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

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)(infinity)[Cu(NO3)(2)(mu-L)] and (2)(infinity)[Cu-2(mu(3)-I)(2)(mu-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)(infinity)[Cu(mu-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)(infinity)[Ag(mu-NO3)(2)(mu-L)], with only bridging bipyrimidine ligands is observed. At a metal excess, a 3-D framework, (3)(infinity)[Ag-3(mu(3)-NO3)(3)(mu(3)-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)(infinity)[Ag-3(CH3CN)(3)(mu(3)-L)(2)]X-3 (X = BF4 or PF6).