Theoretical studies on structures and spectroscopic properties of a series of novel cationic [trans-(C/N)2Ir(PH3)2]+ (C/N = ppy, bzq, ppz, dfppy)

The geometries, electronic structures, and spectroscopic properties of a series of novel cationic iridium(III) complexes [trans-(C/N)(2)Ir(PH(3))(2)]+ (C/N = 2-phenylpyridine, 1; benzoquinoline, 2; 1-phenylpytazolato, 3; 2-(4,6-difluorophenyl)pyridimato, 4) were investigated theoretically. The ground- and excited-state geometries were optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The optimized geometry structural parameters agree well with the corresponding experimental results. The unoccupied molecular orbitals are dominantly localized on the C/N ligand, while the occupied molecular orbitals are composed of Ir atom and C/N ligand. Under the time-dependent density functional theory (TDDFT) level with the polarized continuum model (PCM) model, the absorption and phosphorescence in acetonitrile (MeCN) media were calculated based on the optimized ground- and excited-state geometries, respectively. The calculated results showed that the lowest-lying absorptions at 364 nm (1), 389 nm (2), 317 nm (3), and 344 nm (4) are all attributed to a {[d(yz)(Ir) + pi(C/N)] --> [pi*(C/N)]} transition with metal-to-ligand and intraligand charge transfer (MLCT/ILCT) characters; moreover, the phosphorescence at 460 (1) and 442 nm (4) originates from the 3{[d(yz)(Ir) + pi(C/N)] [pi*(C/N)]} (3)MLCT/(3)ILCT excited state, while that at 505 (2) and 399 nm (3) can be described as originating from different types of (3)MLCT/(3)ILCT excited state (3){[d(xy)(Ir) + pi(C/N)] [pi*(C/N)]}. The calculated results also revealed that the absorption and emission transition character can be altered by adjusting the pi electron-withdrawing groups and, furthermore, suggested that the phosphorescent color can be tuned by changing the pi-conjugation effect of the C/N ligand.     

Theoretical studies on structures and spectroscopic properties of a series of novel mixed-ligand Ir(III) complexes [Ir(Mebib)(ppy)X

The series of novel mixed-ligand iridium(III) complexes Ir(Mebib)(ppy)X (Mebib = bis(N-methylbenzimidazolyl)benzene and ppy = phenylpyridine; X = Cl, 1; X = -C[triple band]CH, 2; X = CN, 3) have been investigated theoretically to explore their electronic structures and spectroscopic properties. The ground and excited state geometries have been fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The optimized geometry structural parameters agree well with the corresponding experimental results. The HOMO of 1 and 3 are mainly localized on the Ir atom, Mebib, and ppy ligand, but that of 2 has significant X ligand composition. Absorptions and phosphorescences in CH2 Cl2 media have been calculated using the TD-DFT level of theory with the PCM model based on the optimized ground and excited state geometries, respectively. The lowest lying absorptions of 1 and 3 at 444 and 416 nm are attributed to a {[d(yz)(Ir) + pi(Mebib) + pi(ppy)] --> [pi*(Mebib)]} transition with metal-to-ligand, ligand-to-ligand, and intra-ligand charge transfer (MLCT/LLCT/ILCT) character, whereas that of 2 at 458 nm is related to a {[d(yz)(Ir) + pi(Mebib) + pi(ppy) + pi(C[triple band]CH)] --> [pi*(Mebib)]} transition with MLCT/LLCT/ILCT and X ligand-to-ligand charge transfer (XLCT) transition character. The phosphorescence of 1 and 3 at 565 and 543 nm originates from the 3{[dy(yz)(Ir) + pi(Mebib) + pi(ppy)] [pi*(Mebib)]} excited state, while that of 2 at 576 nm originates from the 3{[d(yz)(Ir) + pi(Mebib) + pi(ppy) + pi(C[triple band]CH)] [pi*(Mebib)]} excited state. The calculation results show that the absorption and emission transition character can be changed by altering the pi electron-withdrawing ability of the X ligand and the phosphorescent color can be tuned by adjusting the X ligand.     

Excited-state interactions for [Au(CN)(2)(-)](n) and [Ag(CN)(2)(-)](n) oligomers in solution. Formation of luminescent gold-gold bonded excimers and exciplexes.

