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Selected dissociation‐ and correlation‐consistent configuration interaction by a perturbative criterion

  • Merchán Bonete, Manuela
  • González Luque, Remedios
  • Nebot Gil, Ignacio José
We propose a perturbative criterion to select the most important dissociation‐ or correlation‐consistent type of contributions to perform generalized valence bond‐configuration interaction (GVB‐CI) calculations, dissociation‐consistent configuration interaction (DCCI) or correlation‐consistent configuration interaction (CCCI) approach, respectively. The procedure presented is computationally less demanding than the CCCI proposed by Goddard and co‐workers. To ensure the distance consistency of the MOs used, the nonvalence virtual orbitals are obtained by a projection technique. The results obtained for a few test calculations show the ability of the suggested approach to get close results to full CI, DCCI, and CCCI values using a small CI expansion. It seems to be a promising way to treat correlation changes in large molecular systems which would be inaccessible by other methods., Manuela.Merchan@uv.es ; Ignacio.Nebot@uv.es
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Electronic structure of phthalocyanines : Theoretical investigation of the optical properties of phthalocyanine monomers, dimers, and crystals

  • Ortí Guillén, Enrique
  • Brédas, J. L.
  • Clarisse, C.
We present valence effective Hamiltonian (VEH) calculations on the optical absorptions of a series of phthalocyanine compounds: the metal‐free phthalocyanine molecule, a model system for the lithium phthalocyanine molecule, the metal‐free phthalocyanine dimer, and model systems for the lutetium diphthalocyanine and the lithium phthalocyanine crystal. For these compounds, it is found that the major factor influencing the evolution of the optical transitions is not the electronic structure of the metal but rather the geometric structure: phthalocyanine intraring geometry and, in the dimers and crystals, interring separation and staggering angle. The origin of the so‐called Soret or B absorption band is calculated to be significantly more complex than was previously thought on the basis of the simple four‐orbital model., Enrique.Ortí@uv.es
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Magnetism and EPR spectra of the two‐sublattice manganese chain Mn2(EDTA)⋅9H2O

  • Borrás Almenar, Juan José
  • Coronado Miralles, Eugenio
  • Gómez García, Carlos José
  • Gatteschi, S.
  • Zanchini, C.
We report on the magnetic behavior and single‐crystal EPR spectra of the chain complex Mn2(EDTA)⋅9H2O characterized by two different alternating sites for the manganese ions. Magnetic susceptibility data are indicative of weak antiferromagnetic exchange interactions between the manganese ions, showing a maximum of about 3 K. This behavior can be accurately described on the basis of a Heisenberg chain model that assumes classical spins, giving J/k=−0.72 K and g=2.0. The EPR spectra are typically low dimensional, with an angular dependence of the linewidth of the type (3 cos2 θ−1)n (n=4/3 or 2). Nevertheless, such a behavior cannot be reproduced from a one‐dimensional model with dipolar broadening. An alternative broadening mechanism arising from single‐ion zero‐field splitting is then suggested., Juan.J.Borras@uv.es ; Eugenio.Coronado@uv.es ; Carlos.Gomez@uv.es
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1D ferrimagnetism in homometallic chains

  • Coronado Miralles, Eugenio
  • Gómez García, Carlos José
  • Borrás Almenar, Juan José
The magnetic properties of the cobalt zigzag chain Co(bpy)(NCS)2 (bpy=2,2′‐bipyridine) are discussed on the basis of an Ising‐chain model that takes into account alternating Landé factors. It is emphasized, for the first time, that a homometallic chain containing only one type of site can give rise to a 1D ferrimagneticlike behavior., Juan.J.Borras@uv.es , Eugenio.Coronado@uv.es
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Mixed‐valence trinuclear manganese clusters : Influence of the electronic transfer on the magnetic properties

  • Gómez García, Carlos José
  • Coronado Miralles, Eugenio
  • Pourroy, G.
The magnetic behavior of mixed‐valence trinuclear clusters d4‐d4‐d5 is discussed on the basis of a model which takes into account valence delocalization and Heisenberg exchange. This model considers the competing effect between the electronic transfer and the localization of the extra electron due to an asymmetry of the triangular entity. The magnetic properties of the mixed‐valence oxo‐centered Mn(II)‐Mn(III)‐Mn(III) complexes formulated as Mn3O(O2CR)6L3 (R=Me, L=pyridine) are discussed on the basis of the developed model, supporting a significant intramolecular electron transfer. A comparison of these results to those previously reported by assuming a valence‐trapped model is given., Carlos.Gomez@uv.es ; Eugenio.Coronado@uv.es
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The ferrimagnetic compounds CoM[M′(EDTA)]2⋅4H2O(M,M′=Co,Ni) : Magnetic characterization of CoCo[Ni(EDTA)2]⋅4H2O

