Exchange couplings and quantum phases in two dissimilar arrays of similar copper dinuclear units

X-ray structure and EPR spectra of two dinuclear copper compounds allow us to study spin entanglement and quantum phase transitions. Their different 3D arrays and interdinuclear exchange paths produce important effects.

High-field EPR and magnetic susceptibility studies on binuclear and tetranuclear copper trifluoroacetate complexes. X-ray structure determination of three tetranuclear quinoline adducts of copper(II) trifluoroacetate

Magnetic properties and high-field EPR spectra of three previously unknown tetranuclear quinoline adducts of copper(II) trifluoroacetate were studied, and their X-ray structures were determined. Two green complexes containing a mu(4)-oxo bridge, Cu(4)O(CF(3)COO)(6)(quin)(4) x (C(6)H(5)CH(3))(0.6) (orthorhombic, Pbca, a = 15.278(3), b = 23.227(5), c = 34.895(7) A) and Cu(4)O(CF(3)COO)(6)(quin)(4) x (C(6)H(6))(0.8) (monoclinic, P2/c, a = 21.933(4), b = 11.176(2), c = 23.927(5) A, beta = 97.41(3) degrees) are ferromagnetic, whereas the blue complex [Cu(4)(OH)(2)(CF(3)COO)(8)(quin)(2)](2-)(quinH(+))(2) (monoclinic, a = 21.933(4), b = 11.176(2), c = 23.927(5) A, beta = 97.41(3) degrees), formed in humid air from the solid dimeric [Cu(CF(3)COO)(2) x (quin)](2), is antiferromagnetic, as is the tetranuclear blue product formed in humid air of the mu(4)-oxo tetramers. High-field EPR spectra allowed determination of the spin Hamiltonian parameters for the spin quintet state (S = 2) in the ferromagnetic complexes, which facilitated accurate interpretation of their magnetic susceptibility data. "Broken symmetry" DFT calculations were performed to estimate the exchange integrals in all three tetranuclear complexes, showing surprisingly good agreement with experimental results. Negative sign of the zero-field splitting parameter D in two binuclear complexes, [Cu(CF(3)COO)(2) x CH(3)CN](2) and [Cu(CF(3)COO)(2) x (quin)](2), was found from single-crystal high-field EPR spectra, confirming recent results for nonhalogenated dimeric copper carboxylates.

Copper(II), Cobalt(II), and Nickel(II) Complexes with a Bulky Anthracene-Based Carboxylic Ligand: Syntheses, Crystal Structures, and Magnetic Properties

To systematically explore the influence of the bulky aromatic ring skeleton with a large conjugated pi-system on the structures and properties of their complexes, six CuII, CoII, and NiII complexes with the anthracene-based carboxylic ligand anthracene-9-carboxylic acid (HL1), were synthesized and characterized, sometimes incorporating different auxiliary ligands: [Cu2(L1)4(CH3OH)2](CH3OH) (1), [Cu4(L1)6(L2)4](NO3)2(H2O)2 (2), {[Cu2(L1)4(L3)](CH3OH)0.25}infinity (3), [Co2(L1)4(L4)2(micro-H2O)](CH3OH) (4), {[Co(L1)2(L5)(CH3OH)2]}infinity (5), and {[Ni(L1)2(L5)(CH3OH)2]}infinity (6) (L2 = 2,2'-bipyridine, L3 = 1,4-diazabicyclo[2.2.2]octane, L4 = 1,10-phenanthroline, and L5 = 4,4'-bipyridine). 1 has a dinuclear structure that is further assembled to form a one-dimensional (1D) chain and then a two-dimensional (2D) network by the C-H...O H-bonding and pi...pi stacking interactions jointly. 2 takes a tetranuclear structure due to the existence of the chelating L2 ligand. 3 possesses a 1D chain structure by incorporating the related auxiliary ligand L3, which is further interlinked via interchain pi...pi stacking, resulting in a three-dimensional (3D) network. 4 also has a dinuclear structure and then forms a higher-dimensional supramolecular network through intermolecular pi...pi stacking and/or C-H...pi interactions. 5 and 6 are isostructural complexes, except they involve different metal ions, showing 1D chain structures, which are also assembled into 2D networks from the different crystallographic directions by interchain pi...pi stacking and C-H...pi interactions, respectively. The results reveal that the steric bulk of the anthracene ring in HL1 plays an important role in the formation of 1-6. The magnetic properties of the complexes were investigated, and the very long intermetallic distances result in weak magnetic coupling, with the exception of 1 and 3, which adopt the typical paddle-wheel structure of copper acetate and are thus strongly coupled.

