Molecular Deformation, Charge Flow, and Spongelike Behavior in Anion-π {[M(CN)4 ]2- ;[HAT(CN)6 ]}∞ (M=Ni, Pd, Pt) Supramolecular Stacks

Abstract

The synthesis, crystal structures, spectroscopic characterization, and comprehensive quantum-chemical calculations for a novel series of anion-π hybrid salts (XPh₄ )₂ [M(CN)₄ ][HAT(CN)₆ ]⋅3 MeCN (X=P, M=Ni^II (1), Pd^II (3), Pt^II (5); X=As, M=Ni^II (2), Pd^II (4), Pt^II (6); HAT(CN)₆ =1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile) are presented. The systems comprise 1D {[M(CN)₄ ]^2- ;[HAT(CN)₆ ]}_∞ stacks, in which the electron-rich metal complexes adjust their orientation to match the electron-deficient areas of HAT(CN)₆ . Electronic charge-transfer interactions along the stacks result in polarization of electron density within HAT(CN)₆ and in perturbations along the {[M(CN)₄ ]^2- ;[HAT(CN)₆ ]}_∞ contacts. Electronic structure analysis suggests, for example, a relocation of 0.1-0.2 e per molecule from [M(CN)₄ ]^2- to HAT(CN)₆ and anion-π interaction energies of around -65 kcal mol^-1 . A reversible structural single-crystal-to-single-crystal transformation, through desolvation/resolvation processes in the solid state, is also reported and a scheme for the formation of anion-π [M(CN)₄ ]^2- /HAT(CN)₆ adducts in MeCN is proposed.

Keywords: charge transfer; density functional calculations; noncovalent interactions; polycyanide complexes; supramolecular chemistry.