Christian Reber

Texas A&M University, College Station, TX, United States

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Publications (96)255.9 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Luminescence spectra for dithiocarbamate complexes of gold(I) and silver(I) display very different luminescence properties. At room temperature, a narrow band with a maximum at approximately 18 000 cm–1 and a broad band with a maximum at approximately 13 000 cm–1 are observed for the gold(I) and silver(I) compounds, respectively. The luminescence from the gold(I) compounds is strongly affected by external pressure, with maxima shifting to lower energy by approximately −120 cm–1/kbar. In contrast, a silver compound shows a small shift to higher energy by approximately +20 cm–1/kbar. These shifts are analyzed in terms of structure and bridging ligand geometry, revealing the important influence of unsupported metal–metal interactions on pressure-induced shifts of luminescence bands.
    The Journal of Physical Chemistry C. 12/2011; 116(3):2192–2197.
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    ABSTRACT: The structures of novel Tc(V) complexes trans-[TcO(2)(py)(4)]Cl·2H(2)O (1a), trans-[TcO(2)(pic)(4)]Cl·2H(2)O (2a), and trans-[TcO(2)(pic)(4)]BPh(4) (2b) were determined by X-ray crystallography, and their spectroscopic characteristics were investigated by emission spectroscopy and atomic scale calculations. The cations adopt a tetragonally distorted octahedral geometry, with a trans orientation of the apical oxo groups. trans-[TcO(2)(pic)(4)]BPh(4) has an inversion center located on technetium; however, for trans-[TcO(2)(py)(4)]Cl·2H(2)O and trans-[TcO(2)(pic)(4)]Cl·2H(2)O, a strong H bond formed by only one of the oxo substituents introduces an asymmetry in the structure, resulting in inequivalent trans Tc-N and Tc═O distances. Upon 415 nm excitation at room temperature, the complexes exhibited broad, structureless luminescences with emission maxima at approximately 710 nm (1a) and 750 nm (2a, 2b). Like the Re(V) analogs, the Tc(V) complexes luminesce from a (3)E(g) excited state. Upon cooling the samples from 278 to 8 K, distinct vibronic features appear in the spectra of the complexes along with increases in emission intensities. The low temperature emission spectra display the characteristic progressions of the symmetric O═Tc═O and the Tc-L stretching modes. Lowest-energy, triplet excited-state distortions calculated using a time-dependent theoretical approach are in good agreement with the experimental spectra. The discovery of luminescence from the trans-dioxotechnetium(V) complexes provides the first opportunity to directly compare fundamental luminescence properties of second- and third-row d(2) metal-oxo congeners.
    Inorganic Chemistry 06/2011; 50(12):5815-23. · 4.59 Impact Factor
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    ABSTRACT: The potential for reductive elimination of fluorine from dinuclear gold(II) for catalysis has prompted our efforts to synthesize a dinuclear gold(II) fluoride complex. This has been achieved with bis(2,6-dimethylphenyl)formamidinate bridging ligands. In order to obtain this product, it was necessary first to synthesize the corresponding dinuclear gold(II) nitrate, which reacts readily with KF in a metathesis reaction. The nitrate complex and fluoride complexes have been structurally characterized. The Au-Au distance in the dinuclear fluoride, 2.595 Å, is longer than the distance found in the analogous chloride complex, 2.567 Å. This result is consistent with the presence of a fluoride "π electron effect" on the filled Au 5d orbitals. The Raman spectrum shows an Au-Au stretch at 206 cm(-1), which agrees with Woodruff's rules and the density functional theory computational model used for modeling the complex.
    Inorganic Chemistry 05/2011; 50(10):4238-40. · 4.59 Impact Factor
  • John K Grey, Ian S Butler, Christian Reber
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    ABSTRACT: Resolved vibronic structure in electronic spectra provides a detailed view into how molecular structure changes after absorption or emission of a photon. We report temperature- and pressure-dependent luminescence spectra of trans-[ReO2(pyridine)4]I. Low-temperature spectra reveal long vibronic progressions in the totally symmetric O=Re=O (907 cm–1) and Re-pyridine (211 cm–1) stretching modes, indicating large structural displacements along these normal coordinates. The luminescence band maximum is at ca. 15 500 cm–1. Room-temperature spectra are somewhat less-resolved; however, intervals closely matching the O=Re=O frequency (~870 cm–1) persist at higher temperatures. The variable pressure spectra exhibit distinct changes in the vibronic patterns, and luminescence energies decrease by 16 ± 2 cm–1/kbar (1 bar = 100 kPa). Low-temperature spectra are modeled using two-dimensional potential energy surfaces to represent the initial and final electronic states, from which the quantitative normal coordinate offsets can be determined. We then adapt this model to the room-temperature, pressure-dependent data where it is possible to determine how the offsets and other important spectroscopic parameters vary with the pressure-induced changes of the molecular structure. Key words: trans-[ReO2(pyridine)4]I, low-temperature luminescence spectroscopy, high-pressure luminescence spectroscopy, vibronic structure, emitting state distortions.
