Three-dimensional framework structures built of heptacyanotricadmate(II) units providing polyhedral cavities for guests: classification of the zeolite-like structures

Abstract

A series of 17 inclusion compounds of composition [am·xG][Cd₃(CN)₇](x= 1–2) has been obtained from the three-dimensional anionic [Cd₃(CN)₇]^– host and guests of an onium cation am⁺ and a neutral molecule G. The crystal structures of the inclusion compounds reveal a common feature for the host structures, i.e. an infinite chain with repeating –(CN)–Cd(t)–CN–Cd(o)–NC–Cd(t)– units, –(T–O–T)_n–, composed of tetrahedral Cd(t) and octahedral Cd(o) atoms linked by CN groups running along the mirror plane of the unit cell. The three-dimensional hosts are constructed through interchain connections between the mirror planes by out-of-plane CN groups. Six types of structure have been classified according to differences in the mode of bending at both ends of the T–O–T and T–T entities in the chain and in the mode of interchain connections building up the three-dimensional framework structures.