Ab initio and DFT studies on vibrational spectra of some mixed carbonyl-halide complexes of ruthenium(II)

The vibrational spectra of Ru(CO)6(2+) and some of its mixed carbonyl-halide complexes, cis-Ru(CO)2X4(2-), fac-Ru(CO)3X3- and Ru(CO)5X+ (X = F, Cl, Br and I), have been systematically investigated by ab initio RHF and density functional B3LYP methods with LanL2DZ and SDD basis sets. The calculated vibrational frequencies of complexes Ru(CO)6(2+), cis-Ru(CO)2X4(2-) and fac-Ru(CO)3X3- are evaluated via comparison with the experimental values. In the infrared frequency region, the C-O stretching vibrational frequencies calculated at B3LYP level with two basis sets are in good agreement with the observed values with deviations less than 5%. In the far-infrared region, the B3LYP/SDD method achieved the best results with deviations less than 8% for Ru-X stretching and less than 2% for Ru-C stretching vibrational frequencies. The vibrational frequencies for Ru(CO)5X+ that have not been experimentally reported were predicted.     

Theoretical studies on vibrational spectra of mixed cyanide-halide complexes of platinum(IV) and palladium(IV)

The vibrational spectra of mixed cyanide-halide complexes, M(CN)4X 2 2- and M(CN)5X2- (M=Pt and Pd; X=F, Cl, Br and I), have been systematically investigated by ab initio RHF, B3LYP and MP2 methods with LanL2DZ and SDD basis sets. The calculated vibrational frequencies of platinum complexes are evaluated via comparison with the experimental values. In the infrared frequency region, the C--N stretching vibrational frequencies calculated at B3LYP level with two basis sets are in good agreement with the observed values with deviations, -16-4 cm(-1) for Pt(CN)4X 2 2- and -18 to -2 cm(-1) for Pt(CN)5X2-. However, in far-infrared region, the results obtained at RHF level are better than those calculated at B3LYP and MP2 levels. For RHF/SDD method, the deviations for Ptz.sbnd;X and Ptz.sbnd;C stretching vibrational frequencies are -14-1 and -12 to -2 cm(-1) in the complex Pt(CN)4X2 2-, -19 to -11 and -15-14 cm(-1) in the Pt(CN)5X2- complex, respectively. The vibrational frequencies of palladium(IV) and some platinum(IV) complexes that have not been experimentally reported are predicted.     

[M(Im)2X2]型配合物的Far-IR和Raman光谱的理论研究

本文用从头计算RHF和密度泛函B3LYP方法以及LanL2DZ，SDD和6-31G(d)基组计算了配合物M(Im)₂X₂ (Im=imidazole；M=Zn(Ⅱ)，Pd(Ⅱ)，Pt(Ⅱ)；X=F，Cl，Br，I)的几何构型以及Far-IR和Raman振动频率。计算结果表明，对Zn(Ⅱ)配合物而言,B3LYP/6-31G(d)方法得到的几何参数与实验值吻合得最好，B3LYP/SDD次之。在计算Far-IR和Raman振动频率时，发现采用6-31G(d)基组，两种方法计算的结果差别不大。对LanL2DZ和SDD基组而言，对计算结果影响较大的是理论方法，基组影响甚微，个别的振动频率基组影响较大，相比较而言，SDD基组得到的结果更好一些。本文所使用的两种计算方法都能得到与实验值比较吻合的结果，而用从头计算RHF方法计算的结果与实验值更接近一些。在此基础上，预测了Pd(Ⅱ)和Pt(Ⅱ)配合物的Far-IR和Raman振动频率。     

Theoretical studies on vibrational spectra of some halides of Group IIB elements

The vibrational spectra of Group IIB elements halides MX2 and their dimers M2X4 (M=Zn(II), Cd(II) and Hg(II); X=F, Cl, Br and I) have been systematically investigated by ab initio RHF and B3LYP methods with LanL2MB, LanL2DZ and SDD basis sets. The optimized geometries, calculated vibrational frequencies are evaluated via comparison with the experimental data. The vibrational frequencies, calculated by these methods with different basis sets, are compared to each other too. The best results can be obtained by RHF/SDD method, with this method, the deviations for MX2 and Hg2X4 are <7%. Some vibrational frequencies of M2X4 that have not been experimentally reported are also predicted.     