    Canadian Journal of Chemistry 02/2011; 82(6):1083-1091. · 0.96 Impact Factor
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    ABSTRACT: Condensation of 3-(aminomethyl)pyridine with acetylacetone in the presence of 2 equiv. of HCl affordedN,N′-bis(3-pyridylmethyl)-2-amino-4-imino-pent-2-ene, nacnacCH2PyH, a diketimine with pendant pyridine donors.Under the same conditions, 2- and 4-(aminomethyl)pyridine afforded the respective 1-(2-pyridyl)- and 1-(4-pyridyl)-2,4-dimethylpyrrol. The heteroleptic complex (nacnacCH2Py)(nacnacBn)Zn was obtained upon reaction of nacnacCH2PyH with nacnacBnZnEt. Combining 2 equiv. of this ligand with ZnEt2 afforded the homoleptic complex nacnacCH2Py2Zn. The latter forms a 2D coordination polymer upon reaction with [Cu(NCMe)4][PF6], which shows short-lived luminescence at ambient temperature. The coordination polymer and complex (nacnacCH2Py)(nacnacBn)Zn were characterised by single-crystal X-ray diffraction.
    Berichte der deutschen chemischen Gesellschaft 01/2011; 2011(3). · 2.94 Impact Factor
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    ABSTRACT: Diketimines N,N'-dibenzyl-2-amino-4-imino-pent-2-ene (1), S,S-N,N'-di(phenylethyl)-2-amino-4-imino-pent-2-ene (2), N,N'-bis(3,4,5-trimethoxyphenylmethyl)-2-amino-4-imino-pent-2-ene (3), N,N'-bis(pentafluorophenylmethyl)-2-amino-4-imino-pent-2-ene (4) and N,N'-diisobutyl-2-amino-4-imino-pent-2-ene (5) react with CuOtBu in the presence of 2,9-R2-1,10-phenanthroline to give the respective neutral, tetracoordinated diketiminate copper(I) phenanthroline complexes 1a+2a (R = H), 1b, 3b-5b (R = Me) and 1c+3c (R = Ph). Crystal structures were obtained for all complexes except 5b and intramolecular π-stacking between the phenanthroline ligand and one or two N-benzyl substituents were observed in 1a, 2a, 1b and 1c, or 3b and 4b, respectively. UV/vis absorption spectra show two transitions in the visible region, a diketiminate-based transition at 373-386 nm and a transition at 600-666 nm, tentatively assigned as an MLCT to phenanthroline. All complexes were weakly luminescent in the solid state at room temperature with lifetimes of less than 60 ns. Weak luminescence was also observed in solution with lambdamax = 720-830 nm for 1b, 1c, 3b, 4b and 5b and short luminescence lifetimes. Intramolecular pi-stacking interactions, which prevent flattening distortions in the solid state, appear to have advantageous effects on luminescence intensities.
    Dalton Transactions 10/2010; 39(37):8759-68. · 3.81 Impact Factor
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    ABSTRACT: A series of lanthanide-doped nonanuclear yttrium(III) clusters with general formulas (Y(9-x)Ln(x))(acac)(16)(μ(3)-OH)(8)(μ(4)-O)(μ(4)-OH) (Ln = Pr, Eu, Tb, Dy, and Yb) were synthesized. Characterization by single-crystal X-ray diffraction allowed for analysis of relative populations of yttrium (Z = 39) and dopant trivalent lanthanide (Z = 59-70) at every crystallographic metal position. Nonuniform distribution of ions along the three different sites seems to be correlated to the site volume and the ratio of ionic radii. In support, luminescence spectra of europium(III)-doped nonanuclear clusters were measured over a wide range of dopant concentrations. Emission intensities of peaks characteristic of specific sites correlate well with the site population determined through X-ray diffraction.
