The Structurally Flexible Bicyclic Bis(2-hydroxyethanethiolato)bismuth(III) Complex: A Model for Asymmetric Monoanionic Chelation of Bismuth(III)

Reaction of Bi(NO(3))(3) with 2-mercaptoethanol gives [Bi(SCH(2)CH(2)OH)(2)][NO(3)], 5(NO(3)), 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 BiX(3) (X = Cl, Br) with 2-mercaptoethanol. Reaction of Bi(CH(3)COO)(3) with 2-mercaptoethanol gives the conjugate base of 5 which is readily protonated with glacial acetic acid to give the acetate salt 5(CH(3)COO). The compounds have been characterized by IR, Raman, and NMR spectroscopies and APCI mass spectrometry. X-ray crystallographic studies of 5(NO(3)) [crystal data: C(4)H(10)O(5)BiS(2)N.H(2)O, I4(1)/a, a = 20.337(6) Å, b = 20.337(6) Å, c = 11.303(7) Å, Z = 16], 5(Cl) [crystal data: C(4)H(10)O(2)BiS(2)Cl, P2(1)/n, a = 8.653(2) Å, b = 10.618(3) Å, c = 10.564(2) Å, beta = 100.51(2) degrees, Z = 4], and 5(CH(3)COO) [crystal data: C(6)H(13)O(4)BiS(2), P2(1)/c, a = 8.089(2) Å, b = 16.313(3) Å, c = 8.708(2) Å, 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.