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The chemistry of metal–metal (M–M) multiply bonded compounds has fascinated inorganic chemists for a period spanning more than five decades. Since the elucidation of the quadruple bond by Cotton in 1964, thousands of compounds featuring M–M bonds have been isolated and studied. Of these, dinuclear units supported by four bidentate ligands forming a ‘paddlewheel’ motif represent a class of compounds that present unique molecular and electronic structures, and useful electrochemical and magnetic properties.<div><br></div><div>Over the last two and a half decades, our laboratory has focused on studying diruthenium paddlewheel complexes for their easeof preparation, rich electrochemical properties,and remarkable stability. We have isolated a vast number of diverse diruthenium alkynyls in multiple oxidation states, bearing different paddlewheel (equatorial) ligand systems and studied their molecular and electronic structures. Taking advantage of the extended conjugation that exists between the Ru2core and the poly-alkynyl ligand motif, we have also found applications for them in prototypical flash-memory devices. At this juncture, we sought to expand the organometallic chemistry of Ru2to complexes featuring Ru–aryl linkages.<br></div><div><br></div><div>The ‘aryl anion’ is, based on pKa, twenty orders of magnitude more basic than the corresponding acetylide. Arguably, this difference should result in a more electron-rich dinuclear core with new electronic structures waiting to be explored. Although kinetically more reactive than metal–alkynyls, metal–aryls are still more stable than the corresponding metal–alkyls. However, for second-row transition metals like ruthenium, kinetic instability issues are somewhat more suppressed than for their first-row counterparts.<br></div><div><br></div><div>Armed with the knowledge that it was reasonable to expect somewhat stable metal–aryl complexes, the synthesis and characterization, and analyses of molecular and electronic structures of diruthenium aryls were attempted. By employing relatively simple lithium-halogen exchange reactions, both mono and bis-aryl complexes of diruthenium have been isolated. Additionally, two different oxidation states of diruthenium have beenaccessed, namely Ru2(II,III)and Ru2(III,III),by judiciously modifying the paddlewheel ligands. Following this, preliminary reactivity studies of Ru2(II,III) monoaryls of the form Ru2(ap)4Ar were performed, which yielded surprising results. This work led to the conclusion that the diruthenium–aryl interaction is an example of a metal–metal–ligand interaction that can bring reactivity to the distal metal site. Moreover, it was found that even minor changes in axial ligands can bring about major upheavals in electronic structure.<br></div><div><br></div><div>Computational investigations into the electronic structure of the above-mentioned compounds have faced many a barrier because of the complexity of the system. The deep mixing of the metal–metal and metal–ligand valence manifolds is more easily isolated into its constituent parts in the case of relatively simple structures such as the monoaryls, Ru2II,IIIL4Ar. However, electronic structure calculations are fraught with difficulties in the case of heavily distorted axially disubstituted mono and bis-aryls, (X)Ru2III,IIIL4Ar and Ru2III,IIIL4Ar2, respectively. Ru2III,IIIL4Ar2complexes present an interesting case of second order Jahn-Teller distortion (SOJT), which has been adequately modeled. However, the more heavily distorted case of XRu2(ap)4Ar (X = CCH, CN, CO, etc.) pose greater computational challenges, such as low-lying excited states, spin-admixed ground states and difficulties in isolating metal and ligand contributions to the valence manifold. <br></div><div><br></div><div>Our investigations into diruthenium aryls began as a mere curiosity that arose out of a serendipitous discovery. Two years later, our continued efforts in this direction have yielded rather fruitful results. The unusual structures and associated complex bonding motifs in these systems have taught us about the importance of metal–metal–ligand interactions as more than just a sum of metal–metal and metal–ligand parts.<br></div>