    Inorganic Chemistry 10/2010; 49(23):10970-6. · 4.59 Impact Factor
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    ABSTRACT: The crystal structures of [PtCl(2)(ttcn)], [PdCl(2)(ttcn)], [Pt(ethylenediamine)(ttcn)](PF(6))(2), and [Pd(ethylenediamine)(ttcn)](PF(6))(2) (ttcn = 1,4,7-trithiacyclononane) show short apical metal---S(ttcn) distances, qualitatively indicating an interaction. Luminescence spectroscopy was used to study these crystalline complexes at room temperature and variable hydrostatic pressure. The luminescence band maximum of [PdCl(2)(ttcn)] shows a pressure-induced blue shift of +6 cm(-1)/kbar, while the platinum(II) compounds show a red shift of approximately -20 cm(-1)/kbar. This difference is rationalized in terms of a competition between blue shifts due to pressure-induced metal-ligand bond shortening in the equatorial plane and increasing out-of-plane distance of the metal center, and a red shift due to the approach of the apical sulfur donor to the metal center. Density functional theory (DFT) calculations indicate d-d luminescence transitions and a different nature of the highest occupied molecular orbital (HOMO) for [PdCl(2)(ttcn)] than for [PtCl(2)(ttcn)], while the lowest unoccupied molecular orbitals (LUMOs) are identical in character. This electronic structure difference is used to rationalize the different pressure effects.
    Inorganic Chemistry 06/2010; 49(11):4901-8. · 4.59 Impact Factor
  • Etienne Lanthier, Jesper Bendix, Christian Reber
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    ABSTRACT: Luminescence spectra are reported for trans-[MoOCl(CN-t-Bu)(4)]BPh(4) and trans-[MoOF(pyridine)(4)]BPh(4). The maxima of the broad luminescence bands are at energies of 12000 and 13000 cm(-1), respectively. Resolved vibronic structure involves the metal-oxo stretching mode with a vibrational frequency of approximately 950 cm(-1) (Raman) in both compounds. The pressure behavior of the luminescence bands shows a distinct difference: a blue shift of +12 cm(-1) kbar(-1) is observed for [MoOCl(CN-t-Bu)(4)]BPh(4), and a red-shift of -8 cm(-1) kbar(-1) is obtained for [MoOF(pyridine)(4)]BPh(4). At pressures above 25 kbar, the luminescence maximum of [MoOCl(CN-t-Bu)(4)]BPh(4) shows a change from a blue-shift to a red-shift and the Raman peak corresponding to the metal-oxo stretching mode at 954 cm(-1) becomes broad and its maximum decreases with increasing pressure, leading to a strong deviation from the linear increase of +0.24 cm(-1) kbar(-1) observed at pressures below 25 kbar. These unusual pressure effects are rationalized in terms of the influence of pressure on the metal-ligand bonds and oxo-metal-ligand angles using DFT calculations.
    Dalton Transactions 04/2010; 39(15):3695-705. · 3.81 Impact Factor
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    ABSTRACT: In the solid-state, the approximately square planar cation in orange crystals of [Pt(NO(2)phen)(ttcn)](PF(6))(2) (NO(2)phen = 5-nitro-1,10-phenanthroline; ttcn = 1,4,7-trithiacyclononane) has a short apical Pt...S(ttcn) distance (2.9415(15) A). In acetonitrile solution, the electronic spectrum shows a long-wavelength absorption band (412 nm; 2200 M(-1) cm(-1)), consistent with the notion that the axial Pt...S(ttcn) interactions stabilize states having metal-to-ligand charge-transfer (MLCT) character. Reaction with the hexachloroantimonate(V) salt of tris(4-bromophenyl)aminium (TBPA(+)) results in complex redox chemistry, involving the platinum complex, SbCl(5)(2-) and TBPA(+). In the case of Pt(bpy)(ttcn)(2+), orange-yellow crystals of [Pt(bpy)(ttcn)](2)(Sb(4)Cl(16)) were isolated from the reaction, whereas the reaction with Pt(NO(2)phen)(ttcn)(2+) consistently yielded red crystals of [Pt(NO(2)phen)(ttcn)](SbCl(5)) x 2 CH(3)CN. In the latter case, the geometry of the cation, including the apical Pt...S(ttcn) distance (2.9390(12) A), is very similar to that of the PF(6)(-) salt. However, the basal plane of each square pyramidal SbCl(5)(2-) opposes the nearly parallel coordination plane of an adjacent Pt(NO(2)phen)(ttcn)(2+) complex, resulting in an unusually short intermolecular Pt...Sb distance of 3.4259(3) A. The longest wavelength maximum in the diffuse reflectance spectrum and the solid-state emission maximum are shifted by approximately 1200 cm(-1) and approximately 700 cm(-1), respectively, to the red of those of the PF(6)(-) salt, consistent with perturbation of the complex's electronic structure because of the Pt...Sb interaction.
