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Three new Pt(II) complexes [(dpp-DAD)PtCl2] (I), [(Mes-DAD(Me)2)PtCl2] (II) and [(dpp-DAD(Me)2)PtCl2] (III) were synthesized by the direct reaction of [(CH3CN)2PtCl2] and corresponding redox-active 1,4-diaza-1,3-butadienes (DAD). The compounds were isolated in a single crystal form and their molecular structures were determined by X-ray diffraction. The purity of the complexes and their stability in solution was confirmed by NMR analysis. The Pt(II) ions in all compounds are in a square planar environment. The electrochemical reduction of complexes I–III proceeds in two successive cathodic stages. The first quasi-reversible reduction leads to the relatively stable monoanionic complexes; the second cathodic stage is irreversible. The coordination of 1,4-diaza-1,3-butadienes ligands with PtCl2 increases the reduction potential and the electron acceptor ability of the DAD ligands. The synthesized compounds were tested in relation to an adenocarcinoma of the ovary (SKOV3).

The chemical immobilization of cobalt(II) ions in a silica aerogel matrix enabled the synthesis of the first representative example of aerogel-based single-ion magnets. For the synthesis of the lyogels, methyl-trimethoxysilane and N-3-(trimethoxysilyl)propyl ethylenediamine were co-hydrolyzed, then the ethylenediamine groups that were immobilized on the silica matrix enabled the subsequent binding of cobalt(II) ions. Lyogels with various amounts of ethylenediamine moieties (0.1–15 mol %) were soaked in isopropanol solutions of cobalt(II) nitrate and further supercritically dried in carbon dioxide to obtain aerogels with a specific surface area of 210–596 m2·g−1, an apparent density of 0.403–0.740 cm3·g−1 and a porosity of 60–78%. The actual cobalt content in the aerogels was 0.01–1.50 mmol per 1 g of SiO2, which could easily be tuned by the concentration of ethylenediamine moieties in the silica matrix. The introduction of cobalt(II) ions into the ethylenediamine-modified silica aerogel promoted the stability of the diamine moieties at the supercritical drying stage. The molecular prototype of the immobilized cobalt(II) complex, bearing one ethylenediamine ligand [Co(en)(MeCN)(NO3)2], was synthesized and structurally characterized. Using magnetometry in the DC mode, it was shown that cobalt(II)-modified silica aerogels exhibited slow magnetic relaxation in a nonzero field. A decrease in cobalt(II) concentration in aerogels from 1.5 mmol to 0.14 mmol per 1 g of SiO2 resulted in a weakening of inter-ion interactions; the magnetization reversal energy barrier likewise increased from 4 to 18 K.

Heterometallic Coii-Lii compounds with N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), tri phenylphosphine (Ph3P) and pyridine (py), [Co2Li2(Piv)6(IMes)2] (Piv is the anion of pivalic acid), [Co2Li2(Piv)6(Ph3P)2] and [Co2Li2(Fur)6(py)2] (Fur is the anion of 2-furoic acid), respectively, have been prepared and structurally characterized by X-ray crystallography. Easy-plane magnetic anisotropy in Coii complexes with pseudo-tetrahedral cores CoO3X (X = C, P and N) was revealed by measuring the magnetic properties together with quantum-chemical calculations using the SA-CASSCF/NEVPT2 approach. The field-induced slow magnetic relaxation of the complexes was mainly attributed to the Raman and direct processes.

By the interaction of cobalt(II) chloride, sodium hydroxide, and pentafluorobenzoic acid (Hpfb) in water the first heterometallic complex of cobalt with pfb– anions is obtained. According to the X-ray crystallographic analysis, the complex is a cationic 1D polymer with the general formula {[Na2Co(pfb)2(H2O)8](pfb)2}n.