<p>  </p> <p>This thesis will focus on two broad topics: the synthesis and characterization of various diruthenium aryl compounds and of mono- and bis-alkynyl unsymmetric compounds based on Ru(II)(dppm)₂ and Ru(II)(dppe)₂ bridges (dppm = 1,2-bis(diphenylphosphino)methane; dppe = 1,2-bis(diphenylphophino)ethane).</p> <p>Chapters 1–3 focus on multiply bonded metal–metal compounds, utilizing four different ‘paddlewheel’ motifs (dinuclear ruthenium units that are supported by four bidentate ligands). These highly stable mono- and bis-aryl diruthenium compounds are readily prepared using lithium-halogen exchange reactions. Two different oxidation states have been accessed, Ru₂(II,III) and Ru₂(III,III), through modification of the paddlewheel ligands or coordination of a small, π-accepting ligand at the vacant ruthenium site in Ru₂(<em>ap</em>)₄(Ar) compounds (<em>ap</em> = 2-anilinopyridinate; Ar = aryl). Chapter 1 discusses the modification of the bidentate ligand to yield two unique Ru₂(<em>ap</em>')₄(Ar) series, which both exhibit improved solubility over the previously reported un-modified Ru₂(<em>ap</em>)₄(Ar) series, and the structural, electronic, and optical characterizations of the compounds within these two new Ru₂(II,III) series. Chapter 2 builds upon our lab’s previous studies on electron transfer between the two ruthenium centers in [Ru₂(<em>ap</em>)₄]₂(μ-C≡C)_x compounds and applies this towards synthesizing and characterizing mixed-valency within a Ru₂(III,III) phenylene bridged compound [(NC)Ru₂(<em>ap</em>)₄]₂(μ-1,4-C₆H₄). Chapter 3 highlights the synthesis and characterization of bis-aryl and bis-alkynyl Ru2(III,III) compounds, Ru₂(amtfmp)₄(Y)₂ (Y = -C≡CPh, -Ph), supported with the electron-withdrawing paddlewheel ligand amtfmp (amtfmp = 2-amino-3-(trifluoromethyl)pyridinate). </p> <p>Chapters 4 and 5 are focused on the synthesis and characterization of both mono- and bis-alkynyl unsymmetric compounds to study photo-induced electron transfer (PET) processes. Chapter 4 features as an introduction to the synthesis of these Ru(II)(dppm)₂ and Ru(II)(dppe)₂alkynyl compounds along with some material applications. Chapter 5 discusses the mono- and bis-alkynyl compounds based on Ru(II)(dppm)₂ and Ru(II)(dppe)₂ bridges that utilized a highly electron-withdrawing chromophore ‘acceptor’ ligand, NAP^R (R = isopropyl, mesityl), to generate the <em>B-A</em> (mono-alkynyl) and <em>D-B-A</em> (unsymmetric bis-alkynyl) compounds.</p>

Compostos do tipo [M2(O2CR)4] com ligação múltipla direta entre os centros metálicos apresentam importância do ponto de vista teórico bem como da química aplicada a diversas áreas. Recentemente tem havido um grande interesse voltado, especialmente, para o design de novos materiais construídos com base nestas unidades dimetálicas. O principal objetivo deste trabalho é o estudo de complexos de rutênio que apresentam núcleos M2 de valência mista do tipo Ru2(lI,III) com ligantes dicarboxílicos. A partir do complexo [Ru2(OAc)4CI], foram sintetizados compostos com os ligantes dicarboxilatos -O2C-R-CO2-, em que R são cadeias carbônicas saturadas (succinato, adipato e dodecanodioato) ou anéis aromáticos (tereftalato e 4,4\'-bifenildicarboxilato). Modificando-se a metodologia de síntese, foi possível isolar dois tipos de compostos: [Ru2(O2C-R-CO2)2CI] (R = succ, adip, dode, tere e bife) e [Ru4(O2C-R-CO2)5(H2O) 2] (R = adip e dode). Todos os compostos apresentam bandas de absorção na região do visível, ao redor de 450 nm, e do infravermelho próximo, ao redor de 1100 nm, que podem ser atribuídas, respectivamente às transições eletrônicas &#960; (Ru-O, Ru2) &#8594; &#960;* (Ru2) e &#948; (Ru2) &#8594; &#948;* (Ru2). Estas transições são características de espécies de [Ru2]5+, comprovando a manutenção das ligações metal-metal nos derivados. Os valores dos momentos magnéticos efetivos (&#181;eff), calculados com base em medidas de susceptibilidade magnética, estão na faixa de 3,8-4,4 M.B para os compostos [Ru2(O2C-R-CO2)2CI] (R = succ, adip e dode) e correspondem à configuração eletrônica do estado fundamental do tipo &#963;2 &#181;4 &#948;2 (&#181;*)2 (&#948; *)1, com três elétrons desemparelhados, que é observada para carboxilatos de dirutênio (lI,III). Valores de &#181;eff um pouco mais altos foram obtidos para os demais compostos, provavelmente devido à existência de algum tipo de acoplamento magnético. Nos espectros vibracionais FT-IR, observam-se bandas na faixa de 1470 a 1390 cm-1, que é típica das frequências de estiramentos &#957;a e &#957;s dos grupos COO- de carboxilatos ligados em ponte. Bandas relativas às frequências de estiramento das ligações metal-metal, &#957;(Ru-Ru), são observadas nos espectros Raman ao redor de 330 cm-1. Estes dados indicam que os compostos apresentam estruturas do tipo gaiola em que os ligantes carboxilatos formam pontes equatoriais (via grupo COO-) entre dois íons metálicos, estabilizando a ligação múltipla Ru-Ru. Devido à presença de dois grupos COO- para cada íon dicarboxilato, ocorre também a formação de pontes equatoriais entre centros de [Ru2]5+, gerando espécies poliméricas constituídas por unidades [Ru2(O2C-R-CO2)2]+. As posições axiais são ocupadas pelos ânions cloreto ou carboxilato, respectivamente nos casos dos compostos [Ru2(O2C-R-CO2)2CI] e [Ru4(O2C-R-CO2)5(H2O)2], que também formam pontes entre unidades