Pseudopolymorphism deriving from variable π⋯π stacking modes: Discrete tetranuclear cadmium(II) phosphonate clusters with 1,10-phenanthroline as auxiliary ligand

Hydrothermal reactions of Cd(ClO4)2 or CdSO4 with [(dibenzylamino)-methyl]-phosphonic acid (H2L) as well as 1,10-phenanthroline (phen) afforded two tetranuclear cadmium(II) phosphonate cluster compounds with the formula of [Cd4(L)4(phen)4]·nH2O (n = 4 or 6). The two compounds are supramolecular pseudoisomers which derive from two different π⋯π stacking modes of the 1,10-phenanthroline ligands in them, and such supramolecular isomerism is induced by the distinct counter-ions of the starting cadmium source.