Structural features and dynamical behaviour of the copper(II) bis-complexes with glycine, D-alanine, D-valine, L-serine, L-aspartic acid, L-glutamic acid, L-lysine, L-proline, and sarcosine were studied by combined EPR and NMR relaxation methods. The cis and trans isomers were unambiguously assigned and characterized by EPR data. It was found that addition of a salt background has an influence on the cis–trans isomer equilibrium in favour of the formation of the cis isomer. By comparison of NMRD, DFT computations, and structural data it was shown that only one water molecule is coordinated in the axial position of these complexes. The increased exchange rates of this molecule found for Cu(L-Asp)₂ ²⁻, Cu(L-Glu)₂ ²⁻, Cu(L-LysH)₂ ²⁺, and Cu(L-Pro)₂ were attributed to its pushing out by side chain groups of the ligands. By simulation of NMRD profiles an increase of lifetimes of the copper(II) 2nd coordination sphere water molecules was revealed in the presence of additional carboxylic, alcoholic, or ammonium groups of the ligands, as well as the pyrrolidine ring of proline. The very short lifetimes of the 2nd coordination sphere water molecules (4–13 ps at 298 K) were explained in terms of the Frank–Wen structural model by the existence of cavities which draw in quickly enough water molecules from the 2nd coordination sphere.

The formation of copper(II) complexes with L- and DL-histidine (HisH) has been studied by means of pH-potentiometry and spectrophotometry over a wide range of pH (2–14), ligand-to-metal ratio (1 : 1–15 : 1), and temperature (15–55 °C) in aqueous solutions with 1.0 mol dm⁻³KNO₃ as background. Formation constants and spectral characteristics of 13 complex types were found. Fine stereoselective effects have been detected with preferential coordination of two ligands with identical configuration in Cu(His)(HisH)⁺ and opposite configuration in Cu(His)₂. The stereoselective effect for Cu(His)(HisH)⁺ is explained by hydrogen bond formation between the carboxyl and imidazolyl groups of neighboring ligands at cis-arrangement of amino groups (3N_eq-form). The opposite sign of stereoselective effect for Cu(His)₂ is derived from favourable axial coordination of the imidazole group in meso-form with cis-structure (3N_eqN_ax-form). A significant tetrahedral distortion was revealed for the first time in the prevalent cis-isomer of the Cu(L-His)₂ 4N_eq-form. These findings were confirmed by EPR data and DFT computations at the B3LYP/TZVP level. The prevalence of cis-isomers for these complexes has been assigned to the rather strong trans effect of the amino groups. The structures of other detected complexes are briefly discussed on the basis of spectroscopic data. Chemical exchange reactions in the copper(II)- L/DL-hishidine systems have been investigated by the NMR relaxation of water protons. A unique proton exchange reaction with short-term proton dissociation from the coordinated imidazolyl group catalyzed by hydroxide ion was characterised for the first time. The discovered enantioselective effects in the ligand exchange reactions between Cu(His)₂ and HisH or His⁻ species were attributed to the associative substitution mechanism.

Four new Ni^II, Co^II, Zn^II, and Cu^II complexes with the promising anti-tuberculosis drug (E/Z)-N′-((5-Hydroxy-3,4-bis(hydroxymethyl)-6-methylpyridin-2-yl)methylene)-isonicotino-hydrazide (LH) were synthesized and characterized by structural methods: single-crystal X-ray diffraction, vibrational spectroscopy, and mass spectrometry. The Ni^II, Co^II, and Zn^II metal ions form only amorphous phases with various morphologies according to mass spectrometry and IR spectroscopy. The Cu^II forms a crystalline 1D coordination polymer with the relative formula $\left\{\left[\mathrm{Cu}L\mathrm{Cl}\right]·0.5{\mathrm{H}}_2\mathrm{O}\right\}_{\infty }^1$. Even though the LH ligand in the crystalline state includes a mixture of E-/Z-isomers, only the tautomeric iminol E-/Z-form is coordinated by Cu^II in the crystal. The copper(II) complex crystallizes in the monoclinic P2₁/n space group with the corresponding cell parameters a = 16.3539(11) Å, b = 12.2647(6) Å, and c = 17.4916(10) Å; α = 90°, β = 108.431(7)°, and γ = 90°. DFT calculations showed that the Z-isomer of the LH ligand in solution has the lowest formation energy due to intramolecular hydrogen bonds. According to the quantum chemical calculations, the coordination environment of the Cu^II atom during the transfer of the molecule into the solution remains the same as in the crystal, except for the polymeric bond, namely, distorted trigonal bipyramidal. Some of the complexes investigated can be used as effective sensors in biosystems.