Quasi-two-dimensional magnetism in spin- square lattice compound Cu[C₆H₂(COO)₄][H₃N-(CH₂)₂-NH₃] · 3H₂O

We report the crystal growth and structural magnetic properties of quasi two-dimensional $S=1/2$ quantum magnet Cu[C$_6$H$_2$(COO)$_4$][H$_3$N-(CH$_2$)$_2$-NH$_3$]$\cdot$3H$_2$O. It is found to crystallize in a monoclinic structure with space group $C2/m$. The CuO$_4$ plaquettes are connected into framework $ab$-plane through anions [C$_6$H$_2$(COO)$_4$]$^{4-}$ (pyromellitic acid). [H$_3$N-(CH$_2$)$_2$-NH$_3$]$^{2+}$$\cdot$3H$_2$O groups located between layers provide weak interlayer connection via hydrogen (H...O) bonds. temperature dependent susceptibility well described by frustrated square lattice ($J_1-J_2$) model nearest-neighbor interaction $J_1/k_{\rm B} \simeq 5.35$ K next-nearest-neighbor $J_2/k_{\rm -0.01$ K. Even, our analysis using rectangular ($J_{1a,b}-J_2$) confirms almost isotropic nearest-neighbour interactions ($J_{\rm 1a}/k_{\rm 5.31$ $J_{\rm 1b}/k_{\rm 5.38$ K) B}\simeq-0.24$ Further, isothermal magnetization at $T=1.9$ also non-frustrated 5.2$ Based on $J_2/J_1$ ratio, compound can be placed N\'{e}el antiferromagnetic state $J_1 - J_2$ phase diagram. No signature long-range-order was detected down 2