The Structurally Flexible Bicyclic Bis(2-hydroxyethanethiolato)bismuth(III) Complex: A Model for Asymmetric Monoanionic Chelation of Bismuth(III)
journal contributionposted on 18.06.1997, 00:00 by Lisa Agocs, Glen G. Briand, Neil Burford, T. Stanley Cameron, Witold Kwiatkowski, Katherine N. Robertson
Reaction of Bi(NO3)3 with 2-mercaptoethanol gives [Bi(SCH2CH2OH)2][NO3], 5(NO3), independent of stoichiometry. Other salts or derivatives of 5, 5(Cl) and 5(Br), are readily prepared by anion exchange reactions and can also be obtained by reaction of BiX3 (X = Cl, Br) with 2-mercaptoethanol. Reaction of Bi(CH3COO)3 with 2-mercaptoethanol gives the conjugate base of 5 which is readily protonated with glacial acetic acid to give the acetate salt 5(CH3COO). The compounds have been characterized by IR, Raman, and NMR spectroscopies and APCI mass spectrometry. X-ray crystallographic studies of 5(NO3) [crystal data: C4H10O5BiS2N·H2O, I41/a, a = 20.337(6) Å, b = 20.337(6) Å, c = 11.303(7) Å, Z = 16], 5(Cl) [crystal data: C4H10O2BiS2Cl, P21/n, a = 8.653(2) Å, b = 10.618(3) Å, c = 10.564(2) Å, β = 100.51(2)°, Z = 4], and 5(CH3COO) [crystal data: C6H13O4BiS2, P21/c, a = 8.089(2) Å, b = 16.313(3) Å, c = 8.708(2) Å, β = 98.37(3)°, Z = 4] show them to each contain the bicyclic bis(2-hydroxyethanethiolato)bismuth framework 5. The conformational features of 5 are dramatically different in each of the structures, perhaps reflecting the relative donor capabilities of the anions. The observations reveal a substantial thermodynamic preference for the thiolate−alcohol chelate in a 2:1 stoichiometry over other possible structural arrangements, which is interpreted in terms of hard and soft acid−base theory and mediation of the acidity of the bismuth site by the double hydroxyl coordination.