Binuclear ruthenium complexes of a neutral radical bridging ligand. A new "spin" on mixed valency.

The electronic structures of (LX)2Ru(Vd)Ru(LX)2 complexes (Vd = 1,5-diisopropyl-3-(4,6-dimethyl-2-pyrimidinyl)-6-oxoverdazyl radical; LX = acac (acetylacetonate) or hfac (hexafluoroacetylacetonate)) in multiple charge states have been investigated experimentally and computationally. The main focus was to probe the consequences of the interplay between the ruthenium ions and the redox-active verdazyl ligand for possible mixed-valent behavior. Cyclic voltammetry studies reveal one reversible reduction and one reversible oxidation process for both complexes; in addition the acac-based derivative possesses a second reversible oxidation. Analysis of a collection of experimental (X-ray structures, EPR, electronic spectra) and computational (TD-DFT (PCM)) data reveal that the ruthenium ancillary ligands (acac vs hfac) have dramatic consequences for the electronic structures of the complexes in all charge states studied. In the hfac series, the neutral complex is best regarded as a binuclear Ru(II) species bridged by a neutral radical ligand. Reduction to give the anionic complex takes place on the verdazyl ligand, whereas oxidation to the cation (a closed shell species) is shared between Vd and ruthenium. For the acac-based complexes, the neutral species is most accurately represented as a Ru(II)/Ru(III) mixed valent complex containing a bridging verdazyl anion, though some bis(Ru(II))-neutral radical character remains. The monocation complex contains a significant contribution from a "broken symmetry" singlet diradical structure, best represented as a bis-Ru(III) system with an anionic ligand, with significant spin coupling of the two Ru(III) centers via the Vd(-1) ligand (calculated J = -218 cm(-1)). The dication, a spin doublet, consists of two Ru(III) ions linked (and antiferromagnetically coupled) to the neutral radical ligand. Computed net σ- and π-back-donation, spin densities, and orbital populations are provided. Time dependent DFT is used to predict the optical spectra and assign experimental data.

[1]  B. le Guennic,et al.  Simultaneous bridge-localized and mixed-valence character in diruthenium radical cations featuring diethynylaromatic bridging ligands. , 2011, Journal of the American Chemical Society.

[2]  W. Kaim.  Concepts for metal complex chromophores absorbing in the near infrared , 2011 .

[3]  J. Yao,et al.  Charge delocalization in a cyclometalated bisruthenium complex bridged by a noninnocent 1,2,4,5-tetra(2-pyridyl)benzene ligand. , 2011, Journal of the American Chemical Society.

[4]  A. Lever,et al.  Electronic structure investigations of neutral and charged ruthenium bis(β-diketonate) complexes of redox-active verdazyl radicals. , 2011, Journal of the American Chemical Society.

[5]  R. McDonald,et al.  Redox properties of zinc complexes of verdazyl radicals and diradicals , 2011 .

[6]  Qiang Shi,et al.  Electronic coupling between two cyclometalated ruthenium centers bridged by 1,3,6,8-tetrakis(1-butyl-1H-1,2,3-triazol-4-yl)pyrene. , 2011, Inorganic chemistry.

[7]  K. Costuas,et al.  Polynuclear carbon-rich organometallic complexes: clarification of the role of the bridging ligand in the redox properties. , 2011, Dalton transactions.

[8]  B. Sarkar,et al.  Energy-level tailoring in a series of redox-rich quinonoid-bridged diruthenium complexes containing tris2-pyridylmethyl)amine as a co-ligand. , 2011, Chemistry.

[9]  D. Yufit,et al.  Spectroscopic and Computational Studies of the Ligand Redox Non-Innocence in Mono- and Binuclear Ruthenium Vinyl Complexes , 2011 .

[10]  W. Khairul,et al.  The electronic structures of diruthenium complexes containing an oligo(phenylene ethynylene) bridging ligand, and some related molecular structures. , 2010, Dalton transactions.

[11]  M. Drescher,et al.  Fully Delocalized (Ethynyl)(vinyl)phenylene-Bridged Diruthenium Radical Complexes , 2010 .

[12]  W. Kaim,et al.  Quantum chemical interpretation of redox properties of ruthenium complexes with vinyl and TCNX type non-innocent ligands , 2010 .

[13]  D. O′Hare,et al.  Electronic communication through unsaturated hydrocarbon bridges in homobimetallic organometallic complexes. , 2010, Chemical reviews.

