A new redox-active tetradentate ONNO-type ligand containing electron-withdrawing chlorine substituents in the phenylene ring, namely N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-4,5-dichloro-1,2-phenylenediamine (LH4), has been synthesized. Its coordination behavior was studied with tin(IV), zinc(II), and cadmium(II) ions. The reaction with Sn(IV) precursor yields the complex LSnMe2 (1), where the ligand is fully deprotonated and coordinated in its dianionic form. However, in solution, L undergoes intramolecular cyclization within the metal coordination sphere, resulting in the formation of a phenoxazine moiety and, consequently, a new ligand L' in the isolated complex L'SnMe2 (2). For Zn(II) and Cd(II), the structures of the resulting compounds - (LH)2Zn (3), (LH)2Cd (4), L'2Zn (5), and L'2Cd (6) - are determined by the choice of oxidant (p-benzoquinone or atmospheric oxygen) used during the synthesis. The structures of the synthesized complexes were established using a combination of NMR, IR, and UV spectroscopy, along with elemental analysis. SC-XRD was carried out for the tin(IV) and zinc(II) compounds. It was shown that the obtained derivatives possess redox-amphoteric properties and exhibit intense absorption in the near-IR region.

New unsymmetrical sulfoxides containing a redox-active sterically hindered catechol fragment and a nonpolar hydrocarbon substituent at the sulfoxide group were synthesized via the oxidation of the corresponding catechol thioethers with hydrogen peroxide. The yield of the reaction products ranges from 42 to 89%. The crystal structures of catechol sulfoxides with isopropyl, cyclopentyl, adamantyl, benzyl and 1-naphthyl moieties were established by single-crystal X-ray analysis. The possibility of forming intra- and intermolecular hydrogen bonds has been shown for these compounds. The electrochemical behavior of sulfoxides was studied in comparison with that of the parent catechol thioethers. The redox transition corresponding to catechol fragment oxidation is shifted to the anodic region relative to the initial thioethers, which is attributed to the more electron-withdrawing nature of the S=O group. The second redox stage characterizes the transformation of the sulfoxide fragment and is observed in most cases at 1.82–1.91 V. The radical-scavenging activity and antioxidant properties of the unsymmetrical sulfoxides and their precursor thioethers were evaluated using the reaction with the 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH) and the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS+•). In both assays, the lowest IC50 values among the studied catechol sulfoxides were found for compounds bearing isopropyl and tert-butyl substituents on the sulfoxide group.

A new redox-active tetradentate ONNO-type ligand containing electron-withdrawing chlorine substituents in the phenylene ring, namely N,N'-bis(3,5-di‑tert‑butyl‑2-hydroxyphenyl)-4,5-dichloro-1,2-phenylenediamine (LH4), has been synthesized. Its coordination behavior was studied with tin(IV), zinc(II), and cadmium(II) ions. The reaction with Sn(IV) precursor yields the complex LSnMe2 (1), where the ligand is fully deprotonated and coordinated in its dianionic form. However, in solution, L undergoes intramolecular cyclization within the metal coordination sphere, resulting in the formation of a phenoxazine moiety and, consequently, a new ligand L' in the isolated complex L'SnMe2 (2). For Zn(II) and Cd(II), the structures of the resulting compounds — (LH)2Zn (3), (LH)2Cd (4), L'2Zn (5), and L'2Cd (6) — are determined by the choice of oxidant (p-benzoquinone or atmospheric oxygen) used during the synthesis. The structures of the synthesized complexes were established using a combination of NMR, IR, and UV spectroscopy, along with elemental analysis. SC-XRD was carried out for the tin(IV) and zinc(II) compounds. It was shown that the obtained derivatives possess redox-amphoteric properties and exhibit intense absorption in the near-IR region.

