The occurrence of both amide and thiolate forms of the benzoxazole-2-thionate anion (C₇H₄ONS^-) in the same molecule: Synthesis and crystal structure of C₇H₄ONSNa[μ-OP(NMe₂)₃] ₃NaC₇H₄ONS

The reaction of benzoxazole-2(1H)-thione (C₇H₅ONS) with either solid NaOH or NaH, in toluene solution, in the presence of hexamethylphosphoramide (hmpa), afforded the new complex C₇H₄ONSNa(μ-hmpa)₃NaC₇H ₄ONS 1 in good yield. In contrast to similar lithium and calcium complexes, 1 resists the incorporation of water into the metal co-ordination sphere. Characterisation by single-crystal X-ray diffraction revealed that, in the solid state, complex 1 is dimeric through three bridging hmpa ligands. This dimer is unsymmetrically co-ordinated by C₇H₄ONS^- anions, one metal centre being co-ordinated by a N,S-chelated anion formally derived from the thiol tautomer, the other being co-ordinated only through N of an anion formally derived from the amine tautomer of benzoxazole-2(1H)-thione. In addition to these unusual structural features, the dimeric complex 1 is further associated by weak C-H ⋯ O and C-H ⋯ S hydrogen bonding interactions.