Solutions of K[Au(CN)(2)] and K[Ag(CN)(2)] in water and methanol exhibit strong photoluminescence. Aqueous solutions of K[Au(CN)(2)] at ambient temperature exhibit luminescence at concentration levels of > or =10(-2) M, while frozen methanol glasses (77 K) exhibit strong luminescence with concentrations as low as 10(-5) M. The corresponding concentration limits for K[Ag(CN)(2)] solutions are 10(-1) M at ambient temperature and 10(-4) M at 77 K. Systematic variations in concentration, solvent, temperature, and excitation wavelength tune the luminescence energy of both K[Au(CN)(2)] and K[Ag(CN)(2)] solutions by >15 x 10(3) cm(-1) in the UV-visible region. The luminescence bands have been individually assigned to *[Au(CN)(2)(-)](n) and *[Ag(CN)(2)(-)](n) excimers and exciplexes that differ in "n" and geometry. The luminescence of Au(I) compounds is related for the first time to Au-Au bonded excimers and exciplexes similar to those reported earlier for Ag(I) compounds. Fully optimized unrestricted open-shell MP2 calculations for the lowest-energy triplet excited state of staggered [Au(CN)(2)(-)](2) show the formation of a Au-Au sigma single bond (2.66 A) in the triplet excimer, compared to a weaker ground-state aurophilic bond (2.96 A). The corresponding frequency calculations revealed Au-Au Raman-active stretching frequencies at 89.8 and 165.7 cm(-1) associated with the ground state and lowest triplet excited state, respectively. The experimental evidence of the exciplex assignment includes the extremely large Stokes shifts and the structureless feature of the luminescence bands, which suggest very distorted excited states. Extended Hückel (EH) calculations for [M(CN)(2)(-)](n) and *[M(CN)(2)(-)](n) models (M = Au, Ag; n = 2, 3) indicate the formation of M-M bonds in the first excited electronic states. From the average EH values for staggered dimers and trimers, the excited-state Au-Au and Ag-Ag bond energies are predicted to be 104 and 112 kJ/mol, respectively. The corresponding bond energies in the ground state are 32 and 25 kJ/mol, respectively.     

An ab initio study on luminescent properties and aurophilic attraction of binuclear gold(I) complexes with phosphinothioether ligands

Electronic structures and spectroscopic properties of the binuclear head-to-tail [Au(2)(PH(2)CH(2)SH)(2)](2+) (1) complex were investigated by ab initio calculations. The solvent effect of the complex in the acetonitrile solution was taken into account by the weakly solvated [Au(2)(PH(2)CH(2)SH)(2)](2+).(MeCN)(2) (2) moiety in the calculations. The ground-state geometries of 1 and 2 were fully optimized by the MP2 method, while their excited-state structures were optimized by the CIS method. Aurophilic attraction apparently exists between the two Au(I) atoms in the ground state and is strongly enhanced in the excited state. A high-energy phosphorescent emission was calculated at 337 nm for 1 in the absence of the interactions with solvent molecules and/or counteranion in solid state; however the lowest-energy emission of 2 was obtained at 614 nm with the nature of (3)A(u)(s(sigma)) --> (1)A(g)(d(sigma)) (metal-centered, MC) transition. The coordination of acetonitrile to the gold atom in solution results in a dramatic red shift of emission wavelength. The investigations on the head-to-tail [Au(2)(PH(2)CH(2)SCH(3))(2)](2+) (5) and [Au(2)(PH(2)CH(2)SCH(3))(2)](2+).(MeCN)(2) (6) moieties indicate that the CH(3) substituent on the S atom causes blue shifts of emission wavelength for 5 and 6 with respect to 1 and 2. By comparison between Au(I) thioether 1 and head-to-tail Au(I) thiolate [Au(2)(PH(2)CH(2)S)(2)] (7), it is concluded that the S-->Au dative bonding results in evidently different transition characteristics from the S-Au covalent bonding in the Au(I) thioether/thiolate complexes.     

