‘All twisted up’: a dinuclear helicate with a highly contorted pyridazine bridge

Two homotopic homostranded dinuclear helicates displaying tripodal coordination at each metal atom were synthesised by reaction of bis-3,6-(di-2-pyridylmethyl)pyridazine with M(BF4)2 salts (where M=Ni, Cu), and characterised by single crystal X-ray crystallography. The structures represent closely related examples of this class of helicate, possess a very compact overall size and differ primarily in the coordination geometry of the metal atom. In the nickel helicate the ligand strands adopt a highly contorted bridging geometry which is relieved in the corresponding square pyramidal copper helicate by releasing one of the metal–nitrogen interactions.