A unique example of a co-crystal of [Ag(atr) 2][Cr(dipic) 2] (dipic = dipicolinate; atr = 3-amino-1H-1,2,4-triazole) and dinuclear [Cr(H 2O)(dipic)( μ-OH)] 2, with different coordination environment of Cr(III) ions

Abstract

Treatment of a neutral aqueous solution of dipicolinic acid (dipicH 2), 3-amino-1H-1,2,4-triazole (atr) and CrCl 3·6H 2O in the presence of AgNO 3 (in molar ratio 1:1:1:3) under hydrothermal condition led to the formation of a co-crystal of {[Ag(atr) 2][Cr(dipic) 2]} 2·[Cr(H 2O)(dipic)( μ-OH)] 2·4H 2O ( 1). Compound 1 was characterized by elemental analyses, IR and UV–Vis spectroscopy as well as X-ray diffraction studies. The structure consists of two [Ag(atr) 2] + cations, two [Cr(dipic) 2] − anions, one co-crystallized neutral dinuclear chromium(III) complex, [Cr(H 2O)(dipic)( μ-OH)] 2, and four co-crystallized water molecules. Silver(I) ion in [Ag(atr) 2] + is coordinated by two monodentate 3-amino-1H-1,2,4-triazole ligands, bound via endocyclic nitrogen atoms, in a linear fashion. Chromium(III) ion is octahedrally coordinated by two O,N,O-tridentate dipicolinate ligands in anionic complex. Each chromium(III) ion in neutral dinuclear complex, [Cr(H 2O)(dipic)( μ-OH)] 2, is octahedrally coordinated by one O,N,O-tridentate dipicolinate ligand, one water molecule and two bridging μ-OH ions in cis position. Thermal methods (TGA/DTA) confirm the number of co-crystallized water molecules in 1.