196,199 research outputs found
Tailoring Transition Metal Complexes for Nonlinear Optics Applications. 2. A Theoretical Investigation of the Second-Order Nonlinear Optical Properties of M(CO)5L Complexes (M = Cr, W; L = Py, PyCHO, Pyz, PyzBF3, BPE, BPEBF3)
No full textThe authors report an ab initio study of 2nd-order nonlinear optical (NLO) properties and absorption electronic spectra of push-pull transition metal chromophores [M(CO)5L] (M = Cr, W; L = pyridine (Py), 4-formyl-pyridine (PyCHO), pyrazine (Pyz), trans-1,2-bis(4-pyridyl)ethylene (BPE)). Pyz and BPE are considered either with 1 N atom free or interacting with the strong acceptor BF3. All of the mol. properties were calcd. using 2 different and methodol. independent approaches: the time dependent and coupled perturbed d. functional theories (TDDFT and CPDFT) and the sum-over-states (SOS) approach, where the excited states are obtained via the single CI (SCI) ab initio method. DFT results are in acceptable agreement with the exptl. energy values of electronic transitions (with the exception of chromophores with the large greek p-delocalization, like BPE); SCI calcns. overestimate excitation energies and produce an inversion in the order of dM greek pi*L and dM greek p*CO transitions. The SCI-SOS approach gives 1st-order hyperpolarizabilities, basically in agreement as trend and values with the expts. and seems to be a tool generally suitable for the evaluation of these properties also for transition metal complexes. However, the 1st-order hyperpolarizabilities computed using the CPDFT approach are consistently overestimated in comparison with the exptl. results, esp. in the case of a ligand with large greek p-delocalization. Also the 2-level approxn. taking into account only the lowest energy charge transfer excitation (e.g., dM greek p*L) is not applicable to chromophores with the extended greek p-delocalized ligand (BPE) coordinated to a transition metal, due to significant contributions originating from intraligand greek pL greek p*L transitions. This study reports a detailed anal. and comparison of electronic NLO effects of transition metal complexes computed with DFT and ab initio SCI-SOS methodol
The synthesis and behaviour of pyrazine mononuclear carbonyl complexes of Rh(I), Ir(I), Ru(II) and Os(II)
No full textThe synthesis in high yields and the dissociative behaviour in the solid state and in solution of the mononuclear complexes [cis-M(CO)2Cl(pyz)] (M=Rh, Ir; pyz=pyrazine) and [fac-M(CO)3Cl2(pyz)] (M=Ru, Os) are reported. The mononuclear complexes of Rh and Ir are relatively labile with respect to pyrazine release. Particularly in the case of rhodium they generate even in the solid state the corresponding dinuclear complexes [cis-Cl(CO)2M(pyz)cis-M(CO)2Cl] (M=Rh, Ir). The 1H NMR spectra of these mononuclear Rh and Ir complexes in CHCl3 solution show, at 25 and 60 °C, respectively, a fast and reversible dissociation of metal coordinated pyrazine, which is hindered by lowering the temperature. Crystallographic aspects of [cis-Ir(CO)2Cl(pyz)] have been investigated via single crystal X-ray diffraction. The mononuclear complexes of Ru and Os are more stable. In the solid state they do not rearrange, with release of pyrazine, to generate the related dimeric complexes with pyrazine as bridge. In solution, at room temperature, they do not dissociate quickly, although a mixture of monomeric and dimeric pyrazine complexes (ratio monomer to dimer 9:1 and 15:1 for Ru and Os, respectively) is slowly formed by a process which is reverted by addition of excess pyrazine, as expected for a dissociative equilibrium
Tailoring transition metal complexes for non linear optics applications - A theoretical investigation of the electronic structure of M(CO)(x)ClyL complexes (M = Cr, W, Re, Ru, Os, Rh, Ir; L = Pyz, PyzBF(3), BPE, BPEBF3)
No full textDensity functional theory (DFT) investigations of title organometallic compounds led to identification of electronic features which determine the magnitude and the orientation of the dipole moment. The analysis of our theoretical results shows that the presence of a strong acidic BF3 group, or more generally, the substitution of ligands in the M(CO)xCl yL complexes can affect the orientation of the dipole moments, out of the direction of the first charge transfer (CT) excitation and, as a consequence, the magnitude of the vector part of the second order hyperpolarizabilities
Low oxidation state ruthenium chemistry . IV. The reactions of M(CO)2(PPh3)3 complexes (M=Fe, Ru) and the hydrogenation and isomerization of alkenes catalysed by cis-Ru(H)2(CO)2(PPh3)2
