Synthesis, Ethanolysis, and Hydrolysis of Bismuth(III) ortho

Organometallics 2009, 28, 3999–4008 DOI: 10.1021/om9002158

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Synthesis, Ethanolysis, and Hydrolysis of Bismuth(III) ortho-Nitrobenzoate Complexes en Route to a Pearl Necklace-like Polymer of Bi10 Oxo-Clusters Philip C. Andrews,* Glen B. Deacon, Peter C. Junk, Ish Kumar, and Jonathan G. MacLellan School of Chemistry, Monash University, P.O. Box 23, Melbourne, Victoria 3800, Australia Received March 20, 2009

In exploring the formation of heteroleptic bismuth benzoates and their conversion to polynuclear bismuth oxo-clusters through hydrolysis, ortho-nitrobenzoic acid (= LH) was treated with triphenylbismuth under various reaction conditions. The simple 2:1 stoichiometric reaction in ethanol produced four crystalline products; [{BiL2(OEt)(EtOH)}2]¥ (2) and [Ph2BiL]¥ (4) initially crystallized together, while [BiL3(H2O)]¥ (1) appeared later from the filtered mother liquor. Compound 2 results from the in situ ethanolysis of [PhBiL2]n (3) and subsequently undergoes hydrolysis to give crystals of the Bi10 oxo-cluster [Bi10O8L14(EtOH)x.(EtOH)y(H2O)z]¥ (5). This latter process was confirmed through the formation of the moisture-sensitive compound [PhBiL2]n under solvent-free, inert atmosphere conditions, which on treatment with dry ethanol produced [{BiL2(OEt)(EtOH)}2]¥ (2). Compound 4 was obtained as a single isolable product from the 1:1 reaction of o-(NO2)C6H4CO2H with BiPh3 in diethyl ether at room temperature. Single-crystal X-ray diffraction studies on four of the five compounds (1, 2, 4, and 5) show them all to be polymeric in the solid state, having distinct coordination modes and methods of polymer formation. Complexes 1, 4, and 2 are carboxylate-bridged (1, 4) or carboxylate- and ethoxide-bridged (2) polymers in which Bi is nine, eight, and five (with additional Bi-π(Ar) interactions) coordinate respectively. In 5, Bi10O8L14 cluster units are linked in a pearl necklace motif by bridging carboxylate groups. These oxo-clusters have a distorted rhombic dodecahedral Bi6O8 core with four additional Bi atoms sited above alternate oxygen atoms.

Introduction Bismuth oxides have a number of important properties that make them attractive for use in solid state materials.1 For example, Bi2O3 has a high refractive index, dielectric permittivity, and a large energy band gap and is photoconductive, and its ternary compounds can display interesting superconducting2 and magnetic properties.3 Both organometallic (Bi-C) and metal-organic bismuth compounds constitute important precursors for the formation of BixOy phases and for the incorporation of bismuth oxide into ternary and quaternary mixed metal oxide films.4 Current studies on bismuth oxo-clusters continue to provide a better understanding of the hydrolysis and polycondensation processes associated with the decomposition

pathways of hydrolytically sensitive bismuth complexes. Detailed studies on bismuth alkoxides,5,6 phenolates,7,8 and siloxides9,10 have shown that upon hydrolysis small aggregates of metal oxo-clusters are readily formed, for example, [(Bi9(μ3-O)8(μ3-OEt)6]5+, [Bi8(μ4-O)2(μ3-O)2(μ-OC6F5)16], and [Bi22O26(OSiMet2Bu)14]. Other metal-organic compounds can provide similar oxo-clusters; examples include [Bi38O45(hfac)24],11 [Bi14O10(O3PtBu)10(HO3PtBu)2],12 and [Bi6O4(OH)4(tfa)6]2 3 3[Bi(tfa)3]13 (hfac=hexafluoroacetylacetonate, tfa=trifluoroacetate), although studies on these various ligand classes have been fewer and less systematic.

*To whom correspondence should be addressed. E-mail: phil.andrews@ sci.monash.edu.au. (1) Leontie, L.; Caraman, M.; Delibas, M.; Rusu, G. I. Mater. Res. Bull. 2001, 36, 1629. (2) Vehkam€ aki, M.; Hatanp€a€a, T.; Ritala, M.; Leskel€a, M. J. Mat. Chem. 2004, 14, 3191. (3) Wang, J.; Neaton, J. B.; Zheng, H.; Nagarajan, V.; Ogale, S. B.; Liu, B.; Viehland, D.; Vaithyanathan, V.; Schlom, D. G.; Waghmare, U. V.; Spaldin, N. A.; Rabe, K. M.; Wuttig, M.; Ramesh, R. Science 2003, 299, 1719. (4) Mehring, M. Coord. Chem. Rev. 2007, 251, 974.

(5) Thurston, J. H.; Swenson, D. C.; Messerle, L. Chem. Commun. 2005, 4228. (6) Sauer, N. N.; Garcia, E.; Ryan, R. Mater. Res. Soc. Symp. Proc. 1990, 180, 291. (7) Jones, C. M.; Burkart, M. D.; Whitmire, K. H. J. Chem. Soc., Chem. Commun. 1992, 1638. (8) Whitmire, K. H.; Hoppe, S.; Sydora, O.; Jolas, J. L.; Jones, C. M. Inorg. Chem. 2000, 39, 85. (9) Mansfeld, D.; Mehring, M.; Sch€ urmann, M. Angew. Chem., Int. Ed. 2005, 44, 245. (10) Mehring, M.; Mansfeld, D.; Paalasmaa, S.; Sch€ urmann, M. Chem.;Eur. J. 2006, 12, 1767. (11) Dikarev, E. V.; Zhang, H.; Li, B. Angew. Chem., Int. Ed. 2006, 45, 5448. (12) Mehring, M.; Sch€ urmann, M. Chem. Commun. 2001, 2354. (13) Kugel, B.; Frank, W. Z. Anorg. Allg. Chem. 2002, 628, 2178.

