The electrical and magnetic properties of a series of 12 isostructural TCNQ salts of bis-pyridinium cations are reported and these properties are related to the structural characteristics. The role of the cation lattice in stabilising a regular TCNQ stack in these salts is discussed. For comparison with this series, the electrical and magnetic properties of two TCNQ salts of bis-pyridinium cations with ordered structures and two salts of dialkyldiphenylphosphonium cations are reported. Within the isostructural series of salts, the stoichiometry takes values of between 1:3 and 1:5, and the cation length determines the stoichiometry. In all these salts, the hydrated cation lattice is disordered and the TCNQs stack in regular columns. The room temperature conductivities, measured along the stacking axis, are in the range 0.05 to 500 S/cm with the highest conductivities observed in dehydrated salts having the approximate stoichiometry, 1:4.5. The 1:5 salts possess the lowest conductivity of the series and in these salts the cation lattice is partially ordered. The 1:3 and 1:4 salts are small band gap semi-conductors whereas the conductivity of the 1:5 salts is not simply activated within the experimental range of temperatures. In these salts the conductivity obeys the empirical power law: [mathematical equation]. The temperature dependence of the magnetic susceptibility of all but the 1:3 salts of the isostructural series is characteristic of a system of partially localised triplet excitons. The magnitude of the singlet-triplet exchange energy exhibits a stoichiometric dependence and is lower in the 1:5 salts where the spin concentration is lower. The magnetic susceptibility of the 1:3 salts varies with temperature according to the Curie-Weiss law. The apparent low spin concentration supports the evidence found for alloy formation in these salts where the cation lattice is partially occupied by neutral or monoquaternised base.

SILVA, M. S. P. Síntese e caracterização de complexos bipiridínicos de rutênio com ligantes polinitrilados. 2007. 69 f. Dissertação (Mestrado em Química Inorgânica) – Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2007. / Submitted by irlana araujo (irlanaaraujo@gmail.com) on 2011-12-29T16:06:49Z No. of bitstreams: 1 2007_dis_Mar Silva.pdf: 4361976 bytes, checksum: 5d026e36da8e46a99cf7b943340c149b (MD5) / Approved for entry into archive by Aline Nascimento(vieiraaline@yahoo.com.br) on 2012-02-14T14:53:15Z (GMT) No. of bitstreams: 1 2007_dis_Mar Silva.pdf: 4361976 bytes, checksum: 5d026e36da8e46a99cf7b943340c149b (MD5) / Made available in DSpace on 2012-02-14T14:53:15Z (GMT). No. of bitstreams: 1 2007_dis_Mar Silva.pdf: 4361976 bytes, checksum: 5d026e36da8e46a99cf7b943340c149b (MD5) Previous issue date: 2007-07-31 / In this work, the [Ru(bpy)(dcbpy)(TCNQ)Cl] and [Ru(bpy)(dcbpy)(TCNE)Cl] complexes, called Ru-TCNQ and Ru-TCNE, respectively, where bpy = 2,2’- bipyridine and dcbpy = 4,4’-dicarboxy-2,2’-bipyridine, were synthesized and characterized by spectroscopy and electrochemical techniques. The absorption spectra of the Ru-TCNQ and Ru-TCNE complexes showed bands assigned to metalto-ligand charge transfer transitions (MLCT). The luminescence spectra, with excitation at the MLCT, exhibited emission with maximum of intensity at 570 and 605 nm for the Ru-TCNQ and Ru-TCNE complexes, respectively. The luminescence decay of the complexes follows a biexponential law, with the Ru-TCNQ complex showing shorter lifetime than the Ru-TCNE complex. The infrared vibrational spectra of the complexes show a larger number of nitrile stretching bands, comparatively to the free ligands of coordination. These suggesting that the TCNX compounds are coordinated to the ruthenium atom. Upon coordenation, the shifts of these bands for lower energy values are indicative of the TCNX reduced form (TCNX⋅–). These results are confirmed by EPR spectra with g = 2.007 and 2.010 for Ru-TCNQ and Ru-TCNE complexes, respectively. The degree of charge transfer (Z) for the Ru-TCNQ and Ru-TCNE compounds was evaluated as 0.66 and 0.78, respectively. The RuIII/II redox potentials of the Ru-TCNQ (0.70V) and Ru-TCNE (1.30V) compounds, shifted for more positive potentials, when compared to the starting complex, cis- [Ru(dcbpy)(bpy)Cl2] (0,67V). These results inducate that the ligands acts as π-acceptor allowing a π-back-bonding interaction which imply in a thermodynamic