Two bimetallic tetranuclear three-blade propeller shaped complexes with helical water chains: Crystal structures, second-order nonlinear optical (NLO) properties and thermal decomposition mechanisms

Two isostructural bimetallic tetranuclear chiral complexes, [K(18-crown-6)]3[Fe(ox)3] · 9H2O and [K(18-crown-6)]3[Cr(ox)3] · 9H2O, crystallize in rhombohedral R3 space group, the tetranuclear cluster is respectively built from one [Fe(ox)3]3− or [Cr(ox)3]3− species with three K(18-crown-6 ether) supramolecular cations linked by oxalate groups, and lattice water molecules form the double helical chains. Two complexes are second-harmonic-generation (SHG) active with the SHG response about 0.5 times that of urea.