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Results and Discussion

The formation and growth patterns of the various oxoclusters have been the subject of a recent detailed review by Mehring.4 The general feature of these clusters is one of distorted bismuth-oxygen polyhedra, normally representative of known polymorphic phases of Bi2O3, shrouded by the ligands external to the cluster core. The cluster size is largely determined by variations in the steric and electronic properties of the ligand, and as such, the nuclearity is often unpredictable and the formative processes are largely uncontrolled. In addition to the more typical hydrolytically unstable ligands, bismuth carboxylates can also act as precursors to such ligand-encapsulated oxo-clusters. Carboxylates as ligands are generally highly versatile and can display a large variety of possible bonding modes. They are among the most widely studied derivatives of bismuth, having a long history as chemotherapeutic agents.14 Their tendency to form species containing oxide has long been recognized in the sub epithet of many simple bismuth compounds, e.g. subsalicylate, subcitrate. However, the greater stability of the Bi-O bond in bismuth carboxylates over alkoxide-type compounds provides a reduction in the rate of hydrolysis and a variation in stability of the complexes toward decomposition. In fact, polyaminocarboxylates are known to give bismuth complexes with high stability constants and appear to be completely stable under aqueous conditions.15 Therefore, carboxylates are good candidates for exploring the hydrolysis and oxo-cluster forming process. In the course of our previous studies on bismuth benzoates, we reported the reproducible synthesis and solid state characterization of two bismuth oxo-salicylate clusters of high nuclearity, [{Bi38O44(Hsal)26(Me2CO)16(H2O)2} 3 (Me2CO)4] and [{Bi9O7(Hsal)13(Me2CO)5} 3 (Me2CO)1.5] (H2sal = salicylic acid), formed on slow hydrolysis of amorphous Bi(Hsal)3 in acetone.16 The rate of hydrolysis and final cluster size is uncontrolled, and deposited crystals represent the thermodynamic minima of a dynamic system. Interestingly though, crystals of an oxo-species having a different nuclearity have not yet been obtained from acetone solution. The sulfur analogue, thiosalicylate (tsal = thiosalicylate dianion), does not hydrolyze to an oxo-cluster but gives an octanuclear species from dimethylformamide, [Bi8(Htsal)12(DMF)6] 3 6DMF, presumably stabilized by the more favorable and hydrolytically stable Bi 3 3 3 S interactions.17 Certainly, a better understanding of the chemical and physical parameters that promote or inhibit cluster growth would assist in the more rational use and/or design of ligands and cluster precursors. Herein, we now report on the reaction of o-nitrobenzoic acid (= LH) with BiPh3, in varying stoichiometries and under differing conditions, leading to the formation of four clearly defined o-nitrobenzoate-containing Bi compounds with varying degrees of substitution and ultimately the formation of the first solid state authenticated Bi10 oxocluster, [Bi10O8L14(EtOH)x 3 (EtOH)y(H2O)z]¥, arranged in a pearl necklace-like polymer.

The 2:1 stoichiometric reaction of o-nitrobenzoic acid with BiPh3 in ethanol under reflux has afforded four distinct and well-defined bismuth complexes: two tris-substituted complexes, [BiL3(H2O)]¥ (1) and [{BiL2(OEt)(EtOH)}2]¥ (2) ([{BiL2(OEt)}2]¥ 2a), a mono-substituted complex, [Ph2BiL]¥ (4), and a polymeric ligand-encapsulated oxo-cluster, [Bi10O8L14(EtOH)x 3 (EtOH)y(H2O)z]¥ (5). The bis-substituted complex, [PhBiL2]¥ (3), was formed and subsequently isolated only as a solid from a solvent-free reaction performed under a dry N2 gas atmosphere. The synthetic routes to these complexes are illustrated in Scheme 1. The solid state structures of 1, 2, 4, and 5 have been obtained by single-crystal X-ray diffraction, and a summary of the important bond lengths and angles is presented in Tables 1-4, with the data collection parameters summarized in Table 5. In contrast to Gilman’s early assertion that reactions involving BiPh3 with protic ligands give predominantly bissubstituted complexes in preference to fully substituted species,18 it is now generally found that the tris-substituted complexes are most often the most favored and stable products. In addition, there are reports that the synthesis of PhBi(O2CR)2 complexes can be complicated by disproportionation reactions, which allow the subsequent formation of Ph2Bi(O2CR) and Bi(O2CR)3,19 though Whitmire has shown with various salicylates that bis-substituted species can be stabilized through complexation with the bidentate donors 1,10-phenanthroline and 2,20 -bipyridine.20 We have previously reported that the tris-substituted BiL3 product can be formed from the treatment of (o-NO2)C6H4CO2H (= LH) with BiPh3 in a 3:1 ratio either under solvent-free conditions or in toluene under reflux.21 In contrast, we have found the synthetic outcomes from the 2:1 reaction to be more complicated. In attempting to constrain the final product of the reaction by limiting the potential for ligand redistribution, initial attempts (on a 1 mmol scale) were undertaken in various solvents at room temperature. From 1H NMR spectra it was apparent that the roomtemperature reactions in Et2O, thf, and ethanol produced mixtures of substituted products in combined low yields. Reflux conditions were therefore employed to increase yields. Again, and perhaps somewhat expectedly, compound mixtures were observed in the 1H NMR spectra, with the trissubstituted complex BiL3 dominant. However, while only powders were isolated from the reactions in Et2O and thf, the ethanol solution produced a variety of crystals, which could be separated and examined by single-crystal X-ray diffraction. In ethanol, the 2:1 reaction proceeds effectively. On completion, the hot ethanol solution is colorless and clear, and remains so on cooling slowly to room temperature. A large number of crystals grew over a period of a few weeks. These crystals were identified as two heteroleptic complexes: [{BiL2(OEt)(EtOH)}2]¥ (2) and [Ph2BiL]¥ (4). The first product, 2, is presumed to result from the thermally promoted

(14) Briand, G. G.; N.; Burford, N. Chem. Rev. 1999, 99, 2601. (15) Stavila, V.; Davidovich, R. L.; Gulea, A.; Whitmire, K. H. Coord. Chem. Rev. 2006, 250, 2782. (16) Andrews, P. C.; Deacon, G. B.; Forsyth, C. M.; Junk, P. C.; Kumar, I.; Maguire, M. Angew. Chem. Int. Ed. 2006, 45, 5638. (17) Asato, E.; Katsura, K.; Arakaki, T.; Mikuriya, M.; Kotera, T. Org. Lett. 1994, 2123.

