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Gonzalez-Navarrete P.,Jaume I University | Gonzalez-Navarrete P.,CNRS Theoretical Chemistry Laboratory | Calatayud M.,CNRS Theoretical Chemistry Laboratory | Calatayud M.,Institut Universitaire de France | And 3 more authors.
Journal of Physical Chemistry A | Year: 2013

A theoretical investigation using density functional theory (DFT) has been carried out in order to understand the molecular mechanism of dihydrogen activation by means of transition metal dioxides MO2 (M = Ti, Zr, and Hf) according to the following reaction: MO2 + H2 → MO + H2O. B3LYP/6-311++G(2df,2pd)/SDD methodology was employed considering two possible reaction pathways. As the first step hydrogen activation by Mi=O bonds yields to metal-oxo hydride intermediates Oi=MH(OH). This process is spontaneous for all metal dioxides, and the stability of the Oi=MH(OH) species depends on the transition metal center. Subsequently, the reaction mechanism splits into two paths: the first one takes place passing through the M(OH)2 intermediates yielding to products, whereas the second one corresponds to direct formation of the product complex OM(H2O). A two-state reactivity mechanism was found for the TiO2 system, whereas for ZrO2 and HfO2 no spin-crossing processes were observed. This is confirmed by CASSCF/CASPT2 calculations for ZrO2 that lead to the correct ordering of electronic states not found by DFT. The results obtained in the present paper for MO2 molecules are consistent with the observed reactivity on surfaces. © 2013 American Chemical Society.


Marinho M.V.,University Of Valeincia | Simoes T.R.G.,Federal University of Minas Gerais | Ribeiro M.A.,Federal University of Minas Gerais | Pereira C.L.M.,Federal University of Minas Gerais | And 7 more authors.
Inorganic Chemistry | Year: 2013

A new compound of formula (Bu4N)2[Mn 2{Cu(opba)}2ox] (1) [Bu4N+ = tetra-n-butylammonium cation, H4opba = 1,2-phenylenebis(oxamic acid), and H2ox = oxalic acid] has been synthesized and magneto-structurally investigated. The reaction of manganese(II) acetate, [Cu(opba)]2-, and ox2- in dimethyl sulfoxide yielded single crystals of 1. The structure of 1 consists of heterobimetallic oxamato-bridged CuIIMnII chains which are connected through bis-bidentate oxalate coordinated to the manganese(II) ions to afford anionic heterobimetallic layers of 63-hcb net topology. The layers are interleaved by n-Bu4N+ counterions. Each copper(II) ion in 1 is four-coordinate in a square planar environment defined by two amidate-nitrogen and two carboxylate-oxygen atoms from the two oxamate groups of the obpa ligand. The manganese(II) ion is six-coordinate in a somewhat distorted octahedral surrounding that is built by two oxalate-oxygen and four carbonyl-oxygen atoms from two [Cu(opba)]2- units. The magnetic properties of 1 in the temperature range 1.9-300 K correspond to those expected for the coexistence of intralayer antiferromagnetic interactions of the type copper(II)-manganese(II) across oxamato and manganese(II)-manganese(II) through oxalato bridges plus a weak spin canting in the very low temperature domain. Simulation of the magnetic data through quantum Monte Carlo methodology reveals the magnitude of the intralayer magnetic interactions [JCuMn = -32.5(3) cm-1, and JMnMn = -2.7(3) cm-1], their values being within the range of those previously observed in lower nuclearity systems. © 2013 American Chemical Society.

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