TAUTOMERIC CONVERSION OF A THIOUREA LIGAND UPON FORMATION OF A HYPERVALENT TELLURIUM(II) COMPLEX - SYNTHESIS, AND X-RAY STRUCTURAL STUDIES OF N-PHENYL-N'-(1,3-THIAZOL-2-YL)-THIOUREA AND BROMOPHENYL HIAZOL-3'-IUM-2'-YL)-ISOTHIOUREIDATO]TELLURIUM(II)

The divalent tellurium title complex (II) has been synthesized by addi tion of Ph2Te2 and Br-2 to the ligand 1-phenyl-3-(2-thiazolyl)-2-thiou rea (I). The molecular structures of I and II were subsequently determ ined by X-ray crystallographic methods. As a result, it was found that upon complexation, the ligand had undergone a transition from a thiou rea to to an isomeric isothiourea, involving a transfer of a thiourea proton to the thiazolyl ring. This does not seem to influence the bond ing properties of the ligand, and the reasons for this are discussed. The central tellurium atom is three-coordinate and its coordination sp here is T-shaped with a linear S-Te-Br sequence with bond lengths Te(1 )-S(1) and Te(1)-Br(1) equal to 2.548(1) and 2.883(1) Angstrom, respec tively, and angle S(1)-Te(1)-Br(1)=174.49(2)degrees. At nearly right a ngles to this sequence, there is a Te(1)-C(11)(phenyl) bond of 2.127(3 ) Angstrom.