The kinetic and mechanistic features of a new series ofplatinum-thallium cyano compounds containing a direct andunsupported by ligands metal-metal bond have been studied insolution, using standard mix–and–measurespectrophotometric technique and stopped–flow method.These reactions are interpreted as oxidative addition of the cspecies to the square planar Pt(CN)42-complex. Each of these processes was found to befirst-order in Pt(CN)42-, the corresponding TIIIIcomplex and a cyanide ion donating species whichacts as a catalyst. Both di- and trinuclear complexes werestudied, and the kinetically significant thallium complexes intheir formation and the catalytically active cyanide sourcesare as follows: [(CN)5PtTl(CN)3]3-: Tl(CN)4–(alkaline region), Tl(CN)3(slightly acidic region) and CN–; [(CN)5Pt–Tl(CN)]–: Tl(CN)2+and Tl(CN)2+; [(CN)5Pt–Tl–Pt(CN)5]3-: [(CN)5Pt–Tl(CN)]–and HCN. Appropriatemechanisms were postulated for the overall reactions in allcases, which include i) metal–metal bond formation stepand ii) coordination of an axial cyanide ion to the platinumcenter. Two experimentally indistinguishable kinetic modelswere proposed for the formation of the dinuclear complexeswhich are different in the sequence of the two steps. In thecase of the trinuclear complex, experimental evidence isavailable to exclude one of the alternative reaction paths, andit was proven that the metal–metal bond formation precedesthe axial cyanide coordination. The cyanide ligands coordinated to TIIIIin the Pt–Tl complexes could be replacedsuccessfully with aminopolycarboxylates e.g.: mimda2-, nta3-, edta4-. The [(CN)5Pt–Tl(edta)]4-complex, with a direct metal–metal bond hasbeen prepared in solution by two different reactions: a)dissolution of [(CN)5Pt–Tl](s) in an aqueous solution of edta, b)directly from Pt(CN)42-and Tl(edta)(CN)2-. The decomposition reaction is greatlyaccelerated by cyanide and significantly inhibited by edta. Itproceeds through the [(CN)5Pt–Tl(CN)3]3-intermediate. The formation of [(CN)5Pt–Tl(edta)]4-can proceed via two different pathways dependingon the ratio of the cyanide to the edta ligand concentrations.The’direct path’at excess of edta means theformation of intermediate[(CN)4Pt···Tl(CN)(edta)]4-, followed by a release of the cyanide from theTl–centre followed by coordination of a cyanide from thebulk to the Pt–centre of the intermediate. The’indirect path’dominates in the absence of extraedta and the formation of the Pt–Tl bond occours betweenPt(CN)42-and Tl(CN)4–. Homoligand MTl(CN)4(M = TlI, K, Na) and, for the first time, Tl(CN)3species have been synthesized in the solid stateand their structures solved by single crystal X–raydiffraction method. Interesting redox processes have been foundbetween TIIIIand CN–in non–aqueous solution and in Tl2O3-CN–aqueous suspension. In the crystal structureof Tl(CN)3·H2O, the thallium(III) ion has a trigonal bypiramidalcoordination geometry with three cyanides in the trigonalplane, while an oxygen atom of the water molecule and anitrogen atom from a cyanide ligand attached to a neighboringthallium complex, form a linear O–Tl–N fragment.Cyanide ligand bridges thallium units forming an infinitezigzag chain structure. Among the thallium(III) tetracyanocompounds, the isostructural M[Tl(CN)4](M = Tl and K) and Na[Tl(CN)4]·3H2O crystallize in different crystal systems, but thethallium(III) ion has in all cases the same tetrahedralgeometry in the [Tl(CN)4]–unit. Three adducts of mercury(II) (isoelectronic with TIIII) (K2PtHg(CN)6·2H2O, Na2PdHg(CN)6·2H2O and K2NiHg(CN)6·2H2O) have been prepared from Hg(CN)2and square planar transition metal cyanides MII(CN)42-and their structure have been studied by singlecrystal X–ray diffraction, XPS and Raman spectroscopy inthe solid state. The structure of (K2PtHg(CN)6·2H2O consists of strictly linear one dimensional wireswith PtIIand HgIIcenters located alternately, dHg–Pt= 3.460 Å. The structure of Na2PdHg(CN)6·2H2O and K2NiHg(CN)6·2H2O can be considered as double salts, the lack ofhetero–metallophilic interaction between both the HgIIand PdIIatoms, dHg–Pd= 4.92 Å, and HgIIand NiIIatoms, dNi–Pd= 4.60 Å, seems obvious. Electronbinding energy values of the metallic centers measured by XPSshow that there is no electron transfer between the metal ionsin all three adducts. In solution, experimental findingsclearly indicate the lack of metal–metal bond formation inall studied HgII–CN-–MII(CN)42-systems (M = Pt, Pd and Ni). It is in contrary tothe platinum–thallium bonded cyanides. KEYWORDS:metal–metal bond, platinum, thallium,kinetics, mechanism, stopped flow, oxidative addition, cyanocomplexes, edta, redox reaction, metal cyanides, X–raydiffraction, Raman, NMR, mercury, palladium, nickel, onedimensional wire

