Trinuclear, Tetranuclear, and Polymeric Cu^II Complexes from the First Use of 2-Pyridylcyanoxime in Transition Metal Chemistry: Synthetic, Structural, and Magnetic Studies

The first use of 2-pyridylcyanoxime, (py)C(CN)NOH, in transition metal chemistry is described. Depending on the nature of the metal starting material and the reaction conditions employed, the CuII/(py)C(CN)NOH system has provided access to complexes [Cu3O{(py)C(CN)NO}3(NO3)(H2O)2(MeOH)] (1), [Cu4O{(py)C(CN)NO}4(O2CMe)2] (2), [Cu4(OH)2{(py)C(CN)NO}2(O2CPh)4]2n·n[Cu4(OH)2{(py)C(CN)NO}2(O2CPh)4] (3), and [Cu{(py)C(CN)NO}2]n (4). The molecule of 1 consists of three CuII atoms in a strictly equilateral arrangement bridged by a central μ3-oxide group. The molecule of 2 consists of a tetrahedron of CuII atoms held together by a central μ4-oxide ion, four η1:η1:η1:μ-(py)C(CN)NO− ligands and two η1:η1:μ-MeCO2− groups. The crystal structure of 3 consists of [Cu4(OH)2{(py)C(CN)NO}2(O2CPh)4]2n double chains and discrete cluster [Cu4(OH)2{(py)C(CN)NO}2(O2CPh)4] molecules. The crystal structure of 4 consists of neutral polymeric chains based on centrosymmetric mononuclear [Cu{(py)C(CN)NO}2] units. The CuII atoms are doubly bridged by the oximate groups of two η1:η1:η1:μ-(py)C(CN)NO− ligands. Variable-temperature, solid-state direct current (dc) magnetic susceptibility studies were carried out for 1−4. The data indicate very strong antiferromagnetic exchange interactions for 1−3. The obtained J values are discussed in depth on the basis of the structural parameters of the complexes, literature reports, and existing magnetostructural correlations

Trinuclear, Tetranuclear, and Polymeric Cu^II Complexes from the First Use of 2-Pyridylcyanoxime in Transition Metal Chemistry: Synthetic, Structural, and Magnetic Studies

The first use of 2-pyridylcyanoxime, (py)C(CN)NOH, in transition metal chemistry is described. Depending on the nature of the metal starting material and the reaction conditions employed, the CuII/(py)C(CN)NOH system has provided access to complexes [Cu3O{(py)C(CN)NO}3(NO3)(H2O)2(MeOH)] (1), [Cu4O{(py)C(CN)NO}4(O2CMe)2] (2), [Cu4(OH)2{(py)C(CN)NO}2(O2CPh)4]2n·n[Cu4(OH)2{(py)C(CN)NO}2(O2CPh)4] (3), and [Cu{(py)C(CN)NO}2]n (4). The molecule of 1 consists of three CuII atoms in a strictly equilateral arrangement bridged by a central μ3-oxide group. The molecule of 2 consists of a tetrahedron of CuII atoms held together by a central μ4-oxide ion, four η1:η1:η1:μ-(py)C(CN)NO− ligands and two η1:η1:μ-MeCO2− groups. The crystal structure of 3 consists of [Cu4(OH)2{(py)C(CN)NO}2(O2CPh)4]2n double chains and discrete cluster [Cu4(OH)2{(py)C(CN)NO}2(O2CPh)4] molecules. The crystal structure of 4 consists of neutral polymeric chains based on centrosymmetric mononuclear [Cu{(py)C(CN)NO}2] units. The CuII atoms are doubly bridged by the oximate groups of two η1:η1:η1:μ-(py)C(CN)NO− ligands. Variable-temperature, solid-state direct current (dc) magnetic susceptibility studies were carried out for 1−4. The data indicate very strong antiferromagnetic exchange interactions for 1−3. The obtained J values are discussed in depth on the basis of the structural parameters of the complexes, literature reports, and existing magnetostructural correlations

Acetate/Di-2-pyridyl Ketone Oximate “Blend” as a Source of High-Nuclearity Nickel(II) Clusters: Dependence of the Nuclearity on the Nature of the Inorganic Anion Present

The use of di-2-pyridyl ketone oxime [(py)2CNOH] in reactions with Ni(O2CMe)2·4H2O, in the presence or absence of extra inorganic anions (N3- and SCN-) has led to Ni4, Ni5, and Ni7 clusters; the magnetic study of the heptanuclear nickel(II) complex reveals an S = 3 ground state

Polynuclear Nickel(II) Complexes: Preparation, Characterization, Magnetic Properties, and Quantum-Chemical Study of [Ni₅(OH)(Rbta)₅(acac)₄(H₂O)₄] (RbtaH = Benzotriazole and 5,6-Dimethylbenzotriazole)