The effect of a bulky phenyl substituent on the formation and stability of pivalate complexes of 3d transition metals is studied on the example of 2-phenylpyridine (phpy). Quantum chemical calculations in the B3LYP/Def2-TZVP approximation are used to optimize binuclear molecules of [M2(μ-piv)4L2] complexes, where M = Co, Ni, Cu, $$\text{piv} = \text{Me}_3\text{CCO}^-_2$$ , L = 2,3-lutidine (lut) for which the analyzed compounds are known, phpy, and 7,8-benzoquinoline (bquin). The calculated energy characteristics indicate a significant stability of lut complexes and suggest that similar compounds with phpy can be prepared. The accuracy of theoretical calculations is confirmed by the successful synthesis of complex [Cu2(piv)4(phpy)2] (3). The computational simulation of binuclear coordination compounds with bquin suggests that there is a theoretical possibility of their formation; however, the fact that such structures have lower stabilization energies than those of reference complexes ([M2(piv)4(DMF)2]) indicates that their preparative isolation is hindered. Molecular structures of novel molecular complexes [Ni9(OH)6(piv)12(Hpiv)2(phpy)]·C6H6 (2) and [Li2Co2(piv)6(phpy)2] (4) are isolated and determined.

The reaction of copper(II) trimethylacetate, [Cu(Piv)2]n (Piv = C(Me)3COO–), with caffeine (L) (Cu : L = 1 : 1) in anhydrous acetonitrile yielded the binuclear complex [Cu2(Piv)4(L)2] ⋅ 2CH3CN (I). The structure of the complex in the crystal was established by X-ray diffraction (CIF file CCDC no. 2 006 753), and the electronic structure was studied by ESR. The effect of caffeine coordination to the biogenic complexing agent was established: the in vitro biological activity of the obtained complex towards the non-pathogenic strain Mycolicibacterium smegmatis was eight times higher than that of free caffeine.

Heterometallic carboxylate complexes are of paramount interest in pure and applied coordination chemistry. Despite that plurality of such type compounds have been published to date, synthetic aspects of their chemistry often remain in the shadow of intriguing physical properties manifesting by these species. Present review summarizes reliable data on direct synthesis of low nuclearity molecular compounds as well as coordination polymers on their base with carboxylate-bridged {M2Mg} (M = Co2+, Ni2+, Cd2+), {M2Li2} (M = Co2+, Ni2+, Zn2+, VO2+), {M2Ln2} and {M2Ln} (M = Cu2+, Zn2+, Co2+) metal cores. Structural features and stabilization factors are considered and principal outcomes are confirmed by quantum-chemical calculations. Particular attention is paid to consideration of ligand-exchange reactions that allow controllable modification of heterometallic metal core under mild conditions giving diverse molecular complexes with modified ligand environment or Metal-Organic Frameworks with permanent porosity.

A new complex [Zn(Piv)2(Pyzphen)] (I) was prepared by the reaction of pyrazino[2,3-f][1,10]phenanthroline (Pyzphen) with Zn(II) pivalate [Zn(Piv)2]n. An X-ray diffraction study (CIF file CCDC no. 1912821) revealed that complex I has a mononuclear structure, with ZnN2O4 coordination unit being a distorted trigonal prism. Quantum chemical simulation of dimerization of complex I, resulting in the hypothetical binuclear product [Zn(Piv)2(Pyzphen)]2 (II), showed that two energy demanding transition states present on the path of association of the complex molecules may prevent the experimental isolation of binuclear complex II. According to the results of luminescence studies of the Pyzphen ligand and complex I, the ligand emission band shifts to the blue region upon coordination to zinc(II) ion.

Data on the synthesis and study of the crystal structure of [Li10(Piv)10(MeCN)2]n (I) and [Li6(Piv)6(MeCN)2]n (II) are presented. According to X-ray diffraction data (CIF files CCDC nos. 1957855 (I); 1955569 (II)), compounds I and II are 1D polymers composed of deca- and hexanuclear fragments, respectively, in which the lithium atoms are linked to one another by μ3- and μ4-bridging pivalate anions.

New Ni(II) and Pd(II) complexes (Ia and Ib) are synthesized on the basis of the azomethine compound 2-[(E)-[4-methyl-2-[(Z)-p-tolylazo]phenyl]iminomethyl]phenol. The structures and properties of the complexes are characterized by IR spectroscopy, 1Н NMR spectroscopy, and X-ray diffraction analysis (СIF files CCDC nos. 1899223 (Ia) and 1899224 (Ib)). The complex formation affords cyclometallated chelates. According to the X-ray diffraction data, the crystals of the Ni(II) and Pd(II) complexes are isostructural with the square geometry of the coordination mode (MCN2O, M = Ni, Pd) and formation of two five-membered and one six-membered metallocycles.

