Structural and magnetic properties of spin-1/2 dimer compound Cu₂(IPA)₂(DMF)(H₂O) with a large spin gap

We present the synthesis and a detailed investigation of structural and magnetic properties of metal-organic compound Cu₂(IPA)₂(DMF)(H₂O) by means of x-ray diffraction, magnetization, and heat capacity measurements. Single crystals of the title compound were synthesized by judicious selection of organic ligand and employing a selective hydrothermal reaction route. It crystallizes in an orthorhombic structure with space group Cmca. The structural analysis revealed that two Cu²⁺ ions are held together by the organic component (-O-C-O-) in a square paddle-wheel to form spin dimers which are aligned perpendicular to each other and are further coupled through organic ligands (isophthalic acid) forming two-dimensional layers. Temperature dependent magnetic susceptibility $\chi \left(T\right)$ could be described well using spin-1/2 dimer model. The spin susceptibility ${\chi }_{\text{spin}}\left(T\right)$ shows an exponential decrease in the low temperature region, below the broad maximum, confirming the singlet ground state with a large spin gap of $\Delta /k_{\text{B}}\simeq 414$ K. The heat capacity C _p measured as a function of temperature also confirms the absence of magnetic long-range-order down to 2 K. (paper)