Complexation of Cobalt(II), Nickel(II), Copper(II), and Zinc(II) Hexafluorosilicates with Nicotinamide in Aqueous Solution

The new complexes [M(NA)₂(H₂O)₄]SiF₆ ⋅ 2H₂O, where M²⁺ = Co, Ni, Zn (complexes I, II, and III, respectively), and NA = C₆H₆N₂O is nicotinamide, [Cu(NA)₂(SiF₆)(H₂O)₂] ⋅ 2H₂O (IV), and (HNA)₂SiF₆ (V) have been synthesized from aqueous solutions and studied by chemical, IR spectroscopic, and X-ray diffraction analyses. Their unit cell parameters are a = 16.2448(18) Å, b = 6.8834(8) Å, c = 10.0767(11) Å, β = 102.765(3)°, V = 1098.92 ų, space group C2 for I; a = 16.1591(7) Å, b = 6.8777(3) Å, c = 10.0314(5) Å, β = 102.410(1)°, V = 1088.82 ų, space group C2 for II; a = 16.2265(6) Å, b = 6.8965(3) Å, c = 10.0696(5) Å, β = 102.390(1)°, V = 1100.60 ų, space group C2 for III; a = 6.5915(4) Å, b = 7.7670(4) Å, c = 10.1506(5) Å, α = 110.7390(10)°, β = 105.824(2)°, γ = 95.448(2)°, V = 456.868 ų, space group P\(\overline{1}\) for IV; and a = 14.1904(7) Å, b = 9.0468(4) Å, c = 11.8160(7) Å, β = 106.277(2)°, V = 1456.1 ų, space group C2/c for V. Complexes I–III are isostructural and represent ionic compounds formed by hexafluorosilicate anions and complex cations. The coordination polyhedron of the metal is a slightly distorted octahedron built of the O atoms of four coordinated water molecules and the two N atoms of two pyridine rings of two nicotinamide molecules in trans positions of the polyhedron. Complex IV has a polymeric chain structure. The coordination polyhedron of the copper cation represents an octahedron, which is elongated along its axis and built of the two N atoms of two pyridine rings of two nicotinamide molecules, the two O atoms of coordinated water molecules, and the two F atoms of hexafluorosilicate anions acting as bridges between neighboring cations. In the structure of complex V, the nitrogen atom of the pyridine ring HNA⁺ is protonated. The geometry of hexafluorosilicate anions is identical in all the five complexes. The structures have branched networks of hydrogen bonds.