Ab initioenergy‐adjusted pseudopotentials for the noble gases Ne through Xe: Calculation of atomic dipole and quadrupole polarizabilities

Structure and ultrafast dynamics of the charge-transfer excited state and redox activity of the ground state of mono- and binuclear platinum(II) diimine catecholate and bis-catecholate complexes: a transient absorption, TRIR, DFT, and electrochemical study

A series of mononuclear complexes of the type [Pt(Bu(2)cat)(4,4'-R(2)-bipy)] [where Bu(2)cat is the dianion of 3,5-(t)Bu(2)-catechol and R = H, (t)Bu, or C(O)NEt(2)] and analogous dinuclear complexes based on the "back-to-back" bis-catechol ligand 3,3',4,4'-tetrahydroxybiphenyl have been studied in detail in both their ground and excited states by a range of physical methods including electrochemistry, UV/vis/near-IR, IR, and electron paramagnetic resonance spectroelectrochemistry, and time-resolved IR (TRIR) and transient absorption (TA) spectroscopy. Density functional theory calculations have been performed to support these studies, which provide a detailed picture of the ground- and excited-state electronic structures, and excited-state dynamics, of these complexes. Notable observations include the following: (i) for the first time, the lowest-energy catecholate → bipyridine (bpy) ligand-to-ligand charge-transfer (LL'CT) excited states of these chromophores have been studied by TRIR spectroscopy, showing a range of transient bands associated with the bpy radical anion and semiquinone species, and back-electron-transfer occurring in hundreds of picoseconds; (ii) strong electronic coupling between the two catecholate units in the bridging ligand of the dinuclear complexes results in a delocalized, planar (class 3) "mixed-valence" catecholate(2-)/semiquinone(•-) state formed by one-electron oxidation of the bridging ligand; (iii) in the LL'CT excited state of the dinuclear complexes, the bridging ligand is symmetrical and delocalized, whereas the bpy radical anion is localized at one terminus of the complex. This study is the first example of an investigation of excited-state behavior in platinum(II) catecholate complexes, performed with the use of picosecond TRIR and femtosecond TA spectroscopy.

Synthesis, characteristic and theoretical investigation of the structure, electronic properties and second-order nonlinearity of salicylaldehyde Schiff base and their derivatives

A series of asymmetric donor-acceptor substituted salen-type Schiff-bases have been synthesized and their structures, electronic properties and second order nonlinearities were investigated by DFT methods. In order to verify the stable of these Schiff-base derivates, the IR spectrum of these Schiff-base derivates were calculated, the result showed that these compounds are stable. The results of TD-DFT calculation indicate that the derivatives with the electron-donating group (CH3, OCH3 or N(C2H5)2) have a red shift absorption compared to derivatives with the electron-withdrawing group (NO2). The analysis of MOS indicates that the CN group has contribution to the LUMO orbital while the groups of OCH3, N(C2H5)2 and NO2 have contribution to the HOMO orbital. OCH3, N(C2H5)2 as electron rich groups, made the derivates have a larger first static hyperpolarizability. However, the compound (II) with a NO2 substituent, also has a large first static hyperpolarizability. This is probably because of the special transition model, namely the values of two oscillator strength f (fHOMO-1-LUMO=0.405, fHOMO-LUMO=0.321) are almost equal. In order to understand the influence of the energy gap (ΔE) between the HOMO and the LUMO orbitals on the first static hyperpolarizability, we calculated the energy gap (ΔE) of all Schiff-base compounds. The results show that the smaller the HOMO-LUMO energy gap is, the larger the first static hyperpolarizability is.

Interaction and Electron Density Properties of MKr42+ (M=Cu, Ag and Au): ab initio Calculation

Quantum chemical calculations of the structures and stabilities of the MKr42+ series at the CCSD(T) theoretical level have been performed. The role of the interaction was investigated using the natural bond orbital (NBO), Laplacian, electron density deformation, electron localization function and reduced density gradient analysis. The results show that a covalent contribution occurs in the Kr-M2+ bonding.

