Preparations of copper(I) and bismuth(III) complexes of hydrotris(4-ethyl-3-methyl-5-thioxo-1,2,4-triazolyl)borate (Tr(Et,Me)) are described. These complexes have been characterized by means of spectroscopy and microanalysis. Molecular structures of [Cu(Tr(Et,Me))](2) x 2.5CH(3)CN x 0.5H(2)O (3a) and [Bi(Tr(Et,Me))(2)]NO(3) x 2CHCl(3) (4a) have been determined by single-crystal X-ray diffraction. In the centrosymmetric dimeric copper(I) complex, Tr(Et,Me) acts in the k(3)S,S',H:kS' ' coordination mode. The metal is found in a distorted trigonal geometry as the ligand exhibits an "S(3)-inverted" conformation at the boron center so that a weak [B-H.Cu] agostic interaction renders the overall coordination of the (3 + 1) type. On the other hand, in the bismuth complex, Tr(Et,Me) presents the k(3)S,S',S' ' coordination mode and the "S(3)-normal" conformation. The metal is found in a regular octahedral geometry bound by six thioxo groups of two ligands. Species distributions in solution have been studied using electrospray ionization mass spectrometry upon dissolution of 3a and 4a crystals in acetonitrile. Monomeric and polynuclear copper(I) complexes with different M:L ratios are present in solution, while for 4a only the monomeric species is present.

Reacting the heterocycle 5-thioxo-1,4-dihydro-4-ethyl-3-methyl-1,2,4-triazole (thioxotriazoline) with sodium tetrahydroborate in the molar ratio of approximately 2:1 at 130 degrees C provides the new ligand dihydrobis(thioxotriazolinyl)borato, [Bt(Et,Me)](-), as its sodium salt. The neutral complexes of this anionic ligand with zinc(II), bismuth(III), and nickel(II) have been synthesized and characterized by X-ray crystallography. In every complex, the ligand is coordinated to the metal in the S(2) mode, generating eight-membered chelate rings. The bismuth and nickel complexes exhibit two M.H-B interactions responsible for the dodecahedral and octahedral geometries, respectively. For the zinc complex, the trigonal-bipyramidal coordination is achieved with an apical Zn.H-B interaction. The crystal structures for the three complexes are described, and ab initio calculations on Bi(III), Ni(II), and Zn(II) compounds have been performed in order to assess the nature of the M.H-B interaction and its role for the definition of the molecular geometries.

The ligand hydrotris (1,4-dihydro-3-methyl-4-phenyl-5-thioxo-1,2,4-triazolyl)borato (Tr-Ph,Tr- Me) was synthetized as natrium salt and the complexes [Zn(Tr-Ph,Tr-Me)(2)] (.) 7.5H(2)O (.) 1.5CH(3)CN (2a), [Zn(Tr-Ph,Tr-Me)(2)]. 8DMF (2b), [Co(Tr-Ph,Tr-Me)(2)] (.) 8DMF (3a), [Ni(Tr-Ph, (Me))(2)] (.) H2O (.) 6DMSO (4a), [Bi(Tr-Ph,Tr-Me)(2)]NO3 (5), have been isolated and structurally characterized by X-ray diffraction. In the zinc derivatives the ligand adopts different denticity and coordination modes, eta(2) and [S-2] for 2a and eta(3) and [N-3] for 2b, depending on the crystallization solvent, giving rise to tetrahedral and octahedral geometry, respectively. In the octahedral cobalt and nickel complexes the ligand is eta(3) and [N-3] coordinated whereas in the bismuth complex the eta(3) and [S-3] coordination is exhibited.