No full textThe complexes M(CO)2(PPh3)3 (I, M = Fe; II, M = Ru) readily react with H2 at room temperature and atmospheric pressure to give cis-M(H)2(CO)2(PPh3)2 (III, M = Fe;IV,M = Ru). I reacts with O2 to give an unstable compound in solution, in a type of reaction known to occur with II which leads to cis-Ru(O2)(CO)2(PPh3)2(V). Even compound IV reacts with O2 to give V with displacement of H2; this reaction has been shown to be reversible and this is the first case where the displacement of H2 by O2 and that of O2 by H2 at a metal center has been observed. III and IV are reduced to M(CO)3(PPh3)2 by CO with displacement of H2; Ru(CO)3- (PPh3)2 is also formed by treatment of IV with CO2, but under higher pressure. Compounds II and IV react with CH2CHCN to give Ru(CH2CHCN)(CO)2- (PPh3)2(VI) which reacts with H2 to reform the hydride IV. cis-Ru(H)2(CO)2(PPh3)2(IV) has been studied as catalyst in the hydrogenation and isomerization of a series of monoenes and dienes. The catalysts are poisoned by the presence of free triphenylphosphine. On the other hand the ready exchange of H2 and O2 on the "Ru(CO)2(PPh3)2" moiety makes IV a catalyst not irreversibly poisoned by the presence of air. It has been found that even Ru(CO)2(PPh3)3(II) acts as a catalyst for the isomerization of hex-1-ene at room temperature under an inert atmosphere
The reaction of molibdenum(VI) dioxo derivatives with hetrocumulenes
No full textThe reactions of ArNSO (Ar = p-MeC6H4) with cis-Mo(O)2(chel)2 (chel = S2CNEt2, CH3COCH- COCHH3) give the molybdenum(VI) oxo-arylimido derivatives, Mo(O)(NAr)(hel)2, and sulphur dioxide. From cis-Mo(O)2(S2CNEt2)2 and CyNCO (Cy = C6H11) the dimeric Mo2O3(S2CNEt2)4 is obtained, with the concomitant formation of carbon dioxide and biuret, (CyNHCO)2NCy. The spectroscopic properties of the molybdenum(VI) oxo-arylimido derivatives are reported and the possible reaction mechanisms are discussed
Rationalizing the electronic properties of two classes of push–pull DSSC sensitizers based on Zn(II) di- or tetrarylporphyrinates substituted in meso or beta-pyrrolic positions: an electrochemical investigation
No full textPush–pull Zn(II)-porphyrinates have recently shown attracting performances as
light harvesting systems in dye-sensitized solar cells (DSSCs). To fully exploit their
intrinsically high efficiency it is important to finely tune their HOMO and LUMO levels,
which can be achieved by proper choice of the push and pull substituents. Of course
such target-oriented molecular design requires the availability of reliable relationships
between molecular structure and electronic properties; therefore we have carried out
a detailed electrochemical investigation, also supported by spectroscopy and
theoretical computations, on a wide, systematic range of Zn(II)-porphyrinates:
(a) a family of 5,15-meso substituted ones with phenylethynyl linkers, including a
first "benchmark" symmetric series carrying on the opposite terminals the same
substituent (N(CH3)2, OCH3, COOCH3, COOH, NO2); and a second push–pull one,
with the terminal positions carrying one donor and one acceptor group belonging to
the series above. Moreover, two suitably modified porphyrins allowed evaluation of
the effects of (i) the presence or absence of the phenyl group in the linker between
the porphyrin core and the acceptor group, and (ii) the effect of perfluorination on the
same phenyl group;
(b) a family of mono and, for the first time, disubstituted push-pull ZnIIporphyrinates
bearing a variety of ethynyl-phenyl moieties in β-pyrrolic position,
which were compared with their meso analogues, producing evidence that, although
the HOMO-LUMO energy gap of the meso substituted push-pull dyes is lower, the β
mono or disubstituted push-pull porphyrinic dyes show comparable or better
efficiencies when acting as sensitizers in DSSCs, possibly on account of a more
facile charge injection into TiO2.
A rationalization scheme is proposed concerning relationship between structure
and redox properties, affording inter alia interesting clues on the different localization
of the redox centres and the effective conjugation between the porphyrin core and
the side chains as a function of the molecular design.
References:
[1] P. R. Mussini, A. Orbelli Biroli, F. Tessore, M. Pizzotti, C. Biaggic, G. Di Carlo, M.
G. Lobello, F. De Angelis, Electrochimica Acta 85 (2012) 509– 523
[2] G. Di Carlo, A. Orbelli Biroli, M. Pizzotti, F. Tessore, V. Trifiletti, R. Ruffo, A.
