Theoretical Insights into the Ferromagnetic Coupling in Oxalato-Bridged Chromium(III)-Cobalt(II) and Chromium(III)-Manganese(II) Dinuclear Complexes with Aromatic Diimine Ligands

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• 作者：Julia Vallejo ; Isabel Castro ; Mariadel D茅niz ; Catalina Ruiz-P茅rez ; Francesc Lloret ; Miguel Julve ; Rafael Ruiz-Garc铆a ; Joan Cano
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：March 5, 2012
• 年：2012
• 卷：51
• 期：5
• 页码：3289-3301
• 全文大小：615K
• 年卷期：v.51,no.5(March 5, 2012)
• ISSN：1520-510X

文摘

Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)₂Co(Me₂phen)(H₂O)₂][Cr(bpy)(ox)₂]路4H₂O (1) and [Cr(phen)(ox)₂Mn(phen)(H₂O)₂][Cr(phen)(ox)₂]路H₂O (2) (bpy = 2,2鈥?bipyridine, phen = 1,10-phenanthroline, and Me₂phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the 鈥渃omplex-as-ligand/complex-as-metal鈥?strategy by using Ph₄P[CrL(ox)₂]路H₂O (L = bpy and phen) and [ML鈥?H₂O)₄](NO₃)₂ (M = Co and Mn; L鈥?= phen and Me₂phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr^IIIL(ox)₂]^{鈭?/sup>, and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [CrIIIL(ox)(渭-ox)MIIL鈥?H₂O)₂]+[M = Co, L = bpy, and L鈥?= Me₂phen (1); M = Mn and L = L鈥?= phen (2)]. These oxalato-bridged CrIIIMII dinuclear cationic entities of 1 and 2 result from the coordination of a [CrIIIL(ox)₂]鈭?/sup> unit through one of its two oxalato groups toward a [MIIL鈥?H₂O)₂]2+ moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct CrIII ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin MII ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0鈥?00 K) magnetic susceptibility and variable-field (0鈥?.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the CrIII (S_Cr = 3/2) ion and the high-spin CoII (S_Co = 3/2) or MnII (S_Mn = 5/2) ions across the oxalato bridge within the CrIIIMII dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm鈥? (2); H = 鈥?i>JS_Cr路S_M]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 CrIIICoII and S = 4 CrIIIMnII ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the 蟽- and/or 蟺-type pathways of the oxalato bridge, mainly involving the d_yz(Cr)/d_xy(M), d_xz(Cr)/d_xy(M), d_x2鈥?i>y2(Cr)/d_xy(M), d_yz(Cr)/d_xz(M), and d_xz(Cr)/d_yz(M) pairs of orthogonal magnetic orbitals and the d_x2鈥?i>y2(Cr)/d_x2鈥?i>y2(M), d_xz(Cr)/d_xz(M), and d_yz(Cr)/d_yz(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.}