stability of the metal in the reduced state (RuII). The data, all together, suggest that the TCNE compound presents a higher πback-bonding interaction capability than TCNQ compound. / No presente trabalho, os complexos cis-[Ru(dcbpy)(bpy)(TCNQ)Cl] e cis-[Ru(dcbpy)(bpy)(TCNE)Cl], denominados de Ru-TCNQ e Ru-TCNE, respectivamente, (dcbpy = 4,4’-dicarboxi-2,2’-bipiridina e bpy = 2,2’-bipirina) foram sintetizados e caracterizados por técnicas espectroscópicas e eletroquímicas. Os espectros de UV-Visível apresentaram para os complexos Ru-TCNQ e Ru-TCNE bandas de absorção na região do visível, sendo atribuídas às bandas de transferência de carga do tipo MLCT. Os espectros de luminescência apresentaram emissão, quando excitados na região da MLCT (500nm), evidenciando a modificação estrutural com a coordenação dos ligantes polinitrilados ao RuII. Os decaimentos dos compostos forma biexponenciais, com o complexo Ru-TCNQ apresentou tempos de vida muito mais curtos que o Ru-TCNE. No infravermelho, foi observado que os compostos TCNX encontram-se ligados covalentemente ao átomo de rutênio. Essa coordenação se dá através de ligação σ entre o átomo de nitrogênio de uma das nitrilas, evidenciada pelo surgimento de um maior número de bandas referentes ao estiramento C≡N, comparativamente aos ligantes livres de coordenação. A observação do deslocamento dessas bandas para regiões de menor energia, quando comparadas aos ligantes livres, permitiram identificar que os ligantes TCNQ e TCNE encontram-se coordenados em sua forma radicalar (TCNX.–). O grau de transferência de carga (Z) baseado nos espectros de infravermelho para os compostos Ru-TCNQ e Ru-TCNE foi de 0,66 e 0,78, respectivamente. Os espectros de RPE confirmaram a coordenação dos ligantes ao centro metálico na forma reduzida (Ru-TCNQ: g = 2,007 e para Ru-TCNE: g = 2,010). Os potencias redox nos complexos Ru-TCNQ (Ered = 0,70V vs ENH) e Ru-TCNE (Ered = 1,30V vs ENH) foram deslocados para potenciais mais positivos, quando comparados ao precursor cis-[Ru(dcbpy)(bpy)Cl2] (Ered = 0,67V vs ENH), evidenciando o forte caráter π receptor de elétrons dos ligantes TCNX, estabilizando o centro metálico na forma reduzida. Esses resultados evidenciam um caráter retirador de elétrons mais pronunciado para o ligante TCNE em relação ao TCNQ.

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior / O objetivo deste trabalho à contribuir com o desenvolvimento da quÃmica do sistema Fe-cyclam, atravÃs da sÃntese e caracterizaÃÃo de novos complexos metÃlicos deste sistema com duas classes de ligantes: carboxilados (oxalato e acetato) e ligantes polinitrilados (7,7,8,8 âtetracianoquinodimetano e tetracianoetileno ). AtravÃs da caracterizaÃÃo do complexo cis-[Fe(cyclam)ox]PF6 por infravermelho foi possÃvel identificar que o ligante oxalato encontra-se coordenado ao centro metÃlico de forma bidentada, bem como garantir que o ligante macrocÃclico cyclam continua na esfera de coordenaÃÃo do metal. O potencial formal de meia onda do processo redox Fe3+/2+ do complexo foi observado em â39mV vs Ag/AgCl. O potencial observado encontra-se deslocado 240mV para menores valores em relaÃÃo ao complexo precursor, favorecendo ao estado de oxidaÃÃo Fe3+ do metal, devido ao maior efeito σ doador do ligante oxalato frente aos cloretos. O espectro UV-Vis do complexo cisâ[Fe(cyclam)ox]PF6, em meio aquoso, apresentou trÃs bandas: 229nm, atribuÃda a uma transiÃÃo intraligante do cyclam, 293nm e 357nm, atribuÃdas à transferÃncia de carga de orbitais π do ligante para o orbitais dπ* do metal. Os experimentos fotoquÃmicos demonstraram a grande sensibilidade do complexo à luz, sendo observado a labilizaÃÃo do ligante oxalato da esfera de coordenaÃÃo do metal, e a reatividade da espÃcie formada atravÃs da obtenÃÃo do complexo trans-[Fe(cyclam)acet2]PF6, AtravÃs do estudo de Raio-X, obtido a partir do cristal do complexo trans-[Fe(cyclam)acet2]PF6, foi possÃvel comprovar o modo de coordenaÃÃo das duas molÃculas de acetato na posiÃÃo trans, bem como a identificaÃÃo da disposiÃÃo do cyclam no plano da molÃcula atravÃs de um arranjo conformacional trans-III. Os espectros no infravermelho dos complexos cis - [Fe(cyclam)(TCNX)Cl]Cl, onde TCNX representa os ligantes TCNQ ou TCNE, apresentaram um maior nÃmero de bandas referentes aos estiramentos CN, comparativamente aos ligantes livres, confirmando a alteraÃÃo da simetria do ligante causada pela coordenaÃÃo do metal. Com