Ultrafast excited state dynamics of Pt(II) chromophores bearing multiple infrared absorbers

The paper reports the synthesis, structural characterization, electrochemistry, ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopy associated with two independent d (8) square planar Pt(II) diimine chromophores, Pt(dnpebpy)Cl 2 ( 1) and Pt(dnpebpy)(C[triple bond]Cnaph) 2 ( 2), where dnpebpy = 4,4'-(CO 2CH 2- (t) Bu) 2-2,2'-bipyridine and CCnaph = naphthylacetylide. The neopentyl ester substitutions provided markedly improved complex solubility relative to the corresponding ethyl ester which facilitates synthetic elaboration as well as spectroscopic investigations. Following 400 nm pulsed laser excitation in CH 2Cl 2, the 23 cm (-1) red shift in the nu C=O vibrations in 1 are representative of a complex displaying a lowest charge-transfer-to-diimine (CT) excited state. The decay kinetics in 1 are composed of two time constants assigned to vibrational cooling of the (3)CT excited-state concomitant with its decay to the ground state (tau = 2.2 +/- 0.4 ps), and to cooling of the formed vibrationally hot ground electronic state (tau = 15.5 +/- 4.0 ps); we note that an assignment of the latter to a ligand field state cannot be excluded. Ultrafast TA data quantitatively support these assignments yielding an excited-state lifetime of 2.7 +/- 0.4 ps for the (3)CT excited-state of 1 and could not detect any longer-lived species. The primary intention of this study was to develop a Pt (II) complex ( 2) bearing dual infrared spectroscopic tags (C[triple bond]C attached to the metal and CO (ester) attached to the diimine ligand) to independently track the movement of charge density in different segments of the molecule following pulsed light excitation. Femtosecond laser excitation of 2 in CH 2Cl 2 at 400 nm simultaneously induces a red-shift in both the nu C=O (-30 cm (-1)) and the nu C[triple bond]C (-61 cm (-1)) vibrations. The TRIR data in 2 are consistent with a charge transfer assignment, and the significant decrease of the energy of the nu C[triple bond]C vibration suggests a considerable contribution from the acetylide ligands in the highest occupied molecular orbital. Therefore, we assign the lowest energy optical transitions in 2 as a combination of metal-to-ligand and ligand-to-ligand charge transfers. The excited-state of 2 is emissive at RT, with an emission maximum at 715 nm, quantum yield of 0.0012, and lifetime of 23 ns.     

Formation and characterization of carbon monoxide adducts of iron "twin coronet" porphyrins. Extremely low CO affinity and a strong negative polar effect on bound CO

The carbon monoxide (CO) adducts of iron "twin coronet" porphyrins (TCPs) are characterized by UV-vis, resonance Raman (RR), IR, and 13C NMR spectroscopies. A superstructured porphyrin, designated as TCP, was used as a common framework for the four different types of iron complexes. TCP bears two binaphthalene bridges on each side and creates two hydrophobic pockets surrounded by the bulky aromatic rings. In the CO-binding cavities, the hydroxyl groups are oriented toward the center above the heme. The iron complexes investigated are as follows: TCP (which is without a covalently linked axial ligand), TCP-PY (which has a linked pyridine ligand), and TCP-TB and TCP-TG (both of which have a linked thiolate ligand). These complexes were synthesized as ferric forms and identified by the various spectroscopic methods. The UV-vis spectra of TCP-CO and TCP-PY-CO exhibit lambda(max) at 432, 546 and 428, 541 nm, respectively. On the other hand, the CO adducts of TCP-TB and TCP-TG show typical hyperporphyrin spectra for a thiolate-ligated iron(II) porphyrin-CO complex. In the RR spectra, the nu(Fe-CO) bands were observed at 506, 489 cm(-1) (TCP), 465 cm(-1) (TCP-PY), 458, 437 cm(-1) (TCP-TG) and 429 cm(-1) (TCP-TB). Compared with the reported nu(Fe-CO) frequencies of hemoproteins and their model systems, these observed values are unusually low. Further, abnormally high nu(C-O) bands are observed at 1990 cm(-1) (TCP-CO) and 2008 cm(-1) (TCP-PY-CO) in IR spectra. The lower nu(Fe-CO) and the higher nu(C-O) frequencies can be ascribed to the strong negative polar effect caused by the vicinal hydroxyl groups in the cavity. This prediction is further supported by the observation of significant 13C shieldings exhibited by TCP-CO (delta = 202.6 ppm) and TCP-PY-CO (delta = 202.3 ppm), in comparison to hemoproteins and other heme models. The CO affinity of TCP-PY (P1/2CO = 0.017 Torr at 25 C) is unusually lower than other heme models. The unique behavior of these CO adducts is discussed in context of the TCP structures.     