This work presents tin coordination compounds designed for a specific practical application: the development of LL'CT (ligand-to-ligand charge transfer) chromophores. The obtained complexes are built using two types of redox-active ligands and exhibit ligand-to-ligand charge transfer. The donor part of the LL'CT system is represented by the doubly reduced form of 3,6-di-tert-butyl-o-benzoquinone, while the acceptor part is the neutral form of polycyclic phenanthroline derivatives. The complexes were characterized by X-ray diffraction analysis, UV-vis spectroscopy, cyclic voltammetry (CV), and DFT calculations. Both thermal and photothermal properties of the target complexes were investigated. The electronic absorption spectra of the hexacoordinated tin complexes presented herein exhibit a ligand-to-ligand charge transfer band in the visible and near-infrared region, with an extinction coefficient of approximately 8 & times; 102 dm3 & sdot;mol-1 & sdot;cm-1. Charge transfer occurs from the donor (catecholate) ligand to the acceptor (diimine) ligand. The data obtained are in good agreement with the results of quantum-chemical calculations. It is shown that the HOMO and LUMO are predominantly localized on the catecholate and diimine ligands, respectively. The design of the complexes, realized by varying the diimine substituent, allows the photochemical properties to be tuned, thereby controlling the magnitude of the HOMO-LUMO gap.

In this paper, we consider a series of new compact A-π-D photoinitiators consisting of donor aromatic fragments (naphthalene, anthracene, phenanthrene, pyrene and perylene) and a strong acceptor tricyanoethylene group—aryltricyanoethylenes (ArTCNEs). Spectral, photophysical, and electrochemical characteristics of ArTCNEs are studied. One-photon (with LED@405 nm) and two-photon (λ = 780 nm, impulse duration of 100 fs) photopolymerization of PETA can be effectively initiated by ArTCNEs with the tertiary amine N,N-dimethylcyclohexylamine DMCHA and/or the iodonium salt diphenyliodonium chloride Iod. Based on results of experiments on photodegradation, photopolymerization and EPR spectroscopy, a photoinitiation mechanism of radical photopolymerization was proposed for two-component (AntTCNE/DMCHA) and three-component (AntTCNE/DMCHA/Iod) initiating systems. The composition containing PerTCNE/DMCHA as a photoinitiator demonstrated the best reactivity under two-photon nanolithography conditions: the polymerization threshold was 2 mW at a laser beam scanning speed of 100 μm/s, and the widest fabrication window of 11 mW was typical for it. As an example, 3D “cage” structures were fabricated using the AntTCNE-based composition, and the test structure resolution parameters, such as the minimum line width and the distance between lines of 80 and 400 nm, respectively, were achieved. MTT experiments with human dermal fibroblasts showed promising preliminary biocompatibility of the resulting polymers, which opens up possibilities for using the obtained materials in biological applications.

Novel antimony( v ) complexes featuring ONNO redox-active ligands exhibit strong NIR absorption, photothermal activity, and high optical stability.

A wide range of water-soluble quaternary ammonium acylhydrazones based on catecholaldehyde were synthesized and characterized using NMR, IR spectroscopy, and elemental analysis. The total antioxidant capacity of the acylhydrazones discussed herein was estimated via coulometric titration with electrogenerated bromine. Pyridinium derivatives 11a-e exhibited the highest antioxidant capacity. Quaternary ammonium acylhydrazones demonstrated high antimicrobial activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus strains. Furthermore, low hemo- and cytotoxicity and the absence of a negative effect on the hemostatic system were confirmed for the studied compounds. According to the results of a CV test, the antimicrobial effect of the most active acylhydrazones, namely, 9a, 10b, 10c, and 11a, is associated with the destruction of the bacterial cell wall. High or moderate activity against phytopathogens of bacterial origin was observed for all the acylhydrazones evaluated. Anti-aggregation activity was observed for compound 10b; the extent was 1.6-fold greater than that exhibited by acetylsalicylic acid. On the contrary, compound 9d exhibited a pro-aggregant effect (with a 6.3% increase in platelet aggregation and a >15% decrease in the latent period compared to the control). Thus, the data obtained can be considered the basis for further pharmaceutical development of these effective drugs with antithrombotic and hemostatic potential.