ESR, Zero-Field Splitting, and Magnetic Exchange of Exchange-Coupled Copper(II)−Copper(II) Pairs in Copper(II) Tetraphenylporphyrin N-Oxide

The crystal structures of the dimer form of copper(II) tetraphenylporphyrin N-oxide, [Cu(tpp-N-O)]2 (3-dimer), and zinc(II) tetraphenylporphyrin N-oxide, [Zn(tpp-N-O)]2 (4-dimer), were established. The geometry at the copper ion in 3-dimer is essentially square-pyramidal with one oxygen bridge [O(1A)] occupying the apical site, giving a much larger Cu-O bond distance compared to those at the basal plane. The respective Cu...Cu distance and Cu-O-Cu angle in the core of 3-dimer are 3.987(4) A and 148.1(3) degrees. The Zn(1) atom in 4-dimer has a distorted square-pyramidal [4 + 1] coordination geometry that gives a tau-value of 0.19. The respective Zn...Zn distance and Zn-O-Zn angle in the dimeric unit of 4-dimer are 4.025(3) A and 148.1(2) degrees. The 3-dimer displays axial X-band electron paramagnetic resonance spectral features (Es = 0) in the powder state at 4 K, giving g parallel = 2.51 (A(parallel,s) = (9.6 +/- 0.2) x 10-3 cm(-1)) and g(perpendicular) = 2.11 and in the same powder state at 293 K giving Ds = 0.0731 cm(-1) (as derived from DeltaMs = 1 lines) or 0.0743 cm(-1) (as derived from the DeltaMs = 2 lines). In addition, 3-dimer displays a DeltaMs = 2 transition at g = 4.17 indicating the presence of spin-exchange coupling. The anisotropic exchange interaction (Ds(ex)= 0.132 cm(-1)) gives the main contribution to Ds in 3-dimer. The theoretical fit of the susceptibility and effective magnetic moment data of 3-dimer in the temperature range of 5-300 K gives 2J = 68 cm(-1), g = 2.01, p = 0.06, and a temperature-independent paramagnetism of 10(-6) cm3 mol(-1). This magnetic susceptibility data indicates that the copper(II) ions in 3-dimer are coupled in a ferromagnetic manner with the ground-spin triplet stabilized by 68 cm(-1) with regard to the singlet.

Synthesis, Structures, and Magnetic Properties of the Copper(II), Cobalt(II), and Manganese(II) Complexes with 9-Acridinecarboxylate and 4-Quinolinecarboxylate Ligands

