Naphthyridine–imidazole hybrid ligands for the construction of multinuclear architecture

Reaction of 2-imidazolyl-5,7-dimethyl-1,8-naphthyridine (L1) with [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) affords the dinuclear complex [Rh(COD)Cl]2(μ-L1) (1). Elimination of chloride from the metal coordination sphere leads to a self-assembled tetranuclear macrocycle [Rh(COD)L1]4[ClO4]4 (2). A subtle alteration in the ligand framework results in the polymeric chain compound {Rh(COD)(L2)}n(PF6)n (3) (L2 = 2-imidazolyl-3-phenyl-1,8-naphthyridine). In all these complexes, the imidazole nitrogen and one of the naphthyridine nitrogen (away from the imidazole substituent) bind the metal. The ‘parallel’ and ‘perpendicular’ dispositions of nitrogens are observed in these compounds contributing to different Rh···Rh separations. The L1 ligand adopts planar configuration, whereas the naphthyridine–imidazole rings deviate from planarity in L2 yielding a polymeric structure. The extent of deviation is less in the polymeric structure {Mo2(OAc)4(L2)}n (4) in which the ligand exhibits weak axial interactions to the metal.