Synthesis and density functional calculations of the new molecule-based magnet precursor [Fe(H2opba-i)(dmso)2]Cl

Abstract

Um precursor inédito de sistemas magnéticos moleculares, [Fe(H 2 opba-i)(dmso) 2 ]Cl (1), onde opba = orto-fenilenobis(oxamato) na forma tautomérica iminoálcool, foi obtido como produto da reação entre H 4 opba e FeCl 3 . Os dados de análise elementar, espectroscopias de absorção no infravermelho e Mössbauer e medidas magnéticas indicam que este precursor é constituído por uma mistura de isômeros trans (83%) e cis (17%). O valor de χ M T a 298 K (2,1 emu K mol -1 ) corresponde ao Fe III com estado de spin (S) entre 3/2 e 5/2. Cálculos teóricos (PBE/DZVP2) de trans-e cis- [Fe(H 2 opba-i)(dmso) 2 ]+ mostram que ambos os isômeros têm spin S = 1/2 no estado fundamental e S = 3/2 para o trans e S = 5/2 para o cis no primeiro estado excitado. A combinação destes resultados leva a valores de χ M T de 0,375 emu K mol -1 e 2,3 emu K mol -1 a baixas e altas temperaturas, respectivamente, os quais são concordantes com os dados experimentais para 1.A new precursor of molecule-based magnetic systems, [Fe(H 2 opba-i)(dmso) 2 ]Cl (1), with opba = ortho-phenylenebis(oxamato) in an iminoalcohol tautomeric form, was obtained as a product from the reaction between H 4 opba and FeCl 3 . Data from elemental analysis, IR and Mössbauer spectroscopies and magnetic measurements indicate that this precursor is composed of a mixture of trans (83%) and cis (17%) isomers. The χ M T value at 298K (2.1 emu K mol -1 ) corresponds to Fe III with spin state (S) between 3/2 and 5/2. Theoretical calculations (PBE/ DZVP2) of trans-and cis-[Fe(H 2 opba-i)(dmso) 2 ] + show that both isomers have spin S = 1/2 in the ground state and S = 3/2 for the trans and S = 5/2 for the cis in the first excited state. The combination of these results leads to χ M T values of 0.375 and 2.3 emu K mol -1 , at low and high temperature respectively, which are in accordance with the experimental data for 1. Keywords: molecule-based magnet, oxamate, iron(III), PBE/DZVP theoretical calculations, cis/trans isomerism IntroductionThe oxamato-based ligands have an important role in molecular magnetism. In the seventies, the proligand 1,3-propylenebis(oxamato), pba, was synthesized, and some years later it was used in the preparation of molecule-based magnets.1 In 1993, the new precursor [Bu 4 N] 2 [Cu(opba)], opba = ortho-phenylenebis(oxamato), was synthesized and largely used as a building block, due to its high solubility in common organic solvents. 2The majority of the work done with oxamato-based building blocks is with Cu II , most probably due to the stability of the compounds with this metal ion. Another reason for employing this metal ion resides on the ferrimagnetic strategy, which consists in the use of two metal ions with large difference in spin states and with 1535 Souza et al. Vol. 17, No. 8, 2006 antiferromagnetic coupling. In this approach, copper complexes can bridge several metal ions resulting in extended molecular systems (chains, two-and threedimensional networks) and clusters. ExperimentalThe proligand H 4 opba was prepared using an adaptation of a ...

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