Synthesis and characterization of dinickel(II) and dipalladium(II) complexes of the macrocyclic binucleating ligand 3,13-dimethyl-3,13-dinitro-1,5,11,15-tetra-azacycloeicosane-8,18-dithiol (L5). Crystal structure of the complex [Ni2(L5– 2H)][NO2]2·3.5H2O
Abstract
Condensation of the bis(1,5-diaminopentane-3-thiolato)dinickel(II) ion or the dipalladium(II) analogue with formaldehyde and nitroethane in basic methanol yields the dianion of the macromonocyclic ligand 3,13-dimethyl-3,13-dinitro-1,5,11,15-tetra-azacycloeicosane-8,18-dithiol (L5) as the dimetal(II) complex. Spectroscopic properties of the diamagnetic complexes are reported, together with the crystal-structure analysis of the dinickel(II) complex. The nitrite salt of the latter crystallizes in the space group Pbnm, a= 7.762(3), b= 14.921 (3), c= 25.459(3)Å, Z= 4, R= 0.057 for 1 739 ‘observed’ reflections. The complex is a syn isomer, the first time this geometry has been observed from this type of condensation reaction, with the two N2NiS2 planes folded slightly towards each other about the mirror plane through S ⋯ S in a ‘butterfly’ arrangement (interplanar angle 162.8°). Oxygen atoms of the pendant nitro groups form weak axial interactions, the six-membered rings at the ‘ends’ having skew-boat conformations.