Protonation reactions of dinuclear pyrazolato iridium(I) complexes

The complex [[Ir(mu-Pz)(CNBu(t))(2)](2)] (1) undergoes double protonation reactions with HCl and with HO(2)CCF(3) to give the neutral dihydride complexes [[Ir(mu-Pz)(H)(X)(CNBu(t))(2)](2)] (X = Cl, eta(1)-O(2)CCF(3)), in which the hydride ligands were located trans to the X groups and in the boat of the complexes, both in the solid state and in solution. The complex [[Ir(mu-Pz)(H)(Cl)(CNBu(t))(2)](2)] evolves in solution to the cationic complex [[Ir(mu-Pz)(H)(CNBu(t))(2)](2)(mu-Cl)]Cl. Removal of the anionic chloride by reaction with methyltriflate allows the isolation of the triflate salt [[Ir(mu-Pz)(H)(CNBu(t))(2)](2)(mu-Cl)]OTf. This complex undergoes a metathesis reaction of hydride by chloride in CDCl(3) under exposure to the direct sunlight to give the complex [[Ir(mu-Pz)(Cl)(CNBu(t))(2)](2)(mu-Cl)]OTf. Protonation of both metal centers in [[Ir(mu-Pz)(CO)(2)](2)] with HCl occurs at low temperature, but eventually the mononuclear compound [IrCl(HPz)(CO)(2)] is isolated. The related complex [[Ir(mu-Pz)(CO)(P[OPh](3))](2)] reacts with HCl and with HO(2)CCF(3) to give the neutral Ir(III)/Ir(III) complexes [[Ir(mu-Pz)(H)(X)(CO)(P[OPh](3))](2)], respectively. Both reactions were found to take place stepwise, allowing the isolation of the intermediate monohydrides. They are of different natures, i.e., the metal-metal-bonded Ir(II)/Ir(II) compound [(P[OPh](3))(CO)(Cl)Ir(mu-Pz)(2)Ir(H)(CO)(P[OPh](3))] and the mixed-valence Ir(I)/Ir(III) complex [(P[OPh](3))(CO)Ir(mu-Pz)(2)Ir(H)(eta(1)-O(2)CCF(3))(CO)(P[OPh](3))].     

Mechanism of Ir(ppy)2(N--N)+ (N--N = 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline) sensor for F-, CF3COOH, and CH3COO-: density functional theory and time-dependent density functional theory studies

The geometries, electronic structures, and spectroscopic properties of Ir(ppy)2(N--N)(+) (1) (N--N = 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline, ppy = 2-phenylpyridine), Ir(ppy)2(N--N)(+) x F(-) (2), Ir(ppy)2(N--N)(+) x CF3COOH (3/3a), and Ir(ppy)2(N--N)(+) x CH3COO(-) (4) were investigated theoretically. The ground and the excited state geometries of 1-4 were optimized at the B3LYP/LANL2DZ and UB3LYP/LANL2DZ levels, respectively. The optimized geometries agree well with the corresponding experimental results. The HOMOs of 1-4 and 3a are composed of pi(ppy) and d(Ir), and the LUMOs of 1, 2, 3a, and 4 are contributed by pi*(N--N), whereas the LUMO of 3 is composed of pi*(N--N) and pi*(CF3COOH). Under the time-dependent density functional theory level with polarized continuum model model, the absorption and phosphorescence in CH2Cl2 media were calculated on the basis of the optimized ground and excited state geometries, respectively. The lowest-lying absorptions of 1 (412 nm) and 3/3a (409/419 nm) have MLCT/LLCT transition characters, and those of 2 (448 nm) and 4 (427 nm) are contributed by ILCT character. The calculated lowest-energy triplet excited states responsible for phosphorescence of 1 (519 nm) and 3/3a (661/702 nm) have mixing (3)MLCT/(3)LLCT/(3)ILCT characters, but those of 2 and 4 only have (3)ILCT but without (3)MLCT character, which is the reason for the no-emissive character of 2 and 4. Moreover, the phosphorescence character of 3 is hardly changed by different addition sites of CF3COOH group (3a). The calculated results also showed that complex 1 is more suitable for an F(-) sensor than for CF3COOH and CH3COO(-) sensors.     