A new 1D-coordination polymer [Co(Piv)2(NH2(CH2)6NH2)]n (1, Piv is Me3CCO2− anion) was obtained, the mononuclear fragments {Co(O2CR)2} within which are linked by μ-bridged molecules of hexamethylenediamine (NH2(CH2)6NH2). For this compound, two different monoclinic C2/c (α-1) and P2/n (β-1) phases were found at room temperature by single-crystal X-ray diffraction analysis, with a similar structure of chains and their packages in unit cells. The low-temperature phase (γ-1) of crystal 1 at 150 K corresponds to the triclinic space group P-1. As the temperature decreases, the structural phase transition (SPT) in the α-1 and β-1 crystals is accompanied by an increase in the crystal packing density caused by the rearrangements of both H-bonds and the nearest ligand environment of the cobalt atom (“octahedral CoN2O4 around the metal center at room temperature” → “pseudo-tetrahedral CoN2O2 at 150 K”). The SPT was confirmed by DSC in the temperature range 210–150 K; when heated above 220 K, anomalies in the behavior of the heat flow are observed, which may be associated with the reversibility of SPT; endo effects are observed up to 300 K. The SPT starts below 200 K. At 100 K, a mixture of phases was found in sample 1: 27% α-1 phase, 61% γ-1 phase. In addition, at 100 K, 12% of the new δ-1 phase was detected, which was identified from the diffraction pattern at 260 K upon subsequent heating: the a,b,c-parameters and unit cell volume are close to the structure parameters of γ-1, and the values of the α,β,γ-angles are significantly different. Further heating leads to a phase transition from δ-1 to α-1, which both coexist at room temperature. According to the DC magnetometry data, during cooling and heating, the χMT(T) curves for 1 form a hysteresis loop with ~110 K, in which the difference in the χMT values reaches 9%. Ab initio calculations of the electronic structure of cobalt(II) in α-1 and γ-1 have been performed. Based on the EPR data at 10 K and the ab initio calculations, the behavior of the χMT(T) curve for 1 was simulated in the temperature range of 2–150 K. It was found that 1 exhibits slow magnetic relaxation in a field of 1000 Oe.

The [ZnCa(DMF)2(tda)2]n·nDMF and [Zn2Ca(fda)4]n·2n(Me2NH2) metal-organic frameworks have been obtained by the reactions of pre-synthesized [Zn2Ca(piv)6(py)2] (piv is pivalate, and py is pyridine) with 2,5-thiophenedicarboxylic (H2tda) and 2,5-furandicarboxylic (H2fda) acids, respectively. Complex [Zn2Ca(piv)6(py)2] was used as a source of secondary building units with binuclear and trinuclear cores to form porous frameworks. The structure and topology of the compounds have been analyzed in detail.

The reaction of FeIII and LII pivalates with 1,10-phenanthroline (phen) in toluene simultaneously gives the heteronuclear compounds [Fe2Li(O)(Piv)5(phen)2]·2HPiv and [{Li4(Piv)4(HPiv)2}{Fe2LiO(Piv)5(phen)2}2]·2PhMe with a structural organization uncharacteristic of FeIII and alkali metals. According to X-ray diffraction data, the trinuclear metal oxide moiety {Fe2Li (μ3-O)} forms two nonequivalent complex molecules, which form infinite horizontal chains in the crystal due to stacking interactions between aromatic rings.

An adduct of ZnII pivalate with N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene has been prepared and characterized by X-ray diffraction analysis, NMR spectroscopy and DFT calculations. The compound preserves mononuclear structure in solution and does not switch the coordination mode from normal to abnormal.