A new family of oligonuclear cyano compounds incorporatingtransition (Pt) and main group (Tl) metals bound with anon-buttressed Pt-Tl bond was synthesised in aqueous solution.The metal-metal linkage is formed in the reaction betweenplatinum and thallium in their stable oxidation forms, Pt(II)and Tl(III), orvice versa: Pt(IV) and Tl(I). Four binuclear complexeswith a general composition [(CN)5Pt-Tl(CN)n(aq)]n-(n = 0-3) and a trinuclear species [(NC)5Pt-Tl-Pt(CN)5]3-were identified and structurally characterised insolution by multinuclear NMR, EXAFS and vibrationalspectroscopy. In aqueous solution the complexes exist inequilibrium. The distribution between the species can bealtered by varying the molar ratio Pt/Tl, cyanide concentrationand pH. Stability constants of the compounds weredetermined. A new compound (NC)5PtTl was also prepared in solid and its crystalstructure solved by a combination of X-ray powder diffractionand EXAFS. Altogether the values of195Pt-205Tl spin-spin coupling constants (25-71 kHz),interatomic Pt-Tl distances (2.598-2.638 Å), and vibrationstretching frequencies v (Pt-Tl) (159-164 cm-1) are fully indicative of a direct and unsupportedPt-Tl bond. The calculated values of Pt-Tl force constants(1.56-1.74 N· cm-1) are characteristic for single metal-metal bond.The oxidation status in the compounds can be viewed asintermediate between II and IV for platinum, and between I andIII for thallium, as reflected by the chemical shifts of195Pt and205Tl nuclei, C≡ N stretching frequencies andelectron binding energies. The compounds are capable to undergo a photoinducedtwo-electron transfer between the coupled hetero-metal ions.Upon irradiation into the metal-to-metal charge transferabsorption band, effective photoredox reaction takes place. Itresults in scission of the Pt-Tl bond and formation of variouscomplexes of oxidised platinum (Pt(III, IV)) and reducedthallium (Tl(I)). The values of photodecomposition quantumyields were determined from a stationary photolysis study ofthe heterometallic complexes. Nanosecond laser flash photolysisof the heteronuclear Pt-Tl cyano compounds was performed in thetimescale range 1· 10-6- 5· 10-2s and several intermediate species were detectedand characterised by optical spectroscopy. The heteronuclear Pt-Tl cyano compounds can be furthermodified in terms of their stability, solubility, and lightabsorption characteristics. It has been found that the platinumpentacyano unit of the [(NC)5Pt-Tl(CN)n(aq)]n-species is inert towards the tested ligands,whereas the thallium "part" of the complexes can be tunedsignificantly. A number of complexes [(NC)5Pt-Tl(L)m]x-(L-ligand) were prepared and characterised insolution. Compounds [(NC)5Pt-Tl(nta)(H2O)]3-, [(NC)5Pt-Tl(bipy)(DMSO)3], and [(NC)5Pt-Tl(bipy)2]have been prepared in solid and their structuresdetermined by single-crystal X-ray diffraction. <b>Keywords:</b>thallium, platinum, cyanide, metal-metal bond,non-buttressed, heterobimetallic, photoinduced, electrontransfer, redox reaction, NMR, chemical shift, spin-spincoupling constant, Raman, EXAFS, X-ray diffraction,equilibrium, oxidation state, oxidative addition,photolysis