[14]  A. Lever,et al.  Verdazyl radicals as redox-active, non-innocent, ligands: contrasting electronic structures as a function of electron-poor and electron-rich ruthenium bis(beta-diketonate) co-ligands. , 2010, Chemical communications.

[15]  M. Ward,et al.  Trinuclear ruthenium dioxolene complexes based on the bridging ligand hexahydroxytriphenylene: electrochemistry, spectroscopy, and near-infrared electrochromic behaviour associated with a reversible seven-membered redox chain. , 2010, Dalton transactions.

[16]  S. Mobin,et al.  Valence structures of the diastereomeric complexes meso- and rac-[Ru(2)(acac)(4)(mu-Q)](n) (n = 2-, 1-, 0, 1+, 2+) with the multiple quinonoid bridging ligand Q = 1,2,4,5-tetraimino-3,6-diketocyclohexane. , 2009, Dalton transactions.

[17]  Jaroslav V. Burda,et al.  Interactions of the “piano‐stool” [ruthenium(II) (η6‐arene)(en)CL]+ complexes with water and nucleobases; ab initio and DFT study , 2009, J. Comput. Chem..

[18]  M. A. Fox,et al.  Noninnocent Ligand Behavior in Diruthenium Complexes Containing a 1,3-Diethynylbenzene Bridge , 2009 .

[19]  J. Conradie,et al.  Broken-symmetry DFT spin densities of iron nitrosyls, including Roussin's red and black salts: striking differences between pure and hybrid functionals. , 2009, The journal of physical chemistry. B.

[20]  C. Duboc,et al.  Evidence for the dimer-of-(mixed-valent dimers) configuration in tetranuclear {(μ4-TCNX)[Ru(NH3)5]4}8+, TCNX = TCNE and TCNQ, from DFT calculations , 2009 .

[21]  Joel S. Miller,et al.  Oxidation leading to reduction: redox-induced electron transfer (RIET). , 2009, Angewandte Chemie.

[22]  V. Puranik,et al.  Valence-state analysis through spectroelectrochemistry in a series of quinonoid-bridged diruthenium complexes [(acac)(2)Ru(mu-L)Ru(acac)(2)](n) (n=+2, +1, 0, -1, -2). , 2008, Chemistry.

[23]  S. Mobin,et al.  Intramolecular valence and spin interaction in meso and rac diastereomers of a p-quinonoid-bridged diruthenium complex. , 2008, Journal of the American Chemical Society.

[24]  K. Wieghardt,et al.  One- and two-electron reduced 1,2-diketone ligands in [CrIII(L*)3] (S = 0) and Na2(Et2O)2[VIV(LRed)3] (S = 1/2). , 2008, Inorganic chemistry.

[25]  D. Marx,et al.  Magnetostructural Dynamics with the Extended Broken Symmetry Formalism: Antiferromagnetic [2Fe-2S] Complexes. , 2008, Journal of chemical theory and computation.

[26]  W. Kaim,et al.  Ligand-Centered Oxidations and Electron Delocalization in a Tetranuclear Complex of a Tetradonor-Substituted Olefin , 2008 .

[27]  S. Mobin,et al.  Valence-state alternatives in diastereoisomeric complexes [(acac)2Ru(mu-QL)Ru(acac)2]n (QL2- = 1,4-dioxido-9,10-anthraquinone,n = +2, +1, 0, -1, -2). , 2008, Inorganic chemistry.

[28]  Abhishek Dey,et al.  Mixed valent sites in biological electron transfer. , 2008, Chemical Society reviews.

[29]  R. B. Sunoj,et al.  Mixed-valent metals bridged by a radical ligand: fact or fiction based on structure-oxidation state correlations. , 2008, Journal of the American Chemical Society.

[30]  W. Kaim,et al.  Towards new organometallic wires: tetraruthenium complexes bridged by phenylenevinylene and vinylpyridine ligands. , 2007, Chemistry.

[31]  B. Koivisto,et al.  Electrochemical studies of verdazyl radicals. , 2007, Organic letters.

[32]  Michael J. Ferguson,et al.  Probing electronic communication in stable benzene-bridged verdazyl diradicals. , 2007, The Journal of organic chemistry.

[33]  P. Low,et al.  Redox-Active Complexes containing group 8 metal centers linked by C2 bridges , 2007 .