Ab initio and DFT studies on vibrational spectra of some halides of group IIIB elements

The vibrational spectra of some group IIIB elements halides MX(3) and their dimmers, M(2)X(6) (M=Sc(III), Y(III), La(III); X=F, Cl, Br, I), have been systematically investigated by ab initio restricted Hartree-Fock (RHF) and density functional B3LYP methods with LanL2DZ and SDD basis sets. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational frequencies, calculated by two methods with different basis sets, are compared to each other. The effect of the methods and the basis sets used on the calculated vibrational frequencies are discussed. Some vibrational frequencies of these complexes are also predicted.     

锌族和钛族卤化物振动光谱的理论计算

采用ab initio RHF,MP2和B3LYP方法以及LanL2DZ和SDD基组计算了四面体锌族卤素阴离子化合物(MX₄^2-,M=Zn(Ⅱ),Cd(Ⅱ),Hg(Ⅱ);X=F^-,Cl^-,Br^-,I^-)和钛族卤化物(MX₄,M=Ti(Ⅳ),Zr(Ⅳ),Hf(Ⅳ);X=F^-,Cl^-,Br^-,I^-)的几何构型和振动频率。计算结果表明,LanL2DZ基组是合适的基组,能得到合理的电荷分布,几何参数以及振动频率。在锌族卤化物的计算中发现,角弯曲振动频率与实测值相当一致,键伸缩振动频率略为偏低,这主要是由于计算的键长略为偏长所致。MP2方法计算的振动频率更接近于实测值。在钛族卤化物的计算中,三种计算方法都相当地再现了实测值,而以B3LYP方法更为满意。     

Theoretical study of Ca+-X and Y-Ca+-X complexes important in the chemistry of ionospheric calcium (X, Y = H2O, CO2, N2, O2, and O)

Optimized geometries and vibrational frequencies are calculated for Ca(+)-X and Y-Ca(+)-X complexes (X, Y = H2O, N2, CO2, O2, and O), required for understanding the chemistry of calcium in the upper atmosphere. Both MP2 and B3LYP optimizations were performed employing 6-311+G(2d,p) basis sets. In some cases a number of different orientations had to be investigated in order to determine the one of lowest energy, and in cases involving O and O2, different spin states also had to be considered. In order to establish accurate energetics, RCCSD(T) single-point energy calculations were also employed, using aug-cc-pVQZ basis sets. Accurate dissociation energies for the Ca(+)-X and X-Ca(+)-Y species are derived and discussed. Comparison with available experimental results is made where possible.     

Ab initio and density functional theory studies on vibrational spectra of palladium (II) and platinum (II) complexes of methionine and histidine: effect of theoretical methods and basis sets

The vibrational spectra of methionine and histidine-containing palladium (II) and platinum (II) complexes, cis-M(Met)X2 and cis-M(His)X2 (M = Pd and Pt; X = F, Cl, Br and I; Met = methionine, His = histidine), have been systematically investigated by ab initio Restricted Hartree-Fock (RHF) and density functional B3LYP methods with LanL2DZ and SDD basis sets. The geometries of cis-Pd(Met)Cl2, cis-Pt(Met)Cl2, cis-Pd(His)Cl2 and cis-Pt(His)I2 optimized and vibrational frequencies and IR intensities of cis-M(Met)Cl2 and cis-M(His)Cl2 (M = Pd and Pt) calculated are evaluated via comparison with the experimental values. The vibrational frequencies calculated show that the methods, rather than basis sets, affect the accuracy of the calculation. The best results that can reproduce the experimental ones are obtained at B3LYP level without any scale factor used. The vibrational frequencies of cis-M(Met)X2 and cis-M(His)X2 (M = Pd and Pt; X = F, Br and I) that have not yet been experimentally reported are predicted.     

