Abstract
NiC2O4·2NH3 was synthesized hydrothermally, and its structure was solved by single-crystal X-ray diffraction. Accordingly, NiC2O4·2NH3 crystallizes in the centrosymmetric monoclinic space group C2/m (no. 12) with lattice parameters of a = 10.767(5) Å, b = 5.414(2) Å, c = 5.005(2) Å and β = 96.3(4)°. The NiO4N2 octahedra align in a parallel pattern through shared C2O42− units and thus form linear one-dimensional (1D) chains extending along the b-axis. These linear chains are separated along the a-axis by NH3 molecules and weakly coupled with each other through hydrogen bonding. 1H and 13C solid-state NMR revealed isotropic resonances at −115(3) ppm and −312(5) ppm, respectively, for NiC2O4·2NH3, the ammonia protons and oxalate carbons being paramagnetically shifted via the Fermi contact interaction from d8 Ni(II). Room-temperature paramagnetic shift anisotropies of 400(30) ppm for 1H and 780(40) ppm for 13C were determined from simulations of the spinning sideband manifolds. Magnetic susceptibility shows a broad maximum around T(χmax) = 35 K, suggesting well-developed spin–spin correlations along the Ni–C2O4–Ni chains. No long-range order is observed down to 2 K, which is further confirmed by heat capacity results. The intrachain interaction J/k of −31.0 K is estimated by fitting the data with a 1D spin chain model. The isothermal magnetization curve at 2 K shows a field-induced phase transition around 5 T. The magnetization value at 9 T is only 0.087 μB, which is far from saturation. All magnetic results indicate NiC2O4·2NH3 is a good 1D chain quantum antiferromagnet.
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