base nos deslocamentos destas freqÃÃncias para menores valores, comparativamente ao ligante livre, foi possÃvel identificar que os ligantes TCNQ e TCNE estÃo coordenados em sua forma radicalar, estado de oxidaÃÃo â1, sugerindo assim a ocorrÃncia de um processo de transferÃncia de elÃtrons do centro metÃlico, previamente reduzido (Fe2+), para os ligantes TCNX. Os potenciais redox dos Ãtomos de ferro, nos complexos com os ligantes polinitrialados TCNQ (693mV vs ENH) e TCNE (854mV vs ENH), foram deslocados para potenciais mais positivos, comparativamente ao observado no complexo precursor cis-[Fe(cyclam)Cl2]Cl (405mV vs ENH), indicando assim um forte deslocamento de densidade eletrÃnica dπ para os orbitais de simetria π dos ligantes TCNX. Os processos centrados nos ligantes coordenados ficaram mais prÃximos do que nos ligantes livres, indicando uma diminuiÃÃo na barreira de transferÃncia de elÃtrons, que segundos dados da literatura leva a uma melhor conduÃÃo elÃtrica. Os espectros eletrÃnicos dos complexos, em meio aquoso, apresentaram uma banda localizada em baixa energia, atribuÃda a transferÃncias de carga do tipo LMCT dos orbitais pπ das molÃculas de TCNX, para os orbitais dπ* do Ãon Fe3+. No complexo com o ligante TCNQ, esta banda aparece em 764nm e no complexo com o ligante TCNE, em 861nm. Observa-se ainda nos dois complexos a presenÃa das bandas referentes Ãs transiÃÃes LMCT dos cloretos para o Ãon Fe3+ em regiÃes muito prÃximas, em 557 no complexo com TCNE e em 568nm no complexo com TCNQ. A presenÃa desta banda novamente sugere a presenÃa do Ferro no estado oxidado (Fe+3). / The main objective of this work is to contribute with the chemistry of the system Fe-Cyclam through the synthesis and characterization of complexes with carboxylate ligants, acetate and oxalate, and polinitrilate ligands, 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE). The infrared spectra of the cis-[Fe(cyclam)ox]PF6 complex allowed to identify the coordination of the oxalate ligand to the iron metal in a bidentate mode as well as to suggest the presence of the macrocycle in the coordination sphere of the metal. The redox potential of the complex was observed at â39mV vs Ag/AgCl. The potential is dislocated 240mV for more positive potential when compared to that observed for the precursor complex cis-[Fe(cyclamCl2]Cl. This effect can be attributed to the stronger σ effect of the oxalate ligand when compared to the chlorine. The UV-Vis spectra of the complex, presented three bands: 229nm, attributed to a cyclam intraligand transition and the bands 293nm and 357nm, referring to ligand to metal electronic transfer from π orbitals of the oxalate to dπ* of the metal. The photochemical experiments proved the great sensibility of the complex to the light presence, being observed the reactivity effect of the complex formed after the light exposition by the formation of the trans-[Fe(cyclam)acet2]PF6 complex. Through the Ray-X obtained of the crystal of the trans-[Fe(cyclam)acet2]PF6 complex was possible to identify the coordination of two molecules of acetate at the trans position, as well as to identify the disposition of the cyclam ligand on the plane in a trans-III arrange. The infrared spectrum of the complexes cis - [Fe(cyclam)(TCNX)Cl]Cl, where the TCNX represent the ligands TCNQ and TCNE, present a great number of bands referring to the νCN, when compared with the ligands not coordinated, confirming the symetry changed induced by the metal coordination. Through the wavenumber variation of these bands was possible to identify that the TCNQ and TCNE ligands are coordinated in your radical way, oxidation state â1, suggestion this way the occurrence of a electron transfer from the iron, previously reduced (Fe+2), to the TCNX ligands. The redox potentials of the iron metals in the complexes with the polinitrilate ligands TCNQ (693mV vs ENH) and TCNE (854mV vs ENH) were dislocated for more positive potentials, when compared to the cis-[Fe(cyclam)Cl2]Cl precursor complex (405mV vs ENH), indicating the occurrence of an electronic density transfer to the TCNX molecules. The two potentials of the ligands on the complexes were closer than the ligands not coordinated, this approximation of the potential indicate a decrease of the inner electron transfer. The electronic spectra of the complexes, showed bands in the low energy region, attributed to a charge transfer LMCT, from the TCNX pπ orbital to the metal dπ* orbital. In the cis-[Fe(cyclam)(TCNQ)Cl]Cl complex, the band was observed at 764nm while in the complex with the TCNE ligand this band was observed at 861nm. Also, the complexes presented bands at 557nm (TCNE complex) and 568nm (TCNQ complex)referring to the LMCT transitions from the chlorine atoms to the iron metal reinforcing the assignment of the (Fe+3) oxidation state for the metal center.