Valence-Dependent Metal-Metal Bonding and Optical Spectra in Confacial Bioctahedral [Re(2)Cl(9)](z)()(-) (z = 1, 2, 3). Crystallographic and Computational Characterization of [Re(2)Cl(9)](-) and [Re(2)Cl(9)](2)(-)

The geometric structure of the confacial bioctahedral [Re(2)Cl(9)](z)()(-) anion has been determined by single-crystal X-ray diffraction in two distinct oxidation states, Re(IV)(2) and Re(III)Re(IV). [Bu(4)N][Re(2)Cl(9)] crystallizes in the monoclinic space group P2(1)/m [a/? = 10.6363(3), b/? = 11.420(1), c/? = 13.612(1), beta/deg = 111.18(1), Z = 2], while [Et(4)N](2)[Re(2)Cl(9)] crystallizes in the orthorhombic space group Pnma [a/? = 15.82(1), b/? = 8.55(2), c/? = 22.52(3), Z = 4]. The Re-Re separation contracts from 2.704(1) ? in [Bu(4)N][Re(2)Cl(9)] to 2.473(4) ? in [Et(4)N](2)[Re(2)Cl(9)] (or, equivalently, from 2.725 to 2.481 ? after standard corrections for thermal motions), while the formal metal-metal bond order falls from 3.0 to 2.5. SCF-Xalpha-SW molecular orbital calculations show that, despite the {d(3)d(3)} configuration, the single sigma bond in [Re(2)Cl(9)](-) dominates the observed structural properties. For [Re(2)Cl(9)](2)(-), the 0.23 ? contraction in Re-Re is attributed jointly to radial expansion of the Re 5d orbitals and to diminished metal-metal electrostatic repulsion, which act in concert to make both sigma and delta(pi) bonding more important in the reduced species. Computed transition energies and oscillator strengths for the two structurally defined anions permit rational analysis of their ultraviolet spectra, which involve both sigma --> sigma and halide-to-metal change-transfer absorptions. The intense sigma --> sigma band progresses from 31 000 cm(-)(1) in [Re(2)Cl(9)](-) to 36 400 cm(-)(1) in [Re(2)Cl(9)](2)(-), according to the present assignments. For electrogenerated, highly reactive [Re(2)Cl(9)](3)(-) (where conventional X-ray structural information is unlikely to become available), the dominant absorption band advances to 40 000 cm(-)(1), suggesting further strengthening of the metal-metal sigma bond in the Re(III)(2) species.     

Colorless, non-luminescent; colorless, luminescent; and yellow, luminescent crystals of the cation [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](+). The roles of anions and hydrogen bonding in determining the aggregation of two-coordinate gold(I) cations

Crystallographic and luminescence studies on salts of the two-coordinate carbene cation, [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](+), demonstrate the ability of the cation to exist in three different states of aggregation. In colorless, non-luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]Cl the cation crystallizes as a monomer with the nearest gold(i) center 6.7890(11) A away. Colorless, luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]AsF(6) forms dimers with an AuAu separation of 3.1288(4) A. These dimers form weakly associated extended chains of cations with additional AuAu separations of 3.6625(5) A. [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]PF(6) is isostructural. Yellow, luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](3)(AsF(6))(2)Cl.0.5(H(2)O)(2) and [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](3)(PF(6))(2)Cl.0.5(H(2)O)(2) form trimers that further aggregate into extended chains with rather short AuAu separations of 3.1301(14) A, 3.1569(14) A and 3.1415(14) A. Absorption, emission and excitation spectra are reported for these salts. The excitation and emission results from the interactions between the gold centers and involves transitions between the filled d(z)((2)) band and the empty p(z) bands with the z axis pointing along the chain of cations.     

Electronic structures and spectroscopic properties of nitrido-osmium(VI) complexes with acetylide ligands [OsN(C[Triple Bond]CR)4]- R=H, CH3, and Ph by density functional theory calculation

