Bidentate ligands, cyanide-bridged complexes

As noted previously, a second large class of cyanide-bridged trinuclear complexes is characterized by a structure in which the central metal ion is either solvated or protected by one tetradentate, two bidentate, or four monodentate blocking ligands (Table IV). In the majority of these compounds, the peripheral building blocks act as donors of bridging cyanides to the central metal ion. 

Another type of bridged systems contains the central metal atom in the oxidation state + 3. Appropriate bridging ligands are negatively charged molecules as e.g. cyanide, thiocyanate or azide. The displacement of the axial anion X" by bidentate CN , SCN or NJ (L ) in a coordinatively unsaturated compound PcMX (X = Cl, OAc, CCI3COO) provides a direct path to coordination oligomers [PcML] . This route has been utilized for the synthesis of cyano complexes [PcM(CN)] (M = Fe [116], Mn [117]), thiocyanato complexes [PcM(SCN)] (M = Fe [66], Mn [118]), Co [119], and azido complexes [PcM(N3)] (M = Cr [118], Mn [118]). 

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