LIGAND-EXCHANGE REACTIONS BETWEEN METAL(II) CHELATES OF DIFFERENT SULFUR AND SELENIUM CONTAINING LIGANDS .9. EXCHANGE BEHAVIOR OF CHELATES OF 1,3-DITHIOLE-2-THIONE-4,5-DITHIOLATE (DMIT) AND 1,1-DICHALCOGENOLATES - X-RAY STRUCTURE OF BU4N[ZN(DMIT)(ET2DTC)]

Nickel, copper and zinc bis-chelates of 1,3- dithiole-2-thione-4,5-dithiolate react with diethyldithio-, -thioseleno-, and diseleno-carbamates of these metals in acetone forming the mixed ligand complexes [M(dmit)(XYCNEt2)]- (X=Y=S or Se; X=S, Y=Se) exclusively which can be isolated purely as salts of suitable cations. This synthesis can be extended to mixed ligand systems containing other geminal ligands demonstrated by (Bu4N)2 [Ni(dmit)- (i-mnt)] (i-mnt=1,1-dicyanoethene-2,2-dithiolate). EPR measurements on the copper compounds and 1H, 13C and 77Se NMR measurements on the nickel and zinc systems as well show that the four- membered chelate ring gains electron density in disfavor of the five-membered chelate ring during the mixed ligand complex formation. The ligand exchange reaction between the nickel complexes can be followed by means of UV-Vis spectroscopy. All reactions obey formally a second order rate law. The crystal and molecular structure of Bu4N[Zn- (dmit)(Et2dtc)] is reported. The compound crystallizes orthorhombic, space group Pna21 with four molecules in the unit cell; a=22.573(4), b= 9.892(1), c=14.964(3) Å. Distorted tetrahedral coordination geometry is found for the ZnS4 moiety with a dihedral angle of 89.6(2)° between the chelate planes. The ZnS distances in the dithiolene (dmit) part of the molecule are clearly shortened in comparison to (Bu4N)2 [Zn(dmit)2]. © 1990.