<p>A new family of oligonuclear cyano compounds incorporatingtransition (Pt) and main group (Tl) metals bound with anon-buttressed Pt-Tl bond was synthesised in aqueous solution.The metal-metal linkage is formed in the reaction betweenplatinum and thallium in their stable oxidation forms, Pt(II)and Tl(III), or<i>vice versa</i>: Pt(IV) and Tl(I). Four binuclear complexeswith a general composition [(CN)₅Pt-Tl(CN)_n(aq)]^n-(n = 0-3) and a trinuclear species [(NC)₅Pt-Tl-Pt(CN)₅]^3-were identified and structurally characterised insolution by multinuclear NMR, EXAFS and vibrationalspectroscopy. In aqueous solution the complexes exist inequilibrium. The distribution between the species can bealtered by varying the molar ratio Pt/Tl, cyanide concentrationand pH. Stability constants of the compounds weredetermined.</p><p>A new compound (NC)₅PtTl was also prepared in solid and its crystalstructure solved by a combination of X-ray powder diffractionand EXAFS. Altogether the values of¹⁹⁵Pt-²⁰⁵Tl spin-spin coupling constants (25-71 kHz),interatomic Pt-Tl distances (2.598-2.638 Å), and vibrationstretching frequencies v (Pt-Tl) (159-164 cm^-1) are fully indicative of a direct and unsupportedPt-Tl bond. The calculated values of Pt-Tl force constants(1.56-1.74 N· cm^-1) are characteristic for single metal-metal bond.The oxidation status in the compounds can be viewed asintermediate between II and IV for platinum, and between I andIII for thallium, as reflected by the chemical shifts of¹⁹⁵Pt and²⁰⁵Tl nuclei, C≡ N stretching frequencies andelectron binding energies.</p><p>The compounds are capable to undergo a photoinducedtwo-electron transfer between the coupled hetero-metal ions.Upon irradiation into the metal-to-metal charge transferabsorption band, effective photoredox reaction takes place. Itresults in scission of the Pt-Tl bond and formation of variouscomplexes of oxidised platinum (Pt(III, IV)) and reducedthallium (Tl(I)). The values of photodecomposition quantumyields were determined from a stationary photolysis study ofthe heterometallic complexes. Nanosecond laser flash photolysisof the heteronuclear Pt-Tl cyano compounds was performed in thetimescale range 1· 10^-6- 5· 10^-2s and several intermediate species were detectedand characterised by optical spectroscopy.</p><p>The heteronuclear Pt-Tl cyano compounds can be furthermodified in terms of their stability, solubility, and lightabsorption characteristics. It has been found that the platinumpentacyano unit of the [(NC)₅Pt-Tl(CN)_n(aq)]^n-species is inert towards the tested ligands,whereas the thallium "part" of the complexes can be tunedsignificantly. A number of complexes [(NC)₅Pt-Tl(L)_m]^x-(L-ligand) were prepared and characterised insolution. Compounds [(NC)₅Pt-Tl(nta)(H₂O)]^3-, [(NC)₅Pt-Tl(bipy)(DMSO)₃], and [(NC)₅Pt-Tl(bipy)₂]have been prepared in solid and their structuresdetermined by single-crystal X-ray diffraction.</p><p><b>Keywords:</b>thallium, platinum, cyanide, metal-metal bond,non-buttressed, heterobimetallic, photoinduced, electrontransfer, redox reaction, NMR, chemical shift, spin-spincoupling constant, Raman, EXAFS, X-ray diffraction,equilibrium, oxidation state, oxidative addition,photolysis</p>

<p>The kinetic and mechanistic features of a new series ofplatinum-thallium cyano compounds containing a direct andunsupported by ligands metal-metal bond have been studied insolution, using standard mix–and–measurespectrophotometric technique and stopped–flow method.These reactions are interpreted as oxidative addition of the cspecies to the square planar Pt(CN)₄^2-complex. Each of these processes was found to befirst-order in Pt(CN)₄^2-, the corresponding TI^IIIcomplex and a cyanide ion donating species whichacts as a catalyst. Both di- and trinuclear complexes werestudied, and the kinetically significant thallium complexes intheir formation and the catalytically active cyanide sourcesare as follows: [(CN)₅PtTl(CN)₃]^3-: Tl(CN)₄^–(alkaline region), Tl(CN)₃(slightly acidic region) and CN^–; [(CN)₅Pt–Tl(CN)]–: Tl(CN)₂⁺and Tl(CN)₂⁺; [(CN)₅Pt–Tl–Pt(CN)₅]^3-: [(CN)₅Pt–Tl(CN)]–and HCN. Appropriatemechanisms were postulated for the overall reactions in allcases, which include i) metal–metal bond formation stepand ii) coordination of an axial cyanide ion to the platinumcenter. Two experimentally indistinguishable kinetic modelswere proposed for the formation of the dinuclear complexeswhich are different in the sequence of the two steps. In thecase of the trinuclear complex, experimental evidence isavailable to exclude one of the alternative reaction paths, andit was proven that the metal–metal bond formation precedesthe axial cyanide coordination.