Co-ordination engineering: when can one speak of an “understanding”? Case study of the multidentate ligand 2,2′-dimethyl-4,4′-bipyrimidine †

Abstract

The mode of co-ordination of the multidentate ligand 2,2′-dimethyl-4,4′-bipyrimidine (L) was found to depend on the metal ion, the crystallization conditions, the metal-to-ligand ratio, and the anion. With nickel a chelating co-ordination through the endo-dentate nitrogen donor set is observed in the molecular complex [NiCl2(L)(H2O)]·CH3NO2, derived from hot CH3NO2. With Cu(NO3)2 and CuI–CH3CN one- and two-dimensional (1-D and 2-D) co-ordination polymers of formula ∞ 1[Cu(NO3)2(µ-L)] and ∞ 2[Cu2(µ3-I)2(µ-L)] are obtained, where the bipyrimidine ligand is solely bridging through the two exo-dentate nitrogen atoms. On the other hand, a synthesis from CuI and crystallization from hot dimethyl sulfoxide leads to a 1-D iodide-bridged co-ordination polymer ∞ 1[Cu(µ-I)(L)] with a chelating ligand. With AgNO3 two different types of co-ordination polymers were found, depending on the silver-to-ligand ratio. At a 1∶1 ratio in the presence of a co-ordinating anion a 2-D network, ∞ 2[Ag(µ-NO3)2(µ-L)], with only bridging bipyrimidine ligands is observed. At a metal excess, a 3-D framework, ∞ 3[Ag3(µ3-NO3)3(µ3-L)2], forms where L functions both as a chelating and as bridging ligand. A tetradentate co-ordination mode of L towards silver is also found with non-co-ordinating anions, such as BF4– and PF6–, and gives rise to the isostructural 2-D co-ordination polymers of formula ∞ 2[Ag3(CH3CN)3(µ3-L)2]X3 (X = BF4 or PF6).