(18) Gilman, H.; Yale, H. L. J. Am. Chem. Soc. 1951, 73, 2880. (19) Deacon, G. B.; Jackson, W. R.; Pfeiffer, J. M. Aust. J. Chem. 1984, 37, 527. (20) Stavila, V.; Fettinger, J. C.; Whitmire, K. H. Organometallics 2007, 26, 3321. (21) Andrews, P. C.; Deacon, G. B.; Junk, P. C.; Kumar, I.; Silberstein, M. Dalton Trans. 2006, 4852.

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Scheme 1. Suggested Reaction Pathways Involved in the Formation of 1-5 in Ethanol Solution

Table 1. Selected Bond Lengths (A˚), Hydrogen Bond Distances (A˚), and Bond Angles (deg) for 1 Bi(1)-O(1) Bi(1)-O(2) Bi(1)-O(5) Bi(1)-O(6) Bi(1)-O(9) Bi(1)-O(10)a Bi(1)-O(13) Bi(1)-O(9)b Bi(1)-O(10)b d

2.483(5) 2.427(5) 2.327(4) 2.472(5) 2.448(4) 2.435(4) 2.563(5) 2.677(4) 2.723(4)

O(13)[-H(13A)] 3 3 3 O(2)b O(13)[-H(13B)] 3 3 3 O(1)c O(1)-Bi(1)-O(2) O(5)-Bi(1)-O(6) O(9)-Bi(1)a-O(10) O(9)-Bi(1)-O(10)a O(9)-Bi(1)a-O(10)a Bi(1)-O(9)-Bi(1)a Bi(1)-O(10)a-Bi(1)a

2.847(7) 2.775(7) 52.72(14) 53.83(16) 47.93(12) 66.42(13) 67.35(13) 113.53(15) 112.40(16)

Table 4. Selected Average Bond Lengths (A˚) and Angles (deg) for 5 cluster C Bi-Ooxide-inner Bi-Ooxide-outer Bi-Ocarboxylate Bi-Oethanol O-Bi-O0 carboxylate

Bi(1)-O(1) Bi(1)-O(2) Bi(1)-O(5) Bi(1)-O(6) Bi(1)-O(5)b Bi(1)-O(9)a Bi(1)-O(9) Bi(1)-O(10) O(10)[-H(10)] 3 3 3 O(1)a O(2)-Bi(1)-O(1) O(6)-Bi(1)-O(5) O(9)a-Bi(1)-O(9) Bi(1)a-O(9)-Bi(1)

2.705(10) 2.328(10) 2.762(11) 2.270(9) 2.901(11) 2.125(10) 2.520(10) 2.527(11) 2.771(15) 51.5(3) 50.5(3) 68.9(4) 111.1(4)

Bi(2)-O(11) Bi(2)-O(12) Bi(2)-O(15) Bi(2)-O(16) Bi(2)-O(16)c Bi(2)-O(19)d Bi(2)-O(19) Bi(2)-O(20) O(20)[-H(20)] 3 3 3 O(12)c O(11)-Bi(2)-O(12) O(15)-Bi(2)-O(16) O(19)-Bi(2)-O(19)d Bi(2)-O(19)-Bi(2)d

2.253(11) 2.889(11) 2.282(10) 2.823(11) 3.007(11) 2.416(9) 2.136(10) 2.609(10) 2.908(15) 49.2(3) 49.8(3) 67.4(4) 112.6(4)

a -x+1, -y, -z. b -x+2, -y, -z. c -x+2, -y+1, -z+1. d -x+1, -y+1, -z+1.

Table 3. Selected Bond Lengths (A˚) and Angles (deg) for 4 Bi(1)-O(1) Bi(1)-O(2) Bi(1)-O(2)a Bi(1)-C(8) Bi(1)-C(14) C(8)-Bi(1)-C(14) a

2.313(2) 3.081(2) 2.548(2) 2.232(3) 2.245(3) 98.37(11)

C(8)-Bi(1)-O(1) C(14)-Bi(1)-O(1) C(8)-Bi(1)-O(2)a C(14)-Bi(1)-O(2)a O(1)-Bi(1)-O(2)

83.96(9) 90.31(9) 83.22(9) 80.10(9) 46.08(6)

-x+1/2, y-1/2, -z+1/2.

ethanolysis of the expected bis-substituted complex [PhBiL2]n (3), in which the final phenyl group has been

2.28 2.13 2.63 2.83 49.2

Bi-Ooxide-inner Bi-Ooxide-outer Bi-Ocarboxylate Bi-Oethanol O-Bi-O0 carboxylate

2.28 2.12 2.57 2.80 49.3

Table 5. X-ray Data Collection Parameters for 1, 2, 4, and 5 [BiL3(H2O)]¥, [{BiL2(OEt) 1 (EtOH)}2]¥, 2 [Ph2BiL]¥, 4

a x, y+1, z. b -x+3/2, y+1/2, -z+1/2. c -x+3/2, y-1/2, -z+1/2. x, y-1, z.

Table 2. Selected Bond Lengths (A˚), Hydrogen Bond Distances (A˚), and Bond Angles (deg) for 2

cluster D

empirical formula fw temperature (K) cryst syst space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) volume (A˚3) Z Fcalcd (Mg/m3) μ (mm-1) R1 [I > 2σ(I)] wR2 (all data) Goof

cluster 5

BiC21H14 N3O13

Bi2C36H38 N4O20

BiC19H14 NO4

Bi40C434 H356N56O281

725.33 123(2) monoclinic P21/n 12.4029(3) 6.97800(10) 26.3531(4) 90 100.2150(10) 90 2244.64(7) 4 2.146 7.936 0.0390 0.0802 1.003

1264.66 123(2) triclinic P1 8.1576(3) 12.1706(6) 21.4441(8) 77.460(3) 86.468(3) 79.9606(15) 2039.07(9) 2 2.060 8.707 0.0754 0.1393 1.370

529.29 123(2) monoclinic P21/n 13.571(3) 9.2657(19) 13.700(3) 90 100.25(3) 90 1695.2(7) 4 2.074 10.424 0.0155 0.0379 1.065

19210.95 123(2) triclinic P1 17.6559(6) 21.4220(7) 35.9678(11) 89.761(2) 89.313(2) 87.692(2) 13591.8(8) 1 2.347 13.004 0.0630 0.1576 0.988

replaced by ethoxide, and consequent liberation of benzene. The origin of the second product, 4, became apparent after allowing the filtered mother liquor to stand for several more weeks, after which time crystals of the tris-substituted complex [BiL3(H2O)]¥ (1) were isolated and structurally authenticated. It is reasonable to infer that complexes 1 and 4 result from 3 through dismutation. However, we were unable to isolate crystals of 3 from this or subsequent

