title: Iron substitution for sodium in a carboxylate-bridged, heterodinuclear sodium-iron complex.
abstract: The synthesis and structural characterization of the carboxylate-bridged, heterodinuclear iron-sodium complex [NaFe(PIC2DET)(mu-O2CTrp)3] (2), where PIC2DET (1) is a 2,3-diethynyltriptycene-linked dipicolinic methyl ester ligand and Trp is 9-triptycenyl, are described. The metal ions in 2 are bridged by three triptycene carboxylates with an Fe...Na distance of 3.181(2) A, and each is coordinated to a pyridine nitrogen and carbonyl oxygen atom of 1, forming two five-membered chelate rings. A linkage isomer in which Fe1 is bound by the other ester oxygen atom of 1 was identified by X-ray crystallographic analysis. Treatment of 2 with Fe(OTf)2.2MeCN resulted in substitution of sodium by iron(II) to give the cationic diiron(II) complex [Fe2(PIC2DET)(mu-O2CTrp)3][OTf] (3). This reaction was investigated by UV-vis, IR, MS, and stopped-flow spectroscopy. The substitution is first order with respect to 2 and zero order with respect to Fe(OTf)2.2MeCN (kobs = 21 +/- 2 s-1), consistent with a dissociative mechanism. A positive enthalpy of activation (DeltaH = 59 +/- 6 kJ mol-1) and negative entropy of activation (DeltaS = -20 +/- 6 J mol-1 K-1) were calculated from the temperature dependence of the rate-determining dissociation step.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Kodanko
authors.forename: Dong
authors.initials: D
authors.lastname: Xu
authors.forename: Datong
authors.initials: D
authors.lastname: Song
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lippard
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D015394:Molecular Structure; D012964:Sodium / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D012964:Sodium; D007501:Iron