Evidence for partial quenching of orbital angular momentum upon complex formation in the infrared spectrum of OH-acetylene

The entrance channel leading to the addition reaction between the hydroxyl radical and acetylene has been examined by spectroscopic characterization of the asymmetric CH stretching band of the pi-hydrogen bonded OH-acetylene reactant complex. The infrared action spectrum observed at 3278.6 cm(-1) (origin) consists of seven peaks of various intensities and widths, and is very different from those previously reported for closed-shell HF/HCl-acetylene complexes. The unusual spectrum arises from a partial quenching of the OH orbital angular momentum in the complex, which in turn is caused by a significant splitting of the OH monomer orbital degeneracy into (2)A(') and (2)A(") electronic states. The magnitude of the (2)A(')-(2)A(") splitting as well as the A rotational constant for the OH-acetylene complex are determined from the analysis of this b-type infrared band. The most populated OH product rotational state, j(OH)=9/2, is consistent with intramolecular vibrational energy transfer to the nu2 C triple bonded C stretching mode of the departing acetylene fragment. The lifting of the OH orbital degeneracy and partial quenching of its electronic orbital angular momentum indicate that the electronic changes accompanying the evolution of reactants into products have begun to occur in the reactant complex.     

Noncovalent interactions in the gas phase: the anisole-phenol complex

The present paper reports on an integrated spectroscopic study of the anisole-phenol complex in a molecular beam environment. Combining REMPI and HR-LIF spectroscopy experimental data with density functional computations (TD-M05-2X/M05-2X//N07D) and first principle spectra simulations, it was possible to locate the band origin of the S(1) ← S(0) electronic transition and determine the equilibrium structure of the complex, both in the S(0) and S(1) electronic states. Experimental and computational evidence indicates that the observed band origin is due to an electronic transition localized on the phenol frame, while it was not possible to localize experimentally another band origin due to the electronic transition localized on the anisole molecule. The observed structure of the complex is stabilized by a hydrogen bond between the phenol, acting as a proton donor, and the anisole molecule, acting as an acceptor through the lone pairs of the oxygen atom. A secondary interaction involving the hydrogen atoms of the anisole methyl group and the π electron system of the phenol molecule stabilizes the complex in a nonplanar configuration. Additional insights about the landscapes of the potential energy surfaces governing the ground and first excited electronic states of the anisole-phenol complex, with the issuing implications on the system photodynamic, can be extracted from the combined experimental and computational studies.     

Ab initio quantum chemical calculation of the electronic structure of the chelate complex Ni(S2C2H2)2

The electronic structures and equilibrium geometries of the square-planar Ni(S₂C₂H₂)₂ complex and its dianion are calculated at the MP2 level of theory by the ab initio SCF MO LCAO method in the split-valence Gaussian basis set. The calculated two-electron affinity is 57 kJ/mole. In the ground state, the complex has a d⁸ configuration of Ni(II). The square-pyramidal structure of the complex is also considered. The transformation of the complex structure from square-planar to square-pyramidal involves the two-electron d-d transition. Based on the calculated electronic structure of the complex and on the experimental data on its stable dimers, we assumed an unusual valent state of nickel, Ni(IV), in the complex with the d⁶ electronic configuration. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 231–236, March–April, 1996. Translated by I. Izvekova     

草酰胺桥联双核铜配合物结构单元的从头算

运用Gaussian 94W量子化学程序包 ,采用LanL2DZ基组 ,对草酰胺桥联双核铜配 (聚 )合物结构单元Cu2 (oxen) (OH) 2 [H2 oxen =N ,N' 二 ( 2 胺乙基 )草酰胺 ](包括顺、反构型及其单、三重态电子组态 )进行从头算研究 ,探讨该配合物结构单元的稳定性 ,并从电荷布居及分子轨道组成等电子结构特征分析这种配合物反式三重态比较稳定的原因 .计算结果与实验规律相符合 .     