New diorganotin(IV) complexes based on a redox-active tetradentate ONNO ligand, namely N,N'-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-phenylenediamine (LH4), were synthesized. A methodology for the stepwise oxidation of tin(IV)-ONNO derivatives with a stoichiometric amount of p-benzoquinone was developed. This allowed the preparation of tin(IV) complexes containing the ligand in the tetraanionic doubly deprotonated form, in the dianionic state, and a controlled intraligand cyclization to be carried out. It has been found that the diorganotin(IV) compounds with the dianionic form of the ONNO ligand have a ground singlet spin state, but an increase in temperature leads to partial populating of the triplet state and a transition from the diamagnetic form of these complexes to the paramagnetic biradical ones. The UV-vis-NIR spectrum of L2-SnPh2 shows an intense absorption band in the range of 600-1400 nm, corresponding to the intraligand charge transfer (ILCT). The coordination ability of the solvent strongly influences the position of this solvatochromic band. Cyclic voltammetry revealed that this compound undergoes two sequential reversible single-electron oxidations and two sequential reversible single-electron reductions. This cyclic voltammetry remains unchanged even after 100 cycles have been performed.

Two new heteroleptic cobalt(II) complexes (3,6-Cat)Co(R-DAD) (where (3,6-Cat)2− is a dianion of 3,6-di-tert-butyl-o-benzoquinone, R-DAD is diisopropyl-1,4-diaza-1,3-butadiene (R = i-Pr (1)) or dicyclohexyl-1,4-diaza-1,3-butadiene (R = c-Hex (2)) have been synthesized and characterized in detail by IR, UV–Vis–NIR spectroscopy, and elemental analysis. The molecular structure of 1 was determined by X-ray diffraction analysis. Magnetic properties of 1 and 2 were measured both in a solid state and in a solution. According to the single-crystal X-ray diffraction analysis, the metal ion in 1 has a planar coordination environment, but magnetic susceptibility measurements of the microcrystalline samples of 1 and 2 indicate the formation of both forms with tetrahedral (d7, h.s., SCo = 3/2) and planar (d7, l.s., SCo = ½) coordination environments of the metal ion. Absorption spectra of crystalline samples of 1 and 2 possess intense absorption band in the NIR region. Electrochemical measurements of 1 and 2 were also performed.

Magnetically bistable compounds attract considerable attention due to their possible applications in molecular electronics and spintronics devices. Of special interest are spin-crossover (SCO) systems that can interconvert between the low-spin and high-spin states leading to switching of the magnetic properties. Synthesis and comprehensive characterization of a family of ionic ferric-dioxolene complexes [(TPA)Fe(HO-DBCat)]ClO4 (1), [(TPA)Fe(NO2-DBCat)]ClO4 (2) and [(TPA)Fe(MeOCH2-DBCat)]ClO4 (3) (TPA = tris(2-pyridylmethyl)amine; HO-DBCat = dianion of 4,6-di-tert-butyl-1,2,3-trihydroxybenzene, NO2-DBCat = dianion of 4,6-di-tert-butyl-3-nitro-1,2-dihydroxybenzene and MeOCH2-DBCat = dianion of 4,6-di-tert-butyl-3-methoxymethyl-1,2-dihydroxybenzene) are reported. Variable temperature structural, magnetic and spectral analyses revealed that compounds 1-3 undergo a thermally induced SCO in the solid state between the high-spin (S = 5/2) and low-spin (S = 1/2) states. Alternating current magnetic susceptibility measurements indicated that the nitro-substituted complex 2 shows a field supported slow magnetic relaxation in the low-spin state at 5000 Oe. Such duality of magnetic properties makes complex 2 the first ferric compound which demonstrates a complete S = 5/2 → S = 1/2 SCO with a single molecule magnet behavior (SMM, S = 1/2). Electronic structures and magnetic properties of 1, 2 and 3 were investigated with the aid of DFT and SA-CASSCF/NEVPT2 calculations.

