Syntheses, characterization, thermal properties and single crystal structure determination of cobalt(III) complexes with 2,2′-biimidazole and 1,10-phenanthroline ligands

A novel mixed ligand cobalt(III) complex, [Co(phen)2(Hbiim)]Cl2·10H2O, has been utilized in the syntheses of three halogenocadmate(II) complexes [Co(phen)2(Hbiim)][CdCl4]·2H2O (1), [Co(phen)2(Hbiim)][CdBr4]·1.5H2O (2) and [Co(phen)2Hbiim][CdI4]·C3H6O·0.5H2O (3) (where phen = 1,10-phenanthroline and Hbiim = mono-anionic 2,2′-biimidazole). The complex salts 1–3 have been characterized by elemental analyses, spectroscopic techniques (UV–Vis, FT-IR and NMR) solubility product and conductivity measurements. Thermal behaviors and single crystal X-ray structure determination of the complex salts 1–3 are also discussed. The complex salts 1 and 2 are isomorphous and crystallize in space group P1¯, while 3 crystallizes in the monoclinic crystal system with the space group Pc. The two crystallographically different complex cations in 3 correspond to Λ and Δ optical isomers. The crystals of 1 and 2 are centrosymmetric and so both isomers cohabit in the solid state as a racemate. The spatial disposition of the cations in the three complex salts, derived from the existence of the optical isomers, favours the formation of hydrogen bonding, as revealed by the presence of a R22(10) ring motif. The packing analyses of complex salts 1 and 2 shows the presence of open channels in which solvent molecules of crystallization are residing, while in 3 an ABCABC…type layered packing arrangement of constituents has been observed. Non-covalent interactions like C–H···X(Cl/Br/I), C–H···O (second sphere interactions) and O–H···O (water) play a key role in the stabilization of the crystal lattices.

Three novel cobalt(III) complexes, [Co(phen)2(Hbiim)][CdCl4]·2H2O, [Co(phen)2(Hbiim)][CdBr4]·1.5H2O and [Co(phen)2(Hbiim)][CdI4]·C3H6O·0.5H2O, have been synthesized and characterized. The packing analysis has revealed the presence of open channels in which solvent molecules of crystallization are residing in two complexes, while in third complex an ABCABC…type layered packing has been observed. Non-covalent interactions, like C–H···X(Cl/Br/I), play a key role in the stabilization of the crystal lattices.Figure optionsDownload as PowerPoint slideHighlights
► Three new cobalt(III) complexes containing cadmate(II) anions have been synthesized.
► Single crystal X-ray structure determination of these complexes has been described.
► Non-covalent interactions are playing crucial role in crystal lattice stabilization.
► Water molecules are trapped in open channels formed by cationic and anionic groups.