Possible stable structures of various 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) complexes, [Ni(bpy)₃]²⁺, [Co(bpy)₃]²⁺, [Fe(bpy)₃]²⁺ and Fe(phen)₂(NCS)₂, were optimized for different spin states of the metals, and the spectra computed for every form were compared with the experimental IR spectra of the compounds. It is demonstrated that the changes in spin states of the metals influence both geometry and vibrational spectra of the complexes. Spectral changes are predicted not only in the low frequency range, corresponding to metal–ligand vibrations, but also in the mid-IR range, where ligand vibrations are active. Detailed computational analysis in combination with the corresponding spectroscopic experiment shows that the spectral changes are of a similar character for complexes with the same ligands independent on the central metal and can be used as spectroscopic markers of the electronic state of the latter. Found spectral markers have been validated at a number of complexes of Fe(II), Ni(II), Co(II), Zn(II) and Cu(II) with bpy and phen ligands.

A novel type of cyclic P,N-ligands, pyridyl containing phospholanes, has been synthesized in a moderate yield by the reaction of primary phosphines with 1,4-dichlorobutane in a superbasic medium. A series of homo tetranuclear octahedral Cu₄I₄L₂, dinuclear tetrahedral Cu₂I₂L₃, and dinuclear “head-to-tail” Cu₂I₂L₂ luminescent complexes with these ligands were obtained. All the compounds were characterized using a range of spectroscopic and computational techniques, and in the case of some Cu₄I₄L₂ and Cu₂I₂L₃ complexes, by single crystal X-ray diffraction. The structural diversity of the obtained complexes was reflected in their photophysical properties: phosphorescence spectra of the compounds display emission in broad spectral range of 471–615 nm. TD-DFT computations allow the assignment of a single emission band around 550 nm for Cu₂I₂L₃ complexes and 471 nm for Cu₂I₂L₂ complex to a vertical triplet–singlet transition from a metal-to-ligand and halide-to-ligand charge-transfer ³(M + X)LCT excited state, whereas a second band at around 600 nm in the spectra of octahedral Cu₄I₄L₂ complexes was assigned predominantly to Cu₄I₄ cluster-centered (³CC) excited state.

New redox active 1D helical coordination polymers M(fcdHp) (M(II) = Zn(1), Co(2)) have been obtained by utilizing the 1,1′-ferrocenylenbis(H-phosphinic) acid (H2fcdHp) ligand and Zn or Co nitrate salts. Complexes 1 and 2 are isomorphic, crystallizing in the chiral space groups P4₁22 and P4₃22, respectively. Their redox, electrocatalytic and other properties are described. These compounds incorporated into carbon paste electrodes and exhibited reversible redox reactions, arising from the ferrocenyl moiety. These coordination polymers are efficient as electrocatalysts for the reduction of protons to hydrogen. Using N,N-dimethylformamidium ([DMF(H)⁺]) as the acid in the acetonitrile solution, Co CP (2) displays a turnover frequency of 300 s⁻¹, which is among the fastest rates reported for any CP electrocatalyst in CH₃CN. This high rate of catalytic reaction comes at the cost of the 820–840 mV overpotential at the potential of catalysis. As the hydrogen evolution reaction (HER) catalysts, the CPs exhibited in 0.5 M H₂SO₄ the overpotential η₁₀ of 340 or 450 mV, onset overpotential of 220 or 300 mV (vs. RHE), Tafel slope of 110 or 120 mV dec⁻¹, correspondingly for 1 and 2, and considerable long-term stability for the HER.