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Heterobimetallic Bi(III)−Ti(IV) Coordination Complexes:  Synthesis and Solid-State Structures of BiTi4(sal)6(μ-OiPr)3(OiPr)4, and the Cyclic Isomers Bi4Ti4(sal)10(μ-OiPr)4(OiPr)4 and Bi8Ti8(sal)20(μ-OiPr)8(OiPr)8

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posted on 27.12.2004, 00:00 by John H. Thurston, Arvind Kumar, Cristina Hofmann, Kenton H. Whitmire
The reaction of a 1:2 mixture of bismuth(III) salicylate with titanium(IV) isopropoxide in refluxing toluene has been investigated and found to proceed with ligand exchange to produce the new heterobimetallic complexes BiTi4(sal)6(μ-OiPr)3(OiPr)4 (1), Bi4Ti4(sal)10(μ-OiPr)4(OiPr)4 (2), and Bi8Ti8(sal)20(μ-OiPr)8(OiPr)8 (3). Complex 1 is the major product, while 2 and 3 were identified as minor products from the reaction. Compound 1 is produced pure and in high yield by employing stoichiometric amounts of reagents; its crystal structure consists of a [Ti4(sal)6(OiPr)7]3- ion capped by a Bi3+ ion. Complexes 2 and 3 exhibit cyclic ring structures of bismuth and titanium atoms showing crystallographically imposed inversion symmetry. Both structures occlude large quantities of lattice solvent. The compositional and structural parameters from the single crystal studies indicate that complexes 2 and 3 may represent sequential steps in a ligand exchange process between the two metal species, while the reactivity patterns that were observed provide clues about the solution state structure of bismuth(III) salicylate itself. The 2D COSY 1H NMR spectrum of 1 indicates retention of the asymmetric structure in solution as evidenced by the presence of 14 diastereotopic isopropoxide methyl resonances.