Electronic structures and spectroscopic properties of a series of nitrido-osmium (VI) complex ions with acetylide ligands, [OsN(C[Triple Bond]CR)(4)](-) (R[Double Bond]H, (1), CH(3) (2), and Ph (3)) were investigated theoretically. The structures of the complexes were fully optimized at the B3LYP and CIS level for the ground states and excited states, respectively. The calculated bond lengths of Os[Triple Bond]N (1.639 A in 1, 1.642 A in 2, and 1.643 A in 3) and Os-C (2.040 A in 1, 2.043 A in 2, and 2.042 A in 3) in ground state agree well with the experimental results. The bond length of Os[Triple Bond]N bond is lengthened by ca. 0.13 A in the A (3)B(2) excited state compared to the (1)A(1) ground state, which is consistent with the lower vibration frequency of nu(Os-N) ( approximately 780 cm(-1)) in the excited state than that ( approximately 1175 cm(-1)) in the ground state. Among the calculated dipole-allowed absorptions at lambda>250 nm, the intense absorption at 261 nm for 1, 266 nm for 2, and 300 nm for 3 were attributed to the (1)[pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], (1)[pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], and (1)[pi(C[Triple Bond]CPh)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh)], respectively. The lowest energy absorption at lambda(max)=393 nm for 1, 400 nm for 2, and 400 nm for 3 were assigned as (1)[d(xy)(Os)+pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], (1)[d(xy)(Os)+pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], and (1)[d(xy)(Os)+pi(C[Triple Bond]CPh)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh)], respectively. The calculated phosphorescence emission at lambda(max)=581 nm for 1, 588 nm for 2, and 609 nm for 3 were originated from (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C))(1)(d(xy)(Os)+pi(C[Triple Bond]C))(1)], (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C))(1)(d(xy)(Os)+pi(C[Triple Bond]C))(1)], and (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh))(1)(d(xy)(Os)+pi(C[Triple Bond]CPh))(1)] excited state, respectively.     

Luminescent nido-carborane-diphosphine anions [(PR2)2C2B9H10](-) (R = Ph, (i)Pr). Modification of their luminescence properties upon formation of three-coordinate gold(I) complexes

The free nido-diphosphine anions [(PR(2))(2)C(2)B(9)H(10)](-) (R = Ph, (i)Pr) show luminescence properties whereas the closo-diphosphines [(PR(2))(2)C(2)B(10)H(10)] do not. Four families of three-coordinate complexes of stoichiometry [Au[(PR(2))(2)C(2)B(10)H(10)]L]OTf (L = tertiary phosphine) and [Au[(PR(2))(2)C(2)B(9)H(10)]L] have been studied in order to analyze the influence of the closo- or nido-nature of the diphosphine, the monophosphine coordinated to gold and the substituent at the diphosphine on the luminescence of the complexes. Only the nido-derivatives show luminescence. The maxima of the emissions are shifted to lower energies than those of the corresponding free nido-diphosphines. When the substituent at the diphosphine is phenyl, a new emission appears, which has been assigned as arising from a metal to ligand charge transfer [Au-->pi(L)] excited state.     

Efficient blue-emitting Ir(III) complexes with phosphine carbanion-based ancillary ligand: a DFT study

We report a theoretical study on a series of heteroleptic cyclometalated Ir(III) complexes for OLED application. The geometries, electronic structures, and the lowest-lying singlet absorptions and triplet emissions of [(fppy)(2)Ir(III)(PPh(2)Np)] (1), and theoretically designed models [(fppy)(2)Ir(III)(PH(2)Np)] (2) and [(fppy)(2)Ir(III)Np](-)(3) were investigated with density functional theory (DFT)-based approaches, where, fppyH = 4-fluorophenyl-pyridine and NpH = naphthalene. The ground and excited states were, respectively, optimized at the M062X/LanL2DZ;6-31G* and CIS/LanL2DZ:6-31G* level of theory within CH(2)Cl(2) solution provided by PCM. The lowest absorptions and emissions were evaluated at M062X/Stuttgart;cc-pVTZ;cc-pVDZ level of theory. Though the lowest absorptions and emissions were all attributed as the ligand-based charge-transfer transition with slight metal-to-ligand charge-transfer transition character, the subtle differences in geometries and electronic structures result in the different quantum yields and versatile emission color. The newly designed molecular 3 is expected to be highly emissive in deep blue region.     