Electronic structures of ruthenium and osmium complexes of 9,10-phenanthrenequinone

The reaction of 9,10-phenanthrenequinone (PQ) with [M(II)(H)(CO)(X)(PPh(3))(3)] in boiling toluene leads to the homolytic cleavage of the M(II)-H bond, affording the paramagnetic trans-[M(PQ)(PPh(3))(2)(CO)X] (M = Ru, X = Cl, 1; M = Os, X = Br, 3) and cis-[M(PQ)(PPh(3))(2)(CO)X] (M = Ru, X = Cl, 2; M = Os, X = Br, 4) complexes. Single-crystal X-ray structure determinations of 1, 2·toluene, and 4·CH(2)Cl(2), EPR spectra, and density functional theory (DFT) calculations have substantiated that 1-4 are 9,10-phenanthrenesemiquinone radical (PQ(?-)) complexes of ruthenium(II) and osmium(II) and are defined as trans-[Ru(II)(PQ(?-))(PPh(3))(2)(CO)Cl] (1), cis-[Ru(II)(PQ(?-))(PPh(3))(2)(CO)Cl] (2), trans-[Os(II)(PQ(?-))(PPh(3))(2)(CO) Br] (3), and cis-[Os(II)(PQ(?-))(PPh(3))(2)(CO)Br] (4). Two comparatively longer C-O [average lengths: 1, 1.291(3) ?; 2·toluene, 1.281(5) ?; 4·CH(2)Cl(2), 1.300(8) ?] and shorter C-C lengths [1, 1.418(5) ?; 2·toluene, 1.439(6) ?; 4·CH(2)Cl(2), 1.434(9) ?] of the OO chelates are consistent with the presence of a reduced PQ(?-) ligand in 1-4. A minor contribution of the alternate resonance form, trans- or cis-[M(I)(PQ)(PPh(3))(2)(CO)X], of 1-4 has been predicted by the anisotropic X- and Q-band electron paramagnetic resonance spectra of the frozen glasses of the complexes at 25 K and unrestricted DFT calculations on 1, trans-[Ru(PQ)(PMe(3))(2)(CO)Cl] (5), cis-[Ru(PQ)(PMe(3))(2)(CO)Cl] (6), and cis-[Os(PQ)(PMe(3))(2)(CO)Br] (7). However, no thermodynamic equilibria between [M(II)(PQ(?-))(PPh(3))(2)(CO)X] and [M(I)(PQ)(PPh(3))(2)(CO)X] tautomers have been detected. 1-4 undergo one-electron oxidation at -0.06, -0.05, 0.03, and -0.03 V versus a ferrocenium/ferrocene, Fc(+)/Fc, couple because of the formation of PQ complexes as trans-[Ru(II)(PQ)(PPh(3))(2)(CO)Cl](+) (1(+)), cis-[Ru(II)(PQ)(PPh(3))(2)(CO)Cl](+) (2(+)), trans-[Os(II)(PQ)(PPh(3))(2)(CO)Br](+) (3(+)), and cis-[Os(II)(PQ)(PPh(3))(2)(CO)Br](+) (4(+)). The trans isomers 1 and 3 also undergo one-electron reduction at -1.11 and -0.96 V, forming PQ(2-) complexes trans-[Ru(II)(PQ(2-))(PPh(3))(2)(CO)Cl](-) (1(-)) and trans-[Os(II)(PQ(2-))(PPh(3))(2)(CO)Br](-) (3(-)). Oxidation of 1 by I(2) affords diamagnetic 1(+)I(3)(-) in low yields. Bond parameters of 1(+)I(3)(-) [C-O, 1.256(3) and 1.258(3) ?; C-C, 1.482(3) ?] are consistent with ligand oxidation, yielding a coordinated PQ ligand. Origins of UV-vis/near-IR absorption features of 1-4 and the electrogenerated species have been investigated by spectroelectrochemical measurements and time-dependent DFT calculations on 5, 6, 5(+), and 5(-).     