The one-pot synthesis of the Cu(II) complex with hard to access symmetric bis-azoligand is carried out by the reaction of 4,5-dimethyl-1,2-phenylenediamine (Dmpda) with the [Cu2(Piv)4(HPiv)2] complex (Piv is the pivalate anion) in the presence of atmospheric oxygen. The amine form of the ligand takes place and the bis-diiminosemiquinone biradical redox form of the ligand does not take place in the [CuLazo] complex as unambiguously shown by the data of X-ray structure analysis (CIF files CCDC nos. 1877582 (I · DMF) and 1877583 (II), ESR spectroscopy, SQUID magnetometry, and electrochemical and quantum chemical studies. The coordination polymer [Cu2(Piv)4(Dmpda)]n in which the Dmpda molecules perform the bridging function is formed in the same reaction mixture under reduced air pressure.

Complexes of Cu(II), Ni(II), Co(II) and Fe(II) ions with N-[2-[(hydroxyalkylimino)methyl]phenyl]-4-methylbenzenesulfonamides containing the (CH2)n-spacer of a variable length (n = 2–6) were synthesized by chemical and electrochemical methods. All the compounds were characterized by C, H and N elemental analysis, IR, EPR and X-ray absorption spectroscopy data. The dimeric structures of the copper complexes with (CH2)n-spacers (n = 2, 3) were determined by the magnetochemical method and by X-ray diffraction analysis for the copper complex with the (CH2)3-spacer.

Reactions between zinc(II) or cadmium(II) pivalates and 2,2′-bipyridine, various substituted 1,10-phenanthroline derivatives or 2,2′:6′,2″-terpyridine have resulted in ten mono- and binuclear complexes with general formula [M(piv)2L] or [Cd2(piv)4L2], where piv is the pivalate anion, L is N,N′- or N,N′,N″-donor ligand, and M = Zn(II), Cd(II). Molecular and crystal structures as well as optical properties of the obtained homometallic complexes are reported and discussed. Preferable formation of binuclear cadmium compounds depending on type of the ligand are studied and clearly explained by means of DFT calculations.

A series of complexes [(4,4′-diMe-2,2′-bpy)2Zn2Eu2(NO3)4(naphac)6] (1), [(4,4′-dtb-2,2′-bpy)2Zn2Ln2(NO3)2(naphac)8] Ln = Eu (2), Tb (3), [(Py)2Zn2Ln2(naphac)10] Ln = Eu (4), Nd (5), Gd (6), Tb (7), Dy (8), [(Py)2Zn2Tm2(NO3)2(naphac)8] (9) (where naphac is the anion of 1-naphthylacetic acid, 4,4′-diMe-2,2′-bpy = 4,4′-dimethyl-2,2′-bipyridine, 4,4′-dtb-2,2′-bpy = 4,4′-di-tert-butyl-2,2′-bipyridine, Py = pyridine) were synthesized and structurally characterized. Capabilities of several synthetic routes for obtaining the title compounds were evaluated. Molecular and crystal structures as well as luminescence properties of obtained heterometallic complexes are reported and discussed in detail.

Novel Cu(II), Co(II), Ni(II), and Zn(II) complexes of 5-methyl-2-phenyl-4-[(4-phenylazo)anilinemethylylidene]- 2,4-dihydro-3H-pyrazole-3-thione and 5-methyl-4-[4-methyl-2-(4-methylphenylazo)anilinemethylylidene]- 2-phenyl-2,4-dihydro-3H-pyrazole-3-thione, i.e. ligands containing the phenylazo group in the ortho and para positions of the aniline fragment, were synthesized by the chemical and electrochemical methods. The complexes and ligands were characterized by IR, 1H NMR, X-ray absorption spectroscopy and magnetochemistry. The azo group of the ligands is not involved in coordination to the metal.

The reaction of the redox active 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-BIAN) and iron(II) iodide in acetonitrile led to a new complex [(dpp-BIAN)FeIII2] (1). Molecular structure of 1 was determined by the single crystal X-ray diffraction analysis. The spin state of the iron cation in complex 1 at room temperature and the magnetic behavior of 1 in the temperature range of 2–300 K were studied using Mossbauer spectroscopy and magnetic susceptibility measurements, respectively. The neutral character of dpp-BIAN in 1 was confirmed by IR and UV spectroscopy. The electrochemistry of 1 was studied in solution and solid state using cyclic voltammetry. The generation of the radical anion form of the dpp-BIAN ligand upon reduction of 1 in a CH2Cl2 solution was monitored by EPR spectroscopy.