联吡啶Ir(Ⅲ)配合物电子结构及光谱性质的理论研究

采用密度泛函理论(DFT)对配合物Ir(ppy)2(N^N)+ [ppy=2-phenylpyrine, N^N=bpy= 2,2’-bipyridine(1); N^N=H2dcbpy=4.4’-dicarboxy-2,2’-bipyridine(2), N^N=Hcmbpy=4-carboxy-4’-methyl-2,2’-bipyridine(3)] 的基态和激发态几何构型进行优化, 通过TDDFT/B3LYP方法得到这些化合物在乙腈溶液中的吸收光谱和磷光发射光谱及其跃迁性质. 研究结果表明, 化合物1 (384 nm), 2(433 nm)和3 (413 nm) 最低的吸收谱被指认为MLCT/LLCT[dIr+π(ppy)→π*(N^N)]电荷跃迁. 化合物1(486 nm), 2(576 nm)和3 (567 nm)最低的磷光发射可以描述为[dIr+π(ppy)]→[π*(N^N)]跃迁. 这是由于联吡啶配体上吸电子基团的引入, 稳定了相应的空轨道, 导致了化合物2和3的吸收和发射光谱红移. 同时, 化合物非线性光学性质的计算结果表明, 三种化合物均具有较大的一阶超极化率(β), 联吡啶配体中吸电子基团的增加, 使得分子内电子转移增强, 导致一阶超极化率增大.     

The involvement of metal-to-CO charge transfer and ligand-field excited states in the spectroscopy and photochemistry of mixed-ligand metal carbonyls. A theoretical and spectroscopic study of [W(CO)(4)(1,2-ethylenediamine)] and [W(CO)(4)(N,N'-bis-alkyl-1,4-diazabutadiene)

A new interpretation of the electronic spectroscopy, photochemistry, and photophysics of group 6 metal cis-tetracarbonyls [M(CO)(4)L(2)] is proposed, that is based on an interplay between M --> L and M --> CO MLCT excited states. TD-DFT and resonance Raman spectroscopy show that the lowest allowed electronic transition of [W(CO)(4)(en)] (en = 1,2-ethylenediamine) has a W(CO(eq))(2) --> CO(ax) charge-transfer character, whereby the electron density is transferred from the equatorial W(CO(eq))(2) moiety to pi orbitals of the axial CO ligands, with a net decrease of electron density on the W atom. The lowest, emissive excited state of [W(CO)(4)(en)] was identified as a spin-triplet W(CO(eq))(2) --> CO(ax) CT excited state both computationally and by picosecond time-resolved IR spectroscopy. This state undergoes 1.5 ps vibrational relaxation/solvation and decays to the ground state with a approximately 160 ps lifetime. The nu(CO) wavenumbers and IR intensity pattern calculated by DFT for the triplet W(CO(eq))(2) --> CO(ax) CT excited state match well the experimental time-resolved spectrum. For [W(CO)(4)(R-DAB)] (R-DAB = N,N'-bis-alkyl-1,4-diazabutadiene), the W(CO(eq))(2) --> CO(ax) CT transition follows in energy the W --> DAB MLCT transition, and the emissive W(CO(eq))(2) --> CO(ax) CT triplet state occurs just above the manifold of triplet W --> DAB MLCT states. No LF electronic transitions were calculated to occur in a relevant energetic range for either complex. Molecular orbitals of both complexes are highly delocalized. The 5d(W) character is distributed over many molecular orbitals, while neither of them contains a predominant metal-ligand sigma 5d(W) component, contrary to predictions of the traditional ligand-field approach. The important spectroscopic, photochemical, and photophysical roles of M(CO(eq))(2) --> CO(ax) CT excited states and the limited validity of ligand field arguments can be generalized to other mixed-ligand carbonyl complexes.     

Phosphorescence vs fluorescence in cyclometalated platinum(II) and iridium(III) complexes of (oligo)thienylpyridines

Two newly prepared oligothienylpyridines, 5-(2-pyridyl)-5'-dodecyl-2,2'-bithiophene, HL(2), and 5-(2-pyridyl)-5'-dodecyl-2,2':5',2'-ter-thiophene, HL(3), bind to platinum(II) and iridium(III) as N∧C-coordinating ligands, cyclometallating at position C(4) in the thiophene ring adjacent to the pyridine, leaving a chain of either one or two pendent thiophenes. The synthesis of complexes of the form [PtL(n)(acac)] and [Ir(L(n))(2)(acac)] (n = 2 or 3) is described. The absorption and luminescence properties of these four new complexes are compared with the behavior of the known complexes [PtL(1)(acac)] and [Ir(L(1))(2)(acac)] {HL(1) = 2-(2-thienyl)pyridine}, and the profound differences in behavior are interpreted with the aid of time-dependent density functional theory (TD-DFT) calculations. Whereas [PtL(1)(acac)] displays solely intense phosphorescence from a triplet state of mixed ππ*/MLCT character, the phosphorescence of [PtL(2)(acac)] and [PtL(3)(acac)] is weak, strongly red shifted, and accompanied by higher-energy fluorescence. TD-DFT reveals that this difference is probably due to the metal character in the lowest-energy excited states being strongly attenuated upon introduction of the additional thienyl rings, such that the spin-orbit coupling effect of the metal in promoting intersystem crossing is reduced. A similar pattern of behavior is observed for the iridium complexes, except that the changeover to dual emission is delayed to the terthiophene complex [Ir(L(3))(2)(acac)], reflecting the higher degree of metal character in the frontier orbitals of the iridium complexes than their platinum counterparts.     