</p><p>The cyanide ligands coordinated to TI^IIIin the Pt–Tl complexes could be replacedsuccessfully with aminopolycarboxylates e.g.: mimda^2-, nta^3-, edta^4-. The [(CN)₅Pt–Tl(edta)]^4-complex, with a direct metal–metal bond hasbeen prepared in solution by two different reactions: a)dissolution of [(CN)₅Pt–Tl](s) in an aqueous solution of edta, b)directly from Pt(CN)₄^2-and Tl(edta)(CN)^2-. The decomposition reaction is greatlyaccelerated by cyanide and significantly inhibited by edta. Itproceeds through the [(CN)₅Pt–Tl(CN)₃]^3-intermediate. The formation of [(CN)₅Pt–Tl(edta)]^4-can proceed via two different pathways dependingon the ratio of the cyanide to the edta ligand concentrations.The’direct path’at excess of edta means theformation of intermediate[(CN)4Pt···Tl(CN)(edta)]^4-, followed by a release of the cyanide from theTl–centre followed by coordination of a cyanide from thebulk to the Pt–centre of the intermediate. The’indirect path’dominates in the absence of extraedta and the formation of the Pt–Tl bond occours betweenPt(CN)₄^2-and Tl(CN)4^–.</p><p>Homoligand MTl(CN)₄(M = Tl^I, K, Na) and, for the first time, Tl(CN)₃species have been synthesized in the solid stateand their structures solved by single crystal X–raydiffraction method. Interesting redox processes have been foundbetween TI^IIIand CN^–in non–aqueous solution and in Tl₂O₃-CN^–aqueous suspension. In the crystal structureof Tl(CN)₃·H₂O, the thallium(III) ion has a trigonal bypiramidalcoordination geometry with three cyanides in the trigonalplane, while an oxygen atom of the water molecule and anitrogen atom from a cyanide ligand attached to a neighboringthallium complex, form a linear O–Tl–N fragment.Cyanide ligand bridges thallium units forming an infinitezigzag chain structure. Among the thallium(III) tetracyanocompounds, the isostructural M[Tl(CN)₄](M = Tl and K) and Na[Tl(CN)₄]·3H₂O crystallize in different crystal systems, but thethallium(III) ion has in all cases the same tetrahedralgeometry in the [Tl(CN)₄]^–unit.</p><p>Three adducts of mercury(II) (isoelectronic with TI^III) (K₂PtHg(CN)₆·2H₂O, Na₂PdHg(CN)₆·2H₂O and K₂NiHg(CN)₆·2H₂O) have been prepared from Hg(CN)₂and square planar transition metal cyanides M^II(CN)₄^2-and their structure have been studied by singlecrystal X–ray diffraction, XPS and Raman spectroscopy inthe solid state. The structure of (K₂PtHg(CN)₆·2H₂O consists of strictly linear one dimensional wireswith Pt^IIand Hg^IIcenters located alternately, d_Hg–Pt= 3.460 Å. The structure of Na₂PdHg(CN)₆·2H₂O and K₂NiHg(CN)₆·2H₂O can be considered as double salts, the lack ofhetero–metallophilic interaction between both the Hg^IIand Pd^IIatoms, d_Hg–Pd= 4.92 Å, and Hg^IIand Ni^IIatoms, d_Ni–Pd= 4.60 Å, seems obvious. Electronbinding energy values of the metallic centers measured by XPSshow that there is no electron transfer between the metal ionsin all three adducts. In solution, experimental findingsclearly indicate the lack of metal–metal bond formation inall studied Hg^II–CN^-–M^II(CN)4^2-systems (M = Pt, Pd and Ni). It is in contrary tothe platinum–thallium bonded cyanides.</p><p><b>KEYWORDS:</b>metal–metal bond, platinum, thallium,kinetics, mechanism, stopped flow, oxidative addition, cyanocomplexes, edta, redox reaction, metal cyanides, X–raydiffraction, Raman, NMR, mercury, palladium, nickel, onedimensional wire</p>

