Metal-biradical chains from a high-spin ligand and bis(hexafluoroacetylacetonato)copper(II)

The synthesis, X-ray crystal structure, and magnetic studies of a rare example of organic/inorganic spin hybrid clusters extended in infinite ladder-type chain [Cu(C5F6HO2)2]7(C35H35N5O4)2 ([Cu(hfac)2]7(pyacbisNN)2, 2) formed by the reaction of a high spin nitronylnitroxide biradical C35H35N5O4 (pyacbisNN, 1) and bis(hexafluroacetylacetonate)copper(II) = Cu(hfac)2 are described. Single-crystal X-ray structure analysis revealed the triclinic P1 space group of 2 with the following parameters: a = 10.6191(4) A, b = 19.6384(7) A, c = 21.941(9) A, alpha = 107.111(7) degrees, beta = 95.107(8) degrees, gamma = 94.208(0) degrees , Z = 2. Each repeating unit in 2 carries a centrosymmetric cyclic six spin and a linear five spin cluster with four different copper coordination environments having octahedral and square planar geometries. These clusters are interconnected to form infinite chains which are running along the crystallographic b axis. The magnetic measurements show nearly paramagnetic behavior with very small variations over a large temperature range. The magnetic properties are thus result of complex competitions of many weak ferro- and antiferromagnetic interactions, which appear as small deviations from quite linear mu(eff) vs T dependence at low temperature. At high temperature (300-14 K), antiferromagnetic behavior dominates a little, while at very low temperature (14-2 K), a small increase of mu(eff) was observed. The magnetic susceptibility data are described by the Curie-Weiss law [chi = C/(T - theta)] with the optimal parameters C = 4.32 +/- 0.01 emuK/mol and theta = - 0.6 +/- 0.3 K, where C is the Curie constant and theta is the Weiss temperature.     

Magneto-structure relationship in copper(II) and nickel(II) complexes chelated with stable tert-butyl 5-phenyl-2-pyridyl nitroxide and related radicals

We have isolated and characterized a new paramagnetic bidentate ligand, tert-butyl 5-phenyl-2-pyridyl nitroxide (phpyNO). The spin distribution onto the pyridine ring was clarified from the Electron Spin Resonance spectrum. Complexation of phpyNO with nickel(II) and copper(II) ions gave ML 2-type chelated compounds. The magnetic measurements of [Ni(phpyNO) 2(H 2O) 2].(ClO 4) 2 and [Cu(phpyNO) 2(H 2O)].(ClO 4) 2.C 6H 4Cl 2 revealed that the metal-radical exchange couplings were ferromagnetic with 2 J/ k B = +409(10) and +434(12) K, respectively. The torsion angle (varphi) around M-O-N-C 2py can be regarded as a reliable indicator for the plane geometry of chelates; namely, highly planar chelates defined by small varphi exhibit ferromagnetic coupling. An approximate linear relation was found in the J versus varphi plot using the data of the present complexes and related known compounds. The critical angle of varphi, at which the sign of the metal-radical exchange changes from positive to negative, was 12.6(9) degrees . This finding could be almost reproduced by density-functional theory calculation on a model copper(II)-nitroxide dyad. The exchange couplings in equatorially coordinated copper(II)- and nickel(II)-nitroxide complexes are very strongly ferromagnetic by nature.     

Crystal structure of the mixed-ligand complex (hexafluoroacetylacetonato)(benzoylacetonato)copper(II)

Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 3, pp. 96–99, May–June, 1991.     

Homogeneous isotope exchange between copper(II) and bis(resacetophenone oxime)copper(II) complex

Isotope exchange behavior of bis(resacetophenone oxime)copper(II) complex with copper(II) in tri-n-butyl-phosphate and methanol medium has been studied. The studies were carried out at different temperatures varying the concentration of both metal ion and complex. The results show that the complex is labile in the kinetic sense. Increase in temperature increases the isotope exchange rate. The increase in concentration also results in enhancement of the rate of reaction.     