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / No presente trabalho, os complexos cis-[Ru(dcbpy)(bpy)(TCNQ)Cl] e cis-[Ru(dcbpy)(bpy)(TCNE)Cl], denominados de Ru-TCNQ e Ru-TCNE, respectivamente, (dcbpy = 4,4â-dicarboxi-2,2â-bipiridina e bpy = 2,2â-bipirina) foram sintetizados e caracterizados por tÃcnicas espectroscÃpicas e eletroquÃmicas. Os espectros de UV-VisÃvel apresentaram para os complexos Ru-TCNQ e Ru-TCNE bandas de absorÃÃo na regiÃo do visÃvel, sendo atribuÃdas Ãs bandas de transferÃncia de carga do tipo MLCT. Os espectros de luminescÃncia apresentaram emissÃo, quando excitados na regiÃo da MLCT (500nm), evidenciando a modificaÃÃo estrutural com a coordenaÃÃo dos ligantes polinitrilados ao RuII. Os decaimentos dos compostos forma biexponenciais, com o complexo Ru-TCNQ apresentou tempos de vida muito mais curtos que o Ru-TCNE. No infravermelho, foi observado que os compostos TCNX encontram-se ligados covalentemente ao Ãtomo de rutÃnio. Essa coordenaÃÃo se dà atravÃs de ligaÃÃo σ entre o Ãtomo de nitrogÃnio de uma das nitrilas, evidenciada pelo surgimento de um maior nÃmero de bandas referentes ao estiramento C≡N, comparativamente aos ligantes livres de coordenaÃÃo. A observaÃÃo do deslocamento dessas bandas para regiÃes de menor energia, quando comparadas aos ligantes livres, permitiram identificar que os ligantes TCNQ e TCNE encontram-se coordenados em sua forma radicalar (TCNX.â). O grau de transferÃncia de carga (Z) baseado nos espectros de infravermelho para os compostos Ru-TCNQ e Ru-TCNE foi de 0,66 e 0,78, respectivamente. Os espectros de RPE confirmaram a coordenaÃÃo dos ligantes ao centro metÃlico na forma reduzida (Ru-TCNQ: g = 2,007 e para Ru-TCNE: g = 2,010). Os potencias redox nos complexos Ru-TCNQ (Ered = 0,70V vs ENH) e Ru-TCNE (Ered = 1,30V vs ENH) foram deslocados para potenciais mais positivos, quando comparados ao precursor cis-[Ru(dcbpy)(bpy)Cl2] (Ered = 0,67V vs ENH), evidenciando o forte carÃter π receptor de elÃtrons dos ligantes TCNX, estabilizando o centro metÃlico na forma reduzida. Esses resultados evidenciam um carÃter retirador de elÃtrons mais pronunciado para o ligante TCNE em relaÃÃo ao TCNQ. / In this work, the [Ru(bpy)(dcbpy)(TCNQ)Cl] and [Ru(bpy)(dcbpy)(TCNE)Cl] complexes, called Ru-TCNQ and Ru-TCNE, respectively, where bpy = 2,2â- bipyridine and dcbpy = 4,4â-dicarboxy-2,2â-bipyridine, were synthesized and characterized by spectroscopy and electrochemical techniques. The absorption spectra of the Ru-TCNQ and Ru-TCNE complexes showed bands assigned to metalto-ligand charge transfer transitions (MLCT). The luminescence spectra, with excitation at the MLCT, exhibited emission with maximum of intensity at 570 and 605 nm for the Ru-TCNQ and Ru-TCNE complexes, respectively. The luminescence decay of the complexes follows a biexponential law, with the Ru-TCNQ complex showing shorter lifetime than the Ru-TCNE complex. The infrared vibrational spectra of the complexes show a larger number of nitrile stretching bands, comparatively to the free ligands of coordination. These suggesting that the TCNX compounds are coordinated to the ruthenium atom. Upon coordenation, the shifts of these bands for lower energy values are indicative of the TCNX reduced form (TCNX⋅â). These results are confirmed by EPR spectra with g = 2.007 and 2.010 for Ru-TCNQ and Ru-TCNE complexes, respectively. The degree of charge transfer (Z) for the Ru-TCNQ and Ru-TCNE compounds was evaluated as 0.66 and 0.78, respectively. The RuIII/II redox potentials of the Ru-TCNQ (0.70V) and Ru-TCNE (1.30V) compounds, shifted for more positive potentials, when compared to the starting complex, cis- [Ru(dcbpy)(bpy)Cl2] (0,67V). These results inducate that the ligands acts as π-acceptor allowing a π-back-bonding interaction which imply in a thermodynamic stability of the metal in the reduced state (RuII). The data, all together, suggest that the TCNE compound presents a higher πback-bonding interaction capability than TCNQ compound.