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Um estudo da interação entre desordem e polarização de spin no GaMnAs ajuda a compreender a natureza dos estados, estendidos ou localizados, bem como as consequências para as transições observadas sobre as propriedades de transporte e às mudanças na ordem magnética de momentos magnéticos localizados em sítios de Mn. Este estudo pressupõe a ocorrência de uma banda impureza com baixas concentrações de Mn, que merge na banda valência no caso de concentrações mais elevadas. A abordagem teórica, baseada em um formalismo de espalhamento múltiplo auto-consistente, através do cálculo da função de Green para buracos determina-se a função densidade espectral no nível de Fermi. A escolha de uma figura de mérito, com base na largura e sobre a posição do máximo da função densidade espectral no espaço recíproco, leva a um diagrama de fase que determina o caráter metálicos ou não metálicos da amostra. Também é possível identificar a mobility edge, e como consequência, a densidade efetiva de portadores livre. Uma amostra é definida pelo par de parâmetros independentes, a concentração de Mn e a densidade buraco. As melhores amostras, aquelas com os maiores valores de mérito, tem uma relação entre a densidade de buracos estendidos e a concentração de Mn aproximadamente de 0.3, muito próximo do raio de 10-25% observada entre as amostras reais produzidos com a mais alta temperatura de transição. Além disso, a relação entre essas concentrações de Mn correspondente as transições metal-não-metal e não-metal-metal que é de aproximadamente 2.4, muito próximo do valor 2.1 da amostras reais. Uma interpretação da ocorrência de ferromagnetismo com alta temperatura de transição em GaMnAs é dada como uma consequência da interação entre o mecanismo de interação assistido por estados localizados e interações indiretas assistida pelo estdos buraco estendidos. Portadores mediando magnetismo em semicondutores mostram diferenças importantes e potencialmente úteis a diferenças de magnetismo em metais tais como o luz- ou voltagem elétrica -controlando ferromagnetismo. Motivado por experiências reportadas em poços quânticos de GaAs com uma dopagem delta de Mn com altas temperaturas Currier (temperatura de transição) mais elevadas do que em bulk de (Ga, Mn)As, nós exploramos teoricamente a viabilidade do campo elétrico controlar ferromagnetismo em poços quânticos. Nós calculamos auto-consistentemente a interação de troca indireta em Mn-Mn íons e aplicamos a simulação Monte Carlo para encontrar transição temperatura Tc. A nossa abordagem permite-nos estudar sistematicamente os efeitos de confinamento quântico e da posição da camada magnética de Mn e Tc, que vai além da aproximação do campo médio. Nós comparamos nossos resultados com os resultados experimentais e sugerimos caminho para o melhor controle do ferromagnetismo. / A study of the interplay between disorder and spin polarization in the diluted magnetic semiconductor GaMnAs helps to understand the character of states, extended or localized. This study assumes the occurrence of an impurity band which merges into the valence band at higher concentrations. The theoretical approach, based on a self-consistent multiple scattering formalism, determines the spectral density function at the Fermi level from the calculation of the hole's Green's functions. A choice of a figure of merit, based on the width and on the position of the maximum of the spectral density function in the reciprocal space, leads to a phase diagram determining the metallic or non-metallic character of the sample. It is also possible to identify mobility edges and, in consequence, the density of effectively free carriers. A model sample is defined by the pair of independent parameters, Mn concentration and hole density. The best samples, those with the highest figures of merit, have a ratio between the extended hole density and the Mn concentration near 0.3, very close to ratio of 10-30% observed among the real samples produced with the highest transition temperatures. Also, the ratio between those Mn concentrations corresponding to the metal-to-non-metal and non-metal-to-metal transitions is approximately 2.4, very close to the value 2.1 inferred from the real samples. An interpretation of the occurrence of high transition temperature ferromagnetism in GaM-nAs is given as a consequence of the interplay between interaction mechanism assisted by localized states and indirect interactions assisted by extended hole states. Carrier mediated magnetism in semiconductors show important and potentially useful differences from magnetism in metals,such as light- or bias-controlled ferromagnetism. Motivated by experiments reporting higher Currier temperatures in GaAs quantum wells with Mn-delta doping than the ones observed in bulk (Ga,Mn)As, we explore theoretically the feasibility of bias-controlled ferromagnetism these systems. We calculate self-consistently indirect Mn-Mn exchange interaction, and apply Monte Carlo approach to find transition temperature Tc. Our approach allows us to systematically study the eects of quantum confinement and the position of Mn layer on magnetic ordering and Tc, beyond mean field approximation. We compare our findings with the experimental results and suggest paths toward improving the control of ferromagnetism.