The preparation and properties are described of two related NiII5 clusters. The reactions of [Ni(acac)2(H2O)2] (acacH = acetylacetone) with benzotriazole (btaH) and 5,6-dimethylbenzotriazole (5,6diMebtaH) in refluxing Me2CO in the presence of H2O leads to the isolation of [Ni5(OH)(bta)5(acac)4(H2O)4] (1) and [Ni5(OH)(5,6diMebta)5(acac)4(H2O)4] (2) in 70−75 and 40−50% yields, respectively. Complex 1·4Me2CO·0.5C6H14 crystallizes in the triclinic space group P1̄ with (at 25 °C) a = 13.885(1) Å, b = 12.013(1) Å, c = 25.611(2) Å, α = 89.02(1)°, β = 104.76(2)°, γ = 111.78(1)°, and Z = 2. Complex 2·4Me2CO crystallizes in the monoclinic space group C2/c with (at 25 °C) a = 19.085(3) Å, b = 20.142(3) Å, c = 22.574(4) Å, β = 103.30(1)°, and Z = 4. The NiII assemblies of 1 and 2 are composed of a tetrahedral arrangement of four six-coordinate metal ions centered on the fifth. Each of the five η1:η1:η1:μ3 benzotriazolate ligands spans an edge of the Ni4 tetrahedron. The OH- ion bridges three NiII ions and spans the sixth edge of the tetrahedron. A chelating acac- ion and a terminal H2O molecule complete the coordination sphere of each peripheral metal. Variable-temperature magnetic susceptibility data (5.0−295 K), obtained for 1 and 2, show antiferromagnetic interactions for both of them. The data are interpreted using a five-J model, which is based upon the hierarchy of algebras approach. Least-squares fitting of the data gives exchange parameters J for the interactions between the benzotriazolate-bridged peripheral NiII ions in the range from −3.9 to −10.7 cm-1, and for those between the central ion and the peripheral ones in the range from −3.1 to −6.1 cm-1; the J value for the interaction between the O-bridged peripheral nickels is −39.6 cm-1 for 1 and −43.2 cm-1 for 2. Magnetization data are in line with an intermediate spin ground state [S = 0, S = 1] for both clusters. An orbital interpretation of the coupling is proposed

Acetate/Di-2-pyridyl Ketone Oximate “Blend” as a Source of High-Nuclearity Nickel(II) Clusters: Dependence of the Nuclearity on the Nature of the Inorganic Anion Present

The use of di-2-pyridyl ketone oxime [(py)2CNOH] in reactions with Ni(O2CMe)2·4H2O, in the presence or absence of extra inorganic anions (N3- and SCN-) has led to Ni4, Ni5, and Ni7 clusters; the magnetic study of the heptanuclear nickel(II) complex reveals an S = 3 ground state

Octanuclearity in Copper(II) Chemistry: Preparation, Characterization, and Magnetochemistry of [Cu₈(dpk·OH)₈(O₂CCH₃)₄](ClO₄)₄·9H₂O (dpk·H₂O = the Hydrated, <i>gem</i>-Diol Form of Di-2-pyridyl Ketone)

The complexes [Cu8(dpk·OH)8(O2CMe)4](ClO4)4·9H2O (1) and [Cu(dpk·H2O)2](O2CMe)(ClO4)·2H2O (2), where dpk·H2O is the hydrated, gem-diol form of di-2-pyridyl ketone, have been prepared. Complex 1 crystallizes in triclinic space group P1̄ with the following unit cell dimensions at 25 °C:  a = 18.396(1) Å, b = 16.720(1) Å, c = 19.171(1) Å, α = 96.10(1)°, β = 87.68(1)°, γ = 99.14(1)°, Z = 2. Crystal structure data for 2 at room temperature are as follows:  monoclinic, P21/c, a = 13.000(2) Å, b = 8.008(1) Å, c = 27.095(3) Å, β = 93.19(1)°, Z = 4. The two centrosymmetrically related cubanes in the tetracation of 1 are doubly-bridged with two syn, anti acetate groups bridging two CuII atoms. The monoanion dpk·OH- functions as a η1:η3:η1:μ3 ligand. Three CuII atoms have distorted octahedral coordination geometries with CuO3N3 and CuNO5 chromophores, while the fourth CuII center displays a distorted square pyramidal geometry; a terminal monodentate acetate is ligated to this latter CuII atom. In the mononuclear [Cu(dpk·H2O)2]2+ cation of 2, the four pyridyl nitrogens can be viewed as strongly coordinating to the metal (Cu−N = 2.013(4)−2.022(4) Å), while one of the hydroxyl oxygens on each ligand forms a weak bond to CuII (Cu−O = 2.417(4), 2.352(3) Å). Variable-temperature magnetic susceptibility studies on 1 are in line with both an overall antiferromagnetic interaction between CuII atoms and the magnetic behavior of a simple cubane. Exchange parameters, J, derived by using a four-J magnetic model, are found to be J1 = 6 cm-1, J2 = −144 cm-1, J3 = −14 cm-1, J4 = 3 cm-1 and g = 2.29 (adjustable parameter) by least-squares fitting to the spin Hamiltonian H = −2∑ijJijSi·Sj. The thus derived energy level spectrum shows a S = 1 ground state, further supported by the solid-state and solution EPR spectra of 1. Insight concerning the effect of structural parameters on the magnitude of the magnetic exchange interactions was gained through EHMO calculations performed on a model Cu(OR)2Cu moiety. Accordingly, estimates of the J parameters, experimentally derived, were in close agreement both with known magneto−structural correlations established for planar Cu(OR)2Cu moieties and a criterion established by us, holding for the magneto−structural correlations in symmetrical roof-shaped, alkoxo-bridged Cu(OR)2Cu moieties

