Coarse and fine tuning of the electronic energies of triimineplatinum(II) square-planar complexes

[Pt(tbtrpy)X]Y complexes (tbtrpy = 4,4',4' '-tBu3-2,2';6',2' '-terpyridine) exhibit charge-transfer absorption bands that can be drastically red-shifted to long-wavelength visible absorptions with arylthiolates as X. Further extension to the near-IR (NIR) region is achieved with 7,7,8,8-tetracyanoquinodimethane (TCNQ-) as Y-, resulting in black absorbers with continuous UV-vis-NIR absorptions and opening up potential applications in energy research.     

Ethyne-bridged (porphinato)zinc(II)-(porphinato)iron(III) complexes: phenomenological dependence of excited-state dynamics upon (porphinato)iron electronic structure

We report the synthesis, spectroscopy, potentiometric properties, and excited-state dynamical studies of 5-[(10,20-di-((4-ethyl ester)methylene-oxy)phenyl)porphinato]zinc(II)-[5'-[(10',20'- di-((4-ethyl ester)methylene-oxy)phenyl)porphinato]iron(III)-chloride]ethyne (PZn-PFe-Cl), along with a series of related supermolecules ([PZn-PFe-(L)1,2]+ species) that possess a range of metal axial ligation environments (L = pyridine, 4-cyanopyridine, 2,4,6-trimethylpyridine (collidine), and 2,6-dimethylpyridine (2,6-lutidine)). Relevant monomeric [(porphinato)iron-(ligand)1,2]+ ([PFe(L)1,2]+) benchmarks have also been synthesized and fully characterized. Ultrafast pump-probe transient absorption spectroscopic experiments that interrogate the initially prepared electronically excited states of [PFe(L)1,2]+ species bearing nonhindered axial ligands demonstrated subpicosecond-to-picosecond relaxation dynamics to the ground electronic state. Comparative pump-probe transient absorption experiments that interrogate the initially prepared excited states of PZn-PFe-Cl, [PZn-PFe-(py)2]+, [PZn-PFe-(4-CN-py)2]+, [PZn-PFe-(collidine)]+, and [PZn-PFe-(2,6-lutidine)]+ demonstrate that the spectra of all these species are dominated by a broad, intense NIR S1 --> Sn transient absorption manifold. While PZn-PFe-Cl, [PZn-PFe-(py)2]+, and [PZn-PFe-(4-CN-py)2]+ evince subpicosecond and picosecond time-scale relaxation of their respective initially prepared electronically excited states to the ground state, the excited-state dynamics observed for [PZn-PFe-(2,6-lutidine)]+ and [PZn-PFe-(collidine)]+ show fast relaxation to a [PZn+-PFe(II)] charge-separated state having a lifetime of nearly 1 ns. Potentiometric data indicate that while DeltaGCS for [PZn-PFe-(L)1,2]+ species is strongly influenced by the PFe+ ligation state [ligand (DeltaGCS): 4-cyanopyridine (-0.79 eV) < pyridine (-1.04 eV) < collidine (-1.35 eV) < chloride (-1.40 eV); solvent = CH2Cl2], the pump-probe transient absorption dynamical data demonstrate that the nature of the dominant excited-state decay pathway is not correlated with the thermodynamic driving force for photoinduced charge separation, but depends on the ferric ion ligation mode. These data indicate that sterically bulky axial ligands that drive a pentacoordinate PFe center and a weak metal axial ligand interaction serve to sufficiently suppress the normally large magnitude nonradiative decay rate constants characteristic of (porphinato)iron(III) complexes, and thus make electron transfer a competitive excited-state deactivation pathway.     

Characterization of some high-spin iron(II) complexes with urea derivatives. The crystal structure of dichlorotetrakis(thiourea)iron(II)

Summary Urea (ur), thiourea (tu) and diisopropylthiourea (diptu) form high-spin complexes with iron(II), for which⁵⁷Fe Mössbauer quadrupole splitting and spectroscopic data suggest an octahedral distorted geometry. The x-ray diffraction study on Fe(tu)₄Cl₂ confirms this geometry. The crystals are tetragonal, space groupP4₂/n witha=13.71,c=8.94 Å andZ=4. The molecules are centrosymmetric with two axial chlorine atoms (Fe-Cl=2.46 Å) and four equatorial sulfur atoms (Fe-S=2.61 and 2.57 Å respectively). A similartrans-octahedral geometry is proposed for the new Fe(diptu)₄Cl₂ complex and an octahedral metal coordination in the new [Fe(ur)₆]Br₂, Fe(tu)₃Br₂ and Fe(ur)₃Br₂ complexes.     

