Structural dependence of pi-pi interactions in dithiocarbazato and thiosemicarbazato nickel complexes

Structures and stabilization due to pi-pi interactions of N2S2 coordinated nickel(II) complexes NiL2 have been investigated by ESI-MS spectrometry and X-ray diffraction methods. For the systems with HL = 4,5-diazafluoren-9-on e thiosemicarbazone (HL1), fluoren-9-one thiosemicarbazone (HL2) fluoren-9- one dithiocarbazone (HL3) and 4,5-diazafluoren-9-one dithiocarbazone (HL4), the Ni(II) atom in each complex is coordinated in a distorted square-plana r geometry with two aromatic rings positioned on the same side. This cis co nfiguration is stabilized by pi-pi stacking interactions between the aromat ic rings. Detailed structural analyses reveal that whereas the intermolecul ar pi-pi stacking interactions connect NiL21 molecules into a one-dimension al screw chain, the intermolecular pi-pi stacking interactions and the C-H . . . pi interactions link NiL22 molecules into a dimer. The pi-pi stacking interactions and the C-H . . . pi interactions among the two phenyl rings and two fluorene rings of NiL23 form a closed hydrophobic brick. In NiL21 o ne of the two phenyl rings interacts with the two 4,5-diazafluorene rings t o give an opened hydrophobic cavity; the edge-to-face interactions about an other phenyl ring arrange the molecules into a one-dimensional network.