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Figure 1. Molecular structure of [Bi{(o-NO2)C6H4CO2}3(H2O)]¥ (1) showing the asymmetric unit. Thermal ellipsoids are given at 50%.

reaction mixtures under similar conditions. The presence of product 2 suggests that the dismutation and alcoholysis processes are competitive. Scheme 1 depicts our proposed route to each of the five isolated complexes under the abovedescribed reaction conditions. The next task was to target isolable pure forms of the various complexes. Compound 3 is highly sensitive toward protic solvents and could only be successfully prepared by allowing the acid and BiPh3 to react under solvent-free conditions at 100 C for 2 h under a dry N2 atmosphere. Attempts at obtaining accurate elemental analysis on 3 proved difficult, highlighting the sensitivity of the single Ph group toward protolysis with atmospheric H2O. A low carbon content, presumably arising from formation of an oxo-species, was always obtained. As such, NMR data on 3 are provided in the Supporting Information. The 1H NMR spectrum of 3 collected in d6-DMSO shows the ortho, meta, and para protons of the phenyl group resonating at δH 8.75, 7.86, and 7.34, respectively. There is also a small benzene resonance visible at δH 7.36, which is indicative of the extremely labile nature of the remaining phenyl group. To confirm the ethanolysis process, a sample of 3 was reacted with dry ethanol, successfully yielding the ethoxy-substituted complex 2. In the 1H NMR spectrum of 2, also obtained in d6-DMSO, the Ph signals are absent, and the spectrum shows resonances corresponding to an ethoxy group at δH 3.48 (OCH2) and 1.11 (CH3), consistent with the ethanolysis of 3. The slow hydrolysis of the ethoxy complex when left in ethanol solution exposed to the atmosphere gives rise to crystals of the novel Bi10 oxo-cluster-containing, polymeric complex 5. The existence of a Bi10 oxo-species has only previously been inferred from mass spectrometry studies on the hydrolysis products of bismuth salicylate.20 The predicted architecture of the Bi10O8 core20 is now confirmed in the solid state structure of 5 (Figure 7). Deliberate synthesis of the monosubstituted complex 4 was achieved from the stoichiometric 1:1 reaction in Et2O at room temperature. Both the acid and BiPh3 are soluble in Et2O, and stirring over a period of 7 h leads to selective precipitation of [Ph2BiL]¥ in a 59% yield. Both the ortho and

meta chemical shifts are at lower frequencies (δH 8.28 and 7.65) than those observed for the analogous protons in 3 (δH 8.75 and 7.86). In the FT-IR spectrum of 4 the ring modes of the Ph groups are apparent at 726 and 693 cm-1, while in 3 the corresponding bands, which are of lower intensity, are at 734 and 703 cm-1.

Crystal Structure Analysis Four of the five title compounds (1, 2, 4, and 5) have been structurally authenticated by single-crystal X-ray diffraction studies, and their descriptions will be presented here in turn. The crystallographic details are summarized in Table 5, and the cif files are available as Supporting Information. The large atomic radius of bismuth allows for a wide variety of different and interesting coordination environments and often leads to oligomeric or polymeric structures. These four structures follow that pattern, and despite sharing the same metal center and monofunctional ligand system, they show four different polymeric motifs of varying nuclearity and composition. Given the ambiguity in what constitutes a “real” Bi-O contact, for the purposes of this discussion only distances at or below 3.1 A˚ are considered.16 Compound 1. The tris-substituted complex [Bi{(o-NO2)C6H4CO2}3(H2O)]¥ (1), shown in Figure 1, forms a linear ribbon structure that is based on a Bi-Ocarboxylate η2(O,O0 )interaction (Bi-O bond lengths 2.677(4) and 2.723(4) A˚), which orients antiparallel to their neighbors through the polymer (pseudo)plane (shown in Figure 2). A summary of the bond lengths and angles for 1 are given in Table 1. The alternating groups associate through a further two Bi-O bonds (bond lengths 2.435(4) and 2.448(4) A˚) to form a series of planar (BiO)2 rings (sum of bond angles 359.7), giving the carboxylate group an overall μ3-η2(O,O0 )η1(O);η1(O0 )-bonding mode. The Bi atoms are nine-coordinate binding to three crystallographically distinct carboxylate groups, via η2(O, O0 )-bonding to the second and third carboxylate groups, η1(O) to one O each of two symmetry-generated carboxylates and to one molecule of water.

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Figure 2. Crystal structure of the polymeric ribbon chain of [Bi{(o-NO2)C6H4CO2}3(H2O)]¥ (1). All H atoms are omitted except those involved in H bonding.

Figure 3. Molecular structure of one (A) of the two nonidentical repeating dinuclear units in [{Bi{(o-NO2)C6H4CO2}2(OEt)(EtOH)}2]¥ (2).

The second carboxylate group sits on the opposite side of the Bi atom to the carboxylate group that is involved in the polymer plane (C-Bi-C angle of 177.46(18)) with Bi-O bond lengths of 2.327(4) and 2.472(5) A˚ and a bite angle of 53.83(16). The third carboxylate lies roughly perpendicular to the first two with angles between the [BiOCO] planes of 82.07(10) and 88.35(20) to ligands one and two, respectively. The Bi-O bond distances are 2.483(5) and 2.427(5) A˚ with a bite angle of 52.72(14). Each carboxylate O atom on this ligand hydrogen bonds to the water molecule attached to its closest neighboring Bi atom (donor-acceptor distances of 2.775(7) and 2.847(7) A˚). The first carboxylate has a noticeably more acute bite angle of 47.93(12) presumably to

accommodate the extra interactions to its neighboring Bi atoms and as a result of the relatively elongated Bi-O η2(O,O0 ) bond lengths. Compound 2. The bis-substituted complex [{Bi{(o-NO2)C6H4CO2}2(OEt)EtOH}2]¥ (2) consists of dinuclear units, shown in Figure 3, which oligomerize through ethoxy groups and further associate into polymeric chains via Bi-Ocarboxylate interactions (see Figure 4) to form chains of alternating [Bi-Oethoxide]2 and [Bi-Ocarboxylate]2 units with shared Bi vertices. A summary of bond lengths and angles found in 2 is given in Table 2. The asymmetric unit contains two nonidentical repeating units (A and B) each possessing an inversion center in the middle of the central [Bi-Oethoxide]2 ring.

