Infrared and Raman study of some isonicotinic acid metal(II) halide and tetracyanonickelate complexes

In this study the M(IN)2Ni(CN)4 [where M: Co, Ni, and Cd, and IN: isonicotinic acid, abbreviated to M–Ni–IN] tetracyanonickelate and some metal halide complexes with the following stoichiometries: M(IN)6X2 (M: Co; X: Cl and Br, and M: Ni; X: Cl, Br and I) and Hg(IN)X2 (X: Cl, Br, and I) were synthesized for the first time. Certain chemical formulas were determined using elemental analysis results. The FT-IR and Raman spectra of the metal halide complexes were reported in the 4000–0 cm−1 region. The FT-IR spectra of tetracyanonickelate complexes were also reported in the 4000–400 cm−1 region. Vibrational assignments were given for all the observed bands. For a given series of isomorphous complexes, the sum of the difference between the values of the vibrational modes of the free isonicotinic acid and coordinated ligand was found to increase in the order of the second ionization potentials of metals. The frequency shifts were also found to be depending on the halogen. The proposed structure of tetracyanonickelate complexes consists of polymeric layers of |M–Ni(CN)4|∞ with the isonicotinic acid molecules bound directly to the metal atom.