Strategic design and synthesis of osmium(II) complexes bearing a single pyridyl azolate pi-chromophore: achieving high-efficiency blue phosphorescence by localized excitation

We present the strategic design and synthesis of Os(II) complexes bearing a single pyridyl azolate pi-chromophore with an aim to attain high efficiency blue phosphorescence by way of localized transition. It turns out that our proposal of localized excitation seems to work well upon anchoring a single pi-chromophore on the Os(II) complexes such that the control of MLCT versus pipi* (or even LLCT) transitions is more straightforward. Among the titled complexes, [Os(CO)3(tfa)(fppz)] (1) and [Os(CO)3(tfa)(fbtz)] (5) (tfa=trifluoroacetate, (fppz)H=3-(trifluoromethyl)-5-(2-pyridyl)pyrazole, and (fbtz)H=3-(trifluoromethyl)-5-(4-tert-butyl-2-pyridyl)-1,2,4-triazole) give the anticipated blue phosphorescence with efficiencies of 0.26 (lambdamax=460 nm) and 0.27 (lambdamax=450 nm), respectively. For their halide analogues [Os(CO)3(X)(fppz)] (2, X=Cl; 3, X=Br; 4, X=I) and phosphine-substituted isomeric derivatives [Os(tfa)(fppz)(PPh2Me)2(CO)] (6-8), the localization of the excitation energy seems to populate at certain vibrational modes with weak bonding strength and hence an associated shallow potential energy surface to induce a facile radiationless transition. Furthermore, their ancillary ligands play an important role in fine-tuning not only the energy gap but also the emission intensity, i.e., in manifesting the radiationless transition pathways. Our results clearly show that there is always a tradeoff upon varying the parameters in an aim to optimize the hue and efficiency of phosphorescence toward blue.     

Theoretical and experimental study on metal(II) halide complexes of 1,3-bis(4-pyridyl)propane

We report the results of detailed experimental and theoretical studies on the molecular structure and vibrational spectra of metal(II) halide complexes of 1,3-bis(4-pyridyl)propane [M(N₂C₁₃H₁₄)X₂, where M represents Zn or Hg, and X represents Cl, Br, or I]. The FT–infrared spectra (FT-IR) and FT-Raman spectra of the metal complexes of the 1,3-bis(4-pyridyl)propane molecule in the powder form were recorded between the 400–4000 and 5–3500 cm^?1 regions, respectively. The molecular geometry and vibrational frequencies of the metal complexes of 1,3-bis(4-pyridyl)propane in the ground state were calculated using density functional theory (B3LYP functional) with LANL2DZ and SDD as basis sets. The total energy distributions (TED) among the symmetry coordinates of the normal modes were computed for the low-energy structure of the molecules. Complete vibrational assignments based on the calculated TED values are given.     

Theoretical investigation of CO interaction with copper sites in zeolites: periodic DFT and hybrid quantum mechanical/interatomic potential function study

Periodic DFT and combined quantum mechanics/interatomic potential function (QM-pot) models were used to describe the interaction of CO with the Cu+ sites in FER. The CO stretching frequencies were calculated using omega(CO)(CCSD(T))/r(CO)(DFT) scaling method relating frequencies determined using a high-level quantum-chemical (coupled clusters) method for simple model carbonyls to CO bond lengths calculated using periodic DFT and QM-pot methods for the Cu+-zeolite system. Both periodic DFT and QM-pot models together with omega(CO)/r(CO) scaling describe the CO stretching dynamics with the "near spectroscopic accuracy", giving nu(CO) = 2156 cm(-1) in excellent agreement with experimental data. Calculations for various Cu+ sites in FER show that both types of Cu+ sites in FER (channel-wall sites and intersection sites) have the same CO stretching frequencies. Thus, the CO stretching frequencies are not site-specific in the CO/Cu+/FER system. The convergence of the results with respect to the model size was analyzed. When the same exchange-correlation functional is used the adsorption energies from periodic DFT and QM-pot are in good agreement (about 2 kcal/mol difference) but substantially larger than those of the experiment. The adsorption energy calculated with the B3LYP functional agrees with available experimental data. The overestimation of the adsorption energy in DFT calculations (periodic or QM-pot) is related to a red-shift of the CO stretching mode, both result from an underestimation of the HOMO(5sigma)-LUMO(2pi) gap of CO and the consequent overestimation of the Cu(+)(d)-CO(2pi*) back-donation. For the adsorption energy, this can be overcome by the use of hybrid B3LYP exchange-correlation functional. For the frequency calculations, the DFT problem can be overcome by the use of the omega(CO)(CCSD(T))/r(CO)(DFT) correlation.     

