Interpenetrating three-dimensional coordination networks with a rare 4-connected (65.8) topology and unusual geometrical features

Abstract

The reactions of Cu(NO₃)₂, Co(NO₃)₂ and Ni(NO₃)₂ with bp_pen = 1,5-bis(4-pyridyl)pentane yield three-dimensional coordination polymers [M(bp_pen)₂(NO₃)₂] with M = Cu (1), Co (2), Ni (3). These are four-connected uninodal 3D nets exhibiting a rare (6⁵.8) topology defined by metal centres (nodes) and bipyridyl ligands (edges). The reaction of CuNO₃ with bp_hep = (1,7-bis(4-pyridyl)heptane yielded a similar net in the structure of [Cu₂(bp_hep)₄(NO₃)₃](NO₃)(H₂O) (4). A characteristic of the networks of 1–4 is that their shortest edge is by far (50%) longer than the shortest distance between two neighbouring nodes. This unusual geometrical feature is facilitated by the long and flexible bp_pen and bp_hep spacers. All four investigated crystal structures are composed of three interpenetrating (6⁵.8) nets.