    Inorganic Chemistry 02/2010; 49(6):2808-15. · 4.59 Impact Factor
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    ABSTRACT: The reaction of CuCl with the neutral guanidine Hhpp ligand (1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) yields two crystalline polymorphs of the neutral dimer, bis(1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) dichloro-di-copper(I) with the shortest distance known for a bridging unsupported copper(I)-copper(I) interaction.
    Chemical Communications 01/2010; 46(1):136-8. · 6.38 Impact Factor
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    ABSTRACT: A series of lanthanide-doped nonanuclear yttrium(III) clusters with general formulas (Y 9-x Ln x)(acac) 16 (μ 3 -OH) 8 -(μ 4 -O)(μ 4 -OH) (Ln = Pr, Eu, Tb, Dy, and Yb) were synthesized. Characterization by single-crystal X-ray diffraction allowed for analysis of relative populations of yttrium (Z = 39) and dopant trivalent lanthanide (Z = 59-70) at every crystallographic metal position. Nonuniform distribution of ions along the three different sites seems to be correlated to the site volume and the ratio of ionic radii. In support, luminescence spectra of europium(III)-doped nonanuclear clusters were measured over a wide range of dopant concentrations. Emission intensities of peaks characteristic of specific sites correlate well with the site population determined through X-ray diffraction. Introduction Although a general approach to the fabrication of nanoen-tities in a precisely controlled manner is not yet available, it is widely accepted that coordination chemistry offers an attrac-tive approach to create sophisticated and single-sized nano-scale polynuclear clusters relevant to chemistry, physics, and biology. In this context and as part of our focus on the magnetism and optical properties of polynuclear metal com-plexes incorporating lanthanide ions, 1-3 we recently reinves-tigated the coordination chemistry of β-diketone ligands. We reported an interesting case of rational cluster nuclearity control that allowed the study of the optical properties of penta-, octa-, and nonanuclear europium(III) and terbium(III) clusters. 4 Our interest in lanthanide clusters comes from the well-established relevance of lanthanide ions and their partially filled 4f shell for both magnetism and optical properties. 5-7
    Inorganic Chemistry 01/2010; 49:10970--10976. · 4.59 Impact Factor
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    ABSTRACT: The reaction of CuCl with the neutral guanidine Hhpp ligand (1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) yields two crystalline polymorphs of the neutral dimer, bis(1,3,4,6,7,8-hexahydropyrimido[1,2-a]pyrimidine) dichloro-di-copper(I) with the shortest distance known for a bridging unsupported copper(I)–copper(I) interaction.
    Chemical Communications 01/2010; 46(1). · 6.38 Impact Factor
  • ChemInform 01/2010; 32(52).
  • John K. Grey, Ian S. Butler, Christian Reber
    ChemInform 01/2010; 33(44).
  • D. WEXLER, J. I. ZINK, C. REBER
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 26(2).
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    ABSTRACT: Temperature- and pressure-dependent Raman and luminescence spectra of four crystalline complexes of palladium(II) and platinum(II) with chelating diethyldithiocarbamate (EDTC) and pyrrolidine-N-dithiocarbamate (PDTC) ligands are reported. The crystal structure of [Pd(PDTC)2] was resolved at 120 K. Luminescence band maxima are observed at approximately 14 500 cm–1 and 16 000 cm–1 for the palladium(II) and platinum(II) complexes, respectively. Pressure leads to blue shifts of the band maxima by +9 and +13 cm–1/kbar for [Pd(EDTC)2] and [Pd(PDTC)2], and +15 cm–1/kbar for [Pt(EDTC)2]. These spin-forbidden d–d luminescence transitions have lifetimes of approximately 600 µs at temperatures below 20 K. Luminescence intensities at room temperature are low, but they increase significantly with external pressure. The experimental results show that strong increases of luminescence intensities caused by pressure are not limited to complexes with monodentate ligands, a result providing insight on the coordinates with emitting-state distortions responsible for this effect.