Modeling structures and vibrational frequencies for dinitrosyl iron complexes (DNICs) with density functional theory

The biochemical and physiological importance of nitric oxide (NO) in signaling and vasodilation has been studied for several decades. The discovery of both protein-bound and free low molecular weight dinitrosyl iron complexes (DNICs) suggests that such compounds might play roles in biological NO storage and transport. These complexes have important distinguishing spectroscopic features, including EPR and M?ssbauer spectra, and NO vibrational frequencies (ν((NO))). The latter are particularly sensitive to modifications of the ligand environment and metal oxidation states. Examinations of functionals and basis sets delineate their effect on the NO vibrational frequencies and allow development of a methodology to calculate these frequencies in other DNICs. Three complexes of the form (L)(CO)Fe(NO)(2) (L = CO, N,N'-dimethyl-imidazol-2-ylidene (IMe) or 1-methylimidazole (MeImid)), where {Fe(NO)(2)}(10) is in its reduced form, have been used to calibrate the vibrational frequencies. The functional BP86 paired with a basis set of SDD/ECP on the metal and 6-311++G(d,p) on the ligand atoms exhibits the most accurate results, with deviations from experimental vibrational frequencies of no more than ±40 cm(-1). Subsequent investigations were performed on a series of diiron trinitrosyl complexes of the form {Fe(NO)}(7)-{Fe(NO)(2)}(9) bridged by sulfurs, namely, [(ON)Fe(μ-S,S-C(6)H(4))(2)Fe(NO)(2)](-), [Fe(NO)(2){Fe(NS(3))(NO)}-μ-S,S'], and [(ON)Fe(bme-dach)Fe(NO)(2)-μ-S,S'](+), with the ideal functional/basis set pair determined via the aforementioned test set. The ground state energetics (singlet/triplet/singlet, respectively), geometric parameters, and nitrosyl vibrational frequencies were calculated. The results for the former two complexes correlated well with the experimental work, and in contrast with what was reported in an earlier computational study, a stable triplet ground state structure was optimized for [Fe(NO)(2){Fe(NS(3))(NO)}-μ-S,S']. For [(ON)Fe(bme-dach)Fe(NO)(2)-μ-S,S'](+), whose synthesis and structure were recently reported, the geometric parameters, vibrational frequencies, and total energies compare well to experimental ones and favor a singlet ground state.     

The infrared spectra and theoretical calculations of frequencies of fac-tricarbonyl octahedral complexes of manganese(I)

The carbonyl stretching frequencies in the infrared spectra of 38 fac-tricarbonyl octahedral complexes of manganese(I) prepared in this laboratory were determined. These complexes may be grouped into three types: (a) neutral complexes of the structure (CO)(3)Mn(P-P)Z where P-P represents depe, dppe, or dppp, and Z represents various anionic functional groups bonded to the manganese; (b) ionic complexes of the structure [(CO)(3)Mn(P-P)Z](+)BF(4)(-) where Z represents various neutral molecules possessing one phosphorous, nitrogen, or oxygen atom coordinated to the manganese; (c) complexes of the structure (CO)(3)Mn(pn)Z where the chelating pn represents 1,1-diphenylphosphino-2,2-dimethylaminoethane, Ph(2)PCH(2)CH(2)NMe(2). All of these complexes show three carbonyl stretching modes (2A' + A"). The effects on the frequencies of these modes induced by both the various Z groups and the various ligands are discussed. Theoretical calculations (B3LYP/6-31G) with optimization of the full molecule make it possible to distinguish between the three stretching modes and to make unambiguous assignments of appropriate symmetry species to each.     

ZEKE spectroscopy and theoretical calculations of copper-methylamine complexes

The copper-monomethylamine and -dimethylamine complexes were produced in a supersonic jet and examined using single-photon zero kinetic energy (ZEKE) photoelectron spectroscopy and theoretical calculations. The adiabatic ionization potentials (I.P.) of the complexes and vibrational frequencies of the corresponding ions were measured from their ZEKE spectra. The equilibrium geometries, binding energies, and vibrational frequencies of the neutral and ionized complexes were obtained from MP2 and B3LYP calculations. The observed vibrational frequencies of the ionic complexes were well-reproduced by both calculations, whereas the Franck-Condon intensity patterns of the spectra were simulated better by MP2 than B3LYP. The observed I.P. and vibrational frequencies of the Cu-NH(n)(CH3)(3-n) (n = 0-3) complexes were compared, and methyl substitution effects on their ZEKE spectra were discussed.     

