COORDINATION-COMPOUNDS OF DIMETHYLTHALLIUM(III) WITH 5-(2-PYRIDINYLMETHYLENE)RHODANINE OR 5-(2-PYRIDINYLMETHYLENE)2-THIOHYDANTOIN - AN UNUSUAL CASE OF DESMOTROPIC ISOMERISM

Reaction of dimethylthallium(III) hydroxide with HPyRd (5-(2-pyridinyl methylene) rhodanine) or HPyTd (5-( 2-pyridinylmethylene)2-thiohydanto in) gave [TlMe(2)(PyRd)] (I) or [TlMe(2)(PyTd)] (II), respectively. Th e crystal structures of I and II were determined by X-ray diffraction (I: monoclinic, space group P2(1)/n (No. 14); a = 10.7867(5), b = 11.7 658(6), c = 11.2804(8) Angstrom, beta = 100.679(5)degrees, V = 1406.8( 1) Angstrom(3), Z = 4, II: triclinic, space group P (1) over bar (No. 2); a = 7.183(1), b = 13.169(2), c = 14.702(3) Angstrom, alpha = 97.84 (1), beta = 95.65(1), gamma = 99.95(1)degrees, V = 1346(1) Angstrom(3) , Z= 2). Complex I consists of dimeric [TlMe(2)(PyRd)] 2 units in whic h each almost linear TlMe(2) moiety is coordinated to the exocyclic S and deprotonated. N atoms of one PyRd ligand and the O atom of the oth er; these dimers are interconnected throughout the lattice by a furthe r, weak interaction between their Tl atoms and the exocyclic S atoms o f neighboring dimers. The PyTd ligands in complex II exist in two desm otropic forms: one results from deprotonation of HPyTd at N(3), and co ordinates to two TlMe(2) moieties as described for PyRd; the other res ults from deprotonation of HPyTd at N(1), and chelates a single TlMe(2 ), moiety via its N(1) and pyridine N(4) atoms. The two types of coord ination entity are interconnected by weak Tl-S-Tl bridges and O...H-N( 3) hydrogen bonds to form tetrameric units. Solid state IR and solutio n phase H-1, C-13 and Tl-205 NMR properties of the complexes and ligan ds are also discussed.