Design of organic semiconductors: tuning the electronic properties of pi-conjugated oligothiophenes with the 3,4-ethylenedioxythiophene (EDOT) building block

Hybrid oligothiophenes based on a various combinations of thiophene and 3,4-ethylenedioxythiophene (EDOT) groups have been synthesized. UV/Vis absorption spectra show that the number and relative positions of the EDOT groups considerably affect the width of the HOMO-LUMO gap and the rigidity of the conjugated system. Analysis of the crystallographic structure of two hybrid quaterthiophenes confirms that insertion of two adjacent EDOT units in the middle of the molecule leads to a self-rigidification of the conjugated systems by intramolecular SO interactions. Cyclic voltammetry data shows that the first oxidation potential of the oligomers decreases with increasing chain length and increasing number of EDOT groups for a given chain length. Electrochemical studies and theoretical calculations show that the positions of the EDOT units in the conjugated chain control the potential difference (DeltaE(p)) between the first and second oxidation steps. Moving the EDOT groups from the outer to the inner positions of the conjugated system increases DeltaE(p). Theoretical calculations confirm that this phenomenon reflects an increase of the intramolecular coulombic repulsion between positive charges in the dication. A thin-film field-effect transistor was fabricated by vacuum sublimation of a pentamer with alternating thiophene-EDOT structure, and the hole mobility was determined.     

Properties and electronic structure of tetrahalogenocuprate (II)-complexes

Several salts containing the complex anions [CuCl ₄]= or [CuBr ₄]= have heen prepared, and their spectra have been measured and interpreted in terms of ligand-field theory. They exhibit a d-d band with about 8–9000 cm^–1, and several well defined charge-transfer bands in the visible and near ultraviolet spectral range. Several experimental facts, supported by theoretical considerations, indicate that the structure of the [CuX ₄]= anions is not a truly tetrahedral, but a flattened tetrahedral one, of symmetry D _2d . Details on the course of the endothermic solvolysis reactions which occur in polar organic solvents, and on the probable nature of the solvolysis products are reported and discussed.

---

Zusammenfassung Mehrere Salze der komplexen Anionen [CuCl ₄]^2– und [CuBr ₄]^2– wurden dargestellt, ihre Spektren gemessen und ligandenfeldtheoretisch interpretiert. Die Spektren zeigen eine d d-Bande mit im Gebiet von 8000 bis 9000 cm^–1 und mehrere wohldefinierte Elektronenüberführungsbanden im sichtbaren und nahen ultravioletten Spektralbereich. Mehrere experimentelle Befunde, die von theoretischen Überlegungen unterstützt werden, deuten darauf hin, daß die [CuX ₄]^2/s--Anionen nicht rein tetraedrisch gebaut sind, sondern längs einer zweizähligen Achse gestauchte Tetraeder der Symmetrie D _2d darstellen.Einzelheiten über den Verlauf der endothermen Solvolysereaktionen in polaren organischen Lösungsmitteln und über die wahrscheinlichen Solvolyseprodukte werden mitgeteilt und diskutiert.

---

Résumé Plusieurs sels des anions complexes [CuCl ₄]^2– et [CuBr ₄]^2– ont été préparés et leurs spectres mesurés et interprétés dans le cadre de la théorie du champ des ligands.Ils montrent une bande d d avec dans la région de 8000 à 9000 cm^–1 et plusieurs bandes bien définies du type «transfer de charges» dans le visible et l'ultraviolet proche. Plusieurs résultats expérimentaux, soutenus par des considérations théoriques, indiquent que la structure des ions [CuX ₄]^2– n'est pas celle d'un tétraèdre véritable mais celle d'un tétraèdre déformé, de symétrie D _2d , Des détails sur le cours des réactions endothermiques de solvolyse, qui ont lieu dans les solvants organiques polaires et sur la nature probable des produits de la solvolyse sont rapportés et discutés.

     

Unusual electronic structure of bis-isocyanide complexes of iron(III) porphyrinoids

A series of isocyanide complexes, [Fe(Porphyrinoid)((t)BuNC)(2)](+), were synthesized and examined for their physicochemical properties. The molecular structure of the bis((t)BuNC) adduct of the iron(III) porphycene (1) and corrphycene (2) adopting the (d(xy))(2)(d(xz), d(yz))(3) ground state were determined for the first time. Furthermore, 1 and 2 showed unusual crossover phenomena between different electron configurations, (d(xy))(2)(d(xz), d(yz))(3) ground state and (d(xz), d(yz))(4)(d(xy))(1) ground state, by the addition of the external stimuli.     

