Synthesis and Structure of Heterospin Compounds Based on the [Mn₆(O)₂Piv₁₀]-Cluster Unit and Nitroxide

Reaction of [Mn6(O)2Piv10(Thf)4]·Thf with 2,4,4,5,5-pentamethyl-4,5-dihydro-1H-imidazolyl-3-oxide-1-oxyl (NIT-Me) produces different heterospin compounds depending of the solvent used in the synthesis. Among the latter a new molecular magnet [Mn6(O)2Piv10(Thf)2(NIT-Me)Mn6(O)2Piv10(Thf)(CH2Cl2)(NIT-Me)] with Tc = 3.5 K has been found

Problem of a Wide Variety of Products in the Cu(hfac)₂−Nitroxide System

The stereochemically flexible Cu(hfac)2 metal−ligand system when combined with polyfunctional nitroxides leads to a variety of solids with varying structure and composition. While investigating the products of Cu(hfac)2 interaction with spin-labeled pyrazole 4,4,5,5-tetramethyl-2-(1-methyl-1H-pyrazol-4-yl)-imidazoline-3-oxide-1-oxyl, we have isolated a family of (12) heterospin compounds differing in structure and composition in the solid state. In synthetic systems, these compounds often cocrystallize and must be separated mechanically. It is also shown that minor variation of the structure of the solid heterospin complex can substantially change the magnetic properties of compounds

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 P1̄ space group of 2 with the following parameters:  a =10.6191(4) Å, b = 19.6384(7) Å, c = 21.941(9) Å, α = 107.111(7)°, β = 95.107(8)°, γ = 94.208(0)°, 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 μeff 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 μeff was observed. The magnetic susceptibility data are described by the Curie−Weiss law [χ = C/(T − θ)] with the optimal parameters C = 4.32 ± 0.01 emuK/mol and θ = − 0.6 ± 0.3 K, where C is the Curie constant and θ is the Weiss temperature

2D and 3D Cu(hfac)₂ Complexes with Nitronyl Nitroxide Biradicals

Reactions between Cu(hfac)2 and nitronyl nitroxide biradicals 1,4-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]butane (L4) and 1,8-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]octane (L8) gave respectively a framework compound [Cu(hfac)2]2L4 and a layered polymer compound [Cu(hfac)2]2L8. The framework of [Cu(hfac)2]2L4 consists of 66-membered condensed metallocycles. Inside the framework, the structure has macrohelixes (pitch ∼25 Å) extending along the [001] crystallographic direction. All the helixes have the same direction of winding; the crystals, therefore, are optically active, the structure corresponding either to P-isomer (P41212) or to M-isomer (P43212). The long distances between the Cu atoms and the O atoms of the coordinated >N−O groups (Cu−O 2.351−2.467 Å) are responsible for ferromagnetic exchange interactions in Cu2+−O−NN−O−Cu2+−O−N< exchange clusters

Synthesis, Structure, and Magnetic Properties of (6−9)-Nuclear Ni(II) Trimethylacetates and Their Heterospin Complexes with Nitroxides

New polynuclear nickel trimethylacetates [Ni6(OH)4(C5H9O2)8(C5H10O2)4] (6), [Ni7(OH)7(C5H9O2)7(C5H10O2)6(H2O)]·0.5C6H14·0.5H2O (7), [Ni8(OH)4(H2O)2(C5H9O2)12] (8), and [Ni9(OH)6(C5H9O2)12(C5H10O2)4]·C5H10O2·3H2O (9), where C5H9O2 is trimethylacetate and C5H10O2 is trimethylacetic acid, have been found. Their structures were determined by X-ray crystallography. Because of their high solubility in low-polarity organic solvents, compounds 6−9 reacted with stable organic radicals to form the first heterospin compounds based on polynuclear Ni(II) trimethylacetate and nitronyl nitroxides containing pyrazole (L1−L3), methyl (L4), or imidazole (L5) substituent groups, respectively, in side chain [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L1)2(H2O)]·0.5C6H14·H2O (6+1a), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L2)2(H2O)]·H2O (6+1b), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L3)2(H2O)]·H2O (6+1c), [Ni6(OH)3(C5H9O2)9(C5H10O2)4(L4)]·1.5C6H14 (6‘ ‘), and [Ni4(OH)3(C5H9O2)5(C5H10O2)4(L5)]·1.5C7H8 (4). Their structures were also determined by X-ray crystallography. Although Ni(II) trimethylacetates may have varying nuclearity and can change their nuclearity during recrystallization or interactions with nitroxides, this family of compounds is easy to study because of its topological relationship. For any of these complexes, the polynuclear framework may be derived from the [Ni6] polynuclear fragment {Ni6(μ4-OH)2(μ3-OH)2(μ2-C5H9O2−O,O‘)6(μ2-C5H9O2−O,O)(μ4-C5H9O2−O,O,O‘,O‘)(C5H10O2)4}, which is shaped like an open book. On the basis of this fragment, the structure of 7-nuclear compounds (7 and 6+1a−c) is conveniently represented as the result of symmetric addition of other mononuclear fragments to the four Ni(II) ions lying at the vertexes of the [Ni6] open book. The 9-nuclear complex is formed by the addition of trinuclear fragments to two Ni(II) ions lying on one of the lateral edges of the [Ni6] open book. This wing of the 9-nuclear complex preserves its structure in another type of 6-nuclear complex (6‘ ‘) with the boat configuration. If, however, two edge-sharing Ni(II) ions are removed from [Ni6] (one of these lies at a vertex of the open book and the other, on the book-cover line), we obtain a 4-nuclear fragment recorded in the molecular structure of 4. Twinning of this 4-nuclear fragment forms highly symmetric molecule 8, which is a new chemical version of cubane