Interpenetrating Three-Dimensional Diamondoid Lattices and Antiferromagnetic Ordering (Tc = 73 K) of MnII(CN)2

Thermolysis of either the 3-D, bridged-layered [NEt4]­MnII3(CN)7 or 2-D, layered [NEt4]2MnII3(CN)8 forms MnII(CN)2. Rietveld analysis of the high-resolution synchrotron powder X-ray diffraction data determined that MnII(CN)2 is cubic [a = 6.1488(3) Å] (space group = Pn3̅m) consisting of two independent, interpenetrating networks having the topology of the diamond lattice. Each tetrahedrally coordinated MnII is bonded to four orientationally disordered cyanide ligands. MnII(CN)2 magnetically orders as an antiferromagnet with a Tc = 73 K determined from the peak in d­(χT)/dT. Exchange coupling estimated via the mean field Heisenberg model from the transition temperature (J/kB = −4.4 K) and low temperature magnetic susceptibility of the ordered phase (J/kB = −7.2 K) indicate that MnII(CN)2 experiences weak antiferromagnetic coupling. The discrepancy between those estimates is presumably due to local anisotropy at the MnII sites arising from the CN orientational disorder or interactions between the interpenetrating lattices.