A semiempirical MO study of the electronic structure and excited states of the Tris(2,2′-bipyridyl)Iron(II) and Tris(glyoxal-Bis-N-methylimine)iron(II)Ions

A semi-empirical SCF-MO method, the PEEL method, has been applied in an investigation of the electronic structure and excited states of two iron compounds, [Fe(II)-(GMI)₃]⁺⁺ and [Fe(II)-(bipy)₃]⁺⁺.The electronic absorption spectra have been recorded. The calculations show that it is necessary to account for the trigonal distortion and the covalency in order to explain these spectra quantitatively. Mössbauer measurements have also been performed. The calculated electronic population of the iron is in accord with Mössbauer isomer shift data, indicating that a realistic electron distribution has been obtained by the PEEL method.

---

Zusammenfassung Eine semiempirische SCF-MO-Methode, die PEEL-Methode, wurde zur Untersuchung der Elektronenstruktur sowie von angeregten Zuständen der beiden Eisenverbindungen [Fe(II)-(GMI)₃]⁺⁺ und [Fe(II)-(bipy)₃]⁺⁺ angewendet.Die elektronischen Absorptionsspektren wurden aufgenommen. Die Berechnungen zeigen, daß die trigonale Verzerrung und die Kovalenz berücksichtigt werden müssen, um die Spektren quantitativ zu erklären. Mössbauer-Messungen wurden ebenfalls durchgeführt. Die berechnete Elektronenverteilung am Eisenatom ist in Übereinstimmung mit den Daten der Isomerenverschiebung der Mössbauer-Messungen, wodurch gezeigt wird, daß mit der PEEL-Methode eine realistische Elektronen-Verteilung erhalten wurde.

---

Résumé Une méthode SCF-MO semi-empirique, la méthode PEEL, a été appliquée à une étude de la structure électronique et des états excités de deux composés ferreux: [Fe(II)-(bipy)₃]⁺⁺ et [Fe(II)-(GMI)₃]⁺⁺. Les spectres d'absorption électronique ont été enregistrés. Les calculs montrent qu'il est nécessaire de rendre compte de la distorsion trigonale et de la covalence pour expliquer ces spectres quantitativement.Des mesures de l'effet Mössbauer ont aussi été effectuées. La population électronique calculée du fer est en bon accord avec les données sur le déplacement isomérique de Mössbauer, ce qui indique que la méthode PEEL fournit une distribution électronique réaliste.

     

Relativistic electronic structure of cadmium(II) multidecker phthalocyanine compounds

Cadmium phthalocyanines (Pc) give rise to multilayered compounds, which may have potential application in material science. The Cd(II) single macrocycle (1) (C_4v), double decker [CdPc₂] (2) (D₄), triple decker [Cd₂Pc₃] (3) (D_4h) and quadruple decker [Cd₃Pc₄] (4) (D_4d), are already characterized experimentally. The electronic structures of the multidecker compounds were compared against the single macrocycle (1) which is used as benchmark. Relativistic electronic structure were carried out via DFT calculations using the two components ZORA Hamiltonian including both scalar and spin–orbit effects. Double point groups were used to take into account the inclusion of the spin–orbit coupling, and their group correlation is shown. The calculations show that the quadruple decker is the most reactive and behaves like a one-dimensional molecular metal.     

Molecular and electronic structure of five-coordinate complexes of iron(II/III) containing o-diiminobenzosemiquinonate(1-) pi radical ligands