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Um estudo da interação entre desordem e polarização de spin no GaMnAs ajuda a compreender a natureza dos estados, estendidos ou localizados, bem como as consequências para as transições observadas sobre as propriedades de transporte e às mudanças na ordem magnética de momentos magnéticos localizados em sítios de Mn. Este estudo pressupõe a ocorrência de uma banda impureza com baixas concentrações de Mn, que merge na banda valência no caso de concentrações mais elevadas. A abordagem teórica, baseada em um formalismo de espalhamento múltiplo auto-consistente, através do cálculo da função de Green para buracos determina-se a função densidade espectral no nível de Fermi. A escolha de uma figura de mérito, com base na largura e sobre a posição do máximo da função densidade espectral no espaço recíproco, leva a um diagrama de fase que determina o caráter metálicos ou não metálicos da amostra. Também é possível identificar a mobility edge, e como consequência, a densidade efetiva de portadores livre. Uma amostra é definida pelo par de parâmetros independentes, a concentração de Mn e a densidade buraco. As melhores amostras, aquelas com os maiores valores de mérito, tem uma relação entre a densidade de buracos estendidos e a concentração de Mn aproximadamente de 0.3, muito próximo do raio de 10-25% observada entre as amostras reais produzidos com a mais alta temperatura de transição. Além disso, a relação entre essas concentrações de Mn correspondente as transições metal-não-metal e não-metal-metal que é de aproximadamente 2.4, muito próximo do valor 2.1 da amostras reais. Uma interpretação da ocorrência de ferromagnetismo com alta temperatura de transição em GaMnAs é dada como uma consequência da interação entre o mecanismo de interação assistido por estados localizados e interações indiretas assistida pelo estdos buraco estendidos. Portadores mediando magnetismo em semicondutores mostram diferenças importantes e potencialmente úteis a diferenças de magnetismo em metais tais como o luz- ou voltagem elétrica -controlando ferromagnetismo. Motivado por experiências reportadas em poços quânticos de GaAs com uma dopagem delta de Mn com altas temperaturas Currier (temperatura de transição) mais elevadas do que em bulk de (Ga, Mn)As, nós exploramos teoricamente a viabilidade do campo elétrico controlar ferromagnetismo em poços quânticos. Nós calculamos auto-consistentemente a interação de troca indireta em Mn-Mn íons e aplicamos a simulação Monte Carlo para encontrar transição temperatura Tc. A nossa abordagem permite-nos estudar sistematicamente os efeitos de confinamento quântico e da posição da camada magnética de Mn e Tc, que vai além da aproximação do campo médio. Nós comparamos nossos resultados com os resultados experimentais e sugerimos caminho para o melhor controle do ferromagnetismo. / A study of the interplay between disorder and spin polarization in the diluted magnetic semiconductor GaMnAs helps to understand the character of states, extended or localized. This study assumes the occurrence of an impurity band which merges into the valence band at higher concentrations. The theoretical approach, based on a self-consistent multiple scattering formalism, determines the spectral density function at the Fermi level from the calculation of the hole's Green's functions. A choice of a figure of merit, based on the width and on the position of the maximum of the spectral density function in the reciprocal space, leads to a phase