[34]  S. Mobin,et al.  Non-innocent behaviour of ancillary and bridging ligands in homovalent and mixed-valent ruthenium complexes [A2Ru(mu-L)RuA2]n, A = 2,4-pentanedionato or 2-phenylazopyridine, L(2-) = 2,5-bis(2-oxidophenyl)pyrazine. , 2007, Dalton transactions.

[35]  M. Zeller,et al.  A nickel(II) di-μ2-phenolato bridged dinuclear complex: Weak antiferromagnetic interactions in nickel(II) dimers , 2007 .

[36]  Jun Li,et al.  Basis Set Exchange: A Community Database for Computational Sciences , 2007, J. Chem. Inf. Model..

[37]  W. Kaim,et al.  Unconventional mixed-valent complexes of ruthenium and osmium. , 2007, Angewandte Chemie.

[38]  Joel S. Miller,et al.  Synthesis, structure, and magnetic properties of valence ambiguous dinuclear antiferromagnetically coupled cobalt and ferromagnetically coupled iron complexes containing the chloranilate(2-) and the significantly stronger coupling chloranilate(*3-) radical trianion. , 2007, Journal of the American Chemical Society.

[39]  E. Baerends,et al.  Kohn-Sham Density Functional Theory: Predicting and Understanding Chemistry , 2007 .

[40]  R. B. Sunoj,et al.  An Experimental and Density Functional Theory Approach Towards the Establishment of Preferential Metal‐ or Ligand‐Based Electron‐Transfer Processes in Large Quinonoid‐Bridged Diruthenium Complexes [{(aap)2Ru}2(μ‐BL2–)]n+ (aap = 2‐Arylazopyridine) , 2006 .

[41]  B. Koivisto,et al.  Magnetostructural studies of copper(II)–verdazyl radical complexes , 2006 .

[42]  D. D’Alessandro,et al.  Intervalence charge transfer (IVCT) in trinuclear and tetranuclear complexes of iron, ruthenium, and osmium. , 2006, Chemical reviews.

[43]  D. D’Alessandro,et al.  Current trends and future challenges in the experimental, theoretical and computational analysis of intervalence charge transfer (IVCT) transitions. , 2006, Chemical Society reviews.

[44]  D. D’Alessandro,et al.  Multisite effects on intervalence charge transfer in a clusterlike trinuclear assembly containing ruthenium and osmium. , 2006, Inorganic chemistry.

[45]  C. Duboc,et al.  Mixed-valent and radical states of complexes [(bpy)2M(μ-abpy)M′(bpy)2]n+, M,M′ = Ru or Os, abpy = 2,2′-azobispyridine: Electron transfer vs. hole transfer mechanism in azo ligand-bridged complexes , 2006 .

[46]  O. Sato,et al.  Valence tautomeric transitions with thermal hysteresis around room temperature and photoinduced effects observed in a cobalt-tetraoxolene complex. , 2006, Journal of the American Chemical Society.

[47]  S. Alvarez,et al.  Spin density distribution in transition metal complexes , 2005 .

[48]  C. Sangregorio,et al.  Dinuclear ruthenium bipyridine complexes with a bis(iminodioxolene)-meta-phenylene ligand: magnetic coupling and mixed valence character of the semiquinonato species. , 2005, Dalton transactions.

[49]  D. J. Brook,et al.  Synthesis of 1,5-diisopropyl substituted 6-oxoverdazyls. , 2005, Organic & biomolecular chemistry.

[50]  R. Winter,et al.  Electron delocalization in mixed-valence butadienediyl-bridged diruthenium complexes , 2005 .

[51]  R. B. Sunoj,et al.  Theoretical and experimental evidence for a new kind of spin-coupled singlet species: isomeric mixed-valent complexes bridged by a radical anion ligand. , 2005, Angewandte Chemie.

[52]  M. Ward.  Near-infrared electrochromic materials for optical attenuation based on transition-metal coordination complexes , 2005 .

[53]  R. B. Sunoj,et al.  2,5-Dioxido-1,4-benzoquinonediimine (H2L2-), a hydrogen-bonding noninnocent bridging ligand related to aminated topaquinone: different oxidation state distributions in complexes [{(bpy)2Ru}2(mu-H2L)]n (n=0,+,2+,3+,4+) and [{(acac)2Ru}2(mu-H2L)]m (m=2-,-,0,+,2+). , 2005, Chemistry.

[54]  M. Ward,et al.  Facile preparation of a visible- and near-infrared-active electrochromic film by direct deposition of a ruthenium dioxolene complex on an ITO/glass surface , 2005 .