Acetate/Di-2-pyridyl Ketone Oximate “Blend” as a Source of High-Nuclearity Nickel(II) Clusters: Dependence of the Nuclearity on the Nature of the Inorganic Anion Present

The use of di-2-pyridyl ketone oxime [(py)2CNOH] in reactions with Ni(O2CMe)2·4H2O, in the presence or absence of extra inorganic anions (N3- and SCN-) has led to Ni4, Ni5, and Ni7 clusters; the magnetic study of the heptanuclear nickel(II) complex reveals an S = 3 ground state

A Known Iron(II) Complex in Different Nanosized Particles: Variable-Temperature Raman Study of Its Spin-Crossover Behavior

The spin-crossover (SCO) polymorph B (complex 1) of the known compound [FeII{N­(CN)2}2(abpt)2], where abpt is 4-amino-3,5-bis­(pyridin-2-yl)-1,2,4-triazole, has been prepared in three different particle sizes averaging ∼300 (sample 1a), ∼80 (sample 1b), and ∼20 nm (sample 1c). Two independent octahedral molecules possessing Fe1 and Fe2 were found to be present in the crystal of B. Magnetostructural relationships had established that at room temperature both FeII sites are in the high-spin state (HS-HS), whereas a decrease in the temperature to 90 K induces the complete high-spin to low-spin conversion of the Fe1 site, with Fe2 remaining in the high-spin state (LS-HS). The three samples have been characterized by elemental analyses, ATR spectra, solution UV/vis spectra (to exclude resonance Raman effects) and powder X-ray diffraction patterns, while their morphological characteristics have been examined by scanning electron microscopy (SEM). The SCO behavior of the originally prepared sample 1a has been monitored in detail by variable-temperature Raman studies in the 300–80 K range using mainly low-frequency ν­(Fe–N) and δ­(NFeN) modes and the ν­(CN) mode of the axial dicyanamido groups as spin-sensitive vibrations. The new peaks that appear in the low-temperature Raman spectra of the LS-HS form of the complex are reproduced in the calculated spectrum of the LS state of [FeII{N­(CN)2}2(abpt)2]. The influence of the average particle size on the SCO properties of 1 has also been studied by variable-temperature Raman spectra. The studies indicate that, during the HS-HS → LS-HS transition, the latter form of the complex appears at higher temperatures for the smaller particles; the T1/2 shift accomplished by manipulating the particle size within a range of roughly 1 order of magnitude (300–20 nm) may be as high as ∼30 K. The SCO features of 1, as deduced from the Raman study, are in excellent agreement with those derived from a traditional variable-temperature magnetic susceptibility study, indicating the utility of the former

A Known Iron(II) Complex in Different Nanosized Particles: Variable-Temperature Raman Study of Its Spin-Crossover Behavior

The spin-crossover (SCO) polymorph B (complex 1) of the known compound [FeII{N­(CN)2}2(abpt)2], where abpt is 4-amino-3,5-bis­(pyridin-2-yl)-1,2,4-triazole, has been prepared in three different particle sizes averaging ∼300 (sample 1a), ∼80 (sample 1b), and ∼20 nm (sample 1c). Two independent octahedral molecules possessing Fe1 and Fe2 were found to be present in the crystal of B. Magnetostructural relationships had established that at room temperature both FeII sites are in the high-spin state (HS-HS), whereas a decrease in the temperature to 90 K induces the complete high-spin to low-spin conversion of the Fe1 site, with Fe2 remaining in the high-spin state (LS-HS). The three samples have been characterized by elemental analyses, ATR spectra, solution UV/vis spectra (to exclude resonance Raman effects) and powder X-ray diffraction patterns, while their morphological characteristics have been examined by scanning electron microscopy (SEM). The SCO behavior of the originally prepared sample 1a has been monitored in detail by variable-temperature Raman studies in the 300–80 K range using mainly low-frequency ν­(Fe–N) and δ­(NFeN) modes and the ν­(CN) mode of the axial dicyanamido groups as spin-sensitive vibrations. The new peaks that appear in the low-temperature Raman spectra of the LS-HS form of the complex are reproduced in the calculated spectrum of the LS state of [FeII{N­(CN)2}2(abpt)2]. The influence of the average particle size on the SCO properties of 1 has also been studied by variable-temperature Raman spectra. The studies indicate that, during the HS-HS → LS-HS transition, the latter form of the complex appears at higher temperatures for the smaller particles; the T1/2 shift accomplished by manipulating the particle size within a range of roughly 1 order of magnitude (300–20 nm) may be as high as ∼30 K. The SCO features of 1, as deduced from the Raman study, are in excellent agreement with those derived from a traditional variable-temperature magnetic susceptibility study, indicating the utility of the former