To explore the relationships between the structures of ligands and their complexes, we have synthesized and characterized a series of metal complexes with two structurally related ligands, 9-acridinecarboxylic acid (HL(1)) and 4-quinolinecarboxylate acid (HL(2)), [Cu(2)(mu(2)-OMe)(2)(L(1))(2)(H(2)O)(0.69)](n) 1, [Cu(2)(L(1))(4)(CH(3)OH)(2)] 2, [Cu(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 3, [Mn(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 4, [Co(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 5, [Cu(L(2))(2)](n) 6, [Mn(L(2))(2)(H(2)O)](n) 7, and [Co(L(2))(2)(H(2)O)](n) 8. 1 is a three-dimensional (3D) polymer with an interpenetrating NbO type network showing one-dimensional (1D) channels, whereas 2 and 3 take bi- and trinuclear structures, respectively, because of the differences in basicity of the reaction systems in preparing the three complexes. 4 and 5 have trinuclear structures similar to that of 3. In 1-5, ligand L(1) performs different coordination modes with N,O-bridging in 1 and O,O'-bridging in 2-5, and the metal ions also show different coordination geometries: square planar in 1, square pyramidal in 2, and octahedral in 3-5. 6 has a two-dimensional structure containing (4,4) grids in which L(2) adopts the N,O-bridging mode and the Cu(II) center takes square planar geometry. 7 and 8 are isostructural complexes showing 1D chain structures, with L(2) adopting the O,O-bridging mode. In addition, the intermolecular O-H...N hydrogen bonds and pi-pi stacking interactions further extend the complexes (except 1 and 6), forming 3D structures. The magnetic properties of 2-7 have been investigated and discussed in detail.

Coordination Polymers Assembled from Angular Dipyridyl Ligands and CuII, CdII, CoII Salts: Crystal Structures and Properties

Six new metal-organic coordination networks based on linking unit 2,5-bis(4-pyridyl)-1,3,4-thiadiazole (L(1)) or 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L(3)) and inorganic Cu(II), Cd(II), and Co(II) salts have been prepared and structurally characterized by single-crystal X-ray analysis. Using L(1) to react with three different Cu(II) salts, Cu(OAc)(2).H(2)O, Cu(NO(3))(2).3H(2)O, and CuSO(4).5H(2)O, respectively, two different one-dimensional (1-D) coordination polymers, [[Cu(2)L(1)(mu-OAc)(4)](CHCl(3))(2)](n) (1) [triclinic, space group P1, a = 7.416(3) A, b = 8.207(3) A, c = 14.137(5) A, alpha = 100.333(7) degrees, beta = 105.013(6) degrees, gamma = 94.547(6) degrees, Z = 1] and [[CuL(1)(NO(3))(2)](CHCl(3))(0.5)](n) (2) [monoclinic, space group C2/c, a = 28.070(8) A, b = 9.289(3) A, c = 15.235(4) A, beta = 113.537(5) degrees, Z = 8], and a chiral 3-D open framework, [[CuL(1)(H(2)O)(SO(4))](H(2)O)(2)](n) (3) [orthorhombic, space group P2(1)2(1)2(1), a = 5.509(2) A, b = 10.545(4) A, c = 29.399(11) A, Z = 4], were obtained. Reaction of L(1) and Cd(ClO(4))(2).6H(2)O or Co(ClO(4))(2).6H(2)O, in the presence of NH(4)SCN, yielded another 3-D open framework, [[CdL(1)(NCS)(2)](CH(3)OH)(1.5)](n) (4) [monoclinic, space group C2/c, a = 28.408(10) A, b = 9.997(5) A, c = 7.358(4) A, beta = 99.013(8) degrees, Z = 4], or a 2-D network, [[Co(L(1)())(2)(NCS)(2)](H(2)O)(2.5)](n) (5) [orthorhombic, space group Pnna, a = 22.210(5) A, b = 12.899(3) A, c = 20.232(4) A, Z = 4]. When L(1) was replaced by L(3) to react with Co(ClO(4))(2).6H(2)O and NH(4)SCN, another 2-D coordination polymer, [Co(L(3))(2)(NCS)(2)](n) (6) [monoclinic, space group P2(1)/c, a = 8.120(3) A, b = 9.829(4) A, c = 17.453(6) A, beta = 103.307(6) degrees, Z = 2], was constructed. These results indicate that the nature of the ligands, metal centers, or counteranions plays the critical role in construction of these novel coordination polymers. The interesting porous natures of two 3-D open frameworks 3 and 4 were investigated by TGA and XPRD techniques, and the magnetic properties of the Cu(II) and Co(II) complexes were studied by variable-temperature magnetic susceptibility and magnetization measurements.