Synthesis, crystal structures, and luminescence spectra of the coordination compounds of cadmium(II) iodide with hexamethylenetetramine

Coordination compounds Cd_1.5I₃(HMTA) · H₂O] (I) and CdI₂(HMTA) · H₂O] (II) are synthesized by the reaction of CdI₂ with hexamethylenetetramine (HMTA, C₆H₁₂N₄) with the 1: 1 ratio in ethanol, and their structures are determined. The crystals of compound I are triclinic, space group P $ \bar 1 $ , a = 8.027(1), b = 9.391(1), c = 10.382(1)?, ?? = 66.64(1)°, ?? = 86.18(1)°, ?? = 73.63(1)°, V = 749.2(1) ?³, ??_calcd = 3.136 g/cm³, Z = 2. The crystals of compound II are triclinic, space group P $ \bar 1 $ , a =7.713(1), b = 8.192(1), c = 12.101(1)?, ?? = 80.32(1)°, ?? = 89.57(1)°, ?? = 7.30(1)°, V = 725.0(1) ?³, ??_calcd = 2.402 g/cm³, Z = 2. Structure I includes two types of cadmium complexes. The Cd(1) atom is coordinated through the octahedral mode by three pairs of the I, N(HMTA), and O(H₂O) atoms. The coordination polyhedron of the Cd(2) atom is a distorted tetrahedron (three I atoms and one N atom). The structure contains infinite strips consisting of tetranuclear cyclic fragments joined by the Cd(1) atoms due to the bridging iodine and nitrogen atoms. In structure II, the Cd atom is coordinated through the tetrahedral mode by two iodide ions and the N(HMTA) and O(H₂O) atoms. The interaction between the complexes occurs due to hydrogen bonds O-H??N to form supramolecular chains along the direction 010]. In each HMTA molecule, one of four nitrogen atoms is a proton acceptor in the hydrogen bonds, one nitrogen atom is coordinated, and two N atoms are terminal. Compound II in the solid state has photoluminescence with maxima at 443, 470, and 518 nm.