Structure and vibrational assignment of the enol form of 1,1,1-trifluoro-2,4-pentanedione

Molecular structure of 1,1,1-trifluoro-pentane-2,4-dione, known as trifluoro-acetylacetone (TFAA), has been investigated by means of Density Functional Theory (DFT) calculations and the results were compared with those of acetylacetone (AA) and hexafluoro-acetylacetone (HFAA). The harmonic vibrational frequencies of both stable cis-enol forms were calculated at B3LYP level of theory using 6-31G** and 6-311++G** basis sets. We also calculated the anharmonic frequencies at B3LYP/6-31G** level of theory for both stable cis-enol isomers. The calculated frequencies, Raman and IR intensities, and depolarization ratios were compared with the experimental results. The energy difference between the two stable cis-enol forms, calculated at B3LYP/6-311++G**, is only 5.89 kJ/mol. The observed vibrational frequencies and Raman and IR intensities are in excellent agreement with the corresponding values calculated for the most stable conformation, 2TFAA. According to the theoretical calculations, the hydrogen bond strength for the most stable conformer is 57 kJ/mol, about 9.5kJ/mol less than that of AA and about 14.5 kJ/mol more than that of HFAA. These hydrogen bond strengths are consistent with the frequency shifts for OH/OD stretching and OH/OD out-of-plane bending modes upon substitution of CH(3) groups with CF(3) groups. By comparing the vibrational spectra of both theoretical and experimental data, it was concluded that 2TFAA is the dominant isomer.     

Comparison between optimized geometries and vibrational frequencies calculated by the DFT methods for the Anderson-type heteropolyanion: hexamolybdoaluminate(III), [AlIII(OH)6Mo6O18]3-

Optimized geometries and vibrational frequencies were calculated for the hexamolybdoaluminate(III), [AlIII(OH)6Mo6O18]3-, Anderson-type heteropolyanion with the HF, B3LYP, B3PW91, B3P86 and B1LYP methods of theory using the LanL2DZ, SDD and combination of LanL2DZ with 6-31G (d, p) basis sets. The agreement between the optimized and experimental geometries was in the decreasing order: HF, B3P86, B3PW91, B1LYP and B3LYP. The calculated frequencies by the B3LYP have the smallest mean root mean square (RMS) error. The effect of the basis set on the calculated bond lengths and frequencies by the density functional calculations (DFT) methods was minor. The agreement between the previously reported IR and Raman spectra and the calculated values is, in general, good.     

Quantum chemical investigations and bonding analysis of iron complexes with mixed cyano and carbonyl ligands

The equilibrium structures and vibrational frequencies of the iron complexes [Fe(CN)(x)(CO)(y)](q) (x = 0-6 and y = 0-5) have been calculated at the BP86 level of theory. The nature of the Fe-CN and Fe-CO has been analyzed with an energy partitioning method. The calculated Fe-CO bond lengths are in good agreement with the results of X-ray structure analysis whereas the Fe-CN bonds are calculated somewhat longer than the experimental values. The theoretically predicted vibrational frequencies of the C-O stretching mode are always lower and the calculated CN(-) frequencies are higher than the observed fundamental modes. The results of the bonding analysis suggest that the Fe-CO binding interactions have approximately 55% electrostatic character and approximately 45% covalent character. There is a significant contribution of the pi orbital interaction to the Fe-CO covalent bonding which increases when the complexes become negatively charged. The strength of deltaE(pi) may even be larger than deltaE(sigma). The Fe-CN(-) bonds have much less pi character. The calculated binding energy of the Fe-CO pi-interactions correlates very well with the C-O stretching frequencies.     