The organometallic fac-[(CO)3Mn(H2O)3]+ aquaion: base-hydrolysis and kinetics of H2O-substitution

The novel organometallic aqua complex [(CO)(3)Mn(H(2)O)(3)](+) (1(+)) was obtained through hydrolysis of the analogous acetone complex. IR [nu(CO) = 2051, 1944 cm(-)(1)] and (17)O NMR spectroscopy revealed the presence of a fac tricarbonyl unit. Potentiometric titrations established that the trimer [(CO)(3)Mn(3)(OH)(4)](-) was the principal condensation product in the pH range >6 prior to slow formation of the tetramer [[(CO)(3)Mn](OH)](4). Water exchange in 1(+), determined by NMR line broadening as k(ex) = 19 +/- 4 s(-)(1) at 298 K, is four orders faster than with the analogous Re complex. The activation volume DeltaV(++) = -4.5 +/- 0.4 cm(3) mol(-1) is indicative of an associatively activated (I(a)) process.     

Pi-acid/pi-base carbonyloxomolybdenum(IV) complexes and their oxomolybdenum(VI/IV) precursors

Brown TpiPrMoO(SR)(CO) (TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate; R = Et, iPr, Ph, p-tol, Bz) are formed when TpiPrMoO(SR)(NCMe) react with CO gas in toluene. The carbonyloxomolybdenum(IV) complexes exhibit nu(CO) and nu(Mo=O) IR bands at ca. 2025 and 935 cm(-1), respectively, and NMR spectra indicative of C(1) symmetry, with delta(C)(CO) ca. 250. The crystal structure of TpiPrMoO(SiPr)(CO), the first for a mononuclear carbonyloxomolybdenum complex, revealed a distorted octahedral geometry, with d(Mo=O) = 1.683(3) A, d(Mo-C) = 2.043(5) A, and angle(O=Mo-C) = 90.87(16) degrees . The blue-green acetonitrile precursors are generated by reacting cis-TpiPrMoO2(SR) with PPh3; they are unstable, display a single nu(Mo=O) IR band at ca. 950 cm(-1), and exhibit NMR spectra consistent with C1 symmetry. Red-brown cis-TpiPrMoO2(SR) (R = as above and tBu) are formed by metathesis of TpiPrMoO2Cl and HSR/NEt3 in dichloromethane. The complexes exhibit strong nu(MoO2) IR bands at ca. 925 and 895 cm(-1), and NMR spectra indicative of Cs symmetry; the isopropyl, p-tolyl, and benzyl derivatives possess distorted octahedral geometries, with d(Mo=O)(av) = 1.698 A and angle(MoO(2))(av) = 103.5 degrees.     

(NEt(4))(2)[Fe(CN)(2)(CO)('S(3)')]: an iron thiolate complex modeling the [Fe(CN)(2)(CO)(S-Cys)(2)] site of [NiFe] hydrogenase centers