4-Methyl-N-{2-([1-alkyl-2-[2-(p-tolylsulfonylamino)phenyl]benzimidazol-5-yl]iminomethyl)phenyl}-benzenesulfamides (H2L) and zinc complexes on their basis Zn2L2 have been synthesized. The structure of the ligands and complexes has been studied by IR, UV, 1Н NMR spectroscopy, X-ray absorption spectroscopy, and X-ray diffraction analysis.

N-{2-[5-(2-Hydroxyphenylmethyleneamino)-1-alkylbenzimidazol-2-yl]phenyl}-4-methyl-benzenesulfamides (H2L) and their zinc complexes Zn2L2 were synthesized. The structure of the ligands and complexes was studied by IR, UV, 1Н NMR, X-ray absorption spectroscopy, and X-ray diffraction analysis. The complexes show green photoluminescence (λfl = 492 nm) with quantum yields φ = 0.07–0.17.

Two novel binuclear nickel(II) complexes [Ni2(O2CR)4(2,3-lut)2] (O2CR is anion of 3,5-di(tert-butyl)benzoic acid (bzo, 1) and 4-hydroxy-3,5-di(tert-butyl)benzoic acid (hbzo, 2); 2,3-lut is 2,3-lutidine) with four carboxylate bridges were synthesized. The structure of complex 1 was determined by X-ray diffraction. Both dimers 1 and 2 were characterized by elemental analysis, IR spectroscopy, and magnetic measurements. The presence of the α-substituent in the apical lutidine ligand leads to a distortion of the geometry of the metal carboxylate core in complex 1 as a result of short steric contacts Me(Lut)…O(OOCR) (3.134(7) A). This is apparently responsible for a considerable decrease in the exchange parameters of complexes 1 and 2 (J =–30.0 and–23.6 cm–1, respectively) as compared to known analogues. Density functional calculations of the structure and magnetic properties of 1 and 2 were carried out by the UB3LYP/6-31G(d,p) method.

The systematic series of Zn–Ln trinuclear carboxylate molecular complexes of general formula [Zn2Ln(NO3)(phbz)6(L)2] (Ln = Eu, Gd, and Tb, where phbz is the anion of 4-biphenylcarboxylic acid, and L is pyridine, 2,3-lutidine or 2,2′-bipyridine) were synthesized. It was found that [Zn2Eu(NO3)(phbz)6(py)2] can be obtained in two phases, crystallized in the triclinic P and monoclinic P21/n space groups, and solvated acetonitrile molecules are able to prevent the formation of intermolecular π–π stacking interactions between the aromatic fragments of [Zn2Eu(NO3)(phbz)6(py)2]. Heterometallic Zn2Eu and Zn2Tb compounds possess bright metal-centered luminescence with quantum yields up to 62%. The influence of an N-donor ligand type on the efficiency of luminescence sensitization was studied.

A series of eight adducts of aminoazoles and aminoazines of a bis-chelate Zn(II) on the basis of 1-phenyl-3-methyl-4-formylpyrazole-5-one (HL) of common formula [ZnL 2 (NH 2 Het) n ] (n = 1, 2) ( 3a – h), where NH 2 Het = 1-aminoisoquinoline ( 3a ), 6-aminoquinoline ( 3b ), 3-aminoquinoline ( 3c ), 5-amino-4,6-dimethylquinoline ( 3d ), 2-aminopyridine ( 3e ), 2-amino-5-bromopryridine ( 3f ), 3-amino-5-methylisoxazole ( 3g ), and 2-amino-1-ethylbenzimidazole ( 3h ), were synthesized. Formulation of all compounds is based upon satisfactory C, H, N, Zn elemental analyses, IR, and 1 H NMR spectrоscopies. The structure of complex 3a has been determined by X-ray single-crystal diffraction. Optical properties of zinc complexes were investigated by UV–vis and photoluminescence spectroscopy.