Synthesis and structural characterization of a family of germanium-dioxolene complexes with ditopic N-donor ligands (L 1 -L 5 ) (L 1 =1,2-bis(pyridin-2-ylmethylene)hydrazine L 2 =1,6-bis-(pyridin-2-yl)-2,5-diaza-1,5-hexadiene, L 3 =N,N-bis(pyridin-2-ylmethylene)-1,4-benzenediamine, L 4 =N,N-bis(pyridin-2-ylmethylene)-(biphenyl)-4,4-diamine, L 5 =2,2’-azopyridine) is reported. The reaction of germanium bis-catecholate with bridging ligands L 1 – L 4 , differing by the nature of the linker between pyridine sites gives rise to dinuclear digermanium complexes (36Cat 2 Ge) 2 L 1−4 (36Cat=dianion of 3,6-di- tert -butylcatechol) 1–4 of DMAMD type (donor-metal-acceptor-metal-donor) with a charge transfer in the UV-Vis region. In opposite, the interaction of the 36Cat 2 Ge with 2,2’-azopyridine (L 5 ) results in the two-electron transfer from the donor 36Cat 2− ligands to the azopyridine bridge forming stable open-shell complex 5 [(36SQ)(36CatGe)] 2 (L 5 ) 2− (36SQ=radical-anionic semiquinonate ligand). Molecular structures of compounds 3 and 5 were determined by single crystal X-ray diffraction analysis. Electronic structures of complexes 1–5 were studied by means of DFT calculations.

Upon the reaction of glyoxal-bis(2-hydroxy-5-chlorophenyl)imine LH2 with diethyltin dichloride in the presence of a base (Et3N) in DMSO, the 1D-coordination polymer 1 was obtained, in which formally the L’(SnEt2)2 fragment acts as a monomeric unit. It was found that during the reaction, the initial ligand L undergoes transformation in the tin atom’s coordination sphere. This transformation results in the formation of a new ditopic 1,4-bis((5-chloro-2-oxidophenyl)imino)but-2-ene-2,3-bis(olate) ligand L’. The structure of the resulting complex 1 was examined by single-crystal X-ray diffraction analysis, elemental analysis, IR, and UV spectroscopy.

Two new A-pi-D-type photoinitiators based on indane-1,3-dione with methacrylate Dye 2 and isobutyrate Dye 3 groups were synthesized and characterized by NMR, IR- and UV-Vis spectroscopy. The spectral, photoluminescent and electrochemical properties of Dye 2 and Dye 3 compounds were investigated. Compounds Dye 2 and Dye 3 with tertiary amines N,N-dimethylaniline (DMA), N,N-dimethylcyclohexylamine (DMCHA) initiate both one- (LED with lambda = 405 nm) and two-photon (lambda = 780 nm and scale of impulse duration 100 fs) photopolymerization of PETA. The polymerization threshold of the Dye 2-based composition (Dye 2-DMA-PETA) under two-photon initiation conditions was 6.5 mW at a scanning speed of 100 mu m/s. Cage-like scaffold structures were fabricated by DLW-nanolithography using Dye 2 and Dye 3-based compositions. Structures with a line thickness of 90 nm located at a distance of 220 nm were obtained from the Dye 2-DMCHA-PETA composition, and for the Dye 3-DMCHA-PETA composition lines with a thickness of 140 nm at a distance of 310 nm were obtained. Due to the presence of methacrylate groups, Dye 2 has the ability to link into polymer networks and improves the thermal and physical-mechanical characteristics of polymers and increases the printing resolution under two-photon photopolymerization conditions. Additionally, it reduces the migration of the photoinitiator from the polymer matrix, compared to Dye 3. These advantages will allow the development of photopolymerizable compositions and biocompatible polymers based on them with high thermal stability and physical and mechanical characteristics.

A series of dimethylindium complexes of general formula (R-ONN)InMe2 (R = H (1), Me (2), Cl (3), NO2 (4)) have been synthesized by the reaction of Me3In with an appropriate...

Reactions of Schiff base ligands HL1-4 (wherein HL1 is 2-((pyridin-4-ylmethylene)amino)phenol, HL2 is 4-methyl-2-((pyridin-4-ylmethylene)amino)phenol, HL3 is 4-chloro-2-((pyridin-4-ylmethylene)amino)phenol, HL4 is 4-nitro-2-((pyridin-4-ylmethylene)amino)phenol) with Me3In in a molar ratio of 1:1 lead to the formation of dimethylindium complexes of the general formula (L1-4)InMe2 (1-4). The molecular structures of 1-4 have been determined by single crystal X-ray analysis. In the crystal, all complexes form centrosymmetric dimers via coordination of bridging mu 2-O atoms of the phenolate fragment to the metal atom of the neighboring molecule. The crystal packing of 1-4 represents infinite chains due to short contacts between each indium in the dimer and the pyridine nitrogen of the adjacent dimeric molecule. UV-vis absorption spectra of 1-4 have been recorded in various organic solvents. The position of the absorption band assigned to intraligand charge transfer (ILCT) in the UV-vis absorption spectra of 1-4 depends on the nature of the substituent in the phenolate moiety of L1-4 and shifts hypsochromically with increasing of the electron acceptor properties of the substituents in the Schiff bases. The HOMO-LUMO energy gap calculated from the CV measurements for 1-3 also narrows with the introduction of the electron donor substituents in the ligand L. All complexes show fluorescence with broad emission bands in the range of 500-700 nm both in Me-THF solution and in the solid state.