In the search for complexes modeling the [Fe(CN)(2)(CO)(cysteinate)(2)] cores of the active centers of [NiFe] hydrogenases, the complex (NEt(4))(2)[Fe(CN)(2)(CO)('S(3)')] (4) was found ('S(3)'(2-)=bis(2-mercaptophenyl)sulfide(2-)). Starting complex for the synthesis of 4 was [Fe(CO)(2)('S(3)')](2) (1). Complex 1 formed from [Fe(CO)(3)(PhCH=CHCOMe)] and neutral 'S(3)'-H(2). Reactions of 1 with PCy(3) or DPPE (1,2-bis(diphenylphosphino)ethane) yielded diastereoselectively [Fe(CO)(2)(PCy(3))('S(3)')] (2) and [Fe(CO)(dppe)('S(3)')] (3). The diastereoselective formation of 2 and 3 is rationalized by the trans influence of the 'S(3)'(2-) thiolate and thioether S atoms which act as pi donors and pi acceptors, respectively. The trans influence of the 'S(3)'(2-) sulfur donors also rationalizes the diastereoselective formation of the C(1) symmetrical anion of 4, when 1 is treated with four equivalents of NEt(4)CN. The molecular structures of 1, 3 x 0.5 C(7)H(8), and (AsPh(4))(2)[Fe(CN)(2)(CO)('S(3)')] x acetone (4 a x C(3)H(6)O) were determined by X-ray structure analyses. Complex 4 is the first complex that models the unusual 2:1 cyano/carbonyl and dithiolate coordination of the [NiFe] hydrogenase iron site. Complex 4 can be reversibly oxidized electrochemically; chemical oxidation of 4 by [Fe(Cp)(2)PF(6)], however, led to loss of the CO ligand and yielded only products, which could not be characterized. When dissolved in solvents of increasing proton activity (from CH(3)CN to buffered H(2)O), complex 4 exhibits drastic nu(CO) blue shifts of up to 44 cm(-1), and relatively small nu(CN) red shifts of approximately 10 cm(-1). The nu(CO) frequency of 4 in H(2)O (1973 cm(-1)) is higher than that of any hydrogenase state (1952 cm(-1)). In addition, the nu(CO) frequency shift of 4 in various solvents is larger than that of [NiFe] hydrogenase in its most reduced or oxidized state. These results demonstrate that complexes modeling properly the nu(CO) frequencies of [NiFe] hydrogenase probably need a [Ni(thiolate)(2)] unit. The results also demonstrate that the nu(CO) frequency of [Fe(CN)(2)(CO)(thiolate)(2)] complexes is more significantly shifted by changing the solvent than the nu(CO) frequency of [NiFe] hydrogenases by coupled-proton and electron-transfer reactions. The "iron-wheel" complex [Fe(6)[Fe('S(3)')(2)](6)] (6) resulting as a minor by-product from the recrystallization of 2 in boiling toluene could be characterized by X-ray structure analysis.     

An IR study of (CO2)(+)n (n=3-8) cluster ions in the 1000-3800 cm-1 region

Infrared photodissociation (IRPD) spectra of carbon dioxide cluster ions, (CO(2))(n) (+) with n=3-8, are measured in the 1000-3800 cm(-1) region. IR bands assignable to solvent CO(2) molecules are observed at positions close to the vibrational frequencies of neutral CO(2) [1290 and 1400 cm(-1) (nu(1) and 2nu(2)), 2350 cm(-1) (nu(3)), and 3610 and 3713 cm(-1) (nu(1)+nu(3) and 2nu(2)+nu(3))]. The ion core in (CO(2))(n) (+) shows several IR bands in the 1200-1350, 2100-2200, and 3250-3500 cm(-1) regions. On the basis of previous IR studies in solid Ne and quantum chemical calculations, these bands are ascribed to the C(2)O(4) (+) ion, which has a semicovalent bond between the CO(2) components. The number of the bands and the bandwidth of the IRPD spectra drastically change with an increase in the cluster size up to n=6, which is ascribed to the symmetry change of (CO(2))(n) (+) by the solvation of CO(2) molecules and a full occupation of the first solvation shell at n=6.     

Syntheses and Vibrational and (13)C MAS-NMR Spectra of Bis(carbonyl)mercury(II) Undecafluorodiantimonate(V) ([Hg(CO)(2)][Sb(2)F(11)](2)) and of Bis(carbonyl)dimercury(I) Undecafluorodiantimonate ([Hg(2)(CO)(2)][Sb(2)F(11)](2)) and the Molecular Structure of [Hg(CO)(2)][Sb(2)F(11)](2)

