Curly-curly, loop-loop : homoleptic metal(ii) complexes of pyridinecarbaldehyde 4'-(2,2':6',2''-terpyridyl)hydrazones and their coordination polymers

The ligands 4-, 3- and 2-pyridinecarbaldehyde 4`-(2,2`:6`,2 ``-terpyridyl)hydrazone (1,2 and 3) have been prepared and characterized. In the homoleptic iron(II) and ruthenium( II) complexes, the nitrogen donor atoms of the pendant pyridine rings subtend an obtuse angle (approximate to 155 degrees) at the metal centre, thus providing an expanded ligand, which can be used for the assembly one-dimensional coordination polymers with an undulating backbone. Protonation of the pendant pyridine rings in [FeL2](2+) (L = 1, 2, 3) or [RuL2](2+) ( L = 1, 2) leads to a colour change from purple to blue, or red to pink, respectively, as the MLCT band shifts to a lower energy. The structural data for [Fe(H-2)(2)][PF6](3)center dot 3.5MeCN center dot 2.5H(2)O (where [H-2](+) is the monoprotonated ligand) show that the [Fe(H2)(2)](3+) cations form one-dimensional chains supported by NpyH center dot center dot center dot N-py hydrogen bonds and that the undulating chains pack to give a porous material, with channels that accommodate the anions and solvent molecules. A single-crystal X-ray diffraction determination of [Fe(NCS)(2)(Ru(1)(2))(2)][Fe-2(NCS)(6)(OEt)(2)(EtOH)(2)][NCS](2) center dot 4EtOH center dot H2O(n) reveals that pairs of [Ru(1)(2)](2+) cations connect Fe(NCS)(2) units to give a one-dimensional polymer comprising of linked metallamacrocycles.