Low-Temperature Heat Capacity of Ni(CH3COO)2· 4H2O

The heat capacity of Ni${\left(\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{O}\mathrm{O}\right)}_2$·4${\mathrm{H}}_2$O has been measured between 0.43 and 10.73 K revealing a Schottky anomaly with $C_{pmax}=1.182\mathrm{}$ cal/mole K at $T_{max}=1.98\mathrm{}$ K. An octahedral crystal field with axial and rhombic distortions plus spin-orbit interaction split the triplet ground state completely, the upper components lying $3.52k$ and $8.06k$ above the lowest. The lattice contribution to $C_p$ is estimated to be $3.69\times {10}^{-4\mathrm{}}{T}^3$ cal/mole K. Comparison of the ground-state splittings with those inferred from magnetic-susceptibility data suggests the presence of a small interaction between ${\mathrm{Ni}}^{++}$ ions. This is described by an antiferromagnetic molecular-field coefficient $\frac{A}{k}=+0.08\mathrm{}$ K which may be largely of dipolar origin.