Strong intramolecular ferromagnetic couplings in nickel(II) and copper(II) complexes chelated with tert-butyl 5-methoxy-2-pyridyl nitroxide

We successfully isolated a new paramagnetic bidentate ligand tert-butyl 5-methoxy-2-pyridyl nitroxide (meopyNO). Complexation of nickel(II) and copper(II) perchlorates with meopyNO gave the corresponding ML₂-type bis-chelated compounds. The magnetic studies showed that they were ground high-spin molecules with 2J/k_B = +288(5) and +178(3) K for [M(meopyNO)₂(H₂O)₂] · (ClO₄)₂ (M = Ni and Cu, respectively), where the spin Hamiltonian is defined as H = ?2J(S₁ · S₂ + S₂ · S₃). From the crystallographic analysis, the torsion angles (?) around M–O–N–C_2py were 4.2(3)° and 6.87(19)°, respectively, being so small that the orthogonality between the magnetic radical π1 and the metal dσ orbitals would be guaranteed.     

DFT investigation for 1:2 complexes of bis(hexafluoroacetylacetonato)copper(II) coordinated with 4-(N-tert-butyl-N-oxyamino)pyridine

With the aim to explore the nature of interaction between organic radicals and paramagnetic ion, unrestricted density functional theory (UDFT) and restricted open shell DFT (RO-DFT) calculations using 6-31G(d) and LANL2DZ basis sets have been performed on the 1:2 complexes of bis(hexafluoroacetylacetonato)copper coordinated with 4-(N-tert-butyl-N-oxyamino)pyridine, complex 1. Structural data revealed by X-ray crystal analysis are used. It is found that the calculated results depend on the selected functionals, model orientation, basis set form and symmetry constraint. The proper chemical models for investigated system are RO-B3LYP, RO-BLYP, RO-PBE, and RO-PBE0.     

Crystal and molecular structure of (4-amino-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl) bis(hexafluoroacetylacetonato)copper(II)

Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 3, pp. 92–96, May–June, 1991.     

Polyether-bridged bis(tert-butyl nitroxide) paramagnetic hosts showing receptor ability to calcium(II) and barium(II) ions

The title compounds, Ph2bNO and Ph3bNO, were designed as a biradical paramagnetic host, and their chelation ability was confirmed by inclusion of a size-matched alkaline-earth metal ion. The crystal structures of [Ca(hfac)₂(Ph2bNO)] and [Ba(hfac)₂(Ph3bNO)] were determined, where Hhfac stands for 1,1,1,5,5,5-hexafluoropentane-2,4-dione. The solution electron paramagnetic resonance spectra showed switching behavior. Five lines were found for Ph3bNO and charecterized as the hyperfine splitting due to the two nitrogen atoms. After addition of barium(II) ion, the spectrum turned to be three lines. Removal of the barium ion recovered the five line pattern. The present system can be regarded as a reversible magnetic-coupling switch by means of a supramolecular technique.     

Crystal and molecular structure of (hexafluoroacetylacetonato) (pivaloylacetonato)copper(II)

The crystal structure of (hexafluoroacetylacetonato)(pivaloylacetonato)copper(II) has been determined. Crystal data for CuO₄C₁₃H₁₄F₆: a = 8.288(2) Å, b = 8.682(2) Å, c = 12.307(2) Å; α = 90.75(3)°, β = 94.29(3)°, γ = 106.60(3)°; V = 845.7(3) ų, space group \(P\overline 1 \), Z = 2, d_calc = 1.617 g/cm³. The coordination polyhedron of the copper atom is formed by four oxygen atoms of two different β-diketonate ligands with Cu-O distances within 1.874–1.946 Å; the O-Cu-O bond angles are 94.8° and 90.6°. The complexes are united into centrosymmetrical “dimers” with Cu...Cu distances of 4.365 Å.