The work presented herein focuses on the synthesis and characterization of new cyanide bridged molecular magnetic materials that form discrete molecules as well as three dimensional networks. This research is inspired by the recognition that the Prussian blue (PB) family exhibits a wide range of interesting magnetic properties such as photomagnetism, spin crossover, and high TC magnets owing to the presence of the cyanide bridge that promotes magnetic communication between adjacent metal spins. An underexplored facet of this research is the systematic development of the topic with anisotropic metal ions research that was undertaken as part of this dissertation. The resulting discoveries are materials that exhibit a wide range of bistable magnetic properties, including photomagnetism, long range magnetic ordering, SMM, and exchange-biased SMM behavior. New Prussian Blue analogs are presented in Chapter II of this thesis that are based on the nearly unexplored hexacyanoosmate(III) ion. A family of CoII PB derivatives of OsIII were found to exhibit photomagnetic and charge transfer induced spin transition (CTIST) behavior and a study of alkali metal cation dependence revealed marked differences in both the photomagnetic and CTIST properties, with the highest ordering temperature being observed for the K+ analog which exhibits a TC of 28.5 K. The phenomenon of linkage isomerism reported for PB analogs and other molecular materials that incorporate the [Cr(CN)6]3- ion wherein the CN ligand reverses its binding mode between the two metal centers was studied in detail as described in Chapter III. Small molecule models that incorporate [Cr(CN)6]3- and CoII ions were investigated by single crystal X-ray crystallography, magnetism, and solution IR studies and the data led to useful mechanistic information about the nature of the cyanide reversal process. The use of the anisotropic hexacyanoosmate(III) anion to form a trinuclear species with MnIII was undertaken in the study described in Chapter IV. The first SMM based on the hexacyanoosmate(III) ion was discovered and found to exhibit a very rare exchange biased SMM phenomena in one of its crystal forms. In Chapter V new building blocks with the pentadentate MPPA ligand are described which are ideally suited for the preparation of a range of model compounds of the dinuclear and trinuclear variety.

The field of molecular electronics has been under investigation by materials scientists for the last two decades, activity that has increased in recent years as their potential to be components in modern quantum computing devices began to be discussed in a more sophisticated manner. In this field, the challenge is to obtain stable highly conducting materials and to manipulate their properties with external stimuli. As one of the most stable organic radicals, the singly reduced form of TCNQ (7,7,8,8-tetracyanoquinodimethane) has played a central role in the design of many unprecedented conducting materials including the first purely organic conductor (TTF)(TCNQ) (TTF = tetrathiafulvalene) which is nearly metallic and the electrically bistable switching material Cu(TCNQ). The research in this dissertation focused on the application of TCNQ and its derivatives in order to tune the structure and conductivity of these materials, with the overarching goal being to understand the mechanism of conductivity. This dissertation reports the details of the first main-group TCNQ binary compound, Tl(TCNQ). Two distinct polymorphs have been discovered and a remarkable water-induced phase transition from one to the other was observed. With different modes of TCNQ stacking (alternating or homogenous distances), the two polymorphs exhibit very different conductivities, namely 2.4×10^-4 S/cm and 5.4×10^-1 S/cm. With this inspiration, a series of semiconductors, Tl(TCNQX2) (X =Cl, Br, I) was prepared and structurally characterized. The steric effect of the halogen substituents leads to a variety of structures and a band structure simulation has suggested a clear structure-property relationship that involves perturbation of the Tl 6s orbital into the conduction band. Inspired by the switching material Ag(TCNQ), semiconducting frameworks Ag(TCNQCl2) and Ag(TCNQBr2) were prepared by electrocrystallization methods. Importantly, the former material exhibits a high room temperature conductivity of 0.25 S/cm and an unusual room temperature negative differential resistance (NDR) which is the source of intrinsic switching behaviors. The effect of solvent on the structure of these binary phases was also investigated. The series M(TCNQX2)(MeCN)n (M = Cu, Ag; X = Br, I; n =1, 2) was discovered and the interconversion of these solvated phases was studied. The effect of coordinated solvent molecules decreases the density of conducting stacks, consequently leading to a decrease of conductivity.

