The first known paramagnetic, tetrahedral cyanide complex, [Mn-II(CN)(4)](2-), is formed by the photoinduced decomposition of [Mn-IV(CN)(6)](2-) in nonaqueous solutions or by thermal decomposition in the solid state. In acetonitrile or dichloromethane, photoexcitation into the ligand-to-metal charge transfer band (lambda (max) = 25 700 (-l), epsilon = 3700 cm(-1) M-1) causes the homolytic cleavage of cyanide radicals and reduction of Mn-IV. Free cyanide cm in dichloromethane leads to the isolation of polycyanide oligomers such as [C12N12](2-) and [C4N4](-). which was crystallographically characterized as the PPN+ salt C40H30N5P2: monoclinic space group = I2/a, a = 18.6314(2) Angstrom, b = 9.1926(1) Angstrom, c = 20.8006(1), beta =106.176(2)degrees, Z = 4]. In the solid state Mn-IV-CN bond homolysis is thermally activated above 122 OC, according to differential scanning calorimetry measurements, leading to the reductive elimination of cyanogen. The [Mn-II(CN)(4)](2-) ion has a dynamic solution behavior, as evidenced by its concentration-dependent electronic and electron paramagnetic spectra, that can be attributed to aggregation of the coordinatively and electronically unsaturated (four-coordinate, 13-electron) metal center. Due to dynamics and lability of [Mn-II(CN)(4)](2-) in solution, its reaction with divalent first-row transition metal cations leads to the formation of lattice compounds with both tetrahedral and square planar local coordination geometries of the metal ions and multiple structural and cyano-linkage isomers. alpha -Mn-II[Mn-II(CN)(4)]_ has an interpenetrating sphaleriteor diamond-like network structure with a unit cell parameter of a = 6.123 Angstrom (P43m space group) while a beta -phase of this material has a noninterpenetrating disordered lattice containing tetrahedral [Mn-II(CN)(4)](2-). Linkage isomerization or cyanide abstraction during formation results in alpha -Mn-II[Co-II(CN)(4)] and Mn-II[Ni-II(CN)(4)] lattice compounds, both containing square planar tetracyanometalate centers. alpha -Mn-II[Co-II(CN)(4)] is irreversibly transformed to its beta -phase in the solid state by heating to 135 degreesC, which causes a geometric isomerization of [Co-II(CN)(4)](2-) from square planar (nu (CN) = 2114 cm(-1), S = (1)/(2)) to tetrahedral (nu (CN) = 2158 cm(-1), S = (3)/(2)) as evidenced by infrared and magnetic susceptibility measurements. Mn-II[Ni-II(CN)(4)] is the only phase formed with Ni-II due to the high thermodynamic stability of square planar [Ni-II(CN)(4)](2-).