Crystal structure and magnetic susceptibility of copper (II) chloride tetramethylsulfoxide [Cu${\mathrm{Cl}}_2$(TMSO)] and copper (II) chloride monodimethylsulfoxide [Cu${\mathrm{Cl}}_2$(DMSO)]: Ferromagnetic spin-½ Heisenberg linear chains

The crystal structures of the title compounds [${\mathrm{C}}_4$ ${\mathrm{H}}_8$SO (TMSO), ${\mathrm{C}}_2$ ${\mathrm{H}}_6$SO (DMSO)] have been determined. The TMSO salt is orthorhombic [space group $\mathrm{Pbca}$, $a=13.844\mathrm{}\left(10\right)\mathrm{}$, $b=6.418\mathrm{}\left(12\right)\mathrm{}$, and $c=17.480\mathrm{}\left(16\right)\mathrm{}$ Å] while the DMSO salt is monoclinic [space group $\frac{P{2}_1}{c}$, $a=7.774\mathrm{}\left(1\right)\mathrm{}$, $b=13.557\mathrm{}\left(3\right)\mathrm{}$, $c=6.475\mathrm{}\left(1\right)\mathrm{}$ Å, and $\beta =103.83\mathrm{}\left(1\right)\mathrm{}°$]. Each contain linear chains of Cu ions with three bridging ligands (2 C1, 1 O) between each pair of Cu ions. The bridging Cu-$L$-Cu angles are ∼ 87° for the symmetrical bridges and ∼ 80° for the asymmetrical bridges. In each salt, the copper coordination geometry is severely distorted from octahedral with four short Cu-ligand bonds (three chlorine and one oxygen) and two long Cu-ligand bonds (one chlorine and one oxygen). Adjacent chains are well isolated from each other by the sulfoxide groups in one direction, but short sulfur-sulfur contacts occur between adjacent chains in the other direction. The susceptibility of the salts has been measured between 2.0 and 300 K on a PAR vibrating-sample magnetometer and on a Faraday balance. The high-temperature data show positive deviation from Curie behavior, indicative of ferromagnetic coupling. However, considerable magnetic interactions between chains exist and the $\chi T$ vs $T$ plots show maxima at low temperature. The data have been analyzed with several one-dimensional models. The best fit is obtained with an Heisenberg linear chain with ferromagnetic interaction ($\frac{J}{k}=39\mathrm{}°$K, TMSO; $\frac{J}{k}=45\mathrm{}°$K, DMSO) with a mean-field correction for the antiferromagnetic interchain interactions ($\frac{Z{J}^{\prime }}{k}=-1.6\mathrm{}°$K, TMSO; $\frac{Z{J}^{\prime }}{k}=-4.0\mathrm{}°$K, DMSO). Thus, the relevant ratio defining the ideality of the system, $\frac{J}{J^{\prime }}$, is ∼ 50 for the TMSO salt and ∼ 25 for the DMSO salt.