Bi-nuclear metal complexes of 2,6-bis(1,4,7-triazacyclonon-1-yl-methylene)pyridine with zinc(II), copper(II), and nickel(II)

The coordination chemistry of 2,6-bis(1,4,7-triazacyclonon-1-ylmethyl)pyridine (Lpyx, 1) has been investigated and shown to yield bi-nuclear metal complexes in the presence of zinc(II), copper(II), or nickel(II) ions. The reaction of (Lpyx)·7HCl (2) with Zn(NO3)2 gave the monomeric [Zn2(-Cl)2(Lpyx)(H2O)](ClO4)2 (3) in which the ligand encapsulates a Zn2(-Cl)2 moiety. Similar treatment of 2 with Cu(NO3)2 gave a bi-nuclear complex cation which exists as a 1:1 co-crystal {[Cu(Cl)(Lpyx)Cu(-Cl)(Cl)](BF4)(H2O)}2 and {[Cu(Cl)(Lpyx)Cu(-Cl)(H2O)](BF4)2(H2O)}2 (4) with two discrete CuII centres bridged by the Lpyx ligand and dimerised through an unsymmetrical Cu2(-Cl)2 interaction. Similarly, reaction of 2 with Ni(NO3)2 also gave a dimeric complex {[Ni(Cl)(-Cl)(Lpyx)Ni(NO3)(H2O)](PF6)}2 (5) containing two discrete NiII centres with dimerisation occurring through a symmetrical Ni2(-Cl)2 interaction. In all cases, the Lpyx ligand binding is unsymmetrical between the two metal centres being tridentate to one and tetradentate to the other through an additional coordination of the pyridyl linker