Neste trabalho foram estudados os complexos de transferência de carga resultantes da interação entre as espécies aceptoras de elétrons tetracianoetileno (TCNE) e 7,7,8,8-tetracianoquinodimetano (TCNQ), com aminas mono, bi e tri aromáticas, como espécies doadoras de elétrons, em solução. Também foram estudadas as reações de substituição eletrofílica aromática que ocorre entre o TCNE e aminas. Para tal estudo, foram utilizadas as técnicas espectroscópicas de absorção UV-VIS e Raman, o que permitiu a caracterização dos complexos de transferência de carga, assim como das espécies participantes da reação de tricianovinilação que ocorre entre aminas e TCNE. Para dar suporte aos dados experimentais, cálculos DFT (Teoria do Funcional da Densidade) e TDDFT (Teoria do Funcional da Densidade dependente do tempo) foram realizados, o que permitiu a obtenção das geometrias otimizadas, valores de frequência Raman e energias de transição dessas espécies. Os espectros eletrônicos dos complexos formados entre TCNE e aminas monoaromáticas mostraram que suas energias de transição são proporcionais à capacidade de doação de elétrons da amina. De fato, as energias de transição puderam ser correlacionadas com os valores de potencial de ionização das aminas, apresentando uma correlação linear de acordo com a regra Mulliken. Os espectros Raman permitiram verificar que os modos vibracionais do TCNE envolvidos no processo de transferência de carga apresentam deslocamento para menores números de onda com a diminuição do potencial de ionização da amina, e analogamente, pôde-se obter uma correlação linear entre esses dois parâmetros. No caso das aminas bi e tri aromáticas, a tendência linear entre energia de transição e potencial de ionização foi observada, mas não para os deslocamentos Raman das bandas do TCNE. Na reação de tricianovinilação, os espectros eletrônicos possibilitaram a identificação das espécies participantes da reação, assim como sua caracterização vibracional por espectroscopia Raman ressonante. Através da espectroscopia Raman ressonante, pôde-se, pela primeira vez, caracterizar as espécies intermediárias da reação de tricianovinilação entre TCNE e aminas aromáticas. Os complexos envolvendo TCNQ e aminas monoaromáticas apresentou tendência semelhante à observada em complexos com o TCNE. As energias de transição desses complexos diminuem linearmente, assim como, os modos vibracionais do TCNQ, que apresentam deslocamentos para menores frequências Raman com a diminuição do potencial de ionização da amina. Por outro lado, complexos formados pelo TCNQ e aminas com mais de um anel aromático em sua estrutura, não apresentam correlação entre potencial de ionização do doador e energia de transição e deslocamentos Raman. Os cálculos dos espectros eletrônicos e vibracionais apresentaram boa concordância com os obtidos experimentalmente, porém algumas limitações ficam evidentes na descrição das interações π nesses sistemas modelo. / In this work the charge transfer complexes resulting from the interaction between tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), as electron accepting species and mono, bi and tri aromatic amines, as electron donating species, were studied in solution. Also the electrophilic aromatic substitution that occurs between the TCNE and amines has been studied. For this study, the spectroscopic techniques of UV-VIS absorption and Raman were used, which allowed the characterization of the charge transfer complexes, as well as of the species involved in the reaction of tricianovinylation that occurs between amines and TCNE. In order to support the experimental data, DFT (Density Functional Theory) and TDDFT (Time-dependent Density Functional Theory) calculations were performed, to obtain the optimized geometries, Raman frequency values and theoretical transition energies of such species. The electronic spectra of the complexes formed between TCNE and monoaromatic amines showed that their transition energies are proportional to the amine electron donation capacity. In fact it could be linearly correlated with the ionization potential values of the amines, following the Mullikens rule. The Raman spectra allowed to verify that the vibrational modes of the TCNE involved in the process of charge transfer, were displaced to lower wavenumbers with the reduction of the ionization potential of the amine, and analogously, a linear correlation between these two parameters could be obtained. In the case of bi and tri aromatic amines, the linear trend between transition energy and ionization potential was observed, but not for the Raman shifts of the TCNE bands. In the reaction of tricianovinylation, the electronic spectra enabled the identification of the participating species in the reaction, and their vibrational characterization by resonance Raman. Using resonance Raman spectroscopy, it was possible to characterize the intermediate species of the tricianovinylation reaction between TCNE and aromatic amines for the first time. The complexes involving TCNQ and monoaromatic amines showed a similar trend to that observed in complexes with TCNE. The transition energies of these complexes decrease linearly, as well as the vibrational modes of the TCNQ, which present shifts to lower Raman frequencies with the decrease of the ionization potential of the amine. On the other hand, complexes formed by TCNQ and amines with more than one aromatic ring in their structure do not present correlation between donor ionization potential and transition energy and Raman displacements. The calculations of the electronic and vibrational spectra presented good agreement with those obtained experimentally, however some limitations were evidenced in the description of the π interactions in these model systems.

