Thermal and Magnetic Study of Bonding in CsCuCl3

The heat capacity and magnetic susceptibility of CsCuCl₃ powder have been measured in the ranges 5°–300° and 2°–230°K, respectively. The susceptibility deviates from Curie–Weiss behavior below 55°K and the heat capacity exhibits a sharp peak, characteristic of cooperative behavior, in the neighborhood of 10.4°K. The behavior of this system is interpreted using a molecular orbital picture in which square planar coordinated copper atoms interact via a linear antiferromagnetic exchange above 10.4°K and order three dimensionally below this temperature. The following values are found for the thermodynamic functions: ${\mathrm{S°}}_{\text{298.15}}\text{\hspace{0.17em}=\hspace{0.17em}213.401}\mathrm{J}(\mathrm{gfw}·\mathrm{deg}{)}^{\text{−1}}{\mathrm{),\; -\hspace{0.17em}(G°}}_{\text{298.15}}{\mathrm{\hspace{0.17em}-\hspace{0.17em}H}}_0\text{°)\hspace{0.17em}/\hspace{0.17em}T\hspace{0.17em}=\hspace{0.17em}120.544}\mathrm{J}(\mathrm{gfw}·\mathrm{deg}{)}^{\text{−1}}$ . A least‐squares analysis of ${\chi }_M\mathrm{vs}\text{1\hspace{0.17em}/\hspace{0.17em}(T\hspace{0.17em}+\hspace{0.17em}θ)}$ for all data above 77°K was performed. It was found that $\text{C\hspace{0.17em}=\hspace{0.17em}0.458\hspace{0.17em}±\hspace{0.17em}0.003,}\mathrm{emu}·\mathrm{deg}/\mathrm{mole}{\mathrm{,\; (\chi }}_D{\mathrm{\hspace{0.17em}+\hspace{0.17em}\chi }}_{\mathrm{TIP}}\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}0.000058\hspace{0.17em}±\hspace{0.17em}0.00003,}\mathrm{emu}/\mathrm{mole}$ and $\text{θ\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}3.50°}\mathrm{K}$ . The quoted limits of accuracy are the standard deviations.