diagram determining the metallic or non-metallic character of the sample. It is also possible to identify mobility edges and, in consequence, the density of effectively free carriers. A model sample is defined by the pair of independent parameters, Mn concentration and hole density. The best samples, those with the highest figures of merit, have a ratio between the extended hole density and the Mn concentration near 0.3, very close to ratio of 10-30% observed among the real samples produced with the highest transition temperatures. Also, the ratio between those Mn concentrations corresponding to the metal-to-non-metal and non-metal-to-metal transitions is approximately 2.4, very close to the value 2.1 inferred from the real samples. An interpretation of the occurrence of high transition temperature ferromagnetism in GaM-nAs is given as a consequence of the interplay between interaction mechanism assisted by localized states and indirect interactions assisted by extended hole states. Carrier mediated magnetism in semiconductors show important and potentially useful differences from magnetism in metals,such as light- or bias-controlled ferromagnetism. Motivated by experiments reporting higher Currier temperatures in GaAs quantum wells with Mn-delta doping than the ones observed in bulk (Ga,Mn)As, we explore theoretically the feasibility of bias-controlled ferromagnetism these systems. We calculate self-consistently indirect Mn-Mn exchange interaction, and apply Monte Carlo approach to find transition temperature Tc. Our approach allows us to systematically study the eects of quantum confinement and the position of Mn layer on magnetic ordering and Tc, beyond mean field approximation. We compare our findings with the experimental results and suggest paths toward improving the control of ferromagnetism.

L’objectif de ce travail fut la synthèse de ligands fonctionnels de type N,N'-diphosphanyl-NHC (NHC = carbènes N-hétérocycliques) et l’étude de leur chimie de coordination. La synthèse du nouveau ligand tridentate, stable et rigide, N,N'-diphosphanyl-imidazol-2-ylidene a permis des études expérimentales et théoriques et l’accès à des complexes mono-, di-, tri-, penta-, et hexanucléaires des métaux du groupe 11 (Cu, Ag et Au) originaux et aux propriétés structurales uniques. Les complexes mono- et dinucléaires avec un ou deux atomes de phosphore libres ont permis d’accéder à des complexes hétérotrinucléaires à interactions d10-d10 qui sont luminescents. La transmétallation partielle ou totale des complexes homotrinucléaires de Cu ou d’Ag avec des réactifs contenant du Pd(0) ont conduit à des complexes hétérotrinucléaires à interactions d10-d10. En plus de son comportement pontant, ce ligand peut se agir en chélate dans des complexes du palladium et du chrome. Dans le cas du Cr(III), ils montrent une activité catalytique en oligomérisation de l’éthylène supérieure à celle des complexes du Cr(II) et conduisent principalement à des oligomères. / The purpose of this work was the synthesis of N,N'-diphosphanyl-functionalized NHC ligands andtheir coordination chemistry. The novel stable and rigid tridentate N,N'-diphosphanyl-imidazol-2-ylidene was synthesized and experimental and computational information on its stability weregained. It served as a unique platform for the synthesis of novel mono-, di-, tri-, penta-, hexanuclear complexes with the coinage metals (Cu, Ag and Au), exhibiting rare structural features. The mono- and dinuclear complexes with one or two dangling P-donors provided rational access to heterotrinuclear complexes. All these coinage metal complexes have short metal-metalseparations, indicating the presence of d10-d10 interactions, and display excellent luminescentproperties. Partial or complete transmetallation of the homotrinuclear Cu or Ag complexes withPd(0) precursors led to hetero-trinuclear complexes with d10-d10 interactions. In addition to itsbridging behavior, this ligand also showed its chelating behavior in Pd or Cr(III) complexes. Thelatter displayed superior performance in ethylene oligomerization than the Cr(II) complexes andgave mostly oligomers.