The synthesis of bis(carbonyl)mercury(II) undecafluorodiantimonate(V), [Hg(CO)(2)][Sb(2)F(11)](2), and that of the corresponding mercury(I) salt [Hg(2)(CO)(2)][Sb(2)F(11)](2) are accomplished by the solvolyses of Hg(SO(3)F)(2) or of Hg(2)F(2), treated with fluorosulfuric acid, HSO(3)F, in liquid antimony(V) fluoride at 80 or 60 degrees C, respectively, in an atmosphere of CO (500-800 mbar). The resulting white solids are the first examples of metal carbonyl derivatives formed by a post-transition element. Both salts are characterized by FT-IR, FT-Raman, and (13)C-MAS-NMR spectroscopy. For [Hg(CO)(2)][Sb(2)F(11)], unprecedentedly high CO stretching frequencies (nu(av) = 2279.5 cm(-)(1)) and stretching force constant (f(r) = 21.0 +/- 0.1) x 10(2) Nm(-)(1)) are obtained. Equally unprecedented is the (1)J((13)C-(199)Hg) value of 5219 +/- 5 Hz observed in the (13)C MAS-NMR spectrum of the (13)C labeled isotopomers at delta = 168.8 +/- 0.1 ppm. The corresponding values (nu(av) = 2247 cm(-)(1), f(r) = (20.4 +/- 0.1) x 10(2) Nm(-)(1), (1)J((13)C-(199)Hg) = 3350 +/- 50 Hz and (2)J((13)C-(199)Hg) 850 +/- 50 Hz) are found for [Hg(2)(CO)(2)][Sb(2)F(11)](2), which has lower thermal stability (decomposition point in a sealed tube is 140 degrees C vs 160 degrees C for the Hg(II) compound) and a decomposition pressure of 8 Torr at 20 degrees C. The mercury(I) salt is sensitive toward oxidation to [Hg(CO)(2)][Sb(2)F(11)](2) during synthesis. Both linear cations (point group D(infinity)(h)()) are excellent examples of nonclassical (sigma-only) metal-CO bonding. Crystal data for [Hg(CO)(2)][Sb(2)F(11)](2): monoclinic, space group P2(1)/n; Z = 2; a = 7.607(2) ?; b = 14.001(3) ?; c = 9.730(2) ?; beta = 111.05(2) degrees; V = 967.1 ?(3); T = 195 K; R(F) = 0.035 for 1983 data (I(o) >/= 2.5sigma(I(o))) and 143 variables. The Hg atom lies on a crystallographic inversion center. The Hg-C-O angle is 177.7(7) degrees. The length of the mercury-carbon bond is 2.083(10) ? and of the C-O bond 1.104(12) ? respectively. The structure is stabilized in the solid state by a number of significant secondary interionic Hg- - -F and C- - -F contacts.     

Characterization of the Fe site in iron-sulfur cluster-free hydrogenase (Hmd) and of a model compound via nuclear resonance vibrational spectroscopy (NRVS)

We have used (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the iron site in the iron-sulfur cluster-free hydrogenase Hmd from the methanogenic archaeon Methanothermobacter marburgensis. The spectra have been interpreted by comparison with a cis-(CO)2-ligated Fe model compound, Fe(S2C2H4)(CO)2(PMe3)2, as well as by normal mode simulations of plausible active site structures. For this model complex, normal mode analyses both from an optimized Urey-Bradley force field and from complementary density functional theory (DFT) calculations produced consistent results. For Hmd, previous IR spectroscopic studies found strong CO stretching modes at 1944 and 2011 cm(-1), interpreted as evidence for cis-Fe(CO)2 ligation. The NRVS data provide further insight into the dynamics of the Fe site, revealing Fe-CO stretch and Fe-CO bend modes at 494, 562, 590, and 648 cm(-1), consistent with the proposed cis-Fe(CO)2 ligation. The NRVS also reveals a band assigned to Fe-S stretching motion at approximately 311 cm(-1) and another reproducible feature at approximately 380 cm(-1). The (57)Fe partial vibrational densities of states (PVDOS) for Hmd can be reasonably well simulated by a normal mode analysis based on a Urey-Bradley force field for a five-coordinate cis-(CO)2-ligated Fe site with additional cysteine, water, and pyridone cofactor ligands. A "truncated" model without a water ligand can also be used to match the NRVS data. A final interpretation of the Hmd NRVS data, including DFT analysis, awaits a three-dimensional structure for the active site.     

Structural and kinetic studies on uranyl(V) carbonate complex using 13C NMR spectroscopy

We have measured 13C NMR spectra of uranyl(V) carbonate complex in D2O solution containing 1.003 M Na2(13)CO3 at various temperatures. Two singlet signals corresponding to free and coordinated CO3(2-) were observed at 169.13 and 106.70 ppm, respectively. From the peak area ratio, the structure of the uranyl(V) carbonate complex was determined as [U(V)O2(CO3)3]5-. Furthermore, kinetic analyses of the exchange reaction of free and coordinated CO3(2-) in [U(V)O2(CO3)3]5- were carried out using 13C NMR line-broadening. As a result, the first-order rate constant at 298 K and the activation parameters for CO3(2-) exchange reaction in [U(V)O2(CO3)3]5- were evaluated as 1.13 x 10(3) s(-1) and deltaH(double dagger) = 62.0 +/- 0.7 kJ x mol(-1), deltaS(double dagger) = 22 +/- 3 J x mol(-1) x K(-1), respectively. We suggest that the exchange follows a dissociative mechanism as in the corresponding [U(VI)O2(CO3)3]4- complex.     