A new sterically hindered trialkyl-substituted o-benzoquinone, 4,6-di-tert-butyl-3-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]cyclohexane-3,5-diene-1,2-dione was synthesized. Its spectral, electronic, and structural characteristics were determined, which were found to be similar to those for analogous 3,6- and 3,5-di-tert-butyl-o-benzoquinones. The following sequence was observed for the reactivity in the photoreduction reaction in the presence of N,N-dimethylaniline (DMA): 3,6-di-tert-butyl-o-benzoquinone > 4,6-di-tert-butyl-3-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]cyclohexane-3,5-diene-1,2-dione > 3,5-di-tert-butyl-o-benzoquinone. The new quinone, like 3,6- and 3,5-di-tert-butyl-o-benzoquinones, in combination with DMA was found to initiate radical polymerization under the irradiation by LED sources in the range from 395 to 630 nm. It was found that the introduction of the pyrazole-containing fragment at position 6 of the quinonoid ring of 3,5-di-tert-butyl-o-benzoquinone led to a sharp increase in the activity of the new compound as a photoinitiator compared to 3,5-di-tert-butyl-o-benzoquinone and made the new quinone comparable with 3,6-di-tert-butyl-o-benzoquinone in the photoinitiating activity. At the same time, a photopolymerizable composition containing a photoinitiating system based on 4,6-di-tert-butyl-3-[(3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl]cyclohexane-3,5-diene-1,2-dione was found to be more stable than the photoinitiating system based on 3,6-di-tert-butyl-o-benzoquinone.

A series of 4-hydroxy-4,9-dihydro-4H-xanthen-4-one derivatives were synthesized using the oxidative cyclization reaction of space-shielded catecholphenols. The structure of 1,3,5,7-tetra-tert-butyl-4a,8-dihydroxy-9H-xanthen-4(4aH)-one was determined by X-ray diffraction analysis (CCDC 2345899). The antiradical properties of new compounds were studied by their reaction with 2,2-diphenyl-1-picrylhydrazyl (DPPH radical).

A series of chromophoric complexes NiII(3,6-Cat)(Phen) (1), NiII(3,6-Cat)(DPQ) (2), and NiII(3,6-Cat)(DPPZ) (3) (where 3,6-Cat is 3,6-di-tert-butylcatecholate dianion) has been synthesized using 1,10-phenanthroline (Phen), dipyrido[3,2-d:2',3'-f]quinoxaline (DPQ), and dipyrido[3,2-a:2',3'-c]phenazine (DPPZ). Chromophores 1–3 have a slightly distorted planar structure of the coordination environment and undergo photoinduced ligand-to-ligand intramolecular charge transfer (HOMOdonor → LUMOacсeptor), thus demonstrating strong light absorption in visible and near-IR regions. Complexes 1–3 are characterized by high thermostability and complete transition to the vapor phase under reduced pressure conditions. Compound 1 has high volatility, which makes it a suitable candidate for further testing in the fabrication of optoelectronic devices by “evaporation–deposition” technology.

The possibility of using a series of methacrylate-containing N,N-diethyl-4-(phenyldiazenyl)anilines with various para-substituents (–H, –Br, –NO2) relative to the azo group as photoinitiators of radical polymerization is considered. The electrochemical and photoluminescent properties of these compounds have been studied. In the presence of azo dyes, two-photon photopolymerization of pentaerythritol triacrylate was carried out using focused 780-nm radiation from a femtosecond laser. Structures with minimal dimensions of linear elements of 94 ± 5 nm were obtained by means of the DLW nanolithography technique, and 3D microstructures of complex architecture were fabricated.