Messanae Universitas Studiorum

Spin crossover complexes in non-aqueous solutions

Linert, Wolfgang (1993) Spin crossover complexes in non-aqueous solutions. Accademia Peloritana dei Pericolanti, Classe di Scienze FF. MM. NN., LXXI. pp. 381-406.

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    Abstract

    Cationic complexes with the tridentate e ligand $4X-2,6-bis-(benzimidazol2'-yl)pyridine (L=4-X-bzimpy, X = H, OH and Cl) [Fe(4X-bzimpy)_2]^2^+$ and $[Ni(4-Xbzimpy)_2]^2^+$ were isolated as $ClO_4^-$ salts and were characterized together with the free ligands by elemental analysis, FT-IR spectroscopy, $^1H-NMR$ spectroscopy, and UV-Vis spectroscopy. The syntheses were performed via condensation of 1,2-phenylendiamine with 4-substituted pyridine-2,6-dicarboxylic acids. Ligand fieid parameters are estimated from the respective Ni-complexes. The $[FeL_2]^2^+$ species show thermally induced spin crossover behaviour $(^1A_1 \to \ ^5T_2_g)$ which has been investigated in methanol, nitromethane and 20% (v/v) DMF in MeOH. The spin-crossover behaviour is complicated by two steps of complex dissociation equiiibria, which equiiibrium constants are evaluated. Ligand substitution is reflected in a change of the spinstate in solution $(X=H: \mu\ _e_x_p=2.5O,  X=OH: \mu\ _e_x_p=4.2O \mu\ _B$ and $X=Cl: \mu\ _e_x_p=4.30 \mu\ _B at 295K, in MeOH)$ and in the metal-to-ligands charge-transfer band $(500-557nm): [Fe(bzimpy)_2(ClO_4)_2]$ exhibits a pronounced spincrossover equiiibrium $(^1A_1 \to \ ^5T_2_g)$. In methanolic solution $( \mu \ _e_x_p=1.30 \to \ 3.40 \mu \ _B for 213 \to \ 328K)$. A small variation of the magnetic moments of $[Fe(4 OH-bzimpy)_2(C1O_4)_2] ( \mu \ _e_x_p=3.77 \to \ 4.73 \mu \ _B at 220.0 \to \ 332K)$ might indicate a temperature variable popuiation of the $^5E_g$ sublevel or variation in hydrogen bonding.

    Item Type: Article
    Subjects: M.U.S. - Miscellanea > Atti Accademia Peloritana > Classe di Scienze Fisiche, Matematiche e Naturali > 1993
    M.U.S. - Miscellanea > Atti Accademia Peloritana > Classe di Scienze Medico-Biologiche > 1993
    M.U.S. - Miscellanea > Atti Accademia Peloritana > Classe di Scienze Giuridiche, Economiche e Politiche > 1993
    M.U.S. - Miscellanea > Atti Accademia Peloritana > Classe di Lettere, Filosofia e belle Arti > 1993
    Divisions: UNSPECIFIED
    Depositing User: Dr A F
    Date Deposited: 21 Sep 2012 11:51
    Last Modified: 22 Jan 2013 10:10
    URI: http://cab.unime.it/mus/id/eprint/752

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