Heme/non-heme diiron(II) complexes and O2, CO, and NO adducts as reduced and substrate-bound models for the active site of bacterial nitric oxide reductase

As a first generation model for the reactive reduced active-site form of bacterial nitric oxide reductase, a heme/non-heme diiron(II) complex [(6L)Fe(II)...Fe(II)-(Cl)]+ (2) {where 6L = partially fluorinated tetraphenylporphyrin with a tethered tetradentate TMPA chelate; TMPA = tris(2-pyridyl)amine} was generated by reduction of the corresponding mu-oxo diferric compound [(6L)Fe(III)-O-Fe(III)-Cl]+ (1). Coordination chemistry models for reactions of reduced NOR with O2, CO, and NO were also developed. With O2 and CO, adducts are formed, [(6L)Fe(III)(O2-))(thf)...Fe(II)-Cl]B(C6F5)4 (2a x O2) {lambda(max) 418 (Soret), 536 nm; nu(O-O) = 1176 cm(-1), nu(Fe-O) = 574 cm(-1) and [(6L)Fe(II)(CO)(thf)Fe(II)-Cl]B(C6F5)4 (2a x CO) {nu(CO) 1969 cm(-1)}, respectively. Reaction of purified nitric oxide with 2 leads to the dinitrosyl complex [(6L)Fe(NO)Fe(NO)-Cl]B(C6F5)4 (2a x (NO)2) with nu(NO) absorptions at 1798 cm(-1) (non-heme Fe-NO) and 1689 cm(-1) (heme-NO).     

Infrared spectroscopic study of the carbon dioxide adsorption on the surface of Ga2O3 polymorphs

The adsorption of CO(2) over a set of gallium (III) oxide polymorphs with different crystallographic phases (alpha, beta, and gamma) and surface areas (12-105 m(2) g(-1)) was studied by in situ infrared spectroscopy. On the bare surface of the activated gallias (i.e., partially dehydroxylated under O(2) and D(2) (H(2)) at 723 K), several IR signals of the O-D (O-H) stretching mode were assigned to mono-, di- and tricoordinated OD (OH) groups bonded to gallium cations in tetrahedral and/or octahedral positions. After exposing the surface of the polymorphs to CO(2) at 323 K, a variety of (bi)carbonate species emerged. The more basic hydroxyl groups were able to react with CO(2), to yield two types of bicarbonate species: mono- (m-) and bidentate (b-) [nu(as)(CO(3)) = 1630 cm(-1); nu(s)(CO(3)) = 1431 or 1455 cm(-1) (for m- or b-); delta(OH) = 1225 cm(-1)]. Together with the bicarbonate groups, IR bands assigned to carboxylate [nu(as)(CO(2)) = 1750 cm(-1); nu(s)(CO(2)) = 1170 cm(-1)], bridge carbonate [nu(as)(CO(3)) = 1680 cm(-1); nu(s)(CO(3)) = 1280 cm(-1)], bidentate carbonate [nu(as)(CO(3)) = 1587 cm(-1); nu(s)(CO(3)) = 1325 cm(-1)], and polydentate carbonate [nu(as)(CO(3)) = 1460 cm(-1); nu(s)(CO(3)) = 1406 cm(-1)] species developed, up to approximately 600 Torr of CO(2). However, only the bi- and polydentate carbonate groups still remained on the surface upon outgassing the samples at 323 K. The total amount of adsorbed CO(2), measured by volumetric adsorption (323 K), was approximately 2.0 micromol m(-2) over any of the polymorphs, congruent with an integrated absorbance of (bi)carbonate species proportional to the surface area of the materials. Upon heating under flowing CO(2) (760 Torr), most of the (bi)carbonate species vanished a T > 550 K, but polydentate groups remained on the surface up to the highest temperature used (723 K). A thorough discussion of the more probable surface sites involved in the adsorption of CO(2) is made.     