High resolution electronic spectra of 7-azaindole and its Ar atom van der Waals complex

Rotationally resolved fluorescence excitation spectra of the S(1)<--S(0) origin band of 7-azaindole [1H-pyrrolo(2,3-b)pyridine] and its argon atom van der Waals complex have been recorded and assigned. The derived rotational constants give information about the geometries of the two molecules in both electronic states. The equilibrium position of the argon atom in the azaindole complex is considerably different from its position in the corresponding indole complex. Furthermore, the argon atom moves when the UV photon is absorbed. There are significant differences in the intermolecular potential energy surfaces in the two electronic states. A large, vibration-state-dependent rotation of the S(1)<--S(0) electronic transition moment vector of 7-azaindole relative to that of indole suggests that these differences have their origin in S(1)/S(2) electronic state mixing in the isolated molecule, a mixing that is enhanced by nitrogen substitution in the six-membered ring.     

Spectroscopic and theoretical studies on cobalt(II) complex of maleonitriledithiolate and 5-nitro-1,10-phenanthroline

The molecular structure, electronic and infrared spectroscopic properties for the title complex Co(mnt)(5-NO2-phen) (mnt2-=maleonitriledithiolate, 5-NO2-phen=5-nitro-1,10-phenanthroline) were studied in this paper. With semi-empirical PM3 and non-empirical density functional theory (DFT) methods, the gaseous molecular geometry of the complex was optimized and corresponding vibrational spectra was obtained. The calculated results of structure and frequency from DFT were more reasonable than those from PM3, and the two methods were both agreed with the experimental values. A complete assignment to the IR spectra of such a complicated molecule has been exhibited. An electronic spectra was calculated by ZINDOS/S method. The results showed that the calculated values agreed with the observed ones.     

ANALYSIS OF FRAGMENT INTERACTION AND ASSIGNMENT OF ELECTRONIC SPECTRUM FOR COMPLEX ION[S2MoS2FeCl2]^2—

<正> The electronic structures of complex ion [S2MoS2FeCl2]2- (1) and its fragments MoS42- (2) and FcCl2(3) have been calculated base on the LCAO-HFS method with restricted open shell or closed shell. The interaction between the fragments 3 and 2 and the formation of complex ion 1 have been discussed. It was found that the Fe(Ⅱ) donated electrons to the Mo(Ⅵ)and accepted electrons from the sulphur ligand and that the stability of complex ion 1 is contributed from both direct and indirect interactions through the bridging sulphur atoms. In addtion, the electron transition energies of complex ion 1 were calculated and its electronic absorptions were assigned. It was shown that the calculated wavelengths of the absorption bands are in agreement with the observed ones.     

Multimode Jahn-Teller and pseudo-Jahn-Teller interactions in the cyclopropane radical cation: complex vibronic spectra and nonradiative decay dynamics

The complex vibronic spectra and the nonradiative decay dynamics of the cyclopropane radical cation (CP+) are simulated theoretically with the aid of a time-dependent wave packet propagation approach using the multireference time-dependent Hartree scheme. The theoretical results are compared with the experimental photoelectron spectrum of cyclopropane. The ground and first excited electronic states of CP+ are of X2E' and A2E' type, respectively. Each of these degenerate electronic states undergoes Jahn-Teller (JT) splitting when the radical cation is distorted along the degenerate vibrational modes of e' symmetry. The JT split components of these two electronic states can also undergo pseudo-Jahn-Teller (PJT)-type crossings via the vibrational modes of e', a1' and a2' symmetries. These lead to the possibility of multiple multidimensional conical intersections and highly nonadiabatic nuclear motions in these coupled manifolds of electronic states. In a previous publication [J. Phys. Chem. A 2004, 108, 2256], we investigated the JT interactions alone in the X2E' ground electronic manifold of CP+. In the present work, the JT interactions in the A2E' electronic manifold are treated, and our previous work is extended by considering the coupling between the X2E' and A2E' electronic states of CP+. The nuclear dynamics in this coupled manifold of two JT split doubly degenerate electronic states is simulated by considering fourteen active and most relevant vibrational degrees of freedom. The vibronic level spectra and the ultrafast nonradiative decay of the excited cationic states are examined and are related to the highly complex entanglement of electronic and nuclear degrees of freedom in this prototypical molecular system.     