The structure of bis[2-(1,3-benzoxazol-2-yl-κN)-4,5-dichloro-3-(ethoxycarbonyl)phenolato-κO]-zinc(II) was determined by IR and 1H and 13C NMR spectroscopy, and its structural characteristics were estimated by quantum chemical calculations. The complex showed photoluminescence properties.

A series of novel benzimidazole derivatives 1-alkyl-2-(2’-tosylaminophenyl)-5-nitrobenzimidazoles with common formulas HL (1–3) (R = C2H5 (1); R = n-C3H7 (2); R = n-C4H9(3)) and their mononuclear zinc(II) complexes ZnL2 (4–6) have been synthesized in a molar ratio Zn: HL = 1:2 in methanol solutions. Formulation of 1–6 is based upon satisfactory C, H, N, S elemental analyses, IR and 1H, 13C NMR spectroscopies, while the structures of 2, 3, 5, 6 were determined by X-ray single-crystal diffraction. The optical properties of 1–6 were investigated.

Conditions for chemical assembly of new heterometallic trinuclear pivalates [Cd2M(piv)6L2] (M = Mg, Ca, or Sr; piv is pivalate) were found. Reactions with the nonchelating ligand 2,4-lutidine (lut) gave the crystals of heterometallic complexes [Cd2M(piv)6(lut)2] (M = Mg (1), Ca (2), and Sr (3)). With the chelating ligand 1,10-phenanthroline (phen), only the homometallic dimer [Cd2(piv)4(phen)2] (4) was obtained under these conditions. Yet heterometallic trinuclear complexes with 1,10-phenanthroline ([Cd2Mg(piv)6(H2O)(phen)2] (5), [CaCd2(piv)6(phen)2] (6), and [Cd2Sr(piv)6(phen)2]∙2MeCN (7)) were synthesized by reactions of phen with complexes 1—3. For all the complexes obtained, the molecular and crystal structures as well as the details of their molecular architecture were determined. The thermal behavior of aqua complex 5 was studied by TG and DSC. The complex eliminated the water molecule between 130 and 180 °C with a high endothermic effect (Q = 101 kJ mol–1) due to (1) intramolecular hydrogen bonds that stabilize its molecular architecture and (2) subsequent structural rearrangements.

A series of polynuclear heterometallic cobalt(II) 2-naphthoate complexes with lithium(I), magnesium(II), and europium(III) is synthesized: [(2,2′-Bipy)2Li2Co2(Naph)6], [(2,4-Lut)2Co2Mg(Naph)6], and [(2,2′-Bipy)2(EtOH)2Co2Eu2(Naph)10] (Naph is 2-naphthoic acid anion, 2,2′-Bipy is 2,2′-bipyridine, and 2,4-Lut is 2,4-lutidine). The single crystals of the synthesized compounds are characterized by X-ray diffraction analysis (CIF files CCDC 1401987 (I), 1401988 (II), 1401989 (III), and 1401990 (IV)). The compositions and structures of the molecular heterometallic complexes based on cobalt(II) cations and anions of 2-naphthoic acid are determined by the radius and coordination number of the introduced heterometal: the isomorphic substitution of one of the cobalt(II) ions is observed for the magnesium(II) complex, and tetranuclear complexes are formed in the case of lithium(I) and europium(III).

The chromogenic properties of 2-(2-carbomethoxy-3,4-dichloro-6-hydroxyphenyl)benzoxazole (1) were studied. Solvatochromism of 1 was observed at keto-enol equilibrium due to the ground state intramolecular proton transfer (GSIPT). It was found that solvents with a good hydrogen bond acceptor (β) ability were able to stabilise the keto form of 1. The excited-state intra molecular proton transfer (ESIPT) in molecules of 1 resulted in intense fluorescence with an anomalous Stokes shift of up to 8493 cm−1 and quantum yields of 0.08–0.19. The keto-form of 1 exhibits negative T-type photochromism with a thermally reversible photoconversion to the enol form. The complexes of ligand 1 with Zn(II) and Cd(II) were synthesised. According to X-ray structural analysis, the zinc complex is the neutral complex, which is formed by two oxazole-N and two phenol O donors of ligand 1 which crystallise in a centrosymmetric group with the zinc ion located on the inversion centres. The synthesised complexes possess effective blue fluorescence and resistance to photodegradation.