Intraligand charge transfer in the Pd(II) oxinate complex Pd(qol)2. Site-selective emission, excitation, and optically detected magnetic resonance

The first spectroscopic investigation of Pd(qol)2 (qol- = 8-quinolinolato-N,O = oxinate) dissolved in an n-octane matrix (Shpol'skii matrix) is reported. Application of several spectroscopic methods at liquid helium temperatures (typically, T = 1.2 K), such as site-selective and highly resolved luminescence and excitation spectroscopy, time-resolved emission spectroscopy, optically detected magnetic resonance, microwave recovery, phosphorescence microwave double-resonance, and magnetic fields, allows us to characterize the lowest excited electronic states in detail. In accord with previous assignments for the related Pt(qol)2 it is shown that these lowest states represent-intraligand charge-transfer states, namely, 1ILCT and 3ILCT. The electronic origin of the 1ILCT state lies at 20,617 cm(-1) (site A). It exhibits a nearly homogeneous line width with a half-width of about 80 cm(-1) (fwhm), which corresponds to a lifetime of tau(1ILCT) approximately equals 2 x 10(-13) s. This value is even shorter than that found for Pt(qol)2, presumably due to intersystem crossings and relaxations to dd* states. The electronic origin of the 3ILCT state lies at 16 090 cm(-1) (site A), and its zero-field splittings (zfs) into three sublevels are 2E = 2356 MHz (0.0785 cm(-1)) and D - E = 5241 MHz (0.175 cm(-1)). The emission decay times of the three sublevels are determined as tauI = 90 +/- 30 ms, tau(II) = 180 +/- 10 mus, and tau(II) = 80 +/- 10 mus. (Slightly different values are found for a second site B at 16,167 cm(-1).) From the small values of zfs and the long emission decay times it is concluded that metal-d or MLCT admixtures to 3ILCT are very small. This result clearly reflects the ligand-centered character of the transition. The assignment as an ILCT transition is supported by the occurrence of relatively strong vibrational satellites of Pd-N and Pd-O character in highly resolved emission spectra. Although the transition is ascribed to a charge-transfer process, the geometry changes between the ground state and 3ILCT are very small. The results found for Pd(qol)2 are compared to those of companion studies of Pt(qol)2 and Pt(qtl)2 (qtl- = 8-quinolinethiolato-N,S).     

Synthesis and platinum coordination chemistry of the perfluoroalkyl acceptor pincer ligand, 1,3-(CH(2)P(CF(3))(2))(2)C(6)H(4)

The synthesis of perfluoroalkyl-substituted "pincer"-type PCP ligands, 1,3-C6H4(CH2P(Rf)2)2 (Rf = CF3, C2F5), and platinum coordination studies (Rf = CF3) are reported. 1,3-C6H4(CH2P(CF3)2)2 (CF3PCPH) reacts at ambient temperatures with (cod)Pt(Me)Cl (cod = 1,5-cyclooctadiene) and (cod)PtMe2 to afford unmetalated PCPH-bridged products [(CF3PCPH)Pt(Me)Cl]x and cis-[(CF3PCPH)PtMe2]2, respectively. cis-[(CF3PCPH)PtMe2]2 is soluble and has been spectroscopically and crystallographically characterized. Thermolysis of these compounds results in the loss of methane and the formation of metalated complexes (CF3PCP)PtCl and (CF3PCP)PtMe. Treatment of (CF3PCP)PtCl with MeMgBr provides an alternative route to (CF3PCP)PtMe. The carbonyl cation (CF3PCP)Pt(CO)+SbF6- (nu(CO) = 2143 cm(-1)) was readily prepared by chloride abstraction with AgSbF6 under 1 atm CO. nu(CO) data indicates that RfPCP ligands are electronically analogous to trans acceptor phosphine complexes such as trans-((C2F5)2PMe)2Pt(Me)(CO)+ (nu(CO) = 2149 cm-1).     