Visible light induced photocleavage of DNA by a mixed-metal supramolecular complex: [[(bpy)(2)Ru(dpp)](2)RhCl2]5+

The mixed-metal supramolecular complex, [[(bpy)(2)Ru(dpp)](2)RhCl(2)](PF(6))(5) (bpy = 2,2'-bipyridine and dpp = 2,3-bis(2-pyridyl)pyrazine) coupling two ruthenium light absorbers (LAs) to a central rhodium, has been shown to photocleave DNA. This system possesses a lowest lying metal to metal charge transfer (MMCT) excited state in contrast to the metal to ligand charge transfer states (MLCT) of the bpm and Ir analogues. The systems with an MLCT excited state do not photocleavage DNA. [[(bpy)(2)Ru(dpp)](2)RhCl(2)](PF(6))(5) is the first supramolecular system shown to cleave DNA. It functions through an excited state previously unexplored for this reactivity, a Ru --> Rh MMCT excited state. This system functions when irradiated with low energy visible light with or without molecular oxygen.     

一类[Os(II)(CO)3(tfa)(L)](L=O^O,O^N,N^N)配合物的结构和光谱特征

采用密度泛函理论以及B3LYP方法和单激发组态相互作用(CIS)方法分别优化了一系列[Os(II)(CO)3(tfa)(L)](tfa为三氟乙酸; L=O^O(1), O^N(2), N^N(3), 其中O^O为六氟乙酰丙酮, O^N为羟基喹啉, N^N为3-(三氟甲基)-5-(2-吡啶基)吡唑)配合物的基态和激发态结构. 利用含时密度泛函理论(TD-DFT)结合极化连续溶剂化模型(PCM)计算了配合物在CH2Cl2溶液中的吸收和发射光谱. 研究结果表明, 优化得到的几何结构参数和相应的实验值符合得非常好, 激发态几何构型相对基态变化较小, 这与实验上观察到的较小的斯托克斯频移现象一致. 配合物1-3的最低能吸收分别在342、431和329 nm, 其磷光发射分别在521、638 和488 nm. 配合物1-3的最高占据分子轨道和最低空轨道主要表现为L配体的π和π*轨道特征, 所以它们的最低能吸收归属于π-π*电荷跃迁, 并混有少量的金属到配体的电荷跃迁(MLCT)和配体之间电荷跃迁(LLCT)微扰, 且其高能吸收也表现为配体内部(IL)和配体间(LL)的电荷跃迁. 此外, 它们的磷光发射和吸收有相似的跃迁特征.     

Effects of Pt...Pt bonding, anions, solvate molecules, and hydrogen bonding on the self-association of Chugaev's cation, a platinum complex with a chelating carbene ligand

Five salts, [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)](BPh(4)).CH(3)OH, [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)](PF(6)).CH(2)Cl(2), [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.4H(2)O, [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Br.3.5H(2)O, and [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.0.1H(2)O, have been crystallized and examined by single crystal X-ray diffraction. While the internal structure of the cation is similar in all salts, the interactions between cations vary in the different salts. Yellow [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)](BPh(4)).CH(3)OH and red [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)](PF(6)) form face-to-face dimers with Pt...Pt separations of 3.6617(6) and 3.340(2) A, respectively. In the latter, hydrogen bonding of the chelating ligand to adjacent anions facilitates the close approach of pairs of cations. The salts [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.4H(2)O, [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Br.3.5H(2)O, and [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.0.1H(2)O form columnar structures with Pt...Pt separations that range from 3.2514(5) to 3.5643(6) A. The water molecules and anions surround these columns and form bridges between neighboring columns. The electronic spectra of aqueous solutions of [(C(4)H(9)N(4))Pt(II)(CNCH(3))(2)]Cl.4H(2)O show spectral changes upon increasing concentrations of the platinum complex that are indicative of the formation of a dimer in solution with an equilibrium constant for dimerization of 23(1).     

