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