Catalytic four-electron oxidation of water by intramolecular coupling of the oxo ligands of a bis(ruthenium-bipyridine) complex

A bis(ruthenium-bipyridine) complex bridged by 1,8-bis(2,2':6',2'-terpyrid-4'-yl)anthracene (btpyan), [Ru(2)(μ-Cl)(bpy)(2)(btpyan)](BF(4))(3) ([1](BF(4))(3); bpy = 2,2'-bipyridine), was prepared. The cyclic voltammogram of [1](BF(4))(3) in water at pH?1.0 displayed two reversible [Ru(II),Ru(II)](3+)/[Ru(II),Ru(III)](4+) and [Ru(II),Ru(III)](4+)/[Ru(III),Ru(III)](5+) redox couples at E(1/2)(1) = +0.61 and E(1/2)(2) = +0.80?V (vs. Ag/AgCl), respectively, and an irreversible anodic peak at around E = +1.2?V followed by a strong anodic currents as a result of the oxidation of water. The controlled potential electrolysis of [1](3+) ions at E = +1.60?V in water at pH?2.6 (buffered with H(3)PO(4)/NaH(2)PO(4)) catalytically evolved dioxygen. Immediately after the electrolysis of the [1](3+) ion in H(2)(16)O at E = +1.40?V, the resultant solution displayed two resonance Raman bands at nu = 442 and 824?cm(-1). These bands shifted to nu = 426 and 780?cm(-1), respectively, when the same electrolysis was conducted in H(2)(18)O. The chemical oxidation of the [1](3+) ion by using a Ce(IV) species in H(2)(16)O and H(2)(18)O also exhibited the same resonance Raman spectra. The observed isotope frequency shifts (Δnu = 16 and 44?cm(-1)) fully fit the calculated ones based on the Ru-O and O-O stretching modes, respectively. The first successful identification of the metal-O-O-metal stretching band in the oxidation of water indicates that the oxygen-oxygen bond at the stage prior to the evolution of O(2) is formed through the intramolecular coupling of two Ru-oxo groups derived from the [1](3+) ion.     

The [1+1] two-photon dissociation spectra of CO2 + via A 2Pi u,12(upsilon1upsilon20)<--X 2Pi g,12(000) transitions

In the wavelength range of 235-354 nm, we have obtained the mass-resolved [1+1] two-photon dissociation spectra of CO(2) (+) via A (2)Pi(u,12)(upsilon(1)upsilon(2)0)<--X (2)Pi(g,12)(000) transitions by preparing CO(2) (+) ions in the X (2)Pi(g,12)(000) state via [3+1] multiphoton ionization of CO(2) molecules at 333.06 nm. The vibronic bands of (upsilon(1)20;upsilon(1)=0-11)micro (2)Pi(12) and (upsilon(1)20;upsilon(1)=0-6)kappa (2)Pi(12) involving the bending mode of CO(2) (+)(A (2)Pi(u,12)) were assigned. The spectroscopic constants of T(e)=27 908.9+/-1.1 cm(-1) [above CO(2) (+)(X (2)Pi(g,12))], nu(1)=1126.00+/-0.36 cm(-1), chi(11)=-1.602+/-0.005 cm(-1), nu(2)(micro (2)Pi(12))=402.5+/-13.3 cm(-1), and nu(2)(kappa (2)Pi(12))=493.1+/-23.6 cm(-1) for CO(2) (+)(A (2)Pi(u,12)) are deduced from the data of the A (2)Pi(u,12)(upsilon(1)upsilon(2)0)<--X (2)Pi(g,12)(000) transitions. The observed intensity reversal between (500) (2)Pi(12) and (420)micro (2)Pi(12) can be attributed to the conformational variation of CO(2) (+)(A (2)Pi(u,12)) from linear to bent, then the conversion potential barrier is estimated to be 5209 cm(-1) above CO(2) (+)(A (2)Pi(u,12)(000)). The wavelength and level dependence of the photofragment branching ratios have been measured and the dissociation dynamics of CO(2) (+) via A (2)Pi(u,12) state is discussed.     

Synthesis, structure, and properties of an Fe(II) carbonyl [(PaPy3)Fe(CO)](ClO4): insight into the reactivity of Fe(II)-CO and Fe(II)-NO moieties in non-heme iron chelates of N-donor ligands

