The structurally flexible bicyclic bis(2-hydroxyethanethiolato)bismuth(III) complex: A model for asymmetric monoanionic chelation of bismuth(III)

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: C4H10O2BiS2N . H2O, I4(1)/a, a 20.337(6) Angstrom, b = 20.337(6) Angstrom, c = 11.303(7) Angstrom, Z = 16], 5(NO3) [crystal data: C4H10O2BiS2Cl, P2(1)/n, a = 8.653(2) Angstrom, b = 10.618(3) Angstrom, c = 10.564(2) Angstrom, beta = 100.51(2)degrees, Z = 4], and S(CH3COO) [crystal data: C6H13O4-BiS2, P2(1)/c, a = 8.089(2) Angstrom, b = 16.313(3) Angstrom, c = 8.708(2) Angstrom, beta = 98.37(3)degrees, 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.