Description of the ground-state covalencies of the bis(dithiolato) transition-metal complexes from X-ray absorption spectroscopy and time-dependent density-functional calculations

The electronic structures of [M(L(Bu))(2)](-) (L(Bu)=3,5-di-tert-butyl-1,2-benzenedithiol; M=Ni, Pd, Pt, Cu, Co, Au) complexes and their electrochemically generated oxidized and reduced forms have been investigated by using sulfur K-edge as well as metal K- and L-edge X-ray absorption spectroscopy. The electronic structure content of the sulfur K-edge spectra was determined through detailed comparison of experimental and theoretically calculated spectra. The calculations were based on a new simplified scheme based on quasi-relativistic time-dependent density functional theory (TD-DFT) and proved to be successful in the interpretation of the experimental data. It is shown that dithiolene ligands act as noninnocent ligands that are readily oxidized to the dithiosemiquinonate(-) forms. The extent of electron transfer strongly depends on the effective nuclear charge of the central metal, which in turn is influenced by its formal oxidation state, its position in the periodic table, and scalar relativistic effects for the heavier metals. Thus, the complexes [M(L(Bu))(2)](-) (M=Ni, Pd, Pt) and [Au(L(Bu))(2)] are best described as delocalized class III mixed-valence ligand radicals bound to low-spin d(8) central metal ions while [M(L(Bu))(2)](-) (M=Cu, Au) and [M(L(Bu))(2)](2-) (M=Ni, Pd, Pt) contain completely reduced dithiolato(2-) ligands. The case of [Co(L(Bu))(2)](-) remains ambiguous. On the methodological side, the calculation led to the new result that the transition dipole moment integral is noticeably different for S(1s)-->valence-pi versus S(1s)-->valence-sigma transitions, which is explained on the basis of the differences in radial distortion that accompany chemical bond formation. This is of importance in determining experimental covalencies for complexes with highly covalent metal-sulfur bonds from ligand K-edge absorption spectroscopy.     

Theoretical studies on Ru(fppz)2(CO)L (L = N-heterocyclic ligand): Electronic structure, absorption, phosphorescence, and solvatochromism

A series of ruthenium(II) complexes Ru(fppz)₂(CO)L [fppz = 3-trifluoromethyl-5(2-pyridyl)pyrazole; L = pyridine (1), 4-dimethylaminopyridine (2), 4-cyanopyridine (3)] were designed and investigated theoretically to explore their electronic structures, absorption, and emissions as well as the solvatochromism. The singlet ground state and triplet excited state geometries were fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ level, respectively. The HOMO of 1–3 is composed of d_yz(Ru) atom and π(fppz). The LUMO of 1 and 2 is dominantly contributed by π*(fppz) orbital, but that of 3 is contribute by π*(L). Absorption and phosphorescence in vacuo, C₆H₁₂, and CH₃CN media were calculated using the TD-DFT level of theory with the PCM model based on the optimized ground and excited state geometries, respectively. The lowest-lying absorption of 1 and 2 at 387 and 391 nm is attributed to {[d_yz(Ru) + π(fppz)] → [π*(fppz)]} transition, but that of 3 at 479 nm is assigned to {[d_yz(Ru) + π(fppz)] → [π*(L)]} transition. The phosphorescence of 1 and 2 at 436 and 438 nm originates from ³{[d_yz(Ru) + π(fppz)] [π*(fppz)]} excited state, while that of 3 at 606 nm is from ³{[d_yz(Ru) + π(fppz)] [π*(L)]} excited state. The calculation results showed that the absorption and emission transition character can be changed from MLCT/ILCT to MLCT/LLCT transition by altering the substituent on the L ligand. The phosphorescence of 1 and 2 does not have solvatochromism, but that of 3 at 606 nm (vacuo), 584 nm (C₆H₁₂), and 541 nm (CH₃CN) is strongly dependent on the solvent polarity, so introducing electron-withdrawing group on ligand L will induce remarkable solvatochromism.