Complexes [(dpp-BIAN)0CoIII2]&middot, MeCN (I) and [(Py)2CoI2] (II) were synthesized by the reaction between cobalt(II) iodide and 1,2-bis(2,6-diisopropylphenylimino)acenaphthene (dpp-BIAN) or pyridine (Py), respectively. The molecular structures of the complexes were determined by X-ray diffraction. The Co(II) ions in both compounds are in a distorted tetrahedral environment (CoN2I2). The electrochemical behavior of complex I was studied by cyclic voltammetry. Magnetochemical measurements revealed that when an external magnetic field is applied, both compounds exhibit the properties of field-induced single ion magnets.

The results on the synthesis and study of the crystal structures of molecular complexes of transition metals with anions of α- and β-naphthoic acids and monodentate N-donor ligands (MeCN, 2,3-lutidine) are presented. The compositions and structures of the isolated complexes are determined by the following factors: steric hindrances, intermolecular interactions of the aromatic fragments, and the electronic structure of the metal center.

2-(4′-Bromopyrazolyl-1′)-3-tosylaminopyridine (HL3) and its complex ZnL2 (I) are synthesized, and their structures are studied by IR, UV, and 1H NMR spectroscopy. The molecular structure of complex ZnL2 is determined by X-ray diffraction analysis. The atomic structure of ZnL2 is confirmed by the optimization of the molecular geometry using quantum-chemical calculations in the density functional theory approximation. The experimental bands in the absorption spectrum of complex I are interpreted on the basis of the calculations, and its photoluminescence properties are studied.

1-Alkyl-2-(2-tosylaminophenyl)-5-aminobenzimidazole and related zinc complexes are synthesized. The structure of the complex with zinc pivalate is determined by X-ray diffraction analysis. The fluorescence with the anomalous Stokes shift of the benzimidazole ligand system in solution is transformed into the fluorescence with the normal Stokes shift upon complex formation due to blocking the mechanism of intramolecular proton transfer in the excited state or upon the transition to the crystalline state formed by zwitterionic forms that are generated due to the proton transfer from the sulfonamide group to the amino group.

New complexes of Cu(II), Co(II), and Ni(II) with 1-phenyl-3-methyl-4-[(4-phenylazophenyl)hydrazono]-5H-pyrazol-5-one and 1-phenyl-3-methyl-4-[4-methyl-2-(4-methylphenylazophenyl)hydrazono]-5H-pyrazol-5-one are synthesized by the chemical and electrochemical methods and characterized by IR, 1H NMR, and EXAFS spectroscopy and X-ray diffraction analysis. Depending on the complexing metal and position of the additional azo group, the latter is involved or not in coordination with the metal to form heterounit five- and six-membered metallocycles.

The structures of Schiff bases prepared by the condensation of 2-tosylaminobenzaldehyde with 2-alkylamino-5-nitroanilines were studied by X-ray diffraction. The intramolecular N-H…N hydrogen bonds result in the closure of six-membered hydrogen-bonded rings, which are either planar or nonplanar depending on the substituent. According to the results of quantum-chemical calculations, the distortion of the hydrogen-bonded ring is associated with the character of molecular packing in the crystal.

Tridentate azomethine ligands (H2L) based on 3-allylsalicylaldehyde and o-aminophenol, o-aminothiophenol, or 2-ethylamino-5-nitroaniline were synthesized and identified by IR and 1H NMR spectroscopies. The structure of complexes (Ia-Ic) was studied by magnetochemistry and EXAFS spectroscopy. Complexes Ia and Ib (X = O, S) are binuclear and exhibit antiferromagnetic exchange interaction: 2J = −36.5 and −950 cm−1, respectively. Complex Ic (X = NC2H5) is mononuclear (μeff = 1.75 μB at 275 K and does not change as temperature decreases).

The binuclear chelates of copper(II) based on the tridentate azomethine ligands were synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy, X-ray absorption spectroscopy (XANES and EXAFS), and magnetic measurements. The quantum-chemical study of the structure and calculation of magnetic properties of the obtained metal-chelates was performed using the density functional theory with the broken symmetry technique. The performed magnetochemical studies in the temperature range 2–300 K suggest the existence of antiferromagnetic exchange interaction in all obtained complexes. The parameters of the exchange interaction −2J > 260 cm−1 were determined experimentally for all compounds, the experimental data is in a good agreement with the results of quantum-chemical calculations.

