An unprecedented mononuclear double helicate with a square planar metal ion

Reactions of the 1:2 condensate (L) of benzil dihydrazone and 1-methyl-2-imidazole carboxaldehyde with Cd(ClO4)2 · xH2O and CdI2 yield [CdL2](ClO4)2 (1) and LCdI2 (2), respectively. The yellow ligand L, and its yellow complexes 1 and 2 are characterized by NMR and single crystal X-ray diffraction. Though L contains four N-donor centers, 1 is found to be a four-coordinate double helicate with a square planar Cd(II)N4 core and 2 a spiral coordination polymer with tetrahedral Cd(II)N2I2 moieties. The bidentate nature of L and the occurrence of the square planar coordination of Cd(II) is explained by DFT calculations.