New complexes of Zn(II) and Cd(II) halides with 1,8-diaminonaphthalene: Synthesis, structure, and thermal stability

A series of isostructural metal-organic compounds of a [MeX(1,8-DAN) 2 ]X general formula (where Me denotes Zn or Cd, X = Cl, Br or I, and 1,8-DAN = 1,8-diaminonaphthalene) was synthesized and characterized. The compounds were obtained as powders and only for [CdBr(1,8-DAN) 2 ]Br a single crystal suitable for diffraction-based structure determination was successfully grown. The crystal structure reveals that the compound crystallizes in the monoclinic space group P 2 1 /c (No. 14) and is built of [CdBr(1,8-DAN) 2 ] + units organized into layers. One half of the halide anions are placed between the complex cations compensating their positive charge. X-ray powder diffraction (XRPD) patterns and infrared (IR) spectra confirm that all the studied compounds are isostructural which allowed using the structure model obtained for [CdBr(1,8-DAN) 2 ]Br as the starting point of the structure analyses of other compounds. Unit cell sizes of the studied compounds change according to the changes in the sizes of the ions with unit cell volume higher for cadmium complexes than for the zinc ones. The volume is also increasing in the order from chlorine to iodine. Additionally, thermal stability (175 - 225 degrees C) and decomposition routes of the materials were investigated using non-ambient XRPD measurements while their crystallite habit was studied using SEM images (thin plates of various degrees of crystallization).