  • Sapiña Navarro, Fernando
  • Coronado Miralles, Eugenio
  • Gómez Romero, Pedro
  • Beltrán Porter, Daniel
  • Burriel, R.
  • Carlin, R.L.
We report on the magnetic properties of the ordered bimetallic compound CoCo(NiEDTA)2⋅4H2O (abbreviated as [CoCoNi]). The structure consists of ordered bimetallic layers formed by alternating octahedral sites of Co and Ni(II); tetrahedral Co sites connect different Co‐Ni layers. We discuss the low‐dimensional ferrimagnetic behavior of this compound in terms of a model that assumes three spin sublattices exchange coupled by an Ising interaction., Fernando.Sapina@uv.es ; Eugenio.Coronado@uv.es ; Pedro.Gomez-Romero@uv.es ; Daniel.Beltran@uv.es
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1D antiferromagnetism in spin‐alternating bimetallic chains

  • Coronado Miralles, Eugenio
  • Sapiña Navarro, Fernando
  • Drillon, M.
  • de Jongh, L.J.
The magnetic and thermal properties of the ordered bimetallic chain CoNi(EDTA)⋅6H2O in the very low‐temperature range are reported. The magnetic behavior does not exhibit the characteristic features of 1D ferrimagnets, but a continuous decrease of χmT towards zero at absolute zero. This 1D antiferromagnetic behavior results from an accidental compensation between the moments located at the two sublattices. This behavior, as well as the specific‐heat results, are modeled on the basis of an Ising‐exchange model that considers both alternating spins and Landé factors, and a zero‐field splitting on the Ni site., Eugenio.Coronado@uv.es ; Fernando.Sapina@uv.es
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Crystal structure and magnetism of Co(HPO3)⋅H2O : A novel layered compound of Co(II)

  • Marcos, María Dolores
  • Gómez Romero, Pedro
  • Amorós del Toro, Pedro José
  • Sapiña Navarro, Fernando
  • Beltrán Porter, Daniel
  • Navarro, R.
  • Rillo, C.
  • Lera, F.
The crystal structure and magnetic properties of Co(HPO3)⋅H2O have been determined. The solid crystallizes in space group Pca21, a=8.984(2) Å, b=7.918(2) Å, c=10.139(8) Å, V=721.2 Å3. Z=4 dcalc =2.89 g/cm3. The structure consists of layers only connected by hydrogen bonds. These layers can be viewed as formed by zigzag chains of edge‐sharing Co(II)O6 octahedra interconnected by a three atom bridge (O‐P‐O) and a single oxygen bridge. ac magnetic susceptibility measurements show a sharp peak at Tc =(10.8±0.1) K, and are consistent with a transition from one‐ to two‐dimensional magnetic order, in agreement with the structure. An analysis of the χT/C vs ϵ=(1−Tc/T) data in the critical region, for T>Tc, using a double‐logarithmic plot, yields a critical exponent γ=1.75 for 0.01<ϵ<0.1, which correspond to a two‐dimensional Ising model., Pedro.Amoros@uv.es ; Pedro.Gomez-Romero@uv.es ; Daniel.Beltran@uv.es
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Magnetic exchange interactions in the heteropoly complexes [M4(H2O)2(PW9O34)2]10− [M=Co(II) and Cu(II)]

  • Gómez García, Carlos José
  • Casañ Pastor, N.
  • Baker, L.C.W.
  • Pourroy, G.
  • Coronado Miralles, Eugenio
The magnetic properties of the heteropolyanions [M4(H2O)2(PW9O34)2]10− [M=Co(II) and Cu(II)] down to 4 K are reported. Their individual heteropoly molecules contain a rhomblike arrangement formed by four coplanar MO6 octahedra sharing edges. The magnetic properties support an intramolecular ferromagnetic exchange in the Co(II) tetramer, and antiferromagnetic exchange in the Cu(II) tetramer. These behaviors are discussed assuming anisotropic exchange in the Co(II) compound, and Heisenberg exchange in the Cu(II) compound., Carlos.Gomez@uv.es
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