dimetálicas. As presenças das pontes axiais e das pontes equatoriais entre unidades de [Ru2]5+ gerando estruturas tridimensionais que apresentam dois tipos distintos de lamelas ou camadas foram comprovadas com base nos valores das distâncias interplanares calculadas a partir dos difratogramas de raios-X de pó dos compostos. Os compostos são termicamente estáveis até a temperatura de ~ 250°C, conforme verificado por meio de estudos de análise termogravimétrica. Acima desta temperatura, começam a ocorrer perdas de massa que correspondem às perdas totais dos ligantes equatoriais e axiais, considerando-se o RuO2 como produto final das decomposições térmicas. Os compostos [Ru2(adip)2CI], [Ru2(tere)2CI] e [Ru4(dode)5(H2O)2] apresentam áreas superficiais elevadas, aproximadamente iguais a 170, 100 e 40 m2/g, respectivamente, que podem estar relacionadas à formação de estruturas microporosas. Estes tipos de estruturas com poros podem atuar como adsorvedores de gases, por exemplo, o que torna os compostos bastante promissores para aplicação na área de novos materiais microporosos, especialmente o primeiro cuja área é cerca de duas vezes maior do que a do segundo, o qual está descrito na literatura como bom adsorvedor para N2, O2 e Ar. / Compounds containing dimetal units [M2(O2CR)4] which have metal-metal multiple bonds are of great interest in both theoretical and applied chemistry. Recently they have been investigated as important compounds for the design of new materiaIs. The main goal of this work is the study of mixed valent diruthenium carboxylates. Compounds formed by Ru2(II,III) centers and -O2C-R-CO2- dicarboxylate ligands, where R is a saturated carbon chain (succinate, adipate and dodecanodioate) or aromatic ring (terephthalate and 4,4\'-diphenyldicarboxylate), were synthesized. Two types of compounds were obtained depending on the synthetic methodology: [Ru2( O2C-R-CO2)2CI] (R = succ, adip, dode, tere and bife) and [Ru4(O2C-R-CO2)5(H2O) 2] (R = adip and dode). AlI compounds exhibit absorption bands in the visible region, around 450 nm, and in the near infrared, around 1100 nm, which can be ascribed respectively to the &#960; (Ru-O, Ru2) &#8594; &#960;* (Ru2) and &#948; (Ru2) &#8594; &#948;* (Ru2) electronic transitions. These are characteristic of [Ru2]5+ dimetal species, indicating that the metal-metal bonds are present in the derivatives. The effective magnetic moments (&#181;eff) values calculated from magnetic susceptibilities data are in the range of 3.8 - 4.4 B.M. for the [Ru2(O2C-R-CO2)2CI] (R = succ, adip and dode) compounds, corresponding to the &#963;2 &#181;4 &#948;2 (&#181;*)2 (&#948; *)1 ground state electronic configuration, with three unpaired electrons, that is observed for diruthenium (II,III) carboxylates. Higher &#181;eff values found for the other compounds can be due to some type of magnetic coupling. The FT-IR vibrational spectra show characteristic bands in the region of 1470 1390 cm-1 that is typical of symmetric and asymmetric bridging carboxylate stretching modes. The metal-metal stretching modes, &#957; (Ru-Ru), are observed in the Raman spectra around 330 cm-1. Based on these results, it can be proposed that the compounds exhibit \'lantern\' type structures where the carboxylate ligands bridge two metal ions equatorially by COO- groups, stabilizing the Ru-Ru multiple bound. Due to the presence of two COO- groups for each dicarboxylate ion, there is the occurrence of equatorial bridges between [Ru2]5+ centers too, generating polymeric species constituted by [Ru2(O2C-R-CO2)2]+ units. The chloride or the carboxylate anionic axial ligands, respectively in [Ru2(O2C-R-CO2)2CI] and [Ru4(O2C-R-CO2)5(H2O)2] compounds, can also bridge the dimetal units in the axial direction. The existence of these axial and equatorial bridges between [Ru2]5+ units generate tridimensional network structures that exhibit two different types of layers, as shown by the analysis of the interplanar distances calculated from powder X-ray diffiaction of the solids. The compounds are thermally stable up to 250°C as indicated by thermogravimetric analysis. Above this temperature, there are losses of mass that correspond to the total losses of the equatorial and the axial ligands considering the RuO2 as the product of thermal decomposition. The [Ru2(adip)2CI], [Ru2(tere)2CI] and [Ru4(dode)5(H2O)2] compounds exhibit large superficial areas, about 170, 100 and 40 m2/g respectively, which could be indicative of microporous structures. These kinds of porous structures can be used as adsorbents for gases, for example. It makes the compounds very interesting for application as new microporous materiaIs, specially for the former which has a superficial area twice as bigger as the second one that is described in the literature as good adsorbent for N2, O2e Ar.

