Interpenetrating three-dimensional coordination networks with a rare 4-connected (6(5).8) topology and unusual geometrical features

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 (6(5).8) topology defined by metal centres (nodes) and bipyridyl ligands (edges). The reaction of CuNO3 with bp_ hep = (1,7-bis(4pyridyl) heptane yielded a similar net in the structure of [Cu-2(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 (6(5).8) nets.