A series of new tetranuclear heterometallic Zn(II) -Eu(III) complexes have been synthesized, that is, (bpy)2 Zn2Eu2 (naph)10 (1), (bpy)2 Zn2Eu2 (naph)8 (NO3)2 (2), and (phen)2 Zn2Eu2 (naph)8 (NO3)2 (3), and other ones, where naph(-) is the 1-naphthoate anion, bpy=2,2'-bipyridyl, and phen=1,10-phenanthroline. The solid-phase complexes consist of large supramolecular ensembles due to stacking interactions between the aromatic ligands. Photoluminescence (PL) measurements were carried out to study PL spectra, lifetimes and quantum yields (QY) of the synthesized complexes at different temperatures. The external QY for the solid phases of complexes under UV excitation was found to exceed 20 %. It has been shown that partial replacement of naphthoate ligands in the coordination environment of Eu(3+) by NO3(-) anions influences the PL properties. To investigate the behavior of these complexes in solvent, we dissolved complex 3 in MeCN, put it on a transparent glass as a substrate, and studied the PL properties at room temperature.

Cobalt and zinc complexes with phenylazosalicylaldehyde azomethines were obtained by chemical and electrochemical syntheses. The B3LYP/6-311G(d, p) calculations showed that the azo group in both the ligands and the complexes are mainly in the E-form.

The bidentate chelate Cu(II) complexes of phenylazosalicylaldehyde azomethines are synthesized for the first time and their magnetic properties are studied. The complexes with the intermetallic bridge of the nitrogen atoms are characterized by the antiferromagnetic interaction, whereas the ferromagnetic exchange is typical of analogous coordination compounds with the sulfur bridge.

N-Alkylsalicylideneimines and their complexes with 3d metals were obtained by chemical (from metal salts) and electrochemical methods (from metals in the zero oxidation state). The compounds obtained were characterized by IR and 1H NMR spectroscopy and X-ray diffraction analysis. According to crystallographic data, nickel bis(chelate) exists in the trans-planar configuration. A friction test revealed that the tribotechnical characteristics of lubricating formulations are substantially enhanced in the presence of N-alkylsalicylideneiminates.

New Cu(II), Co(II), and Pd(II) complexes with benzeneazo-N-tosyl-2-naphthylamine are synthesized by chemical and electrochemical methods and characterized by IR, 1H NMR, and XRD. XRD was used to determine that two six-membered metal rings are formed in transplanar Ni(II) and Pd(II) complexes.

Tridentate azomethine ligands with N2O4 and N3donor atoms and their copper complexes were synthesized and characterized. The dimeric structure of copper(II) chelates was confirmed by EXAFS studies. Complexes based on 2-tosylaminobenzaldehyde azomethines tend to undergo ferromagnetic exchange, whereas similar salicylaldehyde derivatives have antiferromagnetic exchange.

Copper chelates with tridentate ligands containing pyridine or pyrazole ring at the azomethine or azo fragment were synthesized by chemical electrochemical methods, and their structure was characterized by the EXAFS spectra. Thermal magnetochemical analysis of the complexes revealed antiferromagnetic exchange interaction in all complexes. The exchange interaction parameter of the complex containing an N-tosylamino group in the ortho position with respect to the azomethine group is much lesser than that of the corresponding complex having an oxygen atom in the same position. The copper chelate derived from azopyrazole ligand shows low-temperature ferromagnetic phase transition.

New azomethine derivatives of salicylidene-3-carboethoxy-4,5-dimethylthiophene and their metal chelates are synthesized. The enolimine tautomeric form of the azomethine system of the ligand is determined from the data of 1H NMR and IR spectroscopy. According to the IR spectral data, the structures of the Co, Ni, Cu, and Zn complexes are octahedral (the structure of the nickel complex is proved by X-ray diffraction analysis), whereas the palladium chelate has a square structure.