Group 12 Metal Complexes of Semirigid 2,6-Pyridinediyl­bis(3-pyridinyl)­methanone: Role of Counteranions and Solvent in Product Formation

In a series of nine group 12 metal complexes of 2,6-pyridine­diyl­bis­(3-pyridinyl)­methanone (abbreviated as L), namely, [Cd­(L)2­Cl2] (1), [Cd­(L)2­(NO3)2]·3.5H2O (2), [Cd­(L)2­(H2O)2]­(NO3)2 (3), [Cd­(L)2­(H2O)2]­(ClO4)2·H2O (4), {[Cd­(L)­(H2O)2]­(ClO4)2·1.5H2O} (5), {[Cd­(L)2­SO(H2O)]·2.8H2O} (6), [Cd­(L)(CH3­CO2)2] (7), [Zn­(L)2­(CH3­CO2)2] (8), and [Hg­(L)2­(CH3­CO2)2] (9), the semirigid multidentate ligand L exhibits flexible ligation modes I–IV in response to the cooperative effect of counteranions and solvent medium, leading to mononuclear (14), helical-chain (6), zigzag-chain (7), and 3D net (5) coordination motifs. The presence of the ancillary aqua ligand is essential for the crystallization of 3 and 5 by addition of deionized water to an organic mixed-solvent medium containing 2 and 4, respectively. The acetate complexes 7 (Cd2+), 8 (Zn2+), and 9 (Hg2+) are isostructural. Unconventional anion−π­(pyridine), CO···CO, O­(NO3/ClO4)···CO, and cohesive nitrate···nitrate interactions are manifested in supramolcular aggregations of the present series of crystalline complexes.