Binding of zinc(II) macrocycles toward carboxylate ligands

Three new zinc(II) complexes, Zn( L1 )(NO 3 ) 2 (1) , {[Zn( L1 )(fumarate)]·2H 2 O} n (2) and {[Zn( L2 )(fumarate)]·DMF} n (3) ( L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0 1.18 ,0 7.12 ]docosane) have been synthesized and characterized by analytical, spectroscopic, thermal and X-ray diffraction methods. The structure of the discrete neutral complex (1) shows that the central zinc(II) ion is coordinated axially by two nitrate ligands. In the structures (2) and (3) , the carboxylate groups of the bridging fumarate ligands are coordinated to zinc(II) macrocycles, resulting in the formation of 1D coordination polymers. Apart from the fairly strong Zn–O bonds in (2) and (3) , it is observed that the hydrogen bonds between the pre-organized N–H groups of the macrocycle and axial ligands appear to be important for the design and development of metal complexes having a strong Zn–O bond.