    Canadian Journal of Chemistry 10/2009; 87(11):1625-1635. · 0.96 Impact Factor
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    ABSTRACT: A series of Eu(III) and Tb(III) clusters as well as their Y(III) analogues with increasing nuclearities of 5, 8 and 9 have been synthesised using beta-diketonate ligands with decreasing steric hindrance. Their molecular structures have been established from X-ray diffraction on single crystals for most clusters and studied by luminescence and Raman spectroscopy. The Raman spectra have distinctive patterns for each nuclearity in accordance with their crystal structure. The luminescence spectra of the Eu(III) and Tb(III) clusters also show distinctive features.
    Dalton Transactions 10/2009; · 3.81 Impact Factor
  • Rémi Beaulac, Christian Reber
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    ABSTRACT: Detailed low-temperature single-crystal polarized absorption and luminescence spectra of Cs2[CrCl2(H2O)4]Cl3 are reported. The luminescence spectrum is a broad band with a maximum at 11,800 cm (-1), indicating that the trans-[CrCl2(H2O)4]+ complex emits from a quartet excited state. The resolved vibronic structure reveals a progression in a nontotally symmetric 445 cm (-1) b1g mode, a manifestation of a Jahn-Teller effect in the emitting state. The absorption spectrum shows completely linearly polarized, magnetic-dipole-allowed electronic origins, defining the tetragonal splitting of the states originating from 4T2g (Oh). An energy gap of approximately 800 cm (-1) is observed between the electronic origins of the emitting state and the onset of the pi-polarized absorption spectrum. Both Jahn-Teller and spin-orbit couplings in the orbitally degenerate 4Eg (D4h) state are necessary to account for the spectroscopic observations.
    Inorganic Chemistry 07/2008; 47(12):5048-54. · 4.59 Impact Factor
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    ABSTRACT: A series of discrete compounds and supramolecular polymers were synthesized by self-assembly of dithioether building blocks and HAuCl4.3H2O. In complexes 1 {[AuL(1-Me)Cl], where L(1-Me) is bis(methylthio)methane} and 2 {[Au2L(2-Ph)Cl2], where L(2-Ph) is 1,2-bis(phenylthio)ethane}, adjacent units are connected via aurophilic interactions. Complex 1, a one-dimensional (1D) supramolecular polymer, and complex 2, a two-dimensional supramolecular network, both feature nearly linear [Au-Au-](infinity) chains. Complexes 4a, 4b, and 4c, all of which contain 1,3-bis(phenylthio)propane (L(3-Ph)), are polymorphs having the composition [Au2L(3-Ph)Cl2]. Complex 3 {[Au2L(1-Ph)Cl2], where L(1-Ph) is bis(phenylthio)methane}and complexes 4a and 4b consist of nearly identical 1D supramolecular polymers formed through Au-Au interactions. The third polymorph, 4c, is a molecular complex, as it does not have metal-metal interactions. Complex 5 {[Au2L(4-Ph)Cl2], where L(4-Ph) is 1,4-bis(phenylthio)butane} is also molecular. UV-vis spectra showed that the absorption bands of these complexes are allowed ligand-centered transitions between 230 and 260 nm. Complexes 1, 2, and 6 {[AuL(3-Me)Cl], where L(3-Me) is 1,3-bis(methylthio)propane} exhibited solid-state luminescence at 5 K with vibronic progressions and band maxima at approximately 570 nm. It is suggested that complex 6 contains [Au-Au-](infinity) chains.
    Inorganic Chemistry 05/2008; 47(8):2964-74. · 4.59 Impact Factor

Publication Stats

194 Citations
255.90 Total Impact Points

Institutions

  • 2011
    • Texas A&M University
      • Department of Chemistry
      College Station, TX, United States
  • 1970–2011
    • Université de Montréal
      • Department of Chemistry
      Montréal, Quebec, Canada
  • 2010
    • University of Cincinnati
      • Department of Chemistry
      Cincinnati, OH, United States
  • 1999–2010
    • Université du Québec à Montréal
      • Department of Chemistry
      Montréal, Quebec, Canada
  • 1992–2010
    • University of California, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Angeles, California, United States
  • 2009
    • Claude Bernard University Lyon 1
      • Laboratoire des multimatériaux et interfaces (LMI)
      Villeurbanne, Rhone-Alpes, France
  • 2002–2004
    • McGill University
      • Department of Chemistry
      Montréal, Quebec, Canada
  • 2001
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France