Neste trabalho foram estudados os complexos de transferência de carga resultantes da interação entre as espécies aceptoras de elétrons tetracianoetileno (TCNE) e 7,7,8,8-tetracianoquinodimetano (TCNQ), com aminas mono, bi e tri aromáticas, como espécies doadoras de elétrons, em solução. Também foram estudadas as reações de substituição eletrofílica aromática que ocorre entre o TCNE e aminas. Para tal estudo, foram utilizadas as técnicas espectroscópicas de absorção UV-VIS e Raman, o que permitiu a caracterização dos complexos de transferência de carga, assim como das espécies participantes da reação de tricianovinilação que ocorre entre aminas e TCNE. Para dar suporte aos dados experimentais, cálculos DFT (Teoria do Funcional da Densidade) e TDDFT (Teoria do Funcional da Densidade dependente do tempo) foram realizados, o que permitiu a obtenção das geometrias otimizadas, valores de frequência Raman e energias de transição dessas espécies. Os espectros eletrônicos dos complexos formados entre TCNE e aminas monoaromáticas mostraram que suas energias de transição são proporcionais à capacidade de doação de elétrons da amina. De fato, as energias de transição puderam ser correlacionadas com os valores de potencial de ionização das aminas, apresentando uma correlação linear de acordo com a regra Mulliken. Os espectros Raman permitiram verificar que os modos vibracionais do TCNE envolvidos no processo de transferência de carga apresentam deslocamento para menores números de onda com a diminuição do potencial de ionização da amina, e analogamente, pôde-se obter uma correlação linear entre esses dois parâmetros. No caso das aminas bi e tri aromáticas, a tendência linear entre energia de transição e potencial de ionização foi observada, mas não para os deslocamentos Raman das bandas do TCNE. Na reação de tricianovinilação, os espectros eletrônicos possibilitaram a identificação das espécies participantes da reação, assim como sua caracterização vibracional por espectroscopia Raman ressonante. Através da espectroscopia Raman ressonante, pôde-se, pela primeira vez, caracterizar as espécies intermediárias da reação de tricianovinilação entre TCNE e aminas aromáticas. Os complexos envolvendo TCNQ e aminas monoaromáticas apresentou tendência semelhante à observada em complexos com o TCNE. As energias de transição desses complexos diminuem linearmente, assim como, os modos vibracionais do TCNQ, que apresentam deslocamentos para menores frequências Raman com a diminuição do potencial de ionização da amina. Por outro lado, complexos formados pelo TCNQ e aminas com mais de um anel aromático em sua estrutura, não apresentam correlação entre potencial de ionização do doador e energia de transição e deslocamentos Raman. Os cálculos dos espectros eletrônicos e vibracionais apresentaram boa concordância com os obtidos experimentalmente, porém algumas limitações ficam evidentes na descrição das interações π nesses sistemas modelo. / In this work the charge transfer complexes resulting from the interaction between tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), as electron accepting species and mono, bi and tri aromatic amines, as electron donating species, were studied in solution. Also the electrophilic aromatic substitution that occurs between the TCNE and amines has been studied. For this study, the spectroscopic techniques of UV-VIS absorption and Raman were used, which allowed the characterization of the charge transfer complexes, as well as of the species involved in the reaction of tricianovinylation that occurs between amines and TCNE. In order to support the experimental data, DFT (Density Functional Theory) and TDDFT (Time-dependent Density Functional Theory) calculations were performed, to obtain the optimized geometries, Raman frequency values and theoretical transition energies of such species. The electronic spectra of the complexes formed between TCNE and monoaromatic amines showed that their transition energies are proportional to the amine electron donation capacity. In fact it could be linearly correlated with the ionization potential values of the amines, following the Mullikens rule. The Raman spectra allowed to verify that the vibrational modes of the TCNE involved in the process of charge transfer, were displaced to lower wavenumbers with the reduction of the ionization potential of the amine, and analogously, a linear correlation between these two parameters could be obtained. In the case of bi and tri aromatic amines, the linear trend between transition energy and ionization potential was observed, but not for the Raman shifts of the TCNE bands. In the reaction of tricianovinylation, the electronic spectra enabled the identification of the participating species in the reaction, and their vibrational characterization by resonance Raman. Using resonance Raman spectroscopy, it was possible to characterize the intermediate species of the tricianovinylation reaction between TCNE and aromatic amines for the first time. The complexes involving TCNQ and monoaromatic amines showed a similar trend to that observed in complexes with TCNE. The transition energies of these complexes decrease linearly, as well as the vibrational modes of the TCNQ, which present shifts to lower Raman frequencies with the decrease of the ionization potential of the amine. On the other hand, complexes formed by TCNQ and amines with more than one aromatic ring in their structure do not present correlation between donor ionization potential and transition energy and Raman displacements. The calculations of the electronic and vibrational spectra presented good agreement with those obtained experimentally, however some limitations were evidenced in the description of the π interactions in these model systems.

