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The reaction of new 2,6-bis(pyrazol-3-yl)pyridine ligand (L) containing a redox-active ferrocenyl substituent with cobalt(II) salt gave the cobalt(II) complex [Co(L)2](ClO4)2 (I), which was isolated in a pure state and characterized by elemental analysis, NMR spectroscopy, cyclic voltammetry, and X-ray diffraction. According to X-ray diffraction data (CIF file CCDC no. 2049714) and the Evans method, which allows determining the spin state of paramagnetic compounds in solution on the basis of NMR spectra, the cobalt(II) ion in complex I occurs in the high-spin state and does not undergo temperature-induced spin transition in the temperature range of 120–370 K.

Abstract New composite materials containing metal-organic framework (MOF-5) particles were manufactured by 3D printing. The optimal composition of the photopolymer formulation and printing conditions ensuring the highest quality of printing were selected. Retention of the metal-organic framework (MOF) structure in the resulting composite objects was demonstrated by powder X-ray diffraction. The distribution of MOF-5 particles over the whole bulk of the 3D product was studied by X-ray computed tomography. In the future, composite materials of this type containing catalytically active MOFs, with their structure and properties being controllable at the micro and macro levels, could find application as catalysts of various chemical processes.

The design of new redox-switchable molecules requires the development of simple and efficient synthetic approaches. This study demonstrates the possibility of ortho-lithiation of ferrocenecarboxaldehyde (aryl)imines (Ia–Ic) followed by the reaction with ketones to give 1,2-disubstituted ferrocenes (IIa–IIc). These products, in turn, can be cyclized by treatment with trimethylsilyl triflate to give the cationic precursors of ferrocene-containing N-heterocyclic carbenes (IIIa–IIIc), in which the heterocycle is annulated to one of the ferrocene cyclopentadienyl ring. Treatment of IIIa–IIIc with a base in the presence of a source of rhodium afforded rhodium carbene complexes (IVa, IVb) in which the carbene ligand resembled cyclic alkylaminocarbenes in the electron-donor properties. Compounds Ib and IVa were studied by X-ray diffraction (CIF file CCDC nos. 2000413 and 2000414, respectively).

The reaction of a new tridentate ligand 2,6-bis(5-tert-butyl-1-(2,6-difluorophenyl)-1H-pyrazol-3-yl)pyridine (L) with the divalent iron salt affords the iron(II) complex [Fe(L)2](BF4)2 (I), which is isolated in the individual state and characterized by elemental analysis, NMR spectroscopy, and X-ray diffraction analysis. According to the X-ray diffraction results and data of the Evans method, which makes it possible to determine the spin state of paramagnetic compounds in a solution from the NMR spectra, the iron(II) ion in complex I exists in the high-spin state (S = 2 for Fe(II)) and undergoes no temperature-induced spin transition in a range of 120–345 K.

The reactions of 2,6-bis(1,4-diphenyl-5-hydroxy-1H-pyrazol-3-yl)pyridine (L), which is the first representative of a series of 2,6-bis(pyrazol-3-yl)pyridine ligands bearing substituents in positions 1 and 4 of the pyrazol-3-yl ring, with the divalent iron and cobalt salts afford new Со(II) and Fe(II) complexes: [Co(L)2](ClO4)2 (I) and [Fe(L)2](ClO4)2 (II). The compounds are isolated in the individual state and characterized by elemental analysis, NMR spectroscopy, and X-ray diffraction analysis (CIF files CCDC nos. 1967892 (I) and 1967893 (II)). According to the data obtained, the transition metal ion in complexes I and II exists in the high-spin state (S = 3/2 for Co(II) and S = 2 for Fe(II)) in a range of 120–345 K, and the proposed modification of the ligand does not lead to the temperature-induced spin transition in both the solution and crystalline state.

The cobalt(II) and iron(II) complexes with 2,6-di(5-amino-1H-pyrazol-3-yl)pyridine (L), CoL2(ClO4)2 (I) and FeL2(ClO4)2 (II), are synthesized by the template reaction, isolated in the individual form, and characterized by elemental analysis, NMR spectroscopy, and thermogravimetry. The structures of complexes I and II (including the iron(II) complex obtained as two new solvate forms (FeL2(ClO4)2 ∙ 2(C2H5)2O ∙ H3CN (IIa) and FeL2(ClO4)2 ∙ (C2H5)2O ∙ CH3CN ∙ 0.75H2O (IIb)) are confirmed by X-ray diffraction analysis. The data obtained in the crystal (by the X-ray diffraction method) and in solutions (using the proposed approach to an analysis of paramagnetic shifts in 1H NMR spectra) indicate that the metal ion in the complexes exists in the high-spin state (S = 3/2 for Co(II) and S = 2 for Fe(II)) and undergoes no temperature-induced spin transition in a range of 120–300 K.

The direct template reactions afford the cobalt(II) complexes (I–III) with the hydroxy- and acetyl-substituted 2,6-bis(pyrazol-3-yl)pyridine ligands containing the phenyl and 4-tert-butylphenyl group in position 1. All compounds are isolated in the individual state and characterized by elemental analysis and NMR spectroscopy. The X-ray diffraction data obtained for crystals of compound I (СIF file CCDC 1577238) and the data for solutions (using the proposed approach to analysis of paramagnetic NMR shifts on the basis of quantum chemical calculations) show that in the complexes the metal ion exists in the high-spin state (S = 3/2) and undergoes no temperature-induced spin transition in a temperature range of 120–300 K.