Platinum(II) complexes of N-N’di-nbutyldithiooxamide showing a peculiar +N-H...Cl- interaction. The crystal and molecular structure of bis-di-nbutyldithiooxamidato-platinum(II)

N,N’-di-butyldithiooxamide, “bu,-DTO, reacts in chloroform with neutral complexes of the type cis-P&Cl,. When L=bz.$ or &COD the tight contact ion pair {Pt(H,-“bu,-DTO),“,(Cl-),} (1)is obtained for any metal to ligand ratio. When L is Me,SO the ion pair {(Me,SO)ClPt(H,-“bu,-DTO+,(Cl-)} (2) separates in the solid state on adding the ligand to platinum in a 1:l ratio. This monochelate complex, however, is unstable in chloroformic solution where a symmetrization equilibrium with the corresponding bis-chelate ion pair 1 and the dichloroplatinum starting material can be found. Compound 1 by reaction with pyridine, dipyridine, phenanthroline or similar nitrogen Lewis bases loses one or both HCl molecules so giving {Pt(H-“bu,-DTO)(H,-‘bu,-DTO)+,(Cl-)} (3) or [Pt(H-“bu,-DTO)z] (4), depending on the base concentration. Dissolution of 1 in a basic solvent (DMF, alcohols) leads to the formation of the neutral species 4, which is also formed when a chloroformic solution of 1 undergoes a double phase reaction with the -OH group of H-OH, =Al-OH or =%-OH. Compound 4 crystallizes in the monoclinic space group K&/c, with a = 10.572(2), b= 10.748(l), c = 12.165(2) A, p = 93.37(2)“, I’= 1379.9(4) k, Z=2 and D,,,,=lSS g cmm3; the structure was refined to R=0.033 and R,=0.038. The [Pt(H-“bu,-DTO)z] complex has imposed square-planar geometry about the Pt atom, two thioamide S atoms of the “bu,-DTO molecule acting as a chelating ligand. The two crystallographically independent values for the Pt-S bond distance are: Pt-S(1) = 2.297(3) 8, and Pt-S(2) = 2.284(2) A, the bond angles are very close to 90”. The deprotonated complex [Pt(H-“buz-DTO)Z] (4) restores the ion pair by a double phase reaction with aqueous HCl, while none of the oxoacids is able to give {Pt(H,-“bu,-DT0),2+,(Ox-)2} (Ox- = oxoanion). As a consequence, the ‘N-H. . . Cl- hydrogen interaction in {Pt(H,-“bu,-DTO):+ ,(Cl-),} is thought to be crucial in stabilizing the tight ion pair.