Versatile Ligand Behavior of Hydrotris(4-ethyl-3-methyl-5-thioxo-1,2,4-triazolyl)borate. Syntheses and Crystal Structures of Cu(I) and Bi(III) Complexes

Preparations of copper(I) and bismuth(III) complexes of hydrotris(4-ethyl-3-methyl-5-thioxo-1,2,4-triazolyl)borate (TrEt,Me)
are described. These complexes have been characterized by means of spectroscopy and microanalysis. Molecular
structures of [Cu(TrEt,Me)]2·2.5CH3CN·0.5H2O (3a) and [Bi(TrEt,Me)2]NO3·2CHCl3 (4a) have been determined by single-crystal X-ray diffraction. In the centrosymmetric dimeric copper(I) complex, TrEt,Me acts in the k3S,S‘,H:kS‘ ‘ coordination
mode. The metal is found in a distorted trigonal geometry as the ligand exhibits an “S3-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, TrEt,Me presents the k3S,S‘,S‘ ‘ coordination mode and the “S3-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.