A planar anthracene–imidazolium/anthracene–benzimidazolium cation system in a spherical polyoxometalate matrix: Synthesis, crystallography and spectroscopy

Abstract

A series of ion–pair compounds, comprising of Lindqvist type isopolyanions viz., [Mo6O19]2−and [W6O19]2−as the counter anions and anthracene–imidazolium/anthracene–benzimidazolium as counter cations, have been described. Structures of the isolated stoichiometric solids have been unambiguously determined by single crystal X-ray diffraction analysis. In spite of the structural incompatibility between anthracene (planar) and the present polyoxometalate anions (spherical), coulombic and several intermolecular weak interactions, e.g. C–H⋯O, C–H⋯π, π–π, etc. compensate the destabilization energy raised due to presence of the structurally mis-matched components in the respective crystal lattices. Single-crystal- as well as powder X-ray-diffraction (PXRD) analyses reveal iso-structural relationship between the hexamolybdates- and hexatungstates-associated ion pair compounds. Conformational variation has been observed in the crystal structures containing benzyl benzimidazolium counter cations. Diffuse reflectance electronic absorption spectral studies are performed to understand the relatively intense color of the title compounds in their solid states in comparison to their respective solution states.