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Figure 4. Crystal structure of the polymeric chain of dinuclear unit B in [{Bi{(o-NO2)C6H4CO2}2(OEt)EtOH}2]¥ (2). All H atoms excluded except those involved in H bonding.

Figure 5. Molecular structure of the asymmetric unit of [Ph2Bi{(o-NO2)C6H4CO2}]¥, 4. Thermal ellipsoids are shown at 50%.

The O-C(H2) bonds lie essentially within this plane (rms deviation of fitted atoms 0.0218 and 0.0095). However, the orientation of the transoid CH2CH3 moieties with respect to the central ring is one of the main differences between the two dinuclear units. In the first dinuclear unit (A) the EtO groups align themselves close to the ring plane (the angle between planes [EtO 3 3 3 OEt] and [BiO]2 is 22.54), whereas in the second dinuclear unit (B) they point distinctly above and below the plane (angle between planes 80.61). In both A and B the two carboxylate groups bind to the Bi centers in a highly asymmetric manner with one short and one long contact averaging 2.30 and 2.73 A˚, and 2.269 and 2.86 A˚, for Bi(1) and Bi(2), respectively. One of the carboxylate groups is bidentate, while the other, which is involved in the [Bi-Ocarboxylate]2 ring, is tridentate with an overall bonding mode of μ2-η2(O,O0 )η1(O). The four carboxylate bite angles vary little, ranging from 49.2(3) to 51.5(3). The manner of the ethanol bonding over the two dinuclear units is also quite different, dictated by the (O)H hydrogen bonding to a carboxylate O atom. In A the (EtO)H 3 3 3 Ocarboxylate interactions lie above and below the [Bi-Oethoxide]2 ring, whereas in B the hydrogen bonding links two neighboring

(symmetry generated) dinuclear units bonding above and below the plane of the [Bi-Ocarboxylate]2 rings. Donoracceptor distances are 2.771(15) and 2.908(15) A˚, respectively. The interdinuclear unit interactions, which lead to the overall polymeric structure with two sets of alternating [BiOethoxide]2 and [Bi-Ocarboxylate]2 rings, which link through shared Bi vertices, differentiate this motif from the polymeric motif of 1, where opposing bidentate bicarboxylate interactions aggregate through shared Bi-O edges, resulting in a ribbon-like arrangement of alternating [BiO]2 and [BiOCO] rings. Compound 4. The mono-substituted complex [Ph2Bi{(o-NO2)C6H4CO2}]¥ (4), shown in Figure 5, also forms a polymeric structure; however, its motif is different again (see Figure 6). Bond lengths and angles found in 4 are summarized in Table 3. Each Bi atom displays much lower coordination, bonding to only five other atoms: to two phenyl groups Bi(1)-C(8) (2.232(3) A˚) and Bi(1)-C(14) (2.245(3) A˚), η2(O, O0 ) from the tridentate carboxylate group Bi(1)-O(1) (2.313 (2) A˚) and Bi(1)-O(2) (3.081(2) A˚), and η1(O) from the oxygen of a neighboring (symmetry generated) carboxylate Bi(1)-O(2a) (2.548(2) A˚). All five contacts are on the same face of the Bi center. In addition, there appears to be a nonclassical Bi 3 3 3 π(Ar) interaction arising from the orientation of the Bi atom below the π-system of a phenyl ring attached to a neighboring Bi atom. Geometrically the Bi atom is aligned normal to the phenyl ring plane with the average Bi-centroid-C angle being 90.00 (range 80.3399.58). However the Bi-C distances are relatively long, with a range of 3.952(3)-4.391(3) A˚ and a bicentroid distance of 3.940 A˚, indicating the interaction is at best a weak one.22 The carboxylate group has a much tighter bite angle than that seen in the other structures at only 46.08(6). The structure is similar to that of the previously reported arenesulfonate [Ph2Bi{(2,4-Me2)C6H3SO3}]¥,23 which has an even lower Bi coordination number of four. Compound 5. The structure of the oxo-cluster compound [Bi10O8{(o-NO2)C6H4CO2}14(EtOH)x 3 (EtOH)y(H2O)z]¥ (5), shown in Figure 7, has two nonidentical Bi10 fragments (C and D) per unit cell, each of which associates into polymeric chains. The central core of each cluster consists of a Bi6O8 (22) Silvestru, C.; Breunig, H. J.; Althaus, H. Chem. Rev. 1999, 99, 3277. (23) Sharutin, V. V.; Sharutina, O. K.; Pavlushkina, I. I.; Egorova, I. V.; Pakusina, A. P; Krivolapov, D. V.; Gubaidullin, A. T.; Litvinov, I. A. Zh. Obshch. Khim. 2001, 71, 87.

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Figure 6. Polymeric structure of [Ph2Bi{(o-NO2)C6H4CO2}]¥, 4.

Figure 7. Molecular structure of [Bi10O8{(o-NO2)C6H4CO2}14(EtOH)x.(EtOH)y(H2O)z]¥, 5, showing one Bi10 cluster, with the Bi10O8 core highlighted.

distorted rhombic dodecahedron with four further Bi atoms sitting atop four (nonadjacent) of the eight O-vertices. Alternatively the Bi6O8 core can be viewed as a Bi6 octahedron where all eight triangular faces are capped by oxygen atoms. The overall charge balance is satisfied by 14 carboxylate ligands per Bi10 unit. This hexanuclear Bi6O8 core is a common central building block for many larger oxo-clusters,4 for example the nonanuclear alkoxide/siloxides [Bi9O7(OC6F5)13],8 [Bi9O7(OSiMe3)13],10 and [Bi9O7(OCH(CF3)2)13],24 where the octahedra are face capped by seven O atoms and three externally positioned Bi atoms. The Bi10O8 motif is an obvious progression of this structural type, and having been earlier predicted by Whitmire20 this is the first time it has been crystallographically authenticated. In this instance two of the four capping bismuth atoms oligomerize through [BiOcarboxylate]2 rings to form undulating pearl necklace-like polymeric chains (Figure 8). The formulation of the cluster is also supported by microanalysis and ESI-MS studies, with the highest m/z value found for the anion [Bi10O8L14(OH)10(MeOH)13(EtOH)2]10- (m/z 522). (24) Andrews, P. C.; Junk, P. C.; Nuzhnaya, I.; Spiccia, L. Dalton Trans. 2008, 2557.

