CRYSTAL-STRUCTURE SPECTROSCOPIC, MAGNETIC, AND ELECTRICAL-PROPERTIES OF COPPER(II) DIMER, MELAMINIUM CHLORO6CU2, EXHIBITING NEW STACKING INTERACTION

The (C3N,H8)Cu2Cl6c ompound (C3N6H8= melaminium dication, hereafter abbreviated as melH2) has been synthesized and its crystal structure determined. A number of its physical properties were examined, including its electronic and vibrational spectra, as well as magnetic and electrical behavior. The crystals are monoclinic, space group E 1 / c ,w ith a = 6.6600 (1) A, b = 10.0598 ( 2 ) A, c = 19.2691 (12) A, = 96.011 (3)O, Z = 4, dald = 2.42 g c ~ n -a~n,d dmad = 2.45 gem-'. The structure, solved by direct methods and refined by least-squares calculations to R = 3.9%, consists of melaminium dications and cuzc162- dimers stacked to form infinite chains in a manner not previously observed. The coordination of the copper atoms may be described as distorted square pyramidal. Electronic and vibrational results are discussed on the basis of the crystal structure. The compound exhibits predominantly antiferromagnetic exchange interactions. An intradimer singlet-triplet energy splitting of M/k = 54 K is deduced, with weaker ferromagnetic coupling between dimers. A comparison with the magnetic behavior of other CU~CI,d~im- ers is given. Electrical conductivity measurements classify the compound as an insulating material.