The [Os-III(CN)(6)](3-) anion is prepared by chemical oxidation in aqueous solution and isolated as yellow prisms of [Ph4P](3)[OSIII(CN)(6)]center dot 6H(2)O (1). This species crystallizes in the triclinic space group Of with cell parameters a = 13.7609(11) angstrom, b = 16.2275(13) angstrom, c = 17.0895(14) angstrom, alpha = 91.4040(10)degrees, beta = 109.3600(10)degrees, gamma = 102.3970(10)degrees, V = 3497.4(5) angstrom(3), and Z = 2. The slightly distorted octahedral moiety displays Os-C and C-N bond lengths that average 2.058 and 1.146 angstrom, respectively, Spin-orbit-coupling splitting of the ground-state term dominates the NIR region of the electronic spectrum and the magnetic behavior of 1. The experimental information points to higher spin delocalization over the coordinated cyanides than in [Fe-III(CN)(6)](3-).