Mark B. Bushuev

Spin Crossover in a Family of Iron(II) Complexes with Hexadentate ligands: Ligand Strain as a Factor Determining the Transition Temperature

This paper reports the synthesis of a family of mononuclear complexes [Fe(L)]X(2) (X=BF(4), PF(6), ClO(4)) with hexadentate ligands L=Hpy-DAPP ({bis[N-(2-pyridylmethyl)-3-aminopropyl](2-pyridylmethyl)amine}), Hpy-EPPA ({[N-(2-pyridylmethyl)-3-aminopropyl][N-(2-pyridylmethyl)-2-aminoethyl](2-pyridylmethyl)amine}) and Hpy-DEPA ({bis[N-(2-pyridylmethyl)-2-aminoethyl](2-pyridylmethyl)amine}). The systematic change of the length of amino-aliphatic chains in these ligands results in chelate rings of different size: two six-membered rings for Hpy-DAPP, one five- and one six-membered rings for Hpy-EPPA, and two five-membered rings for Hpy-DEPA. The X-ray analysis of three low-spin complexes [Fe(L)](BF(4))(2) revealed similarities in their molecular and crystal structures. The magnetic measurements have shown that all synthesized complexes display spin-crossover behavior. The spin-transition temperature increases upon the change from six-membered to five-membered chelate rings, clearly demonstrating the role of the ligand strain. This effect does not depend on the nature of the counter ion. We discuss the structural features accountable for the strain effect on the spin-transition temperature.

Complexes Fe(HTrz)3B10H10 · H2O and Fe(NH2Trz)3B10H10 · H2O (HTrz = 1,2,4-triazole and NH2Trz = 4-amino-1,2,4-triazole). The spin transition 1A1 ⇆ 5T2 in Fe(HTrz)3B10H10 · H2O

Methods for the synthesis of iron(II) complexes with 1,2,4-triazole (HTrz) and 4-amino-1,2,4-triazole (NH2Trz) containing the decahydro-closo-decaborate ion [B10H10]2-were developed. The empirical formulas of the complexes were Fe(HTrz)3B10H10 · H2O (I) and Fe(NH2Trz)3B10H10 · H2O (II). The complexes were examined by static magnetic susceptibility measurements (2–300 K) and Moessbauer, IR, and electronic spectroscopy. Complex I exhibits the reversible spin transition 1A1 ⇄ 5T2 and pink ⇄ white thermochromism. The temperatures of the forward and reverse transitions in complex I were 246 and 233 K, respectively. Complex II remained in the high-spin state over the whole temperature range. The sharp decrease in its effective magnetic moment at T < 78 K was attributed to antiferromagnetic exchange interactions between Fe2+ ions.

Cu(II) and Cu(I) complexes with 2-(3,5-diphenyl-1H-pyrazole-1-yl)-4,6-diphenylpyrimidine: Synthesis and structure. Catalytic activity of Cu(II) compounds in reaction of ethylene polymerization

The Cu(II) and Cu(I) complexes with 2-(3,5-diphenyl-1H-pyrazole-1-yl)-4,6-diphenylpyrimidine (L) of the composition CuLX2 (X = Cl, Br) and CuL(MeCN)Br are synthesized. According to X-ray diffraction data, the complexes have molecular structures. The molecules L are coordinated to the copper atom in bidentate-cyclic mode, i.e., through the N2 atom of pyrazole and N1 atom of pyrimidine rings. The coordination polyhedron of the Cu2+ ion in CuLX2 compounds is completed to a distorted tetrahedron with halide ions, that of the Cu+ ion in CuL(MeCN)Br compounds, with the bromide ion and the nitrogen atom of acetonitrile molecule. The CuLX2 complexes (X = Cl, Br) in combination with cocatalysts (methylaluminoxane and triisobutylaluminium) exhibit catalytic activity in ethylene polymerization.

Three differently coloured concomitant polymorphs: synthesis, structure and packing analysis of (4-(3',5'-dimethyl-1H-pyrazol-1'-yl)-6-methyl-2-phenylpyrimidine)dichlorocopper(II).

