Estimate of the vibrational contribution to the entropy change associated with the spin transition in the d4 systems [MnIII(pyrol) 3tren] and [CrII(depe)2I2]

Yann Garcia*, Hauke Paulsen, Volker Schünemann, Alfred X. Trautwein, Juliusz A. Wolny

*Korrespondierende/r Autor/-in für diese Arbeit
16 Zitate (Scopus)

Abstract

The vibrational contribution to ΔS of the low-spin ( 3T1) to high-spin (5E) spin transition in two 3d4 octahedral systems [MnIII(pyrol)3tren] and [Cr(depe)2I2] have been estimated by means of DFT calculations (B3LYP/CEP-31G) of the vibrational normal-modes frequencies. The obtained value at the transition temperature for the Mn(iii) complex is ΔSvib(44 K) = 6.3 J K-1 mol-1, which is comparable with the proposed Jahn-Teller contribution of R 1n3 = 9.1 J K -1 mol-1 and which is approximately half of the experimentally determined 13.8 J K-1 mol-1. The corresponding value for the Cr(ii) complex is ΔSvib(171.45 K) = 46.5 J K-1 mol-1, as compared to the experimental value of 39.45 J K-1 mol-1. The analysis of the vibrational normal modes reveals that for the d4 systems under study, contrary to Fe(ii) d6 systems, not all metal-ligand stretching vibrations make a contribution. For the Mn(iii) complex, the only vibration that contributes to ΔSvib involve the nitrogens occupying the Jahn-Teller axis, while in the case of Cr(ii) the contributing vibrations involve the Cr-I bonds. Low-frequency modes due to ring vibrations, metal-ligand bending and movement of the molecule as a whole also contribute to the vibrational entropy associated with the spin transition. This journal is

OriginalspracheEnglisch
ZeitschriftPhysical Chemistry Chemical Physics
Jahrgang9
Ausgabenummer10
Seiten (von - bis)1194-1201
Seitenumfang8
ISSN1463-9076
DOIs
PublikationsstatusVeröffentlicht - 07.03.2007

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