Cationic noble gas hydrides: a theoretical investigation of dinuclear HNgFNgH+ (Ng = He-Xe)

Theoretical calculations at the B3LYP, MP2, and CCSD(T) levels of theory disclose the conceivable existence of cationic noble gas hydrides containing two Ng atoms. These species have a general formula of HNgFNgH(+) (Ng = He-Xe), and are the cationic counterparts of the neutral HNgF. The optimized geometries, harmonic frequencies, and bonding properties point to ion-dipole complexes between a fluoride anion and two covalent H-Ng(+) cations, best formulated as (H-Ng(+))(2)F(-). The HXeFXeH(+) is also isoelectronic with the recently experimentally observed HXeOXeH (Khriachtchev et al. J. Am. Chem. Soc. 2008, 130, 6114-6118). The resulting HNgFNgH(+) are thermochemically stable with respect to dissociation into HNg(+) + HNgF and HNg(+) + H + Ng + F, but are largely unstable with respect to both the loss of HF (with formation of HNg(+) + Ng) and H(2)F(+) (with formation of two Ng atoms). These decompositions pass through bent transition structures, and only the heaviest HArFArH(+), HKrFKrH(+), and HXeFXeH(+) are protected by energy barriers large enough (ca. 10-15 kcal mol(-1)) to support their conceivable metastability. In line with other series of noble gas compounds, the neon cation HNeFNeH(+) is the least stable among the various HNgFNgH(+).

Structure of the complex of [Ru(tpm)(dppz)py](2+) with a B-DNA oligonucleotide - a single-substituent binding switch for a metallo-intercalator

We report the synthesis of three new complexes related to the achiral [Ru(tpm)(dppz)py](2+) cation (tpm=tripyridazole methane, dppz=dipyrido[3,2-a:2',3'-c]phenazine, py=pyridine) that contain an additional single functional group on the monodentate ancillary pyridyl ligand. Computational calculations indicate that the coordinated pyridyl rings are in a fixed orientation parallel to the dppz axis, and that the electrostatic properties of the complexes are very similar. DNA binding studies on the new complexes reveal that the nature and positioning of the functional group has a profound effect on the binding mode and affinity of these complexes. To explore the molecular and structural basis of these effects, circular dichroism and NMR studies on [Ru(tpm)(dppz)py]Cl(2) with the octanucleotides d(AGAGCTCT)(2) and d(CGAGCTCG)(2), were carried out. These studies demonstrate that the dppz ligand intercalates into the G(2)-A(3) step, with {Ru(tpm)py} in the minor groove. They also reveal that the complex intercalates into the binding site in two possible orientations with the pyridyl ligand of the major conformer making close contact with terminal base pairs. We conclude that substitution at the 2- or 3-position of the pyridine ring has little effect on binding, but that substitution at the 4-position drastically disrupts intercalative binding, particularly with a 4-amino substituent, because of steric and electronic interactions with the DNA. These results indicate that complexes derived from these systems have the potential to function as sequence-specific light-switch systems.

Photophysical properties and singlet oxygen production by ruthenium(II) complexes of benzo[i]dipyrido[3,2-a:2',3'-c]phenazine: spectroscopic and TD-DFT study

The photophysical properties of a series of Ru(II) complexes containing benzo[i]dipyrido[3,2-a:2',3'-c]phenazine (dppn) as a ligand are reported. Transient absorption spectroscopy studies indicate that, in contrast to related Ru(dppz) complexes (dppz = dipyrido[3,2-a:2',3'-c]phenazine), the excited state of all the dppn systems is a long-lived pipi* triplet state. Computational studies (DFT and TD-DFT) confirm that the excited state is based on the dppn ligand. Near-infrared luminescence studies reveal that the complexes are efficient singlet oxygen sensitizers with yields of 70-83%.

Theoretical Investigation on Structures and Stabilities of CuXenZ (n = 1 - 3, Z = - 1, 0, +1) Clusters

The structures and stabilities of CuXe n Z (n = 1–3, Z = –1, 0, +1) cluster series at the CCSD(T) theoretical level have been investigated. Herein, it is shown that the cations are more stable and have more compact geometries than the anions and neutrals. The role of the interaction is explained using the natural bond orbital, population, and electron density analysis.

Toward improved density functionals for the correlation energy

Eleven density functionals, including some of the most widely used ones, are tested on their ability to predict nonrelativistic, electron correlation energies for the 17 atoms from He to Ar, the 17 cations from Li(+) to K(+), and 11 (1)S state atoms from Ca to Rn. They all lead to relatively poor predictions for the heavier atoms. Reparametrization of these functionals improves their performance for light atoms but does not alleviate their problems with the heavier, closed-shell atoms. Several novel, few-parameter, density functionals for the correlation energy are developed heuristically. Four new functionals lead to qualitatively improved predictions for the heavier atoms without unreasonably compromising accuracy for the lighter atoms. Further progress would be facilitated by reliable estimates of electron correlation energies for more atoms, particularly heavy ones.

