Two Tetranuclear Copper(II) Complexes with Open Cubane-Like Cu4O4 Core Framework and Ferromagnetic Exchange Interactions between Copper(II) Ions: Structure, Magnetic Properties, and Density Functional Study
01 Mar 2014-European Journal of Inorganic Chemistry (John Wiley & Sons, Ltd)-Vol. 2014, Iss: 9, pp 1552-1560
TL;DR: In this paper, two tetranuclear alkoxo-bridged copper(II) tridentate Schiff base complexes have been synthesized and structurally and magnetically characterized.
Abstract: Two alkoxo-bridged copper(II) tridentate Schiff base complexes [{Cu(H2L1)}4] (1) [H2L1 = N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine] and {Cu(H2L2)}4 (2) [H2L2 = N-(2-hydroxyethyl)-4-methoxysalicylaldimine] have been synthesized and structurally and magnetically characterized. X-ray diffraction studies show that 1 and 2 are tetranuclear alkoxo-bridged copper(II) complexes that contain a rather distorted Cu4O4 cubane core of 4+2 type (four short and two long Cu···Cu distances). The coordination of each copper ion can be described as a distorted square pyramid with one nitrogen and four oxygen atoms from three ligands. Variable-temperature magnetic susceptibility measurements on the two tetranuclear complexes 1 and 2 in the range 2–300 K indicate ferromagnetic exchange coupling between copper(II) centers. The magnetic susceptibility data were analyzed by using a simple two-J model with J′ and J″ representing the magnetic exchange couplings through the short and long Cu···Cu exchange pathways, respectively. The J values were as follows: J′ = +28.7 cm–1 and J″ = +7.8 cm–1 for 1, and J′ = +39.8 cm–1 and J″ = +10.2 cm–1 for 2. The sign and magnitude of the exchange coupling constants were justified on the basis of the structural geometric factors of the bridging Cu(O)2Cu fragments, the overlap of the magnetic orbitals, and DFT calculations.
Citations
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TL;DR: Two new copper complexes 3a and 3b with a Cu4O4 cubane core are reported, and the first analysis of single crystal X-ray diffraction studies reveals that both molecules possess a [4 + 2] cubane-type core, and low temperature magnetic measurements show antiferromagnetic behaviour, in agreement with DFT calculations.
Abstract: In the present work, two new copper complexes 3a and 3b with a Cu4O4 cubane core are reported. Both complexes are obtained by means of the in situ conversion of the imine functionality of Schiff's base ligands 1a [(E)-4-chloro-2-((thiazol-2-ylimino)methyl)phenol] and 1b [(E)-4-bromo-2-((thiazol-2-ylimino)methyl)phenol] into amino alcohols 2a (4-chloro-2-(hydroxy(thiazol-2-ylamino)methyl)phenol) and 2b (4-bromo-2-(hydroxy(thiazol-2-ylamino)methyl)phenol), respectively. The ligand transformation may be metal assisted and the generated ligands show an interesting mode of coordination in which the alkoxo-O atom binds in a μ3-manner connecting simultaneously three copper centers and forming a Cu4O4 cubane core. The first analysis of single crystal X-ray diffraction studies reveals that both molecules possess a [4 + 2] cubane-type core, and low temperature magnetic measurements show antiferromagnetic behaviour, in agreement with DFT calculations. However, the best fit and DFT calculations point out three pairs of coupling constants, more coherent with a [2 + 2 + 2] situation, in accordance with the fine analysis of structural data. Finally, phenoxazinone synthase activity has been measured for both molecules, finding kcat = 86.3 h−1 for the chloride derivative copper(II) complex in methanol, whereas the bromide derivative copper(II) complex displays kcat = 3.4026 × 102 h−1 and 10.289 × 102 h−1 in methanol and DMSO, respectively.
64 citations
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TL;DR: A tetranuclear Cu(II) complex [CuII4(L)4] (1) [H2L = N-(2-hydroxyethyl)-3-methoxysalicylaldimine] is found to show overall ferromagnetic exchange coupling as mentioned in this paper.
Abstract: A crystallographically characterized tetranuclear Cu(II) complex [CuII4(L)4] (1) [H2L = N-(2-hydroxyethyl)-3-methoxysalicylaldimine] is found to show overall ferromagnetic exchange coupling. Complex (1) mimics the catalytic activity of the plant enzyme catechol oxidase by oxidising 3,5-di-tert-butylcatechol to its corresponding quinone in methanol and dichloromethane medium in the presence of aerial oxygen. The reaction follows Michaelis–Menten enzymatic reaction kinetics with turnover numbers (Kcat) 6.99 × 103 and 1.85 × 103 h−1 in methanol and dichloromethane, respectively. 1 is also phenoxazinone synthase active in methanol medium with a turnover number of 1.21 × 105 h−1.
38 citations
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TL;DR: In this article, two bridged copper(II) coordination complexes with NNO donor ligands were characterized using a dual approach comprising experimental and quantum computational studies, and the magnetic exchange coupling constant (J) between the Cu(1)⋯Cu(2) centers for 1 and 2 were determined to be J
28 citations
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TL;DR: Oxygen-bridged tetranuclear copper complexes having a Cu4O4 cubane-like core represent a really fascinating class of compounds, due to their similarity to copper oxidase active sites or to their molecular magnetism as mentioned in this paper.
