L. A. Sheludyakova

1A1 ⇄ 5T2 Spin Transition in New Thermochromic Iron(II) Complexes with 1,2,4-Triazole and 4-Amino-1,2,4-Triazole

New complexes of iron(II) chloride and bromide with 1,2,4-triazole (Htrz) and 4-amino-1,2,4-tri-azole (NH2trz) of composition Fe(Htrz)3Cl2 · 1.5H2O, Fe(NH2trz)3Cl2 · 2H2O, Fe(Htrz)3Br2 · 2H2O, and the Fe(NH2trz)3SO4 · H2O complex were synthesized and studied by magnetochemical, electronic, IR and Mössbauer spectroscopy methods. Magnetochemical studies showed that these complexes exhibit 1A1 ⇄ 5T2 spin transition accompanied by thermochromism (a reversible pink ⇄ white change of color).

Spin crossover in iron(II) complexes with tris(pyrazol-1-yl)methane

Mononuclear iron(II) coordination compounds with tris(pyrazol-1-yl)methane (HC(Pz)3) described as [Fe{HC(Pz)3}2]A2 × nH2O, where A = Cl−, Br−, I−, 1/2 SO42−, n = 0–7, were synthesized. The compounds were studied by static magnetic susceptibility measurements, IR and UV/Vis spectroscopy, and powder X-ray diffraction. The crystal and molecular structures of all compounds were determined by single crystal X-ray diffraction.

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.

Iron(II) Complexes with 4-R-1,2,4-Triazoles (R = Ethyl, Propyl) Exhibiting 1A1 ⇄ 5T2 Spin Transition

Iron(II) complexes with 1,2,4-triazoles of composition FeL3A2 · nH2O were synthesized, where L is 4-ethyl- or 4-propyl-1,2,4-triazole (Ettrz, Prtrz, respectively) and A = NO–3, ClO–4, Br–; n = 0.5, 1, 2. Magnetochemical studies showed that all these compounds exhibit 1A1 ⇄ 5T2 spin transition (ST) which is accompanied by thermochromism (a reversible pink ⇄ white change of color). The ST pattern, i.e., the temperature of a direct (Ts↑) and reverse (Ts↓) transition, and its contrast substantially depend on the nature of both the ligand and anion and on the availability of water molecules in the complex structure. The highest ST temperatures were observed for Fe(Ettrz)3Br2 · 2H2O: Ts↑ = 327 K, Ts↓ = 314 K.

Co(II), Ni(II) and Cu(II) Complexes with 1-(4-Hydroxyphenyl)-1H-1,2,4-Triazole

New complexes of Co(II), Ni(II), and Cu(II) with 1-(4-hydroxyphenyl)-1H-1,2,4-triazole (L) of the composition ML2(H2O)2(NO3)2 · nH2O (M = Co(II), n = 3; M = Ni(II), n = 0; M = Cu(II), n = 0) were synthesized and studied by photoelectron and IR spectroscopy, magnetochemistry, thermogravimetry, and X-ray powder diffraction analysis. The type of μeff(T) relationship suggests that paramagnetic centers in the Co(II) chloride and Cu(II) nitrate and bromide complexes are involved in antiferromagnetic exchange interactions. The exchange energy values were estimated by the molecular field method.

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.

Synthesis, Crystal and Molecular Structures, and Properties of Optically Active Copper(II) Complexes with 3-N,N-Dimethylaminocaran-4-one-oxime

Copper(II) complexes with 3-N,N-dimethylaminocaran-4-one-oxime (HL) were synthesized and characterized by X-ray diffraction analysis, photoelectronic, IR, and EPR spectroscopy, magnetic susceptibility, and thermal analysis methods, and their optical activities were studied. The [Cu2(HL)2Cl4] complex is a dimer with weak exchange interactions between unpaired electrons of the Cu(II) ions. The [Cu3L3(OH)Cl]Cl · 8H2O structure is composed of triangular trinuclear complex cations, outer-sphere Cl–anions, and water molecules. The exchange parameter Jfor the trinuclear exchange cluster is –190 cm–1. The title complexes are optically active in the visible range of the spectrum.

Synthesis and structure of a complex with the coordinated triaminoguanidinium(2+) ion, [Cu(TAGH2)Cl3]Cl·H2O

Abstract The title compound has been isolated upon the reaction of copper(II) chloride and triaminoguanidine hydrochloride in concentrated HCl. An X-ray study has shown that the crystal structure of this complex is composed of [Cu(TAGH2)Cl3]+ cations, Cl− anions and water molecules. The complex cation involved the coordinated triaminoguanidinium(2+) cation bonded to the Cu(II) ion via N atoms of the amino group and the CN moiety as a chelate bidentate ligand. The square-planar environment of the Cu atom is formed by two Cl atoms (2.2769(9) and 2.3002(9) A) and two N atoms (CuN 1.987(2) and 2.043(2) A). The long CuCl bonds (2.728(1) and 2.941(1) A) which complement the environment to a distorted square bipyramid allow us to separate the staggered cation chains. μef values are 1.83 and 1.86 μB at 78 and 300 K, respectively.

Preparation of metal-polymer composites through the thermolysis of Fe(II), Co(II), and Ni(II) maleates

Metal-polymer composites have been prepared through the thermolysis of the [M1(H2O)2(C4H2O4)] · H2O (M1 = Co(II), Ni(II)) neutral maleates and [M2(H2O)4(C4H3O4)2] (M2 = Fe(II), Co(II), Ni(II)) acid maleates. In the polymer matrix of the Fe-containing composite, we identified metal, Fe2O3, and Fe3O4 particles, with slight densification of the matrix around them. The polymer matrix of the cobalt maleate-derived composite contained four types of nanoparticles: α-Co, β-Co, and CoO in polymer shells and Co3O4 with no polymer shell. The decomposition of the nickel maleates yielded homogeneous nickel nanoparticles (4–5 nm) covered with two to five graphene layers. The Co-containing composite was found to be a dielectric. The Ni-containing composite exhibited variable range hopping conduction in the range T ≤ 50 K.