A square pyramidal copper(II) complex of a Schiff base ligand: synthesis,crystal structure,antibacterial and DNA interaction studies

A mononuclear Cu(II) complex [Cu(L)Cl₂] has been synthesized from a tridentate Schiff base ligand, piperidin-2-ylmethyl-pyridin-2-ylmethylene-amine (L). The single-crystal X-ray structure of the complex shows a square pyramidal geometry. The complex was tested against several bacteria and showed good antibacterial activities against almost all of the bacteria. The interactions of the title complex with calf thymus DNA (CT-DNA) have been investigated by electronic absorption and fluorescence spectroscopy, showing that the complex interacts with CT-DNA via partial intercalation.     

A (bpy)2Ru-coordinated dehydro[12]annulene with exotopically fused diimine binding sites

Synthesis and electronic properties of a dinuclear (bpy)(2)Ru(II) polypyridyl complex are described in which the bridging ligand consists of two dipyridophenazines fused to a formally antiaromatic dehydro[12]annulene and where the electronic and electrochemical properties of the complex are markedly influenced by the cyclic all-carbon core.     

Electron Spin Resonance (ESR) Spectroscopy of the Transition-Metal Complexes and Clusters Ⅰ.Systematic Investigations of Real-and Complex-Orbital Methods for Calculating the d-Orbital Energies of a Low-Spin(S=1/2)nd~5(t_2~5,~2T_2

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草酰胺衍生物桥联双核镍配合物从头算研究

采用LanL2DZ基组 ,对N,N′ 双(2 苯甲酸根)草酰胺桥联双核镍配合物Ni(obbz)Ni(H2O)4 进行从头计算研究 ,探讨该配合物单、三重态的电子组态的稳定性、电子结构特征及电子自旋布居规律等。计算结果表明 ,该配合物分子的三重态比单重态稳定 ,因此 ,该配合物择型于三重态的电子组态。电子自旋主要布居于八面体环境的Ni(1)中心上 ,而处于四方配位环境的Ni(2)中心则没有发现电子自旋布居。同时 ,Ni(2)中心主要参与的分子轨道都处于低能区 ,表明Ni(2)中心的配位是相当稳定的 ,这与实验规律相符。     

Magnetic studies of a syn-anti triatomic carboxylate-bridging chainlike copper(II) complex exhibiting ferromagnetic exchange

The magnetic properties of triatomic syn-anti carboxylate bridging copper(II) complex, {[Cu(2,2'-bipydine)(maleate)].2H2O}infinity (complex 1), were investigated experimentally and theoretically, suggesting weak ferromagnetic intrachain interaction. The magnetic data were analyzed and interpreted in terms of Heisenberg chain model corrected by a mean molecular field. Fitting parameters obtained for J, g, and zJ' are 3.14 cm(-1), 2.08, and -0.13, respectively. Density functional theory with generalized gradient approximation was applied to calculate the electronic structure and spin distribution of the present complex. The structural and electronic factors controlling the magnetic interactions were also determined. Ferromagnetic intrachain interactions through triatomic syn-anti carboxylate bridge result from nonplanarity of the bridging network, the exchange pathway involving both the sigma and pi orbitals of the carboxylate bridge and the spin delocalization of each magnetic orbital on the atoms of the carboxylate bridge from the copper(II) centers.     

Practical route to relative diffusion coefficients and electronic relaxation rates of paramagnetic metal complexes in solution by model-independent outer-sphere NMRD. Potentiality for MRI contrast agents