Compostos do tipo [M2(O2CR)4] com ligação múltipla direta entre os centros metálicos apresentam importância do ponto de vista teórico bem como da química aplicada a diversas áreas. Recentemente tem havido um grande interesse voltado, especialmente, para o design de novos materiais construídos com base nestas unidades dimetálicas. O principal objetivo deste trabalho é o estudo de complexos de rutênio que apresentam núcleos M2 de valência mista do tipo Ru2(lI,III) com ligantes dicarboxílicos. A partir do complexo [Ru2(OAc)4CI], foram sintetizados compostos com os ligantes dicarboxilatos -O2C-R-CO2-, em que R são cadeias carbônicas saturadas (succinato, adipato e dodecanodioato) ou anéis aromáticos (tereftalato e 4,4\'-bifenildicarboxilato). Modificando-se a metodologia de síntese, foi possível isolar dois tipos de compostos: [Ru2(O2C-R-CO2)2CI] (R = succ, adip, dode, tere e bife) e [Ru4(O2C-R-CO2)5(H2O) 2] (R = adip e dode). Todos os compostos apresentam bandas de absorção na região do visível, ao redor de 450 nm, e do infravermelho próximo, ao redor de 1100 nm, que podem ser atribuídas, respectivamente às transições eletrônicas &#960; (Ru-O, Ru2) &#8594; &#960;* (Ru2) e &#948; (Ru2) &#8594; &#948;* (Ru2). Estas transições são características de espécies de [Ru2]5+, comprovando a manutenção das ligações metal-metal nos derivados. Os valores dos momentos magnéticos efetivos (&#181;eff), calculados com base em medidas de susceptibilidade magnética, estão na faixa de 3,8-4,4 M.B para os compostos [Ru2(O2C-R-CO2)2CI] (R = succ, adip e dode) e correspondem à configuração eletrônica do estado fundamental do tipo &#963;2 &#181;4 &#948;2 (&#181;*)2 (&#948; *)1, com três elétrons desemparelhados, que é observada para carboxilatos de dirutênio (lI,III). Valores de &#181;eff um pouco mais altos foram obtidos para os demais compostos, provavelmente devido à existência de algum tipo de acoplamento magnético. Nos espectros vibracionais FT-IR, observam-se bandas na faixa de 1470 a 1390 cm-1, que é típica das frequências de estiramentos &#957;a e &#957;s dos grupos COO- de carboxilatos ligados em ponte. Bandas relativas às frequências de estiramento das ligações metal-metal, &#957;(Ru-Ru), são observadas nos espectros Raman ao redor de 330 cm-1. Estes dados indicam que os compostos apresentam estruturas do tipo gaiola em que os ligantes carboxilatos formam pontes equatoriais (via grupo COO-) entre dois íons metálicos, estabilizando a ligação múltipla Ru-Ru. Devido à presença de dois grupos COO- para cada íon dicarboxilato, ocorre também a formação de pontes equatoriais entre centros de [Ru2]5+, gerando espécies poliméricas constituídas por unidades [Ru2(O2C-R-CO2)2]+. As posições axiais são ocupadas pelos ânions cloreto ou carboxilato, respectivamente nos casos dos compostos [Ru2(O2C-R-CO2)2CI] e [Ru4(O2C-R-CO2)5(H2O)2], que também formam pontes entre unidades dimetálicas. As presenças das pontes axiais e das pontes equatoriais entre unidades de [Ru2]5+ gerando estruturas tridimensionais que apresentam dois tipos distintos de lamelas ou camadas foram comprovadas com base nos valores das distâncias interplanares calculadas a partir dos difratogramas de raios-X de pó dos compostos. Os compostos são termicamente estáveis até a temperatura de ~ 250°C, conforme verificado por meio de estudos de análise termogravimétrica. Acima desta temperatura, começam a ocorrer perdas de massa que correspondem às perdas totais dos ligantes equatoriais e axiais, considerando-se o RuO2 como produto final das decomposições térmicas. Os compostos [Ru2(adip)2CI], [Ru2(tere)2CI] e [Ru4(dode)5(H2O)2] apresentam áreas superficiais elevadas, aproximadamente iguais a 170, 100 e 40 m2/g, respectivamente, que podem estar relacionadas à formação de estruturas microporosas. Estes tipos de estruturas com poros podem atuar como adsorvedores de