[55]  K. Burke,et al.  Time-dependent density functional theory: past, present, and future. , 2004, The Journal of chemical physics.

[56]  R. Winter,et al.  Bridge dominated oxidation of a diruthenium 1,3-divinylphenylene complex. , 2004, Chemical communications.

[57]  W. Kaim,et al.  Isovalent and mixed-valent diruthenium complexes [(acac)2RuII (-bpytz)RuII(acac)2] and [(acac)2RuII(-bpytz)RuIII(acac)2](ClO4) (acac = acetylacetonate and bpytz = 3,6-bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine): synthesis, spectroelectrochemical, and epr investigation . , 2004, Inorganic chemistry.

[58]  C. Sangregorio,et al.  Thermally and light-induced valence tautomeric transition in a dinuclear cobalt-tetraoxolene complex. , 2004, Angewandte Chemie.

[59]  Frank Neese,et al.  Definition of corresponding orbitals and the diradical character in broken symmetry DFT calculations on spin coupled systems , 2004 .

[60]  W. Kaim,et al.  Characterization of the mixed-valent intermediate (n = 3) of the complex series {(μ, η3 :η3-L)[(Ru(terpy)]2}n+ with the unsaturated bridging ligand N, N'-bis (α-picolinoyl)hydrazido(2-) = l2- , 2004 .

[61]  Andrew P. Meacham,et al.  Mono- and dinuclear ruthenium carbonyl complexes with redox-active dioxolene ligands: electrochemical and spectroscopic studies and the properties of the mixed-valence complexes. , 2003, Inorganic chemistry.

[62]  F. Neese,et al.  Analysis and interpretation of metal-radical coupling in a series of square planar nickel complexes: correlated Ab initio and density functional investigation of [Ni(L(ISQ))(2)] (L(ISQ)=3,5-di-tert-butyl-o-diiminobenzosemiquinonate(1-)). , 2003, Journal of the American Chemical Society.

[63]  Andrew P. Meacham,et al.  A near-infrared electrochromic window based on an Sb-doped SnO2 electrode modified with a Ru-dioxolene complex. , 2003, Angewandte Chemie.

[64]  I. Horváth,et al.  Improved synthesis of 2,2'-bipyrimidine. , 2002, The Journal of organic chemistry.

[65]  F. Neese,et al.  Theoretical evidence for the singlet diradical character of square planar nickel complexes containing two o-semiquinonato type ligands. , 2002, Inorganic chemistry.

[66]  Norman Sutin,et al.  Optical transitions of symmetrical mixed-valence systems in the Class II-III transition regime. , 2002, Chemical Society reviews.

[67]  Wen-Ge Han,et al.  A structural model for the high-valent intermediate Q of methane monooxygenase from broken-symmetry density functional and electrostatics calculations. , 2002, Journal of the American Chemical Society.

[68]  Michael D. Ward,et al.  Non-innocent behaviour in mononuclear and polynuclear complexes: consequences for redox and electronic spectroscopic properties , 2002 .

[69]  Serge I. Gorelsky,et al.  Electronic structure and spectra of ruthenium diimine complexes by density functional theory and INDO/S. Comparison of the two methods , 2001 .

[70]  T. Meyer,et al.  The localized-to-delocalized transition in mixed-valence chemistry. , 2001, Chemical reviews.

[71]  R. Kato.  Conductive Copper Salts of 2,5-Disubstituted N,N′-Dicyanobenzoquinonediimines (DCNQIs): Structural and Physical Properties , 2000 .

[72]  S. Rettig,et al.  Synthesis and X-ray structural characterization of the ruthenium β-diketonato complexes: Ru(hfac)3, cis-Ru(hfac)2(MeCN)2, and cis-Ru(hfac)(acac)(MeCN)2 , 1999 .

[73]  V. Barone,et al.  On the Calculation and Modeling of Magnetic Exchange Interactions in Weakly Bonded Systems: The Case of the Ferromagnetic Copper(II) &mgr;(2)-Azido Bridged Complexes. , 1999, Inorganic chemistry.

[74]  G. Scuseria,et al.  An efficient implementation of time-dependent density-functional theory for the calculation of excitation energies of large molecules , 1998 .

[75]  Colin G. Coates,et al.  Modulation of Electronic Coupling across Dioxolene-Bridged Osmium and Ruthenium Dinuclear Complexes , 1998 .

