Polar and non-polar polytypoids based on the same polymer backbone

Abstract

A set of polytypoids (analogous to polytypes but with differences in chemical composition) provide a useful vehicle for studying the role of non-covalent interactions in establishing the packing arrangements in molecular solids. A group of 1D copolymers based on the same heterometallic {[Cubipy][Co(Orot)2bipy]}n backbone, seen in the Figure, presents both polar and centric modifications (H2Orot = orotic acid, C5H4N2O4; bipy = 2,2\'-bipyridyl, C10H8N2). In each link of the chain, Co and Cu are coordinated to one 2,2\'-bipyridyl ligand each, with the orotate groups acting as bridges. Each unit of the polymer contains hydrogen-bond donor and acceptor groups as well as aromatic groups that can participate in π…π interactions. Further coordination of copper by chloride yields a centric crystal structure in space group P(-1), while coordination by an aqua ligand at the same site yields a polar crystal with the acentric space group P1. Structural evidence points to the formation of non-covalent interactions as the driving force for the appearance of one structure or the other. The polar structure, moreover, undergoes a single crystal to single crystal transformation to produce a second polar structure with the same copolymer backbone. The structural features and non-covalent forces are compared and discussed.