Bis(cyclopentadienyl)dihydrido Mo and W complexes as Lewis bases — A computational study about their adducts with BX3(X = F, Cl) and Al(CH3)3

A computational investigation about the Lewis acid–base adducts between bases Cp2MH2(M = Mo, W) and acids BX3(X = F, Cl) and Al(CH3)3is presented. Density functional methods based on pure and hybrid correlation-exchange functionals and relativistic corrections based on the zero order relativistic approximation (ZORA) have been applied. A comparison with experimental data has been addressed to give insights about the nature of the acid–base interaction with the aim to evaluate the role of the transition metal in charge donation toward the acid centre. In this respect, the likelihood of proposed criteria for recognizing the presence of transition-metal direct charge donation has been discussed.

DFT studies on nonlinear optical properties of neutral nest-shaped heterothiometallic [MOS3Py5Cu3X] (M=Mo, W; X=F, Cl, Br, I) clusters

Theoretical calculations were carried out on some neutral nest-shaped heterothiometallic cluster compounds [MOS(3)Py(5)Cu(3)X] (M=Mo, W; X=F, Cl, Br, I) with the high first static hyperpolarizabilities beta values. The geometries of these cluster compounds were optimized by the restricted DFT method at B3LYP level with LanL2DZ base set without any constrains. In order to understand the relationship between the first static hyperpolarizabilities and the compositions of these clusters, the frontier orbital compositions and energy gaps between the HOMO and LUMO orbitals were calculated and analysed. In these clusters the HOMO orbitals are mainly composed of halogen atoms and the first static hyperpolarizability increases from F to I atom. The LUMO orbitals of clusters [MoOS(3)Py(5)Cu(3)X] are comprised of Mo, O and S atoms while the LUMO orbitals of clusters [WOS(3)Py(5)Cu(3)X] composed of W atom and pyridine ring. The energy gaps between the HOMO and LUMO orbitals of the clusters [MoOS(3)Py(5)Cu(3)X] are smaller than those of the clusters [WOS(3)Py(5)Cu(3)X]. As a result the first static hyperpolarizability values of the clusters [MoOS(3)Py(5)Cu(3)X] are higher than those of the clusters [WOS(3)Py(5)Cu(3)X].

Infrared spectra of SF6(-) x HCOOH x Ar(n) (n = 0-2): infrared triggered reaction and Ar-induced reactive inhibition

We present the infrared spectra of SF(6)(-) x HCOOH x Ar(m) (m=0-2) complexes. We find that the binding motif involves a single hydrogen bond between the SF(6)(-) anion and the OH group of the formic acid, with the CH group weakly tethered to a neighboring F atom. Similar to the case of hydrated SF(6)(-), the SF bond involved in the (OH-F) bond is significantly stretched and weakened by the attachment of the HCOOH ligand. The bare complex undergoes reaction upon infrared absorption in the CH/OH stretching region of the formic acid moiety, leading predominantly to the formation of SF(4)(-) + 2HF + CO(2). The reaction can be inhibited by attachment of two Ar atoms. We discuss a likely reaction mechanism in the framework of ab initio calculations, suggesting that reaction proceeds via tunneling through the potential barrier.

Theoretical Investigation of Square-Planar MXe42+ (M = Cu, Ag, Au) Cations

The structures, stabilities, and bonding mechanism of the square-planar doubly charged MXe42+ (M = Cu, Ag, Au) cations have been investigated at the UB3LYP and UMP2 theoretical levels. At the best theoretical estimate, the M–Xe bond lengths are calculated to be 266.2, 273.6, and 273.8 pm, and the corresponding binding energies with respect to M2+ and four xenon atoms are 771.49, 820.57, and 908.47 kJ mol–1, respectively, along the series Cu – Ag – Au. Owing to an unusually high relativistic effect, gold evidently tends to be strongly bonded to the noble gas atoms in comparison with copper and silver. The electrostatic interactions play an important role in divalent noble-gas–noble-metal bonding. Apart from CuXe42+, the square-planar MXe42+ cations are stable enough to be prepared in experiments.