this leads to the formation of 2D networks. The water · · · water H-bonding forms a dinuclear self-assembled water unit with O · · · O nonbonding distance being 2.97 Å (Figure 9). The presence of a pyrrole group at the C2 carbon also formed a sulfur-bridged dimer 6 which has imino-halogen (-N2H · · · Cl) intramolecular hydrogen bonding instead of amino-halogen as in dimer 5. The same chlorine atom is further intermolecularly hydrogen bonded to a thiophene ring hydrogen atom (CH(thiophene) · · · Cl), and this leads to the formation of a linear chain running parallel to the b axis in the bc plane. The individual chains are bound to each other by C-H · · · π interactions between two pairs of centrosymmetrically related phenyl rings of the PPh3, and this leads to a 2D sheet running parallel to the a axis (Figure 10). The sulfur bridging observed in dimers 5 is attributed to the hydrogen bonding of bromine atoms with the amino hydrogen, pyrrole ring hydrogen (-NH-), and hydrogen atom of water, while in dimer 6, the chlorine atom is hydrogen-bonded to imino hydrogen and thiophene ring hydrogen (-CH-). These interactions in 6 make it difficult for acetonitrile hydrogen atoms to bind to halogen atom, and thus acetonitrile occupies voids between the chains. It may be interesting to point here that in

Crystal Growth & Design, Vol. 8, No. 4, 2008 1209

Figure 7. Hydrogen-bonded 1D chains of [Ag2(µ-Br)2(η1-SHaptsc)2(PPh3)2] 2.

Figure 8. Polymeric 2D network of bromo-bridged dimer [Ag2(µCl)2(η1-S-Hbtsc)2(PPh3)2] 3 (see Supporting Information for compound 4).

Figure 9. Packing diagram of [Ag2Br2(µ-S-Hptsc)2(Ph3P)2] · 2H2O (5).

an analogous sulfur-bridged dimer, [Cu2Cl2(µ-S-Hbtsc)2(PPh3)2] · 2CH3CN, which had imino-halogen (-N2H · · · Cl) intramolecular hydrogen bonding, but acetonitrile was hydrogen bonded to terminal chlorine atoms as phenyl rings of Hbtsc were not involved in hydrogen bonding with halogen.5a In mononuclear compound 7, there is imino hydrogen-bromine intramolecular hydrogen bonding (-N2H · · · Br), and one molecule is linked to the second molecule via C-H(Ph) · · · π(py) interactions {C29-H29 · · · py (centroid) 3.724, 3.085 Å, 127°}, and this leads to the formation of a dimer. Two dimers are further linked via C-H(Ph) · · · π interactions C31H · · · HC36, 3.727, 3.035 Å, 132.5°} between phenyl rings of PPh3 leading to the formation of a tetramer C-H-Ph ring. Acetonitrile is bonded to the sulfur atom and with ring hydrogen of the Ph3P group of the same molecule (Figure 11). Mononuclear complex 8 has imino hydrogen engaged in intramolecular hydrogen bonding with the chlorine atom (-N2H · · · Cl), and zigzag 1D chains are formed via hydrogen bonding between amino hydrogen and nitrogen of pyridine atom (-HN1H · · · N(pyridine), 3.012(2) Å) parallel to the b axis. The two chains are further linked via C-H(Ph) · · · π interactions between phenyl rings of

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Figure 10. Packing diagram of [Ag2Cl2(µ-S-Httsc)2(PPh3)2] (6) in sheet structure.

Figure 11. Packing diagram of [AgBr(η1-S-Hpytsc)(Ph3P)2] · CH3CN (7) (see Supporting Information for compound 8).

PPh3. The acetonitrile molecules are held between two chains by C-HPh · · · N interactions (2.704(2) Å). Silver(I) Nitrate Complexes. The nitrate being weakly coordinating, the bonding trends for thiosemicarbazone used is different from those of silver(I) halide complexes. The bonding and stoichiometry of complexes 9 and 10 are different, which makes their packing diagram all together different. The lattices of dimers 9 and 10 show nitrate groups present in voids in addition to chloroform in 10. The packing diagrams of silver(I) nitrate complexes 9 and 10 with Hftsc and Hptsc, respectively, are discussed below. In dimer 9, no intramolecular hydrogen bonding is present. Both hydrogen atoms of amino group are engaged in intermolecular hydrogen bonding with O atoms of two different nitrate groups (HN1H · · · O1BNO2, 2.856(3) Å; HN1H · · · O2ANO2, 2.837(2) Å), and the third oxygen of the nitrate group forms a hydrogen bond with the imino hydrogen atom (N2H · · · O3BNO2, 2.862(3) Å), resulting in an extended 2D network in the ab plane. Each dimeric unit (purple) in this network may be considered as a part of two hydrogen-bonded octameric synthons formed by four coordination dimers (one purple and three green or one purple and three magenta units) and four nitrate groups (four green or four magenta units) (Figure 12).

Figure 12. Hydrogen-bonding contacts between nitrate groups and the dinuclear unit produces an extended 2D network in the ab plane in [Ag2(µ3-N,S-Hftsc)2(Ph3P)2](NO3)2 (9).

In dimer 10, the imino hydrogen (-N2H) of the terminal ligand forms an intramolecular hydrogen bond with the sulfur of the bridging ligand (-N2H · · · S) and vice-versa, leaving the amino group (N1H2) available for further interactions. One of the oxygen atoms of the nitrate group forms a hydrogen bond with one amino hydrogen of the bridging ligand of one molecule and one amino hydrogen atom of the terminal ligand from the second molecule. Similarly, the second oxygen atom of the same nitrate group forms a hydrogen bond with the amino hydrogen of terminal ligand and pyrrole hydrogen of the bridging ligand from a second dimer molecule to form a 2D network. Two molecules of CHCl3 are present as a solvent of crystallization in the spaces between two chains and form hydrogen bonds with the C2H proton of the ligand (C2H · · · ClCHCl2) (Figure 13). Solution Phase Studies. Proton NMR spectra of the complexes in CDCl3 reveal a low field shift of diagnostic signal due to the -N2H proton in the range of δ 9.46–12.45 ppm visà-vis that of free ligands (δ 9.40–11.5 ppm).22 It confirms the coordination of thiosemicarbazone ligands as neutral ligands. Further, in complexes 1 and 4, both the signals for the amino

Thiosemicarbazones in Networks of Silver(I) Complexes

Crystal Growth & Design, Vol. 8, No. 4, 2008 1211 information is also available from CCDC, 12 Union Road,Cambridge CB2 1EZ, UK (fax: +44–12336033; e-mail:[email protected]) upon request quoting the deposition numbers CCDC 642395–642404 for compounds 1–10, respectively.

References

Figure 13. Packing diagram of [Ag2(η1-S-Hptsc)2(µ-S-Hptsc)2(Ph3P)2](NO3)2 · 2CHCl3 (10).

protons, merged in the phenyl region in the range δ 7.29–7.49 ppm; compounds 3 and 6 showed one signal each at δ 6.40 ppm (second signal is usually obscured by the Ph-P ring, or other ring protons), and finally compounds 2, 5, and 7 showed a pair of signals in the range δ 8.05–8.73 ppm. These amino signals are downfield relative to the free ligands (δ 6.60–8.2 ppm).22 Methyl signals for 1 and 2 appeared at δ 2.49 and 2.44 ppm, respectively. In the 31P NMR spectrum, the halogen-bridged dimers 1-4 showed one signal each with the coordination shifts in the range of δ 12.2–13.7 ppm. Thus, the solution phase behavior of 1-4 is in line with the solid-state structures as discussed earlier. Compound 5 showed two signals, one with a coordination shift of δ 34.7 ppm attributed to its sulfur-bridged structure, and the second with a coordination shift of δ 13.4 ppm, which reveals the formation of the halogen-bridging in the solution state. Further, compound 6 showed only one signal with a coordination shift of δ 12.2 ppm, and it shows the transformation of sulfurbridged dimer into a halogen-bridged dimer. Monomer 7 showed one signal with a coordination shift of δ 10.2 ppm in line with its solid-state structure. The existence of two signals for compound 8 showed two signals (coordination shifts, δ 14.9 and δ 34.9 ppm), and it reveals equilibrium between a monomer and a sulfur-bridged dimer. Conclusion It can be concluded that the halides compete with sulfur donor atoms for binding to silver(I), while weakly coordinating nitrate behaves like a non-coordinating BF4– anion. This has led to the formation of a new series of compounds exhibiting a variety of bonding modes (modes A, B, and D), presenting the first examples of these modes with silver(I). Among silver(I) halides, the nature of the substituents at C2 appears to influence the nuclearity and bonding of the complexes, while for silver(I) nitrate, the nuclearity and bonding of thiosemicarbazone are more at variance with the nature of substituents at C2 carbon. The intermolecular interactions such as NH · · · X (X ) S, Br, Cl, O), CH · · · π, and CH · · · X (X ) S, Cl) have led to the formation of 1D and 2D networks. Interestingly, a novel feature is that some of the 2D networks encapsulate organic molecules in the voids. Acknowledgment. Financial assistance from CSIR, New Delhi (F. No. 9/254(159)/2005-EMR-I) is gratefully acknowledged. Supporting Information Available: Crystal data, bond parameters, and X-ray figures of various complexes. This information is available free of charge via Internet at http://pubs.acs.org. Supplementary

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