The reaction of the ligand N-phenyl-1,2-benzenediamine (N-phenyl-o-phenylenediamine), H2[L(PDI)], in dry acetonitrile with [FeIII(dmf)6](ClO4)3 (dmf = N,N-dimethylformamide) affords the dimer (mu-NH,NH)[FeIII(L(ISQ))(L(PDI))]2 (1), where (L(ISQ))*- represents the pi radical monoanion N-phenyl-o-diiminobenzosemiquinonate and (L(PDI))2- is its one-electron-reduced, closed-shell form. Complex 1 possesses a diamagnetic ground-state St = 0. Addition reactions of tri-n-butylphosphane, tert-butyl isocyanide, cyclohexyl isocyanide, 4,5-diphenylimidazole, and 4-(1-phenylpentyl)pyridine with 1 in acetonitrile or toluene yields [FeII(L(ISQ))2(PBu3)] (2), [Fe(II)(L(ISQ))2(CN-tBu)] (4), [FeII(L(ISQ))2(CNCy)] (5), [FeIII(L(ISQ))2(Ph2Im)] (6), and [FeIII(L(ISQ))(L(PDI))(BuPhCH-py)].BuPhCH-py (7). Oxidation of 1 with iodine affords [FeIII(L(ISQ))2I] (3), and oxidation of 2 with ferrocenium hexafluorophosphate yields [FeIII(L(ISQ))2(PBu3)](PF6) (2ox). The structures of complexes 2, 2ox, 3, 5, 6, and 7 have been determined by X-ray crystallography at 100(2) K. Magnetic susceptibility measurements and EPR, UV-vis, and M?ssbauer spectroscopy have established that mononuclear complexes containing the [FeII(L(ISQ))2X] chromophore (2, 4, 5) are diamagnetic (St = 0) whereas those with an [FeIII(L(ISQ))2X]n chromophore (3, 2(ox), 6) are paramagnetic (St = 1/2) and those with an [FeIII(L(ISQ))(L(PDI))X] chromophore (7) possess an St = 1 ground state. It is established that all ferric species have an intrinsic intermediate spin (SFe = 3/2) which is intramolecularly antiferromagnetically coupled to one or two (L(ISQ))*- ligand radicals yielding an St = 1 (7) or St = 1/2 (2ox, 3, 6) ground state, respectively. In the ferrous complexes 2, 4, and 5 the intrinsic spin at the iron ion is either low spin (SFe = 0) or intermediate spin (SFe = 1). Antiferromagnetic coupling between two radicals (L(ISQ))*- or, alternatively, between the intermediate spin ferrous ion and two radicals yields then the observed diamagnetic ground state. In 1 two [FeIII(L(ISQ))(L(PDI))] halves with S = 1 couple antiferromagnetically affording an St = 0 ground state.     

Pyrazolyl methyls prescribe the electronic properties of iron(II) tetra(pyrazolyl)lutidine chloride complexes

A series of iron(II) chloride complexes of pentadentate ligands related to α,α,α',α'-tetra(pyrazolyl)-2,6-lutidine, pz(4)lut, has been prepared to evaluate whether pyrazolyl substitution has any systematic impact on the electronic properties of the complexes. For this purpose, the new tetrakis(3,4,5-trimethylpyrazolyl)lutidine ligand, pz**(4)lut, was prepared via a CoCl(2)-catalyzed rearrangement reaction. The equimolar combination of ligand and FeCl(2) in methanol gives the appropriate 1:1 complexes [FeCl(pz(R)(4)lut)]Cl that are each isolated in the solid state as a hygroscopic solvate. In solution, the iron(II) complexes have been fully characterized by several spectroscopic methods and cyclic voltammetry. In the solid state, the complexes have been characterized by X-ray diffraction, and, in some cases, by M?ssbauer spectroscopy. The M?ssbauer studies show that the complexes remain high spin to 4 K and exclude spin-state changes as the cause of the surprising solid-state thermochromic properties of the complexes. Non-intuitive results of spectroscopic and structural studies showed that methyl substitution at the 3- and 5- positions of the pyrazolyl rings reduces the ligand field strength through steric effects whereas methyl substitution at the 4-position of the pyrazolyl rings increases the ligand field strength through inductive effects.     

Features of the electronic structure of ruthenium tetracarboxylates with axially coordinated nitric oxide (II)

The electronic structure of Ru₂(μ-O₂CR)₄, Ru₂(μ-O₂CR)₄(L)₂ and Ru₂(μ-O₂CR)₄(NO)₂ (R = H, CH₃, CF₃; L = H₂O, THF) ruthenium tetracarboxylates is analyzed on the basis of calculations by the density functional method with full geometry optimization. It is concluded that the axial coordination of nitric oxide (II) to Ru₂(μ-O₂CR)₄ is accompanied by destruction of the metal-metal π-bond with d _πAO Ru reorientation on bonding with NO molecules.     

Peculiarity in the electronic structure of Cu(II) complex ferromagnetically coupled with bisimino nitroxides

By means of the electron spin resonance (ESR) technique, we have investigated the electronic structures of the tridentate imino nitroxyl diradical complex with copper(II) (Cu-bisimpy), which has a square planar structure and a ground quartet state with an extremely strong ferromagnetic exchange interaction, and its related compounds (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1' H-imidazol-2'-yl)pyridine). It was clarified that Cu-bisimpy had unique magnetic orbitals, compared with the biradical ligand (bisimpy), a zinc(II) biradical complex (Zn-bisimpy) and a copper(II) terpyridine complex (Cu-tpy) (tpy = 2,2';6',2'-terpyridine). Multifrequency ESR spectroscopy provided a reliable set of magnetic parameters of Cu-bisimpy, which has a small g anisotropy ( g x = 2.02, g y = 2.01, g z = 2.08) and small hyperfine coupling with Cu (|A x| = 42.0 MHz, |A y|相似文献   