In cluster C four of the core Ooxide atoms, O(1, 4, 6, 7), are four-coordinate bonding to three Bi atoms in the inner coordination sphere and to one of the capping Bi atoms. The remaining four oxides, O(2, 3, 5, 8), are all threecoordinate bonding only to Bi atoms from the inner coordination sphere. There are two ranges of Bi-Ooxide bond lengths from the inner sphere Bi atoms, 2.083(12)-2.361 (12) A˚ averaging 2.20 A˚ for 20 bonds and 2.572(12)-2.793 (12) A˚ averaging 2.65 A˚ for four bonds. Each of the four outer sphere Bi atoms has only one oxide bond, and these vary little, ranging from 2.076(12) to 2.168(12) A˚, averaging 2.13 A˚. Two of the inner Bi atoms in C are eight coordinate; Bi(2) has two η2(O,O0 ) carboxylate interactions, four oxide, and two Bi-Oethanol ligands, whereas Bi(8) has only one bond to an ethanol but an added η1(O) carboxylate bond. Bi (3, 4, 6, 7) all have four oxide bonds and three η1(O) carboxylate bonds and are seven-coordinate. Bi(5) is sixcoordinate with four oxides but only two η1(O)-carboxylate bonds. The outer Bi(1, 8, 9, 10) atoms are eight-coordinate, except Bi(10), which is nine-coordinate; Bi(9) has two η2(O, O0 ) carboxylate interactions, two η1(O) carboxylate bonds, one oxide bond, and one ethanol bond. Bi(10) has three η2(O, O0 ) carboxylate interactions, one η1(O) carboxylate bond, one oxide bond, and one ethanol bond. Bi(1) and B(8) are ligated by four carboxylate groups with two η2(O,O0 ) and two η1(O) interactions each, and by one oxide and one ethanol. One of the η1(O) interactions to Bi(1, 8) is to the carboxylate groups of neighboring Bi10 clusters. The bonding mode of these carboxylates is formally μ2-η2(O,O0 )η1(O), forming (BiO)2 rings between the clusters. The bond lengths involved in these bridges are Bi(1)-O(9) = 2.707(13) A˚, Bi(1)-O(9a) = 2.639(13) A˚, Bi(8)-O(42) = 2.792(15) A˚, and Bi(8)-O(42b) = 2.850(14) A˚. Of the 14 carboxylate ligands there are four different bonding motifs; three are μ2η1(O)η1(O0 ), seven are μ2-η2(O,O0 )η1(O), two are μ3η1(O)η1(O)η1(O0 ), and two are μ3-η2(O,O0 )η1(O)η1(O0 ). There are 41 Bi-Ocarboxylate bonds over a wide range of 2.185(14)-3.058(12) A˚, averaging 2.63 A˚. There are six EtO (H)-Bi bonds, one to each of the outer Bi atoms and two to Bi(2), one of the inner sphere Bi atoms. These bonds range from 2.668(12) to 2.969(15) A˚, averaging 2.83 A˚. The oxide core atoms in D are essentially the same as in C; O(69, 72, 74, 75) are four-coordinate and O(70, 71, 73, 76) are three-coordinate. Inner sphere Bi-Ooxide bonds range from 2.077(11) to 2.438(10) A˚, averaging 2.21 A˚ for 20 bonds, and 2.546(12) to 2.811(12) A˚, averaging 2.64 A˚ for four bonds. The four outer sphere Bi-O bonds range from 2.082(11) to 2.154(10) A˚, averaging 2.12 A˚. The four outer Bi atoms,

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Figure 8. Crystal structure of [Bi10O8{(o-NO2)C6H4CO2}14(EtOH)x 3 (EtOH)y(H2O)z]¥, 5, showing three of the polymeric “Bi10O8” cluster chains.

Figure 9. Idealized representations of the polymer chains found in 1 (a), 2 (b), 4 (c), and 5 (d).

Bi(11, 18, 19, 20), are eight-, nine-, eight-, and seven-coordinate, respectively, each bonding to one oxide and all, except Bi(20), to one ethanol. They have two η2(O,O0 ) carboxylate interactions, but Bi(18) has three, it also has one η1(O) carboxylate bond, and the others each have two. Just as in the first cluster, the polymeric chain is held together through [Bi-Ocarboxylate]2 rings with bond lengths of 2.644(13) A˚ for Bi(11)-O(77), 2.711(15) A˚ for Bi(11)O(77)c, 2.801(12) A˚ for Bi(19)-O(122), and 2.827(12) A˚ for

Bi(19)-O(122)d. All of the inner Bi atoms have four oxide bonds; Bi(13, 17) are eight-coordinate and have a further four bonds to carboxylate groups [η1(O)]. Bi(12, 14, 16) have only three such contacts and are seven-coordinate. Bi(15) is six-coordinate, having only two η1(O)-carboxylate bonds. The bonding motifs of the carboxylate ligands are two μ2-η1(O)η1(O0 ), eight μ2-η2(O,O0 )η1(O), three μ3-η1(O)η1(O)η1(O0 ), and one μ3-η2(O,O0 )η1(O)η1(O0 ). As in cluster C, after the Bi-Ooxide bonds there are a further

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47 Bi-O bonds, 44 are Bi-Ocarboxylate bonds ranging from 2.189(13) to 3.096 (12) A˚ and averaging 2.57 A˚. This leaves only three ethanol contacts, all of them are to outer Bi(11, 18, 19) atoms at 2.689(12), 2.727(13), and 2.99(2) A˚, respectively. Table 4 shows the average bond lengths and angles for the two clusters, and these vary very little. The main difference between the two clusters is that in cluster C three of the Bi-Ocarboxylate contacts have been replaced by three Bi-Oethanol contacts. The overall molecular formula can be given as [{Bi10O8((o-NO2)C6H4CO2)14(EtOH)3}{Bi10O8((o-NO2)C6H4CO2)14(EtOH)3.5} 3 (EtOH)4(H2O)4]¥.

