Person:
Hernández Sánchez, Raúl

Profile Picture

Email Address

AA Acceptance Date

Birth Date

Research Projects

Organizational Units

Job Title

Last Name

Hernández Sánchez

First Name

Raúl

Name

Hernández Sánchez, Raúl

Filters

2013 - 20153

Settings

Author's Publications: search.filters.isAuthorOfPublication.ebb0fe92-84eb-403a-b850-4b71216bc108

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Publication
    Metal Atom Lability in Polynuclear Complexes
    (American Chemical Society (ACS), 2013) Eames, Emily V.; Hernández Sánchez, Raúl; Betley, Theodore
    The asymmetric oxidation product [(PhL)Fe3(μ-Cl)]2 [PhLH6 = MeC(CH2NHPh-o-NHPh)3], where each trinuclear core is comprised of an oxidized diiron unit [Fe2]5+ and an isolated trigonal pyramidal ferrous site, reacts with MCl2 salts to afford heptanuclear bridged structures of the type (PhL)2Fe6M(μ-Cl)4(thf)2, where M = Fe or Co. Zero-field, 57Fe Mössbauer analysis revealed the Co resides within the trinuclear core subunits, not at the octahedral, halide-bridged MCl4(thf)2 position indicating Co migration into the trinuclear subunits has occurred. Reaction of [(PhL)Fe3(μ-Cl)]2 with CoCl2 (2 or 5 equivalents) followed by precipitation via addition of acetonitrile afforded trinuclear products where one or two irons, respectively, can be substituted within the trinuclear core. Metal atom substitution was verified by 1H NMR, 57Fe Mossbauer, single crystal X-ray diffraction, X-ray fluorescence, and magnetometry analysis. Spectroscopic analysis revealed that the Co atom(s) substitute(s) into the oxidized dimetal unit ([M2]5+), while the M2+ site remains iron-substituted. Magnetic data acquired for the series are consistent with this analysis revealing the oxidized dimetal unit comprises a strongly coupled S = 1 unit ([FeCo]5+) or S = 1/2 ([Co2]5+) that is weakly antiferromagnetically coupled to the high spin (S = 2) ferrous site. The kinetic pathway for metal substitution was probed via reaction of [(PhL)Fe3(μ-Cl)]2 with isotopically enriched 57FeCl2(thf)2, the results of which suggest rapid equilibration of 57Fe into both the M2+ site and oxidized diiron site, achieving a 1:1 mixture.
  • Thumbnail Image
    Publication
    Synthesis of Open-Shell, Bimetallic Mn/Fe Trinuclear Clusters
    (American Chemical Society (ACS), 2013) Powers, Tamara Michelle; Gu, Nina; Fout, Alison R.; Baldwin, Anne M.; Hernández Sánchez, Raúl; Alfonso, Denise Marie; Chen, Yu-Sheng; Zheng, Shao-Liang; Betley, Theodore
    Concomitant deprotonation and metalation of hexadentate ligand platform tbsLH6 (tbsLH6 = 1,3,5-C6H9(NHC6H4-o-NHSiMe2tBu)3) with divalent transition metal starting materials Fe2(Mes)4 (Mes = mesityl) or Mn3(Mes)6 in the presence of tetrahydrofuran (THF) resulted in isolation of homotrinuclear complexes (tbsL)Fe3(THF) and (tbsL)Mn3(THF), respectively. In the absence of coordinating solvent (THF), the deprotonation and metalation exclusively afforded dinuclear complexes of the type (tbsLH2)M2 (M = Fe or Mn). The resulting dinuclear species were utilized as synthons to prepare bimetallic trinuclear clusters. Treatment of (tbsLH2)Fe2 complex with divalent Mn source (Mn2(N(SiMe3)2)4) afforded the bimetallic complex (tbsL)Fe2Mn(THF), which established the ability of hexamine ligand tbsLH6 to support mixed metal clusters. The substitutional homogeneity of (tbsL)Fe2Mn(THF) was determined by 1H NMR, 57Fe Mössbauer, and X-ray fluorescence. Anomalous scattering measurements were critical for the unambiguous assignment of the trinuclear core composition. Heating a solution of (tbsLH2)Mn2 with a stoichiometric amount of Fe2(Mes)4 (0.5 mol equiv) affords a mixture of both (tbsL)Mn2Fe(THF) and (tbsL)Fe2Mn(THF) as a result of the thermodynamic preference for heavier metal substitution within the hexa-anilido ligand framework. These results demonstrate for the first time the assembly of mixed metal cluster synthesis in an unbiased ligand platform.
  • No Thumbnail Available
    Publication
    Coordination Chemistry and Electronic Structure of Iron Clusters
    (2015-05-18) Hernández Sánchez, Raúl; Betley, Theodore A.; Nocera, Daniel; Gordon, Roy
    Mixed valence compounds have been recognized over the past five decades as a unique class of chemical species. Their distinctive spectral, electrochemical, physical and magnetic properties arise from electron delocalization into the sites with uneven valence. A primary consequence of this electron delocalization phenomenon is the stabilization of high spin multiplicities in certain dinuclear synthetic and polynuclear biological clusters. Therefore, the subject of this dissertation is to extend the current knowledge of the analysis of synthetic mixed valence clusters by systematically altering the coordination chemistry and redox states at well-defined synthetic, polynuclear iron clusters. A central focus of this thesis is to investigate the effect of superexchange, direct exchange, and double exchange electronic coupling in dinuclear [Fe2], trinuclear [Fe3], hexanuclear [Fe6], and octanuclear [Fe8] clusters with the goal of better understanding the principles that govern their complex electronic structures. It is concluded that the resulting electronic structure in these polynuclear systems is highly dependent on the extent of electron delocalization which can be tuned by solvation, anation, or chemical redox changes. This finding is highlighted by the observation that small variations on the solvation coordination sphere and redox level one can transverse spin ground states from S = 0 to S = 11 by addition of 6e– into [Fe6].