[76]  Dennis R. Salahub,et al.  Molecular excitation energies to high-lying bound states from time-dependent density-functional response theory: Characterization and correction of the time-dependent local density approximation ionization threshold , 1998 .

[77]  M. Ward,et al.  The Role of Bridging Ligands in Controlling Electronic and Magnetic Properties in Polynuclear Complexes , 1998 .

[78]  J. Malrieu,et al.  Remarks on the Proper Use of the Broken Symmetry Approach to Magnetic Coupling , 1997 .

[79]  D. Astruc.  FROM ORGANOTRANSITION-METAL CHEMISTRY TOWARD MOLECULAR ELECTRONICS : ELECTRONIC COMMUNICATION BETWEEN LIGAND-BRIDGED METALS , 1997 .

[80]  W. Kaim,et al.  Paramagnetism of Tetranuclear Complexes between TCNX Ligands (TCNE, TCNQ, TCNB) and Four Pentaammineruthenium or Dicarbonyl(pentamethylcyclopentadienyl)manganese Fragments. , 1997, Inorganic chemistry.

[81]  K. Wieghardt,et al.  SYNTHESIS, STRUCTURE, MAGNETISM, AND SPECTROSCOPIC PROPERTIES OF SOME MONO- AND DINUCLEAR NICKEL COMPLEXES CONTAINING NONINNOCENT PENTANE-2,4-DIONE BI S(S-ALKYLISOTHIOSEMICARBAZONATE)-DERIVED LIGANDS , 1997 .

[82]  Kizashi Yamaguchi,et al.  Theoretical Approaches to Direct Exchange Couplings between Divalent Chromium Ions in Naked Dimers, Tetramers, and Clusters , 1997 .

[83]  David Feller,et al.  The role of databases in support of computational chemistry calculations , 1996, J. Comput. Chem..

[84]  F. Keene,et al.  Spectral and Electrochemical Properties of the Diastereoisomeric Forms of Azobis(2-pyridine)-Bridged Diruthenium Species , 1996 .

[85]  Ovchinnikov,et al.  Simple spin correction of unrestricted density-functional calculation. , 1996, Physical review. A, Atomic, molecular, and optical physics.

[86]  Neil G. Connelly,et al.  Chemical Redox Agents for Organometallic Chemistry. , 1996, Chemical reviews.

[87]  M. Ward.  A Dinuclear Ruthenium(II) Complex with the Dianion of 2,5-Dihydroxy-1,4-benzoquinone as Bridging Ligand. Redox, Spectroscopic, and Mixed-Valence Properties. , 1996, Inorganic chemistry.

[88]  M. Ward.  Metal-metal interactions in binuclear complexes exhibiting mixed valency; molecular wires and switches , 1995 .

[89]  W. Kaim,et al.  Tetranuclear pentaammineruthenium complexes bridged by {pi}-conjugated tetracyano ligands related to TCNE: Syntheses and spectroscopy of different oxidation states , 1995 .

[90]  R. J. Crutchley,et al.  STRONG METAL-METAL COUPLING IN A DINUCLEAR (TERPYRIDINE)(BIPYRIDINE)RUTHENIUM MIXED-VALENCE COMPLEX INCORPORATING THE BRIDGING LIGAND 1,4-DICYANAMIDOB ENZENE DIANION , 1995 .

[91]  W. Kaim,et al.  When Is an Odd-Electron Dinuclear Complex a Mixed-Valent Species? Tuning of Ligand-to-Metal Spin Shifts in Diruthenium(III,II) Complexes of Noninnocent Bridging Ligands OC(R)NNC(R)O , 1995 .

[92]  R. J. Crutchley,et al.  Solvent trapped valency in the [bis(pentaammineruthenium)-(μ-1,4-dicyanamidobenzene)] trication , 1994 .

[93]  R. J. Crutchley,et al.  Solvent Dependence of Metal-Metal Coupling in a Dinuclear Pentaammineruthenium Complex Incorporating the Bridging Ligand 1,4-Dicyanamido-2,5-dimethylbenzene Dianion , 1994 .

[94]  J. Greedan,et al.  Superexchange metal-metal coupling in dinuclear pentaammineruthenium complexes incorporating a 1,4-dicyanamidobenzene dianion bridging ligand , 1992 .

[95]  A. Dei,et al.  Dinuclear ruthenium complexes with bridging 1,4,5,8-tetraoxonaphthalene : redox properties and mixed-valence interactions , 1990 .

