Self-assembly of square planar rhodium carbonyl complexes with 4,4-disubstituted-2,2’-bipyridine ligands

The impact of non-covalent interactions and reaction conditions on formation and self-assembly of ionic pairs of Rh complexes with 4,4’-disubstituted bipyridine ligands ([Rh(L1)(CO)2][Rh(CO)2Cl2])n (1), [Rh(L1)2Cl2][Rh(CO)2Cl2] (2), ([Rh(L1)(CO)2][Rh(CO)2Cl2][Rh(L1)(CO)2]n([Rh(CO)2(Cl)2])n) (3), ([Rh(L2)CO2] [Rh(CO)2Cl2])n∙EtOH (4), ([Rh(L2)(CO)2])n ([Rh(CO)2Cl2])n (5) (L1 = 4,4’-dimethyl-2,2’-bipyridine, L2 = 4,4’-diamine-2,2’-bipyridine) have been studied. Packing of square planar Rh complexes favor formation of one-dimensional chains. In structure 1, the polymeric chain is formed by the alternating cationic [Rh(L1)(CO)2]+ and the anionic [Rh(CO)2Cl2]- units leading to a neutral pseudo linear 1D chain with metallophilic contacts. In compound 2, the square planar [Rh(CO)2Cl2]- anions form only dinuclear anion pairs instead of polymeric chains. Structure 3 consists of an alternative arrangement of cations and anions compared to 1, the repeating sequence of ions being [Rh(L1)(CO)2]+[Rh(CO)2Cl2]- [Rh(L1)(CO)2]+. The overall positive charge is balanced by outlying [Rh(CO)2Cl2]- counterion. In structures 4 and 5, only the cationic [Rh(L2)(CO)2]+ units are involved in formation of the polymeric chains and the positive charge of the chain is balanced by the [Rh(CO)2Cl2]- (4 and 5). In structures 1 and 3 the metallophilic interactions have an important role in chain formation. In 4 and 5, the arrangement of the square planar building blocks is dominated by the hydrogen bonding between the NH2-substituents of the bipyridine ligand and the chlorides of the anion or solvent of crystallization.