S. V. Larionov

Spin-crossover and thermochromism in complexes of iron(II) iodide and thiocyanate with 4-amino-1,2,4-triazole

Abstract New complexes of iron(II) iodide and thiocyanate with 4-amino-1,2,4-triazole were synthesized. The complexes were characterized by magnetic measurements, reflection, Mossbauer and IR spectra. The coordination of iron(II) is discussed on the basis of these data. The compounds posses reversible thermochromism (colour change from white to pink) due to the spin transition 5 T 2 ⇌ 1 A 1 .

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).

Synthesis and crystal and molecular structure of mixed-ligand compounds Eu(S2CN(C2H5)2)3(2,2′-Bipy) and Eu(S2CN(C2H5)2)3(1,10-Phen)

Synthetic procedures were developed and X-ray diffraction analysis was performed for two mixed-ligand compounds of europium(III) with diethyldithiocarbamate ions and 2,2′-bipyridyl (2,2′-Bipy) or 1,10-phenanthroline (Phen): Eu(S2CN(C2H5)2)3(2,2′-Bipy) (I) and Eu(S2CN(C2H5)2)3Phen (II). The structures of the complexes consist of discrete monomer molecules; the coordination polyhedron of Eu (EuN2S6 is a node) is a distorted dodecahedron.

Influence of magnetic dilution on the spin transition in the complex of iron(II) nitrate with 4-amino-1,2,4-triazole

Influence of magnetic dilution with ZnII ions on the spin transition in the iron nitrate complex of 4-amino-1,2,4-triazole (AT) was studied by magnetochemistry, Mössbauer spectroscopy, and IR spectroscopy. In studies of the properties of solid phases of FexZn1−x(AT)3(NO3)2 (0.01≤x≤0.8), it was demonstrated that magnetic dilution results in a lowered spin transition temperature and an increased share of the high-spin form of the iron(II) complex.

Spin transition in iron(III) and iron(II) complexes

The main stages of the studies on the spin transitions in iron(III) and iron(II) complexes are considered. The types of the spin transitions and the factors responsible for the latter are reported. The problems arising during experiments in this field are discussed.

Metal complexes with new types of chiral ligands based on natural terpenes

Some problems of the chemistry of coordination metal compounds with chiral ligands based on natural organic compounds, especially terpenes, are generalized. The results on the synthesis and study of the structure and properties of the chiral transition metal complexes with several groups of new “hybrid” ligands based on monoterpenes pinene, (+)-3-carene, and limonene and sesquiterpene caryophyllene are considered.

Photochemistry of dithiocarbamate Cu(II) complex in CCl4.

Laser pulse photolysis was used to study the nature and reactions of intermediates in the photochemistry of the flat dithiocarbamate complex Cu(Et(2)dtc)(2) in CCl(4). A nanosecond laser pulse (355 nm) is shown to induce intermediate absorption bands of bivalent copper complex whose coordination sphere contains a dithiocarbamate radical Et(2)dtc(•) and a chloride ion at the axial position ([(Et(2)dtc)Cu(Et(2)dtc(•))Cl(a)]). At room temperature during some microseconds after the laser pulse, this intermediate interacts with the initial complex to form presumably a dimer [Cu(2)(Et(2)dtc)(3)(Et(2)dtc(•))Cl]. The latter vanishes in the second-order reaction. Analysis of kinetic and spectral features gives the arguments for the formation of a cluster [Cu(2)(Et(2)dtc)(3)Cl-tds-Cu(2)(Et(2)dtc)(3)Cl], which produces a new absorption band at 345 nm. The cluster decomposes in ∼5 ms into final products, a binuclear complex [Cu(2)(Et(2)dtc)(3)Cl] and tetraethylthiuramdisulfide (Et(4)tds).

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.