A novel pyrazolylpyrimidine ligand (L) and its complex CuLCl(2) were prepared and structurally characterized. The simultaneous crystallization of three polymorphs of CuLCl(2), green (G), emerald green (EG) and orange (O), was discovered. The molecular structures vary only slightly between the three forms. The Cu atom forms four coordinate bonds with the two N and two Cl atoms, and a shortened Cu...H contact with an H atom of the phenyl ring in L. The structural difference between polymorphs was analyzed with the boundary surfaces of molecular Voronoi-Dirichlet polyhedra. The difference in colour of the polymorphs is likely to be due to the different pi-pi stackings. There is no stacking in the G modification, but EG and O polymorphs demonstrate face-to-face and slipped stacking, resulting in dimers and infinite chains, respectively. The EG and O polymorphs are packed according to the hexagonal close-packing motif, while in G no special topology is found.

Iron(II) Complexes with 4-R-1,2,4-Triazoles (R = Ethyl, Propyl, Isopropyl): Synthesis and Properties

Fe(II) complexes with 4-R-1,2,4-triazoles of compositions FeL3A2 · nH2O (where L is 4-propyl-1,2,4-triazol; A is Br- (n = 4), CF3SO3- (n = 5)), and FeL2A2 · nH2O (where L are 4-ethyl-, 4-propyl-, 4-isopropyl-1,2,4-triazoles (Ettrz, Prtrz, Iprtrz, respectively), A = NCS-, NO3- (n = 0-2)) were synthesized. Magnetochemical studies revealed that FeL3A2 · nH2O complexes exhibit reversible spin transition (ST) 1A1 ⇄ 5T2 that is accompanied by thermochromism (a reversible change of color rose ⇄ white). The temperatures of direct (Ts↑) and reverse (Ts↓) spin transitions are, respectively, 252 and 247 K for Fe(Рrtrz)3Br2 · 4H2O and 207 and 202 K for Fe(Рrtrz)3(CF3SO3)2 · 5H2O. Dehydration of the complexes is attended by significant changes in the type and temperatures of ST.

Zinc(II) complexes with an imidazolylpyridine ligand: luminescence and hydrogen bonding

ZnLCl and [H2L]2[ZnCl4], based on 2-(1-hydroxy-4,5-dimethyl-1H-imidazol-2-yl)pyridine (HL), have been synthesized. There is a short intraionic O–H···N hydrogen bond between the hydroxyimidazolyl and pyridyl of H2L+ cations (N···O 2.608(2) Å) in the structure of [H2L]2[ZnCl4]. The formation of this rather strong hydrogen bond is confirmed by IR spectroscopy through a broad band at 3200–2200 cm−1 and a band at 1655 cm−1. HL crystallizes in the form of a hemihydrate, HL·0.5H2O. HL assemble into infinite helical chains due to N–H···O intermolecular hydrogen bonds between the NH of imidazole and O of the N-oxide (O···N 2.623(2) Å). An unusual mid-IR pattern with three broad bands at 3373, 2530, and 1850 cm−1 is typical for strong hydrogen bonds, explained by resonance-assisted hydrogen bonding occurring in the helical chains. On cooling to 5 K, noticeable changes in the IR spectra of [H2L]2[ZnCl4] and HL·0.5H2O were observed. ZnLCl and [H2L]2[ZnCl4] exhibit bright photoluminescence with maxima of emission at 458 nm (for ZnLCl) and 490 nm (for [H2L]2[ZnCl4]). Graphical Abstract

Luminescent zinc(II) and cadmium(II) complexes based on 2-(4,5-dimethyl-1H-imidazol-2-yl)pyridine and 2-(1-hydroxy-4,5-dimethyl-1H-imidazol-2-yl)pyridine

Complexes ZnL1Cl2, CdL1Cl2, ZnL21Cl2·1.5H2O, CdL21Cl2·2H2O, CdL21Cl2·MeOH·H2O [L1 = 2-(4,5-dimethyl-1H-imidazol-2-yl)pyridine] and inner-complex compounds ZnL22·2H2O, CdL22 [HL2 = 2-(1-hydroxy-4,5-dimethyl-1H-imidazol-2-yl)pyridine] were synthesized. The complexes exhibit bright photoluminescence in the blue region of the spectrum, with the intensity exceeding this characteristic of the compounds L1 and HL2. Compound L1 in aqueous solution is a potential chemosensor for the determination of zinc and cadmium.

