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

Redox-Induced Change in the Ligand Coordination Mode

The reaction of cobalt­(II) pivalate with a spin-labeled Schiff base (HL1) in organic solvents formed trinuclear complex [Co3(Piv)2L12L22]·Solv (Solv is Me2CO and/or C7H16 and CH3CN) containing both nitroxide L1 and the product of its single-electron reduction, nitrone L2. The formation of [Co3(Piv)2L12L22] was a consequence of an unusual phenomenon, which we called “redox-induced change in the ligand coordination mode”. A reduction of L1 to L2 led to a change in the set of donor atoms and even in the size of the metallocycle. This phenomenon was also found for mononuclear [CrL12L2] and [FeL12L2]·Me2CO

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

Redox-Induced Change in the Ligand Coordination Mode

The reaction of cobalt­(II) pivalate with a spin-labeled Schiff base (HL1) in organic solvents formed trinuclear complex [Co3(Piv)2L12L22]·Solv (Solv is Me2CO and/or C7H16 and CH3CN) containing both nitroxide L1 and the product of its single-electron reduction, nitrone L2. The formation of [Co3(Piv)2L12L22] was a consequence of an unusual phenomenon, which we called “redox-induced change in the ligand coordination mode”. A reduction of L1 to L2 led to a change in the set of donor atoms and even in the size of the metallocycle. This phenomenon was also found for mononuclear [CrL12L2] and [FeL12L2]·Me2CO

Redox-Induced Change in the Ligand Coordination Mode

The reaction of cobalt­(II) pivalate with a spin-labeled Schiff base (HL¹) in organic solvents formed trinuclear complex [Co₃(Piv)₂L¹₂L²₂]·Solv (Solv is Me₂CO and/or C₇H₁₆ and CH₃CN) containing both nitroxide L¹ and the product of its single-electron reduction, nitrone L². The formation of [Co₃(Piv)₂L¹₂L²₂] was a consequence of an unusual phenomenon, which we called “redox-induced change in the ligand coordination mode”. A reduction of L¹ to L² led to a change in the set of donor atoms and even in the size of the metallocycle. This phenomenon was also found for mononuclear [CrL¹₂L²] and [FeL¹₂L²]·Me₂CO

Ligand Structure Effects on Molecular Assembly and Magnetic Properties of Copper(II) Complexes with 3‑Pyridyl-Substituted Nitronyl Nitroxide Derivatives

Reaction of Cu­(hfac)2 with methyl- and bromo-3-pyridyl-substituted nitronyl nitroxides (LR) leads to assemble a diverse set of coordination complexes: mononuclear [Cu­(hfac)2L2‑Me], binuclear [{Cu­(hfac)2}2(H2O)­L2‑Me], trinuclear [{Cu­(hfac)2}3(L6‑Br)2], pentanuclear [{Cu­(hfac)2}5(L2‑Me)2], and [{Cu­(hfac)2}5(L2‑Me)4], cocrystals [Cu­(hfac)2(L2‑Br)2]·[Cu­(hfac)2(H2O)2] and [Cu­(hfac)2(L2‑Br)2]·2­[Cu­(hfac)2H2O], one-dimensional polymers [Cu­(hfac)2L2‑Br]n and [Cu­(hfac)2L6‑Br]n, and cyclic dimers [Cu­(hfac)2L5‑Me]2, [Cu­(hfac)2L5‑Br]2, and [Cu­(hfac)2L6‑Me]2. The molecular structures of the obtained complexes are strongly affected by the substituent type and its location in the pyridine heterocycle. Occupation of the second position of the pyridine ring increases the steric hindrance of both imine and nitroxide coordination sites of L2‑R, which is favorable for the formation of various conformers and precipitation of complexes with different molecular structures. The pentanuclear [{Cu­(hfac)2}5(L2‑Me)2] and [{Cu­(hfac)2}5(L2‑Me)4] complexes do not have prior analogues and are valuable model objects for investigation of the mechanism of formation of various coordination polymers. The arrangement of long Cu–ONO bonds in {CuO6} square bipyramids due to the weakening nitroxide donor site in complexes, based on L2‑Me, L2‑Br, and L6‑Br ligands, results in ferromagnetic exchange interactions between spins of Cu2+ ions and nitroxides. Complexes with substituents that do not considerably affect the coordination ability of ligands (L5‑Me, L5‑Br, and L6‑Me) exhibit strong antiferromagnetic exchange interactions between spins of Cu2+ ions and nitroxides