Abbotto, A. Amat, F. De Angelis, P. R. Mussini, Chemistry-a European Journal, in
press (2013)
New water-soluble ruthenium(II) and osmium(II) hydroxo carbonyl complexes
No full textA high-yield procedure is described for the preparation, from [M(CO)3Cl2]2 (M = Ru, Os) and aqueous NaOH, of the new water-soluble and air-stable species [Ru(CO)2Cl(OH)]n, [Ru(CO)2(OH)2]n, [Os(CO)3Cl-(OH)]2, and [Os(CO)3(OH)2]x (x = 2 or n)
Nonlinear-Optical Properties of α-Diiminedithiolatonickel(II) Complexes Enhanced by Electron-Withdrawing Carboxyl Groups
No full textWe report the synthesis, characterization, nonlinear-optical (NLO) properties, and density functional theory (DFT) calculations for three nickel diiminedithiolate complexes [Ni(4,4′-R2carboxy-bpy)(L)] [R = methyl, L = 1,2-benzenedithiolate (bdt), 1; R = ethyl, L = 5,6-dihydro-1,4-dithine-2,3-dithiolate (dddt), 2; R = ethyl, L = 1-(N-methylindol-5-yl)ethene-1,2-dithiolate (mi-5edt), 3]. The crystal structure of 1 shows a square-planar coordination for the nickel ion and bond distances consistent with a diiminedithiolate description for the complex. For all complexes, the cyclic voltammetry measurements show two reversible reduction processes (−1.353/–1.380 V and −0798/–0.830 V, respectively) and an anodic wave (+0.372/+0.601 V). The UV–vis spectra present a band around 600–700 nm (ε = 4880–6000 dm3 mol–1 cm–1) mainly attributed to a charge-transfer highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition, which shows a large negative solvatochromic shift, characteristic of push–pull complexes, and is responsible for the NLO properties of these molecules. The charge-transfer character of this electronic transition is confirmed by DFT calculations, with the HOMO mainly centered on the dithiolate moiety and the LUMO on the bpy ligand, with important contribution given by the carboxyl groups (≈13%). Small contributions from the nickel(II) ion are present in both of the frontier orbitals. The carboxyl groups enhance the optical properties of this class of complexes, confirmed by comparison with the corresponding unsubstituted compounds. The second-order NLO properties have been measured by an electric-field-induced second-harmonic-generation technique using a 10–3 M solution in N,N-dimethylformamide and working with a 1.907 μm incident wavelength, giving for μβ1.907 (μβ0) values of −1095 (−581), −2760 (−954), and −1650 (−618) × 10–48 esu for 1–3, respectively. These values are among the highest in the class of square-planar push–pull complexes, similar to those found for dithionedithiolate compounds. Moreover, spectroelectrochemical experiments demonstrate the possibility of using these complexes as redox-switchable NLO chromophores
Reactions of 2-azidopyridine and 1-pyridinio ylides with transition-metal complexes
No full textThe reactions of 2-azidopyridine (L 1) and 1-pyridinio ylides C 5H 5N +-N -R [R = O 2SC 6H 4Me-p (L 2) or OCC 6H 4Me-p (L 3)] with metal(II) halogeno-complexes give derivatives of formula [MnL 1 2Cl 2], [FeL 1 3Cl 2], [CoL 1Cl 2], [CuL 1Cl 2], [ZnL 1 2Cl 2], [(NiL 1Cl 2) n], [NiL 1 2Br 2], [(NiL 2Cl 2) n], [NiL 2 2Br 2], [PdL 1 2Cl 2], [PdL 2 2Cl 2], [PdL 3 2Cl 2], [Ru(PPh 3) 2L 1 2X 2], and [Ru(SbPh 3) 2L 1 2Cl 2] (X = Cl or Br). The complexes [M(CO) 5L 1] (M = W or Cr) have been obtained from [M(CO) 5(thf)] (thf = tetrahydrofuran) and tetrazolopyridine. In these complexes L 1 is present in its tetrazole form. From [Pt(SMe 2) 2Cl 2] and L 1, [Pt(SMe 2)L 1Cl 2] has been isolated, while L 3 gives a derivative in which the aryl group is metallated in the position ortho to the carbonyl group and the ylide is bidentate. The complex [Ru(PPh 3) 2L 1 2Cl 2] reacts with carbon monoxide to give [Ru(PPh 3) 2(CO)L 1Cl 2]. 2-Azido-5-nitropyridine (RN 3) reacts in its azide form with the hydride [Pt(PEt 3) 2H(Cl)] to give the amido-complex [Pt(PEt 3) 2(NHR)Cl] and with [Pt(PPh 3) 2(C 2H 4)] to give a complex of composition [Pt(PPh 3) 2(N 3)(N 2R)]. The spectroscopic properties of the new complexes are reported and their structures discussed
Electronic Structure and Reactivity of Dioxygen-Platinum Complexes: an ab Initio MO-LCAO Study
No full textAb initio Hartree Fock calculations have been carried out on the complex L2Pt(η2-O2) and its derivatives L2Pt-(OOH)X and L2Pt(OOH)(XY) obtained by reaction with HX (HX = H2O, HCl, HOOCH, NH3) and HXYH (HXYH = oxalic acid, o-catechol, hydrazine, hydroxylamine, ethylendiamine, o-phenylendiamine). In addition also the reaction L2Pt(OOH)X + HX → H2O2 + L2PtX2 leading to the formation of hydrogen peroxide has been studied. The theoretical investigation gave, for all considered species, optimum complex geometry, charge distribution and reaction energies being evaluated by means of a correlation energy density functional. The ability of the HX reagents to form hydrogen peroxide is discussed in terms of absolute acidity and coordinating capability of the X- groups. This allows interpretation of the more peculiar aspects of the chemical activation of dioxygen that leads to the coordinated hydroperoxide species or hydrogen peroxide
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