Synthesis and study of Iron(II) perrhenate complexes with 4-propyl-1,2,4-triazole exhibiting 1 A 1 ⇄ 5 T 2 spin transition

Coordination compounds of iron(II) perrhenate with 4-propyl-1,2,4-triazole (L), [Fe3L6(ReO4)4(H2O)2](ReO4)2(I), [Fe3L6(H2O)6](ReO4)6·H2O(II), and FeL3(ReO4)2(III), were synthesized. Compounds I and III were studied by static magnetic susceptibility measurements and by IR and electronic spectroscopy. These complexes exhibit a reversible 1A1 ⇄ 5T2 spin transition and thermochromism. Compound I exhibits a spin transition without hysteresis at 185 K. The temperatures of forward and reverse transition for III are 250 and 244 K, respectively. Complex II isolated by crystallization from an acidified aqueous solution of compound I has a linear trinuclear structure of the cation (X-ray diffraction data). The structure of complex I was assumed to be similar, while compound III has a polymeric structure.

Cu(II) complexes with 4,6-bis(3,5-dimethyl-1H-pyrazole-1-yl)pyrimidine, 4-(3,5-dimethyl-1H-pyrazole-1-yl)-6-(3,5-diphenyl-1H-pyrazole-1-yl)pyrimidine: Synthesis and catalytic activity in ethylene polymerization reaction

The Cu(II) complexes with 4,6-bis(3,5-dimethyl-1H-pyrazole-1-yl)pyrimidine (L1) and 4-(3,5-dimethyl-1H-pyrazole-1-yl)-6-(3,5-diphenyl-1H-pyrazole-1-yl)pyrimidine (L2) of the composition Cu2L1Br4 and Cu2L2A4 (A = Cl, Br), respectively, were synthesized and studied by IR and magnetochemical methods. The molecular structure of the complexes is likely to be binuclear. In the presence of cocatalysts methylaluminoxane and triisobutylaluminium, the title complexes exhibit catalytic activity in the ethylene polymerization reaction.

Mononuclear coordination compounds based on a novel chelating triazole ligand : 1-vinyl-3-acetylamino-1,2,4-triazole

The synthesis, X-ray structure, magnetic and spectroscopic properties of new Co(II), Ni(II) and Cu(II) complexes with 1-vinyl-3-acetylamino-1,2,4-triazole (vaat) are reported. The crystal structures of [Ni(vaat)2(H2O)2](NO3)2 and [Cu(vaat)2(H2O)2]Cl2 have been determined by X-ray diffraction. In these mononuclear complexes, the metal ion is surrounded by two water molecules in axial positions and two oxygen and two nitrogen (N4) atoms coming from two trans-oriented chelating vaat molecules. Anions are noncoordinated and are involved in a hydrogen bonding network. The complex cations of [Cu(vaat)2(H2O)2]Cl2 are aligned within chains. In the structure of [Ni(vaat)2(H2O)2](NO3)2 the nitrate anions establish a bridge in the plane by hydrogen bonding giving a 2-D character for this compound. In addition, a colour change from pink to blue upon heating has been observed for [Co(vaat)2(H2O)2]Cl2, which is due to the removal of the two coordinated water molecules and the subsequent molecular reorganisation of the molecular structure. The synthesis, structure, magnetic and spectroscopic properties of new Co(II), Ni(II) and Cu(II) complexes with 1-vinyl-3-acetylamino-1,2,4-triazole (vaat) are reported. The crystal structures of [Ni(vaat)2(H2O)2](NO3)2 and [Cu(vaat)2(H2O)2]Cl2 have been determined by X-ray diffraction.