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 mnt2− = 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.