Mid-infrared vibrational spectra of discrete acetone-ligated cerium hydroxide cations

Cerium(iii) hydroxy reactive sites are responsible for several important heterogeneous catalysis processes, and understanding the reaction chemistry of substrate molecules like CO, H(2)O, and CH(3)OH as they occur in heterogeneous media is a challenging task. We report here the first infrared spectra of model gas-phase cerium complexes and use the results as a benchmark to assist evaluation of the accuracy of ab initio calculations. Complexes containing [CeOH](2+) ligated by three- and four-acetone molecules were generated by electrospray ionization and characterized using wavelength-selective infrared multiple photon dissociation (IRMPD). The C[double bond, length as m-dash]O stretching frequency for the [CeOH(acetone)(4)](2+) species appeared at 1650 cm(-1) and was red-shifted by 90 cm(-1) compared to unligated acetone. The magnitude of this shift for the carbonyl frequency was even greater for the [CeOH(acetone)(3)](2+) complex: the IRMPD peak consisted of two dissociation channels, an initial elimination of acetone at 1635 cm(-1), and elimination of acetone concurrent with a charge separation producing [CeO(acetone)](+) at 1599 cm(-1), with the overall frequency centered at 1616 cm(-1). The increasing red shift observed as the number of acetone ligands decreases from four to three is consistent with transfer of more electron density per ligand in the less coordinated complexes. The lower frequency measured for the elimination/charge separation process is likely due to a combination of: (a) anharmonicity resulting from population of higher vibrational states, and (b) absorption by the initially formed photofragment [CeOH(acetone)(2)](2+). The C-C stretching frequency in the complexes is also influenced by coordination to the metal: it is blue-shifted compared to bare acetone, indicating a slight strengthening of the C-C bond in the complex, with the intensity of the absorption decreasing with decreasing ligation. Density functional theory (DFT) calculations using three different functionals (VWN, B3LYP, and PBE0) were used to predict the infrared spectra of the complexes. Calculated frequencies for the carbonyl stretch are within 40 cm(-1) of the IRMPD of the three-acetone complex measured using the single acetone loss, and within 60 cm(-1) of the measurement for the four-acetone complexes. The B3LYP functionals provided the best agreement with the measured spectra, with the VWN modestly lower and PBE0 modestly higher. The C-C stretching frequencies calculated using B3LYP are higher in energy than the measured values by approximately 30 cm(-1), and reproduce the observed trend which shows that the C-C stretching frequency decreases with increasing ligation. Agreement between C-C frequency and calculation was not as good using the VWN functional, but still within 70 cm(-1). The results provide an evaluation of changes in the acceptor properties of the metal center as ligands are added, and of the utility of DFT for modeling f-block coordination complexes.     

Substituent effects on benzdiyne: a density functional theory study

Density functional theory (DFT) studies were performed to investigate the effect of substituents on the properties of benzdiyne derivatives. Twelve substituted benzdiynes-C(6)X(2), where X = F, Cl, Br, Me, CF(3), CN, OH, NO(2), NH(2), OMe, NMe(2), and Ph-were considered along with the unsubstituted 1,4-benzdiyne. The structures, vibrational frequencies, and IR intensities of these benzdiynes were studied with a popular three-parameter hybrid density functional (B3LYP) combined with the split-valence 6-31G(d) basis set and Dunning's correlation-consistent polarized triple-zeta (cc-pVTZ) basis set. The relative stabilities of the substituted benzdiynes were studied with the help of reaction energies of isodesmic reactions, which showed that the electron-withdrawing groups destabilized the benzdiynes more than they did the corresponding benzenes, whereas the electron-donating groups stabilized the benzdiynes more than they did their benzene counterparts. Correlation analyses revealed that field/inductive effects played a more important role than did resonance effects. The changes in atomic charges and spin populations due to the substituents were also studied. The asymmetric nu(Ctbd1;C) stretching modes obtained were close to the 1500-cm(-)(1) mark. Reinvestigation of the experimental results supported these results; a weak IR band at 1486 cm(-)(1) was assigned to this asymmetric stretching mode in C(6)(CF(3))(2) F. Some other benzdiynes also had large IR intensity values for their asymmetric nu(Ctbd1;C) vibrational modes due to the coupling with other vibrational modes. Heats of formation for the substituted benzdiynes were obtained from the reaction energies calculated at the B3LYP/cc-pVTZ level of theory.