Hydrogen bonding effects on the electronic configuration of five-coordinate high-spin iron(II) porphyrinates

The characterization of a new five-coordinate derivative of (2-methylimidazole)(tetraphenylporphinato)iron(II) provides new and unique information about the effects of forming a hydrogen bond to the coordinated imidazole on the geometric and electronic structure of iron in these species. The complex studied has two crystallographically distinct iron sites; one site has an axial imidazole ligand modified by an external hydrogen bond, and the other site has an axial imidazole ligand with no external interactions. The iron atoms at the two sites have distinct geometric features, as revealed in their molecular structures, and distinct electronic structures, as shown by M?ssbauer spectroscopy, although both are high spin (S = 2). The molecule with the external hydrogen bond has longer equatorial Fe-N(p) bonds, a larger displacement of the iron atom out of the porphyrin plane, and a shorter axial bond compared to its counterpart with no hydrogen bonding. The M?ssbauer features are distinct for the two sites, with differing quadrupole splitting and isomer shift values and probably differing signs for the quadrupole splitting as shown by variable-temperature measurements in applied magnetic field. These features are consistent with a significant change in the nature of the doubly populated d orbital and are all in the direction of the dichotomy displayed by related imidazole and imidazolate species where deprotonation leads to major differences. The results points out the possible effects of strong hydrogen bonding in heme proteins.     

Versatility in the binding of 2-pyrazinecarboxylate with iron. Synthesis, structure and magnetic properties of iron(II) and iron(III) complexes

The synthesis and characterization of two new iron(II) complexes, [Fe(pca)2(py)2].py (1) and {[Fe(pca)2(H2O)].H2O}n (2) and one new iron(III) complex, Na2{[Fe(pca)()]2O}.2H2O.2CH3CN (3) (pca- stands for 2-pyrazinecarboxylate), are reported. Complex 1 is obtained from the reaction of iron powder with 2-pyrazinecarboxylic acid. The reaction of Fe(ClO4)3.10H2O with Hpca in the presence of 3 equiv. of Bu4NOH yields 2, whereas the presence of NaOH yields 3. The molecular structure of 1 contains an iron(II) ion with a pseudo-octahedral environment resulting from the coordination of two pca- ligands in a bidentate chelating fashion and two pyridine molecules; pi-pi stacking interactions between pyridine and pyrazine rings lead to a one-dimensional chain. Complex 2 is an iron(II) coordination polymer with an infinite zig-zag motif and an Fe...Fe separation of 7.1 A. In 2, the pi-pi stacking interactions involving the pyrazine rings and the strong hydrogen bonds between the coordinated water molecule and the carboxylate oxygens of two pca- ligands result in a three-dimensional network structure. Complex 3 consists of an anionic micro-oxo-bridged diiron(III) core with two crystallographically distinct iron(iii) ions; the negative charge is compensated by two sodium cations. Complex 3 is assembled in a three dimensional network structure through coordination of Na(I) and hydrogen bond interactions. Temperature dependent magnetic susceptibility and M?ssbauer spectroscopic studies indicate that 1 and 2 have similar magnetic properties. Both complexes are paramagnetic above 12 K, whereas antiferromagnetic ordering is observed below 12 K. The magnetic properties of reveal strong intramolecular antiferromagnetic interactions between the two iron(III) ions with a J value of -221 cm(-1); no long range intermolecular magnetic coupling is observed between 295 and 4.2 K.     

Four-coordinate iron(II) porphyrinates: electronic configuration change by intermolecular interaction

The syntheses and structures of three four-coordinate iron(II) porphyrinates are reported. The three derivatives are tetraarylporphyrin species, where the aryl is either phenyl, p-methylphenyl, or p-methoxyphenyl. One of these derivatives, that of tetraphenylporphyrin, Fe(TPP), is a new crystalline phase that is distinct from the earlier reported phase (Collman, J. P.; et al. J. Am. Chem. Soc. 1975, 97, 2676). This new phase of Fe(TPP) has a very saddled porphyrin core; the prior phase was ruffled. The iron atom has close interactions (approximately 3.10 A) with two pyrrole Cb-Cb bonds above and below the porphyrin plane. M?ssbauer spectra and magnetic susceptibility measurements, different for the two phases, provide strong evidence that the two phases of Fe(TPP) have distinct electronic structures that originate from intermolecular interactions.