Charge transfer salts of Tetracyanoquinodimethane (TCNQ) were synthesised and their electrical and magnetic properties were investigated. These salts show unusual electrical and magnetic behaviour in contrast to conventional organic compounds. These salts have crystal structures which in general consist of TCNQ radical ions stacked in chains, isolated from each other by the diamagnetic cations. They are thus regarded as "one-dimensional" electrical and magnetic systems. The ESR spectra of these salts are attributed to triplet excitons showing that the spin-spin and electronelectron correlation effects are important. In the ESR spectra (Chapter III) of some TCNQ salts dipolar splitting is observed confirming the spin-spin interaction. These triplet excitons are regarded as bound electron-hole pairs. The experimentally determined dipolar splitting tensors are presented in Chapter III and the intensity data in Chapter IV. A large number of fine structure lines are observed in the ESR spectra of Pyridinium-TCNQ and 4-Aminopyridinium-TCNQ apart from regular triplet exciton lines (Chapter III). These lines are attributed to the trapping of excitons on an extended formula finit (TCNQ2 )n. In Chapter IV the temperature dependent magnetic susceptibilities are discussed in terms of Heisenberg antiferromagnetism and Pauli paramagnetism. In Chapter V temperature dependent behaviour of electrical conductivity is discussed in terms of an exciton band model, the lattice structure of the salts and one-dimensional lattice consisting of defects giving rise to high and low conducting segments. Low temperature electrical and magnetic phases are discussed (Chapters IV and VII) in terms of a band and hopping mechanisms.In Chapter VI self consistent field calculations are made with reference to the tight binding one electron band theory using simplified Roothaan equations considering CNDO approximations. Theoretical results are related to experimental band gaps, spinspin interactions and charge alteration.

The cyanide ligand has frequently been used to prepare clusters with novel magnetic properties due to its ability to provide an efficient pathway for superexchange between metal centers that are bound in an end-to-end fashion. One of the common synthetic approaches in this chemistry is to design suitable cyanide containing precursors and then to react such building blocks with metal complexes consisting of accessible sites. The triphos ligand (triphos: 1,1,1-tris(diphenylphosphinomethyl)ethane) has been employed in this vein to prepare metal complexes, one of which is a five coordinate paramagnetic complex (S = 1/2) with a square pyramidal metal center, [CoII(triphos)(CN)2]. A family of molecular squares, [{MIICl2}2{CoII(triphos)(CN)2}2] (M= Mn (2), Fe (3), Co (4), Ni (5), and Zn (6)), has been synthesized by the reaction of CoII(triphos)(CN)2 and MCl2 (M= Mn, Co, Ni, Zn) or Fe4Cl8(THF)6 in CH2Cl2/EtOH mixture. A series of cyanide-bridged trinuclear complexes, {[Co(triphos)(CN)2]2 [M(MeOH)4]}(ClO4)2 ( M = Mn (7), Fe (8), Co (9), and Ni (10)) and tetranuclear complexes, {[Co(triphos)(CN)2]2[M(MeOH)4]2}(ClO4)4 ([Co2M2] M = Mn (11) and Ni (12)) have been synthesized in a similar fashion by the reaction of CoII(triphos)(CN)2 and M(ClO4)2.6H2O (M= Mn, Fe, Co, Ni) in methanol. The trinuclear compounds (7-9), and tetranuclear complexes (2-6, 11, 12), are characterized by antiferromagnetic coupling between metal centers while magnetic behavior of 10 indicates the presence of ferromagnetic interactions between the paramagnetic metal centers. Interactions between magnetic orbitals of Co(II) and M(II) ions were also investigated by means of the density functional theoretical (DFT) calculations. Another triphos containing building block, [(triphos)Re(CN)3] anion (13), has been employed to prepare derivatives of a cubic SMM cluster with four octahedral Re(II) ions and four tetrahedral Mn(II) sites bridging through cyanide ligand. The reactions of Re(II) precursor with MnI2 and solvated Mn(II) ions resulting in derivatives of Re4Mn4 cube with different ligands attached to the Mn center other than the chloride atom were reported. Our efforts on linking these cubes using organo cyanide ligands such as dicyanamide (dca) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) to form extended networks were also discussed.