25 citations
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TL;DR: In this article, a defect dicubane cobalt(II)/cobalt(III) was synthesized and characterized by element analysis, FT-IR, solid UV-Vis spectroscopy and single crystal X-ray diffraction.
24 citations
References
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TL;DR: In this article, a semi-empirical exchange correlation functional with local spin density, gradient, and exact exchange terms was proposed. But this functional performed significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
Abstract: Despite the remarkable thermochemical accuracy of Kohn–Sham density‐functional theories with gradient corrections for exchange‐correlation [see, for example, A. D. Becke, J. Chem. Phys. 96, 2155 (1992)], we believe that further improvements are unlikely unless exact‐exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange‐correlation functional containing local‐spin‐density, gradient, and exact‐exchange terms is tested on 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total atomic energies of first‐ and second‐row systems. This functional performs significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
87,732 citations
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TL;DR: Numerical calculations on a number of atoms, positive ions, and molecules, of both open- and closed-shell type, show that density-functional formulas for the correlation energy and correlation potential give correlation energies within a few percent.
Abstract: A correlation-energy formula due to Colle and Salvetti [Theor. Chim. Acta 37, 329 (1975)], in which the correlation energy density is expressed in terms of the electron density and a Laplacian of the second-order Hartree-Fock density matrix, is restated as a formula involving the density and local kinetic-energy density. On insertion of gradient expansions for the local kinetic-energy density, density-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calculations on a number of atoms, positive ions, and molecules, of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent.
84,646 citations
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TL;DR: This paper could serve as a general literature citation when one or more of the open-source SH ELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination.
Abstract: An account is given of the development of the SHELX system of computer programs from SHELX-76 to the present day. In addition to identifying useful innovations that have come into general use through their implementation in SHELX, a critical analysis is presented of the less-successful features, missed opportunities and desirable improvements for future releases of the software. An attempt is made to understand how a program originally designed for photographic intensity data, punched cards and computers over 10000 times slower than an average modern personal computer has managed to survive for so long. SHELXL is the most widely used program for small-molecule refinement and SHELXS and SHELXD are often employed for structure solution despite the availability of objectively superior programs. SHELXL also finds a niche for the refinement of macromolecules against high-resolution or twinned data; SHELXPRO acts as an interface for macromolecular applications. SHELXC, SHELXD and SHELXE are proving useful for the experimental phasing of macromolecules, especially because they are fast and robust and so are often employed in pipelines for high-throughput phasing. This paper could serve as a general literature citation when one or more of the open-source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination.
81,116 citations
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TL;DR: This work reports a gradient-corrected exchange-energy functional, containing only one parameter, that fits the exact Hartree-Fock exchange energies of a wide variety of atomic systems with remarkable accuracy, surpassing the performance of previous functionals containing two parameters or more.
Abstract: Current gradient-corrected density-functional approximations for the exchange energies of atomic and molecular systems fail to reproduce the correct 1/r asymptotic behavior of the exchange-energy density. Here we report a gradient-corrected exchange-energy functional with the proper asymptotic limit. Our functional, containing only one parameter, fits the exact Hartree-Fock exchange energies of a wide variety of atomic systems with remarkable accuracy, surpassing the performance of previous functionals containing two parameters or more.
45,683 citations
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TL;DR: In this article, the linear quadridentate N2S2 donor ligand 1,7-bis(N-methylbenzimidazol-2′-yl)-2,6-dithiaheptane (bmdhp) forms mono-and di-hydrate 1 : 1 copper(II) complexes which are significantly more stable toward autoreduction than those of the non-methylated analogue.
Abstract: The linear quadridentate N2S2 donor ligand 1,7-bis(N-methylbenzimidazol-2′-yl)-2,6-dithiaheptane (bmdhp) forms mono- and di-hydrate 1 : 1 copper(II) complexes which are significantly more stable toward autoreduction than those of the non-methylated analogue. The deep green monohydrate of the perchlorate salt crystallises as the mononuclear aqua-complex, [Cu(bmdhp)(OH2)][ClO4]2, in the monoclinic space group P21/n, with Z= 4, a= 18.459(3), b= 10.362(2), c= 16.365(3)A, and β= 117.14(1)°. The structure was solved and refined by standard Patterson, Fourier, and least-squares techniques to R= 0.047 and R′= 0.075 for 3 343 independent reflections with l > 2σ(l). The compound consists of [Cu(bmdhp)(OH2)]2+ ions and ClO4– counter ions. The co-ordination around copper is intermediate between trigonal bipyramidal and square pyramidal, with Cu–N distances of 1.950(4) and 1.997(4)A, Cu–O(water) 2.225(4)A, and Cu–S 2.328(1) and 2.337(1)A. In the solid state, the perchlorate dihydrate's co-ordination sphere may be a topoisomer of the monohydrate's. A new angular structural parameter, τ, is defined and proposed as an index of trigonality, as a general descriptor of five-co-ordinate centric molecules. By this criterion, the irregular co-ordination geometry of [Cu(bmdhp)(OH2)]2+ in the solid state is described as being 48% along the pathway of distortion from square pyramidal toward trigonal bipyramidal. In the electronic spectrum of the complex, assignment is made of the S(thioether)→ Cu charge-transfer bands by comparison with those of the colourless complex Zn(bmdhp)(OH)(ClO4). E.s.r. and ligand-field spectra show that the copper(II) compounds adopt a tetragonal structure in donor solvents.
7,886 citations