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 ~2:1 at 130
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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 beensynthesized and characterized by X-ray crystallography. In every complex, the ligand is coordinated to the metalin the S
2 mode, generating eight-membered chelate rings. The bismuth and nickel complexes exhibit two M···H-Binteractions responsible for the dodecahedral and octahedral geometries, respectively. For the zinc complex, thetrigonal-bipyramidal coordination is achieved with an apical Zn···H-B interaction. The crystal structures for thethree complexes are described, and ab initio calculations on Bi(III), Ni(II), and Zn(II) compounds have been performedin order to assess the nature of the M···H-B interaction and its role for the definition of the molecular geometries.