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)

Abstract

N, N′-di-butyldithiooxamide, nbu 2-DTO, reacts in chloroform with neutral complexes of the type cis-PtL 2Cl 2. When L=bz 2S or 1 2 COD the tight contact ion pair {Pt(H 2- nbu 2-DTO) 2 2+,(Cl −) 2} ( 1) is obtained for any metal to ligand ratio. When L is Me 2SO the ion pair {(Me 2SO)ClPt(H 2- nbu 2-DTO +,(Cl −)} ( 2) separates in the solid state on adding the ligand to platinum in a 1:1 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- nbu 2-DTO)(H 2- nbu 2-DTO) +,(Cl −)} ( 3) or [Pt(H- nbu 2-DTO) 2] ( 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 SiOH. Compound 4 crystallizes in the monoclinic space group P21/ c, with a=10.572(2), b=10.748(1), c=12.165(2) Å, β=93.37(2)°, V=1379.9(4) Å 3, Z=2 and D calc=1.58 g cm −3; the structure was refined to R=0.033 and R w=0.038. The [Pt(H- nbu 2-DTO) 2] complex has imposed square-planar geometry about the Pt atom, two thioamide S atoms of the nbu 2-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) Å and PtS(2)=2.284(2) Å, the bond angles are very close to 90°. The deprotonated complex [Pt(H- nbu 2-DTO) 2] ( 4) restores the ion pair by a double phase reaction with aqueous HCl, while none of the oxoacids is able to give {Pt(H 2- nbu 2-DTO) 2 2+,(Ox −) 2} (Ox −=oxoanion). As a consequence, the + NH···Cl − hydrogen interaction in {Pt(H 2- nbu 2-DTO) 2 2+,(Cl −) 2} is thought to be crucial in stabilizing the tight ion pair.