[96]  S. Ernst,et al.  Stable binuclear o- and p-semiquinone complexes of [Ru(bpy)2]2+. Radical ion versus mixed-valence dimer formulation , 1989 .

[97]  L. Curtiss,et al.  Intermolecular interactions from a natural bond orbital, donor-acceptor viewpoint , 1988 .

[98]  W. Kaim,et al.  A Stable Bis(chelate) Analogue of the Creutz‐Taube Ion , 1988 .

[99]  Tadashi Kobayashi,et al.  Diacetonitrilebis(β-diketonato)ruthenium(II) complexes. Their preparation and use as intermediates for the synthesis of mixed-ligand β-diketonato ruthenium(III) complexes , 1988 .

[100]  Tetsuya Tsunekawa,et al.  Ab initio molecular orbital calculations of effective exchange integrals between transition metal ions , 1988 .

[101]  Parr,et al.  Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. , 1988, Physical review. B, Condensed matter.

[102]  H. Taube.  Electron Transfer between Metal Complexes — A Retrospective View (Nobel Lecture) , 1984 .

[103]  B. R. Judd,et al.  Oxidation numbers and oxidation states : by Chr. Klixbull Jørgensen. 290 pages, tables, 6 × 9 in. New York, Springer-Verlag, 1969 , 1970 .

[104]  Richard E. Stanton,et al.  Corresponding Orbitals and the Nonorthogonality Problem in Molecular Quantum Mechanics , 1967 .

[105]  G. G. Hall,et al.  Single determinant wave functions , 1961, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[106]  Robert S. Mulliken,et al.  Electronic Population Analysis on LCAO‐MO Molecular Wave Functions. IV. Bonding and Antibonding in LCAO and Valence‐Bond Theories , 1955 .

[107]  Robert S. Mulliken,et al.  Electronic Population Analysis on LCAO‐MO Molecular Wave Functions. III. Effects of Hybridization on Overlap and Gross AO Populations , 1955 .

[108]  Robert S. Mulliken,et al.  Electronic Population Analysis on LCAO–MO Molecular Wave Functions. II. Overlap Populations, Bond Orders, and Covalent Bond Energies , 1955 .

[109]  R. S. Mulliken.  Electronic Population Analysis on LCAO–MO Molecular Wave Functions. I , 1955 .

[110]  O. Lavastre,et al.  Role of the Bridging Arylethynyl Ligand in Bi- and Trinuclear Ruthenium and Iron Complexes , 2006 .

[111]  W. Kaim,et al.  Controlling metal-ligand-metal oxidation state combinations by ancillary ligand (L) variation in the redox systems [L2Ru(mu-boptz)RuL2]n, boptz = 3,6-bis(2-oxidophenyl)-1,2,4,5-tetrazine, and L = acetylacetonate, 2,2'-bipyridine, or 2-phenylazopyridine. , 2005, Chemistry.

[112]  Arthur J. Epstein,et al.  Tetracyanoethylene-based organic magnets , 1998 .

[113]  F. Keene.  Isolation and characterisation of stereoisomers in di- and tri-nuclear complexes , 1998 .

[114]  M. Ward,et al.  A new redox-tunable near-IR dye based on a trinuclear ruthenium(II) complex of hexahydroxytriphenylene , 1998 .

[115]  Robert J. Crutchley,et al.  Intervalence Charge Transfer and Electron Exchange Studies of Dinuclear Ruthenium Complexes , 1994 .

[116]  S. Ernst,et al.  ESR of homo- and heteroleptic mono- and dinuclear tris(.alpha.-diimine)ruthenium radical complexes , 1990 .

[117]  W. Kaim,et al.  Binuclear radical complexes of heavy-metal fragments containing ruthenium, osmium, rhodium and gold , 1989 .

[118]  W. R. Wadt,et al.  Ab initio effective core potentials for molecular calculations. Potentials for K to Au including the outermost core orbitals , 1985 .

[119]  W. R. Wadt,et al.  Ab initio effective core potentials for molecular calculations , 1984 .

[120]  J. O’Connell.  Modern Theoretical Chemistry 5. Statistical Mechanics, Part A: Equilibrium Techniques : Edited by B.J. Berne. Plenum Press, New York, 1977, xv + 242 pp., ISBN 0-306-33505-0, $47.40 , 1979 .

[121]  Peter Day,et al.  Mixed Valence Chemistry-A Survey and Classification , 1968 .