Ion-pair charge transfer complexes with M...H-bonding interactions: Syntheses, crystal structures, electronic spectra and DFT calculations

Three new ion-pair complexes, consisting of 1-benzyl-4-aminopyridinium with [M(mnt)₂]^2- where mnt^2- = maleonitriledithiolate and M = Ni²⁺, Pd²⁺ or Pt²⁺ for complexes 1-3, have been synthesized and structurally characterized. X-ray single crystal studies revealed that three complexes are isostructural and crystallize in monoclinic space group C2/c, and there exist weak H-bonding interactions between -NH₂ groups of cation and -CN group of anion as well as weak M...H-bonding interactions between anions and cations. The calculations of charge density distribution disclosed that the M...H-bonding interaction in crystals of 1-3 is mainly attributed to static electric interactions. Two types of H-bonding interactions lead to the formation of two-dimensional sheet structure which is parallel to the crystallographic bc-plane in the crystals of 1-3. A near-IR absorbance appears in the UV-vis-NIR spectra of 1 and 3, respectively, while does not come out in the spectra of 2.