Polynuclear Hydroxido-Bridged Complexes of Platinum(IV) with Terminal Nitrato Ligands

For the first time the polynuclear hydroxido-bridged platinum­(IV) nitrato complexes with nuclearity higher than two were isolated from nitric acid solutions of [Pt­(H₂O)₂(OH)₄] and crystallized as supramolecular compounds of macrocyclic cavitands cucurbit­[<i>n</i>]­uril (CB­[<i>n</i>], <i>n</i> = 6,8) and 18-crown-6 ether: [Pt₄(μ₃-OH)₂­(μ₂-OH)₄­(NO₃)₁₀]·CB­[6]·25H₂O (<b>I</b>), [Pt₆(μ₃-OH)₄­(μ₂-OH)₆­(NO₃)₁₂]­(NO₃)₂·CB­[8]·50H₂O (<b>II</b>), and [H₃O⊂18-crown-6]₂­[Pt₂(μ₂-OH)₂(NO₃)₈]­[Pt₄(μ₃-OH)₂­(μ₂-OH)₄(NO₃)₁₀] (<b>III</b>). The isolation of the compounds in the single crystalline state allows the determination of the structure of the tetranuclear and hexanuclear complexes [Pt₄(μ₃-OH)₂­(μ₂-OH)₄(NO₃)₁₀] and [Pt₆(μ₃-OH)₄­(μ₂-OH)₆(NO₃)₁₂]²⁺, which have been previously unknown in the solid state. Stability of Pt_<i>x</i>(OH)_<i>y</i> cores of the polynuclear nitrato complexes toward alkaline hydrolysis was verified by ¹⁹⁵Pt NMR spectroscopy. Analysis of ¹⁹⁵Pt NMR spectra of the compound <b>III</b> reveals that addition of every Pt­(μ-OH)₂Pt ring results in ∼260 ppm downfield shift relative to the mononuclear form, which allows the prediction of signal positions for complexes of higher nuclearity

Polynuclear Hydroxido-Bridged Complexes of Platinum(IV) with Terminal Nitrato Ligands

For the first time the polynuclear hydroxido-bridged platinum­(IV) nitrato complexes with nuclearity higher than two were isolated from nitric acid solutions of [Pt­(H₂O)₂(OH)₄] and crystallized as supramolecular compounds of macrocyclic cavitands cucurbit­[<i>n</i>]­uril (CB­[<i>n</i>], <i>n</i> = 6,8) and 18-crown-6 ether: [Pt₄(μ₃-OH)₂­(μ₂-OH)₄­(NO₃)₁₀]·CB­[6]·25H₂O (<b>I</b>), [Pt₆(μ₃-OH)₄­(μ₂-OH)₆­(NO₃)₁₂]­(NO₃)₂·CB­[8]·50H₂O (<b>II</b>), and [H₃O⊂18-crown-6]₂­[Pt₂(μ₂-OH)₂(NO₃)₈]­[Pt₄(μ₃-OH)₂­(μ₂-OH)₄(NO₃)₁₀] (<b>III</b>). The isolation of the compounds in the single crystalline state allows the determination of the structure of the tetranuclear and hexanuclear complexes [Pt₄(μ₃-OH)₂­(μ₂-OH)₄(NO₃)₁₀] and [Pt₆(μ₃-OH)₄­(μ₂-OH)₆(NO₃)₁₂]²⁺, which have been previously unknown in the solid state. Stability of Pt_<i>x</i>(OH)_<i>y</i> cores of the polynuclear nitrato complexes toward alkaline hydrolysis was verified by ¹⁹⁵Pt NMR spectroscopy. Analysis of ¹⁹⁵Pt NMR spectra of the compound <b>III</b> reveals that addition of every Pt­(μ-OH)₂Pt ring results in ∼260 ppm downfield shift relative to the mononuclear form, which allows the prediction of signal positions for complexes of higher nuclearity