The relaxation of electronic spins S of paramagnetic species is studied by the field-dependence of the longitudinal, transverse, and longitudinal in the rotating frame relaxation rates R1, R2, and R1rho of nuclear spins I carried by dissolved probe solutes. The method rests on the model-independent low-frequency dispersions of the outer-sphere (OS) paramagnetic relaxation enhancement (PRE) of these rates due to the three-dimensional relative diffusion of the complex with respect to the probe solute. We propose simple analytical formulas to calculate these enhancements in terms of the relative diffusion coefficient D, the longitudinal electronic relaxation time T1e, and the time integral of the time correlation function of the I-S dipolar magnetic interaction. In the domain of vanishing magnetic field, these parameters can be derived from the low-frequency dispersion of R1 thanks to sensitivity improvements of fast field-cycling nuclear relaxometers. At medium field, we present various approaches to obtain these parameters by combining the rates R1, R2, and R1rho. The method is illustrated by a careful study of the proton PREs of deuterated water HOD, methanol CH3OD, and tert-butyl alcohol (CH3)3COD in heavy water in the presence of a recently reported nonacoordinate Gd(III) complex. The exceptionally slow electronic relaxation of the Gd(III) spin in this complex is confirmed and used to test the accuracy of the method through the self-consistency of the low- and medium-field results. The study of molecular diffusion at a few nanometer scale and of the electronic spin relaxation of other complexed metal ions is discussed.     

Electron delocalisation in a trinuclear copper(II) complex: high-field EPR characterization and magnetic properties of Na3[Cu3(mal)3(H2O)] x 8H2O

The complex Na3[Cu3(mal)3(H2O)] x 8H2O was obtained from evaporation of an aqueous solution containing Cu(OAc)2, malic acid (HO2CCH2CHOHCO2H) and NaOH and was characterised by X-ray diffraction on single crystal, X-band and high-field EPR spectroscopy (HF-EPR) and magnetic susceptibility measurements. The trinuclear complex [Cu3(mal)3(H2O)]3- is trapped in a three-dimensional network with sodium cations. The three copper atoms are connected by alkoxo bridges and form an almost isosceles triangle with Cu...Cu distances of 3.076(1), 3.504(1) and 3.513(1) A. Two of the copper ions are also bridged by an extra aquo ligand. EPR spectroscopy combined with magnetic susceptibility measurements provide a powerful tool to resolve the electronic structure of the complex. The overall magnetic behaviour corresponds to an antiferromagnetically coupled triangular system. The 285 GHz-EPR spectrum (g = 2; 10.18 T) is characteristic of a spin state S = 1/2, with a rhombic anisotropy of [g]. This rhombic pattern allows us to propose that the electronic spin density is delocalised on the three copper ions.     

Electronic dissymmetry in chiral recognition

The pi-bonding of the beta-diketonate ligands in C2-symmetric (dike)2TiX2 complexes engenders a significant electronic dissymmetry, with the LUMO of the complex resembling a "tipped" dz2 orbital whose tilt with respect to the plane containing the metal and the two X groups is determined by the configuration at titanium. The ability of this electronic dissymmetry to promote chiral recognition has been probed in 1,1'-bi-2-naphtholate complexes (RCOCHCOR)2Ti(BINOL) (R = CH3, Ph, or tBu). The complexes show exclusively one diastereomer by NMR, which has been established as the one predicted on electronic grounds by crystallography of the dibenzoylmethane and 2,2,6,6-tetramethylheptanedione complexes. Confirmation that the selectivity is due to electronic rather than steric factors is given by the behavior of the tin analogues, which are structurally similar but show much smaller diastereoselectivities.     

Photoinduced electron transfer in platinum(II) terpyridinyl acetylide complexes connected to a porphyrin unit

A series of six new dyads consisting of a zinc or magnesium porphyrin appended to a platinum terpyridine acetylide complex via a para-phenylene bisacetylene spacer are described. Different substituents on the 4' position of the terpyridinyl ligand were explored (OC7H15, PO3Et2, and H). The ground-state electronic properties of the dyads are studied by electronic absorption spectroscopy and electrochemistry, and they indicate some electronic interactions between the porphyrin subunit and the platinum complex. The photophysical properties of these dyads were investigated by steady-state, time-resolved, and femtosecond transient absorption spectroscopy in N,N-dimethylformamide solution. Excitation of the porphyrin unit leads to a very rapid electron transfer (2-20 ps) to the nearby platinum complex followed by an ultrafast charge recombination, thus preventing any observation of the charge separated state. The variation in the rate of the photoinduced electron transfer in the series of dyads is consistent with Marcus theory. The results underscore the potential of the para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance.