Reaction of iron powder with 1,3,4,7-tetramethylisoindole at 350° affords the square planar complex octamethyl-tetrabenzporphyriniron(II), whose magnetic moment indicates a spin quintet ground state. Mössbauer measurements at 4.2°K in an applied magnetic field of 50 kG show that the electric field gradient at iron is positive and axially symmetric, consistent with a 5B2g ground term. The bistetrahydrofuran adduct is also high spin, whereas the bispyridine adduct is diamagnetic with 1A1g ground state. Comparisons are made with data for the related tetraphenylporphiniron(II) and phthalocyanineiron(II) derivatives. 相似文献
Transient absorption spectroscopy is used to study the excited‐state dynamics of Co3(dpa)4(NCS)2, where dpa is the ligand di(2‐pyridyl)amido. The ππ*, charge‐transfer, and d–d transition states are excited upon irradiation at wavelengths of 330, 400 and 600 nm, respectively. Similar transient spectra are observed under the experimental temporal resolution and the transient species show weak absorption. We thus propose that a low‐lying metal‐centered d–d state is accessed immediately after excitation. Analyses of the experimental kinetic traces reveal rapid conversion from the ligand‐centered ππ* and the charge‐transfer states to this metal‐centered d‐d state within 100 fs. The excited molecule then crosses to a second d–d state within the ligand‐field manifold, with a time coefficient of 0.6–1.4 ps. Because the ground‐state bleaching band recovers with a time coefficient of 10–23 ps, we propose that an excited molecule crosses from the low‐lying d–d state either directly within the same spin system or with spin crossing via the state 2B to the ground state 2A2 (symmetry group C4). In this trimetal string complex, relaxation to the ground electronic surface after excitation is thus rapid.相似文献
Two nickel compounds having extended metal atom chains (EMACs) with the Ni3(dpa)4L2 core, where dpa is the anion of 2,2′-dipyridylamine and L represents an anthracene derivative, have been synthesized in good yield and excellent purity by reaction of Ni3(dpa)4Cl2 and the respective anthracene derivatives. For the compound Ni3(dpa)4(AnCC)2 (1) AnCC is the anion of 9-ethynylanthracene and for Ni3(dpa)4(AnCOO)2 (2) AnCOO is anthracene-9-carboxylate. The two compounds have been characterized by X-ray crystallography and other techniques. The cyclovoltammograms (CVs) of 1 and 2 display reversible redox processes at E1/2 = 0.911 V and 1.020 V, respectively (vs. Ag/AgCl). The magnetic data suggest that the terminal Ni atoms are in a high spin state while the central Ni atom is diamagnetic, in agreement with other trinickel molecular wires. Although compound 1 is strongly luminescent, and represents the first such example in an EMAC, 2 does not display luminescence. The strong emission in 1 is related to donor–acceptor interactions between the Ni?Ni?Ni wire, the triply bonded CC linking unit, and the conjugated aromatic anthracene derivative, a process that is unavailable for 2 because the carboxylate group is almost perpendicular to the anthracene moiety. 相似文献
MINDO/3 calculations have been made of the molecular structures and energies of seven isomeric forms of the molecular cation (CCl4)+, of the mass spectral fragment pairs: and also of a number of neutral fragment pairs. Reaction energy profiles have been calculated for two fragmentations of (CCl4)+, into [(CCl2)+ + Cl2], and into [(CCl3)+ + Cl?], in the latter of which the reaction proceeds via a rather stable intermediate; for the fragmentation of three electronic states of (CCl3)+ into [(CCl2)+ + Cl?], where the ground singlet state and first triplet state of (CCl3+ yield the ground doublet state of (CCl2)+, but the first excited singlet of (CCl3)+ yields the first excited doublet of (CCl2)+ ; and for the fragmentation of the ground state of (CCl3)+ into [(CCl)+ + Cl2]. 相似文献
In the present work, we report structural and electronic properties of a benzoin monomer named as 2-oxo-1,2-diphenylethyl-2-bromopropanoate (C17H14BrO3). The previously synthesized compound is characterized by single crystal X-ray diffraction. The optimized molecular geometry (bond lengths, and bond angles), HOMO-LUMO analysis and molecular electrostatic potential (MEP) are calculated by density functional theory (DFT) and Hartree-Fock (HF) methods with 6-311G(d) basis set in the neutral ground state and using DFT methods for singly oxidized doublet, singly reduced doublet, and neutral triplet state for the benzoin compound. The X-ray structure determination of the compound is compatible with the geometric parameters calculated at B3LYP/6-311G(d). In the triplet state the HOMO-LUMO energy gap of 2.39?eV which indicates semi-conductor property is recommended for the photovoltaic devices. 相似文献
Oxygen adsorption on Ag(331) is analyzed in a cluster approximation using the density functional theory (DFT) method. Adsorption centers (AC) for the bridge (S2) and three-center (S3) coordinations of oxygen are identified on the stepwise face Ag(331) and the Ag-O bond energies at these centers are calculated. For atomic adsorption, the Ag-O bond strength varies from 50 to 65 kcal/mole, depending on AC. The heat of molecular adsorption DH = 5 kcal/mole for S2(L1-L2) type AC. The molecule is oriented parallel to Ag(110) between the terraces with R(O-O) = 1.34 å Calculations showed that the ground state of the O2Ag20(331) system is a triplet, but a part of spin density is delocalized on silver atoms, so that the spin density on oxygen ρs(O) = 0.46 (ρs = 1.0 for the free O2 molecule). The energy of the singlet state is 9 kcal/mole greater than that of the ground state. 相似文献
The metal string complex [Ni3(dpa)4(ClO4)(Cl)] · CH2Cl2 ( 1 ) [dpa = bis(2‐pyridyl)amine] with different axial ligands was synthesized and characterized by elemental analysis, IR, UV/Vis, and fluorescence spectroscopy and TG analysis. The molecular structure was determined by single‐crystal X‐ray analysis and its electrochemical properties were investigated. This metal string complex is the first example with different axial ligands, and in its structure a different structural packing relative to the metal string complex [Ni3(dpa)4(Cl)2] ( 2 ) with two axial chloride ligands is generated. The intense C–H ··· π interactions observed for 1 provide additional stability. The axial mono‐substitution of Cl– by ClO4– in 1 relative to 2 results in one obviously short Ni–Ni distance and a higher stability towards oxidation. 相似文献
X‐ray magnetic circular dichroism spectroscopy has been used to characterize the electronic structure and magnetic moment of Cr2+. Our results indicate that the removal of a single electron from the 4sσg bonding orbital of Cr2 drastically changes the preferred coupling of the 3d electronic spins. While the neutral molecule has a zero‐spin ground state with a very short bond length, the molecular cation exhibits a ferromagnetically coupled ground state with the highest possible spin of S=11/2, and almost twice the bond length of the neutral molecule. This spin configuration can be interpreted as a result of indirect exchange coupling between the 3d electrons of the two atoms that is mediated by the single 4s electron through a strong intraatomic 3d‐4s exchange interaction. Our finding allows an estimate of the relative energies of two states that are often discussed as ground‐state candidates, the ferromagnetically coupled 12Σ and the low‐spin 2Σ state. 相似文献
Spin-inversion mechanisms in O2 binding to a model heme complex, consisting of Fe(II)-porphyrin and imidazole, were investigated using density-functional theory calculations. First, we applied the recently proposed mixed-spin Hamiltonian method to locate spin-inversion structures between different total spin multiplicities. Nine spin-inversion structures were successfully optimized for the singlet–triplet, singlet–quintet, triplet–quintet, and quintet–septet spin-inversion processes. We found that the singlet–triplet spin-inversion points are located around the potential energy surface region at short Fe–O distances, whereas the singlet–quintet and quintet–septet spin-inversion points are located at longer Fe–O distances. This suggests that both narrow and broad crossing models play roles in O2 binding to the Fe-porphyrin complex. To further understand spin-inversion mechanisms, we performed on-the-fly Born-Oppenheimer molecular dynamics calculations. The reaction coordinates, which are correlated to the spin-inversion dynamics between different spin multiplicities, are also discussed. 相似文献
Extended metal atom chains (EMACs) are molecular linear arrangements of metal atoms featuring magnetic properties. By means of the density functional theory (DFT), we have studied the magnetic coupling constants for [Cu3(dpa)4Cl2]+, Ni3(dpa)4Cl2 and Ni5(tpda)4Cl2 to understand which is the origin of the previously reported theoretical underestimation of J for nickel complexes. We have decomposed J = Jσ + Jδ, finding that the former contribution is underestimated and the latter part is overestimated at the DFT/B3LYP level of computation. Varying the amount of Hartree-Fock exchange, we show that the B3LYP functional fails to describe the σ interaction properly, whereas the δ coupling is exaggerated. 相似文献
57Fe Mössbauer spectra of [FeL4] (ClO4)2 where L = 1,8-naphthyridine have been measured at 4.2°K in external magnetic fields up to 55 kG parallel to the direction of the γ-rays. The spectra have been fitted in the spin hamiltonian approximation assuming an orbital singlet ground state of the 5D multiplet of Fe2+. The fit of the spectra is not unique, yet the possible spin hamiltonian parameter sets found lead to a spin doublet ground state split by less than 1 cm?1. The transition probabilities for spin-lattice relaxation have been calculated for those ground states. Orbach processes via excited spin hamiltonian states cannot be neglected. The results explain the fluctuations observed in the spectra in low external magnetic fields (10 kG).The spin hamiltonian parameters provide information on the orbital energy levels. Therefrom the reduction of the quadrupole splitting by spin—orbit coupling results to be small thus explaining the extremely large quadrupole splitting of 4.54 mm/sec. 相似文献
DFT/BP86 calculations have been carried out on a series of hypothetical binuclear compounds of general formula (L3M)2(C12N2H8) (M?=?Sc–Ni, L3?=?(CO)3, (PH3)3 and Cp?, and C12N2H8?=?phenazine ligand-denoted Phn). The various structures with syn and anti configurations have been investigated, in order to determine the phenazine’s coordination to first-row transition metals of various spin states with syn and anti conformations. The lowest energy structures depend on the nature of the metal, the spin state, and the molecular symmetry. This study has shown that the electronic communication between the metal centers depends on their oxidation state and the attached ligands. The tricarbonyl and the triphosphine ligands gave rise to comparable results in terms of stability order of isomers, metal-metal bond distances, and the coordination modes. Metal-metal multiple bonding has been evidenced for Sc, Ti, and V complexes to compensate the electronic deficiency. The Cr, Mn, Fe, Co, and Ni-rich metals prefer the anti conformation due to the enhancement of the metal valence electron count. The spin density values calculated for the triplet and quintet spin structures point out that the unpaired electrons are localized generally on the metal centers. The Wiberg bond indices are used to evaluate the metal-metal bonding. Furthermore, calculations using the BP86-D functional which take into account the attractive part of the van der Waals type interaction potential between atoms and molecules that are not directly connected to each other gave comparable results to those obtained by BP86 functional in terms of coordination modes, HOMO-LUMO gaps, metal-metal bond orders, and the stability order between isomers, but with slight deviation of M–C, M–N, and M–M bond distances not exceeding 3%. 相似文献
We report the infrared, Raman, and surface‐enhanced Raman scattering (SERS) spectra of triruthenium dipyridylamido complexes and of diruthenium mixed nickel metal‐string complexes. From the results of analysis on the vibrational modes, we assigned their vibrational frequencies and structures. The infrared band at 323–326 cm?1 is assigned to the Ru3 asymmetric stretching mode for [Ru3(dpa)4Cl2]0–2+. In these complexes we observed no Raman band corresponding to the Ru3 symmetric stretching mode although this mode is expected to have substantial Raman intensity. There is no frequency shift in the Ru3 asymmetric stretching modes for the complexes with varied oxidational states. No splitting in Raman spectra for the pyridyl breathing line indicates similar bonding environment for both pyridyls in dpa– , thus a delocalized structure in the [Ru3]6–8+ unit is proposed. For Ru3(dpa)4(CN)2 complex series, we assign the infrared band at 302 cm?1 to the Ru3 asymmetric stretching mode and the weak Raman line at 285 cm?1 to the Ru3 symmetric stretching. Coordination to the strong axial ligand CN– weakens the Ru‐Ru bonding. For the diruthenium nickel complex [Ru2Ni(dpa)4Cl2]0–1+, the diruthenium stretching mode νRu‐Ru is assigned to the intense band at 327 and 333 cm?1 in the Raman spectra for the neutral and oxidized forms, respectively. This implies a strong Ru‐Ru metal‐metal bonding. 相似文献
The magnetic behaviour of the compounds containing the [Ru2(DPhF)3(O2CMe)]+ ion (DPhF?=N,N′‐diphenylformamidinate) shows a strong dependence on the nature of the ligand bonded to the axial position. The new complexes [Ru2(DPhF)3(O2CMe)(OPMe3)][BF4]?0.5 CH2Cl2 ( 1 ? 0.5 CH2Cl2) and [Ru2(DPhF)3(O2CMe)(4‐pic)][BF4] ( 2 ) (4‐pic=4‐methylpyridine) clearly display this influence. Complex 1 ?0.5 CH2Cl2 shows a magnetic moment corresponding to a S=3/2 system affected by the common zero‐field splitting (ZFS) and a weak antiferromagnetic interaction, whereas complex 2 displays an intermediate behaviour between S=3/2 and S=1/2 systems. The experimental data of complex 1 are fitted with a model that considers the ZFS effect using the Hamiltonian ?D= S ? D ? S . The weak antiferromagnetic coupling is introduced as a perturbation, using the molecular field approximation. DFT calculations demonstrate that, in the [Ru2(O2CMe)(DPhF)3(L)]+ complexes, the energy level of the metal–metal molecular orbitals is strongly dependent on the nature of the axial ligand (L). This study reveals that the increase in the π‐acceptor character of L leads to a greater split between the π* and δ* HOMO orbitals. The influence of the axial ligand in the relative energy between the doublet and quartet states in this type of complexes was also analysed. This study was performed on the new complexes 1 ?0.5 CH2Cl2 and 2 . The previously isolated [Ru2(DPhF)3(O2CMe)(OH2)][BF4]?0.5 CH2Cl2 ( 3 ? 0.5 CH2Cl2) and [Ru2(DPhF)3(O2CMe)(CO)][BF4]?CH2Cl2 ( 4 ?CH2Cl2) complexes were also included in this study as representative examples of spin‐admixed and low‐spin configurations, respectively. The [Ru2(DPhF)3(O2CMe)]+ ( 5 ) unit was used as a reference compound. These theoretical studies are in accordance with the different magnetic behaviour experimentally observed. 相似文献
10, 10-dimethylanthracen-9-one single crystal emission and absorption spectra have been recorded at low temperatures, as well as Raman spectra on the melt. The absorption spectra of both the lowest triplet and lowest excited singlet states clearly show the absorption origins of the three different molecular sites in the triclinic unit cell of the crystal. The emission spectra indicate that substantial spin—orbit/vibronic state mixing occurs, giving rise to transitions between the z sub-level of the lowest 3nπ3 state (T1) and both totally and non-totally symmetric vibrations of the ground state. The preferred intensity stealing route is from T1 (z) to S2(1ππ3) by spin—orbit coupling with vibronic mixing of S3 and S4(1ππ3, 1B2). 相似文献