Conclusion It has been demonstrated that the simple 2:1 stoichiometric reaction of o-nitrobenzoic acid (= LH) and triphenylbismuth in ethanol leads to a mixture of heteroleptic polymeric products whose chemical and thermodynamic properties allow them to be separated and characterized. The compounds isolated and characterized by single-crystal X-ray diffraction are the substituted compounds [Ph2BiL]¥ (4) and [BiL3(H2O)]¥ (1), the alcoholysis product [{BiL2(OEt)(EtOH)}2]¥ (2), and the oxo-cluster [Bi10O8L14(EtOH)x 3 (EtOH)y(H2O)z]¥ (5). It is concluded that the expected but “structurally missing” intermediate [PhBiL2]n (3) leads to 2 through in situ alcoholysis and to 4 and 1 through disproportionation. Pure and isolable samples of each compound are obtainable through strict control of stoichiometry, reaction medium, and reaction temperature. Compound 3 can be synthesized and isolated from the solvent-free reaction and subsequently converted into 2 through stirring in dry ethanol. The newly formed alkoxide can then undergo facile hydrolysis to the Bi10 oxo-cluster 5, containing an overall structural motif that is authenticated for such oxo-clusters in the solid state for the first time. The bis-substituted compound 4 can be isolated from the 1:1 stoichiometric reaction of LH and BiPh3 in Et2O at room temperature. The four compounds that have been analyzed by crystallography (1, 2, 4, and 5) are all polymeric but show distinct metal coordination environments, variable carboxylate binding modes, and variable methods of polymerization. These are summarized pictorially in Figure 9.

Experimental Section Triphenylbismuth and ortho-nitrobenzoic acid were purchased from Strem Chemicals Inc. and Aldrich, respectively, and both were used as received. Where dry ethanol was used it was dried prior to use by reflux over Mg turnings and collected by distillation. 1H NMR and 13C NMR spectra were recorded on Bruker DRX 400, or Varian Inova 500 spectrometers as indicated. All spectra were internally referenced using the deuterated solvent signal. Electrospray ionization spectra (ESI) were generated on a Micromass Platform II QMS spectrometer. Electron impact spectra (EI) were recorded on a Shimadzu QP5050A GCMS system. Infrared spectra, as KBr disks or Nujol mulls, were recorded on a Perkin-Elmer FT-IR spectrometer Spectrum RX-1. Elemental microanalyses were performed by the Campbell Microanalytical Laboratory, Department of Chemistry, University of Otago, Dunedin, New Zealand. Bismuth analysis was by acid digestion of the carboxylates at pH = 2 and titration against EDTA using xylenol orange as an indicator and hexamethylenetetramine as a buffer. Melting points were measured on a Stuart Scientific melting point apparatus SMP3. Crystalline samples of compounds 1, 2, 4, and 5 were mounted on glass fibers in highly viscous oil at

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123(2) K and data collected either on an Enraf-Nonius Kappa CCD diffractometer (graphite-monochromated Mo KR X-ray radiation (λ=0.71073 A˚)) and corrected for absorption using the SORTAV25 package or on a Bruker X8 Apex CCD diffractometer (graphite-monochromated Mo KR X-ray radiation (λ= 0.71073 A˚)) and corrected for absorption using the SADABS package.26 The SHELX27 suite of programs was employed for structural solution and refinements using the graphical interface X-Seed.28 One-Pot Synthesis and Crystallization of Compounds 1, 2, and 4. o-Nitrobenzoic acid (0.34 g, 2.0 mmol) and BiPh3 (0.44 g, 1.0 mmol) were refluxed in dry ethanol (30 mL) to give a colorless solution, which remained clear on cooling to room temperature. A large number of crystals grew slowly over a period of a few weeks. The crystals were isolated by filtration and those of different morphology separated by hand, leading to the identification of two heteroleptic complexes, [{BiL2(OEt)(EtOH)}2]¥ (2) and [Ph2BiL]¥ (4). Leaving the filtered mother liquor to stand for several weeks undisturbed yielded crystals of the tris-substituted complex [BiL3(H2O)]¥ (1). Deliberate Syntheses of Compounds 1-5. Synthesis and Characterization of [Bi{(o-NO2)C6H4CO2}3(H2O)]¥, 1. The deliberate synthesis of [Bi{(o-NO2)C6H4CO2}3(H2O)]¥ was achieved, as previously reported,21 from the 3:1 reaction of o-nitrobenzoic acid with Ph3Bi either under reflux in toluene or under solvent-free conditions. All analyses obtained for this product were consistent with those previously reported. Synthesis and Characterization of [Bi{(o-NO2)C6H4CO2}2(OEt)], 2a. [PhBi{(o-NO2)C6H4CO2}2] (3) (0.20 g) was weighed into a Schlenk flask under dry N2 gas. Dry ethanol (15 mL) was added and the reaction mixture heated to reflux for 7 h, producing the yellow-colored product of composition [Bi{(o-NO2)C6H4CO2}2(OEt)]. Yield: 0.31 g (51%), Mp: dec >300 C. FT-IR (Nujol, cm-1): 1654 w, 1588 m, 1524 s, 1346 w, 1264 w, 1147 m, 1136 w, 1076 m, 1036 w, 963 w, 862 m, 833 m, 783 m, 735 m, 698 s, 647 m. 1H NMR (400 MHz, d6-DMSO, 30 C): δ 7.85 (m, 8H, H3,6), 7.69 (m, 8H, H4,5), 3.48 (m, 4H, OCH2), 1.11 (m, 6H, CH3). 13C NMR (100 MHz, d6-DMSO, 30 C): δ 148.5 (C-NO2), 132.4 (CH), 131.2 (CH), 130.4 (CH), 128.3 (CH), 122.7 (CH), 25.1 (OCH2), 18.5 (CH3). MS-ES+: m/z = 440 [Bi4L4(OEt)4(DMSO)]4+. Anal. Found (%): C 33.1, H 1.8, N 4.9, Bi 34.8. Calcd (%) for Bi2C32H26N4O18: C 32.8, H 2.2, N 4.8, Bi 35.7. Recrystallization from dry ethanol gave single crystals of the solvated complex [{Bi(o-NO2C6H4CO2)2(OEt)(EtOH)}2]¥, 2. Synthesis and Characterization of [PhBi{(o-NO2)C6H4CO2}2], 3. o-Nitrobenzoic acid (0.34 g, 2.0 mmol) and BiPh3 (0.44 g, 1.0 mmol) were ground together and placed in a small Schlenk flask before being dried under vacuum for 2 h. The Schlenk flask was then heated to the neck in a Kugelrohr oven at 100 C (note: above 120 C the product decomposes to a glasslike film) under a constant flow of dry N2 gas. At ca. 80 C the reaction mixture became a pale yellow-brown color, and over an initial 30 min, as the temperature was raised to 100 C, benzene was seen to be evolved and condensed at the top of the Schlenk flask. After 2 h at 100 C the flask was cooled and all volatiles were removed under vacuum, leaving a fine pale yellow powder. All subsequent manipulations were carried out in an argon-filled drybox. The precipitate was identified as the bis-substituted complex [PhBi{(o-NO2)C6H4CO2}2]. Yield: 0.58 g (94%). Mp: 126-127 C dec. FT-IR (Nujol, cm-1): 1591 m(br), 1529 vs, 1348 s, 1262 m, 1149 w(br), 1077 m, 996 w, 962 w, 867 m, 846 m, 781 m, 734 m, 703 m, 649 m. 1H NMR (500 MHz, d6-DMSO, 30 C): δ 8.75 (d, 2H, J = 7.0 Hz, o-Ph), (25) (26) 1997. (27) (28)

Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421. Sheldrick, G. M. SADABS; University of G€ ottingen: Germany, Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112. Barbour, L. J. J. Supramol. Chem. 2001, 1, 189.

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7.86 (t, 2H, J = 7.5 Hz, m-Ph), 7.79 (m, 4H, H3,6), 7.64 (m, 4H, H4,5), 7.34 (m, 1H, J = 7.5 Hz, 7.0 Hz, p-Ph). 13C NMR (125 MHz, d6-DMSO, 30 C): δ 170.6 (C-NO2), 150.1 (C-Bi), 138.7 (CH), 137.9 (CH), 133.1 (CH), 132.3 (CH), 131.3 (CH), 131.2 (CH), 129.5 (CH), 128.9 (CH), 124.2 (CH), 124.0 (CH). (Note: signals for benzene impurities observed at δ 7.36 (s, 2H, C6H6) (1H), and at 128.8 (13C)). Anal. Found (%): C 36.13, H 2.1, N 4.7. Calcd (%) for BiC20H13N2O8: C 38.9, H 2.1, N 4.5. Synthesis and Characterization of [Ph2Bi{(o-NO2)C6H4CO2}]¥, 4. o-Nitrobenzoic acid (0.17 g, 1.0 mmol) and BiPh3 (0.44 g, 1 mmol) were dissolved in diethyl ether (20 mL) and stirred overnight at ambient temperature. This resulted in the precipitation of a colorless solid. The solid was collected, filtered, and dried in vacuo. The solid analyzed as the monosubstituted complex [Ph2Bi{(o-NO2)C6H4CO2}]¥. Yield: 0.31 g (59%). Mp: dec >300 C. FT-IR (Nujol, cm-1): 1638 w, 1596 m, 1572 m, 1533 vw, 1520 m, 1307 w, 1264 w, 1153 w, 1077 w, 1038 w, 962 w, 868 vw, 891 w, 780 m, 726 m, 693 s, 647 w. 1H NMR (400 MHz, d6-DMSO, 30 C): δ 8.28 (d, 4H, J = 7.44 Hz, o-Ph), 7.81 (d, 2H, J = 7.64 Hz, H3,6), 7.75 (m, 2H, H4,5), 7.65 (m, 4H, m-Ph), 7.34 (m, 2H, p-Ph). 13C NMR (100 MHz, d6DMSO, 30 C): δ 149.2 (C-NO2), 137.2 (CH), 132.4 (CH), 131.2 (CH), 130.4 (CH), 127.5 (CH), 123.2 (CH). MS-ES+: m/z = 363 [BiPh2]+. MS-ES-: m/z = 695 [BiPh2L2]-. Anal. Found (%): C 42.9, H 2.9, N 2.7, Bi 39.1. Calcd (%) for BiC19H14N1O4: C 43.1, H 2.7, N 2.7, Bi 39.5. Synthesis and Characterization of [Bi10O8{(o-NO2)C6H4CO2}14(EtOH)x 3 (EtOH)y(H2O)z]¥, 5. Half of the mother liquor from which crystals of 2 were obtained was filtered under dry nitrogen into a second Schlenk flask. A small crop of colorless crystals grew slowly over a period of a few weeks. These were identified as the cluster compound [Bi10O8{(o-NO2)C6H4CO2}14(EtOH)x 3 (EtOH)y(H2O)z]¥, 5. FT-IR (KBr, cm-1):

Andrews et al. 1637 m, 1596 m, 1572 m, 1533 vw, 1520 m, 1307 w, 1264 w, 1153 w, 1077 w, 1040 m, 962 w, 868 vw, 891 w, 780 m, 647 w. MS-ES-: m/z = 522 [Bi20O16L14(OH)10(MeOH)13(EtOH)2]10-. Anal. Found (%): C 26.7, H 1.6, N 4.1. Calcd (%) for Bi20O16L28(EtOH)9: C 26.5, H 1.3, N 4.4. X-ray Structural Determinations. Variata. During data collections for compound 2 a curiosity of these crystals meant that the structure could not be fully refined despite several independent collections on two different diffractometers. Non-hydrogen atoms, excluding Bi, could not sustain anisotropic refinement; however the connectivity in the crystal structure is unambiguous. Compound 4 was also affected severely by the large heavy atom content. This, combined with rotational disorder in many of the ligands, meant that anisotropic refinement of all but the Bi atoms could not be sufficiently maintained. Disorder of the o-NO2Phmoiety in ligand 14 (cluster C) has been refined to 54% for the major component. One of the ethanol groups attached to cluster D at Bi(20) has been constrained at 50% occupancy. There are still large solvent-accessible voids present in the structure, which are assumed to contain either ethanol or water lattice molecules; however, there was insufficient electron density to model these properly, and they were therefore excluded.

Acknowledgment. We thank the Australian Research Council, Bayer Schering Pharma, and Monash University for financial support. We would also like to thank Dr. Craig Forsyth for assistance with X-ray crystallography. Supporting Information Available: NMR data on compound 3 and crystallographic data in electronic form as CIF files. This material is available free of charge via the Internet at http:// pubs.acs.org.

Synthesis, Ethanolysis, and Hydrolysis of Bismuth(III) ortho

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