Dans cette thèse est décrite la synthèse et les propriétés magnétiques des composés de coordination contenant des liaisons Co-Co ou Cr-Cr. Le contexte général sera discuté dans la première partie de ce travail en considérant l'évolution historique de ce type de chimie de coordination. Dans le deuxième chapitre, la possibilité d'intégrer un cluster {Co3} avec des ligands dipyridylamide et liaisons intermétalliques, dans des polymères de coordination unidimensionnels est discutée. Les interactions entre les porteurs de spin et l'effet du ligand pontant sont étudiés. Les changements des propriétés de transition de spin sont contrôlés en comparant par rapport au précurseur. Dans le troisième chapitre, les propriétés de molécule aimant d'un cluster de {Cr3} analogue à celui du {Co3}, sont étudiées. L'influence du ligand axial et la symétrie de la molécule sont également considérés et corrélées avec les propriétés de la molécule. Dans le quatrième chapitre, l'effet de la transition de spin induite par la coordination est étudié sur un exemple de cluster de {Co3} avec des ligands dipyridylformamidinate. La rupture et le rétablissement d'une liaison Co-Co est contrôlée par le biais de la température et de la lumière. L'effet de la rupture de la liaison intermétallique sur les propriétés magnétiques et structurales est aussi étudié. / In this thesis is described the synthesis, structures and magnetic properties of coordination compounds containing Co-Co or Cr-Cr bonds. In the first part of this work a general background is given on the historical evolution of this type of coordination chemistry. In the second chapter the possibility of incorporating a {Co3} cluster with dipyridylamide ligands and intermetallic bonds into one-dimentional coordination polymers is discussed. The interactions between spin centers and the effect of the bridging ligand were studied, and changes in the spin crossover properties were monitored and compared to the precursor. In the third chapter the Single-Molecule Magnet properties of a series of {Cr3} clusters are presented. The influence of the axial ligand and the symmetry of the molecule was considered and correlated to the magnetic properties. In the fourth chapter the phenomenon of coordination induced spin transition in a {Co3} cluster with dipyridylformamidinate ligands is discussed. Changes in magnetism and optical properties as a result of the breaking and restoring of a Co-Co bond were monitored as a function of temperature and light irradiation.

Computational chemistry has gained interest as a characterization tool to predict photoluminescence, reactivity and structural properties of organic and transition metal complexes. With the rise of methods including relativity, these studies have been expanded to the accurate modeling of luminescence spectra of complexes with considerable spin-orbit splitting due to heavy metal centers as well as the reaction pathways for these complexes to produce natural products such as hydrogen gas. These advances have led to the synthesis and utility of more effective catalysis as well as the development of more effective organic light emitting diodes (OLEDs) through the incorporation of organometallic complexes as emitters instead of typical organic emitters. In terms of significant scientific advancement presented in this work is in relation to the discovery of significant spin-orbit splitting in a gold(I) alkylphosphine complex, where the splitting results in the states that emit in different colors of the visible region of the electromagnetic spectrum. This work also reveals the discovery both computationally and experimentally, of a genuine polar-covalent bond between two-closed shell metals. This work highlights a complex with an incredibly short gold(I) – copper(I) intermetallic distance leading to a vibrational frequency and dissociation energy that is on par with those of other systems with single-bonded metal centers. Lastly, this work outlines a strategy for the production of hydrogen gas through the use of trinuclear cyclic coinage metal complexes as catalysis to split hydrohalic acids.

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