gases, por exemplo, o que torna os compostos bastante promissores para aplicação na área de novos materiais microporosos, especialmente o primeiro cuja área é cerca de duas vezes maior do que a do segundo, o qual está descrito na literatura como bom adsorvedor para N2, O2 e Ar. / Compounds containing dimetal units [M2(O2CR)4] which have metal-metal multiple bonds are of great interest in both theoretical and applied chemistry. Recently they have been investigated as important compounds for the design of new materiaIs. The main goal of this work is the study of mixed valent diruthenium carboxylates. Compounds formed by Ru2(II,III) centers and -O2C-R-CO2- dicarboxylate ligands, where R is a saturated carbon chain (succinate, adipate and dodecanodioate) or aromatic ring (terephthalate and 4,4\'-diphenyldicarboxylate), were synthesized. Two types of compounds were obtained depending on the synthetic methodology: [Ru2( O2C-R-CO2)2CI] (R = succ, adip, dode, tere and bife) and [Ru4(O2C-R-CO2)5(H2O) 2] (R = adip and dode). AlI compounds exhibit absorption bands in the visible region, around 450 nm, and in the near infrared, around 1100 nm, which can be ascribed respectively to the &#960; (Ru-O, Ru2) &#8594; &#960;* (Ru2) and &#948; (Ru2) &#8594; &#948;* (Ru2) electronic transitions. These are characteristic of [Ru2]5+ dimetal species, indicating that the metal-metal bonds are present in the derivatives. The effective magnetic moments (&#181;eff) values calculated from magnetic susceptibilities data are in the range of 3.8 - 4.4 B.M. for the [Ru2(O2C-R-CO2)2CI] (R = succ, adip and dode) compounds, corresponding to the &#963;2 &#181;4 &#948;2 (&#181;*)2 (&#948; *)1 ground state electronic configuration, with three unpaired electrons, that is observed for diruthenium (II,III) carboxylates. Higher &#181;eff values found for the other compounds can be due to some type of magnetic coupling. The FT-IR vibrational spectra show characteristic bands in the region of 1470 1390 cm-1 that is typical of symmetric and asymmetric bridging carboxylate stretching modes. The metal-metal stretching modes, &#957; (Ru-Ru), are observed in the Raman spectra around 330 cm-1. Based on these results, it can be proposed that the compounds exhibit \'lantern\' type structures where the carboxylate ligands bridge two metal ions equatorially by COO- groups, stabilizing the Ru-Ru multiple bound. Due to the presence of two COO- groups for each dicarboxylate ion, there is the occurrence of equatorial bridges between [Ru2]5+ centers too, generating polymeric species constituted by [Ru2(O2C-R-CO2)2]+ units. The chloride or the carboxylate anionic axial ligands, respectively in [Ru2(O2C-R-CO2)2CI] and [Ru4(O2C-R-CO2)5(H2O)2] compounds, can also bridge the dimetal units in the axial direction. The existence of these axial and equatorial bridges between [Ru2]5+ units generate tridimensional network structures that exhibit two different types of layers, as shown by the analysis of the interplanar distances calculated from powder X-ray diffiaction of the solids. The compounds are thermally stable up to 250°C as indicated by thermogravimetric analysis. Above this temperature, there are losses of mass that correspond to the total losses of the equatorial and the axial ligands considering the RuO2 as the product of thermal decomposition. The [Ru2(adip)2CI], [Ru2(tere)2CI] and [Ru4(dode)5(H2O)2] compounds exhibit large superficial areas, about 170, 100 and 40 m2/g respectively, which could be indicative of microporous structures. These kinds of porous structures can be used as adsorbents for gases, for example. It makes the compounds very interesting for application as new microporous materiaIs, specially for the former which has a superficial area twice as bigger as the second one that is described in the literature as good adsorbent for N2, O2e Ar.