An Fe(II) carbonyl complex [(PaPy3)Fe(CO)](ClO4) (1) of the pentadentate ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy3H, H is the dissociable amide proton) has been synthesized and structurally characterized. This Fe(II) carbonyl exhibits its nu(CO) at 1972 cm(-1), and its 1H NMR spectrum in degassed CD3CN confirms its S = 0 ground state. The bound CO in 1 is not photolabile. Reaction of 1 with an equimolar amount of NO results in the formation of the {Fe-NO}7 nitrosyl [(PaPy3)Fe(NO)](ClO4) (2), while excess NO affords the iron(III) nitro complex [(PaPy3)Fe(NO2)](ClO4) (5). In the presence of [Fe(Cp)2]+ and excess NO, 1 forms the {Fe-NO}6 nitrosyl [(PaPy3)Fe(NO)](ClO4)2 (3). Complex 1 also reacts with dioxygen to afford the iron(III) mu-oxo species [{(PaPy3)Fe}2O](ClO4)2 (4). Comparison of the metric and spectral parameters of 1 with those of the previously reported {Fe-NO}6,7 nitrosyls 3 and 2 provides insight into the electronic distributions in the Fe(II)-CO, Fe(II)-NO, and Fe(II)-NO+ bonds in the isostructural series of complexes 1-3 derived from a non-heme polypyridine ligand with one carboxamide group.     

Infrared absorption spectra of matrix-isolated cis, cis-HOONO and its ab initio CCSD(T) anharmonic vibrational bands

The infrared absorption spectra of matrix-isolated cis, cis-peroxynitrous acid (HOONO and DOONO) in argon have been observed. Six of the nine fundamental vibrational modes for cis, cis-HOONO have been assigned definitively, and one tentatively. Coupled-cluster, ab initio anharmonic force field calculations were used to help guide some of the assignments. The experimental matrix frequencies (cm(-1)) for cis, cis-HOONO are (a' modes) nu1 = 3303+/-1, nu2 = 1600.6+/-0.6, nu3 = 1392+/-1, nu4 = 922.8+/-0.5, nu5 = 789.7+/-0.4, nu6 = 617+/-1; and (a" mode) nu8 = 462+/-1. The fundamentals for the deuterated isotopomer, cis, cis-DOONO, are (a' modes) nu1 = 2447.2+/-0.6, nu2 = 1595.7+/-0.7, nu3 = 1089.1+/-0.4, nu4 = 888.1+/-0.4, nu5 = 786.6+/-0.5, nu6 = 613.9+/-0.9; and (a" mode) nu8 = 456.5+/-0.5.     

Photoinduced carbon monoxide migration in a synthetic heme-copper complex

Time-resolved infrared (TRIR) flash photolytic techniques have been employed to initiate and observe the efficient dissociation of CO from a synthetic heme-CO/copper complex, [((6)L)Fe(II)(CO)..Cu(I)](+) (2), in CH(3)CN and acetone at room temperature. In CH(3)CN, a significant fraction of the photodissociated CO molecules transiently bind to copper (nu(CO)(Cu) = 2091 cm(-)(1)) giving [((6)L)Fe(II)..Cu(I)(CO)](+) (4), with an observed rate constant, k(1) = 1.5 x 10(5) s(-)(1). That is followed by a slower direct transfer of CO from the copper moiety back to the heme (nu(CO)(Fe) = 1975 cm(-)(1)) with k(2) = 1600 s(-)(1). Additional transient absorption (TA) UV-vis spectroscopic experiments have been performed monitoring the CO-transfer reaction by following the Soret band. Eyring analysis of the temperature-dependent data yields DeltaH(double dagger) = 43.9 kJ mol(-)(1) for the 4-to-2 transformation, similar to that for CO dissociation from [Cu(I)(tmpa)(CO)](+) in CH(3)CN (DeltaH(double dagger) = 43.6 kJ mol(-)(1)), suggesting CO dissociation from copper regulates the binding of small molecules to the heme within [((6)L)Fe(II)..Cu(I)](+)(3). Our observations are analagous to those observed for the heme(a3)/Cu(B) active site of cytochrome c oxidase, where photodissociated CO from the heme(a3) site immediately (ps) transfers to Cu(B) followed by millisecond transfer back to the heme.     

Further insights into the spectroscopic properties, electronic structure, and kinetics of formation of the heme-peroxo-copper complex [(F8TPP)FeIII-(O2(2-)-CuII(TMPA)]+

In the further development and understanding of heme-copper O2-reduction chemistry inspired by the active-site chemistry in cytochrome c oxidase, we describe a dioxygen adduct, [(F8TPP)FeIII-(O22-)-CuII(TMPA)](ClO4) (3), formed by addition of O2 to a 1:1 mixture of the porphyrinate-iron(II) complex (F8TPP)FeII (1a) {F8TPP = tetrakis(2,6-difluorophenyl)porphyrinate dianion} and the copper(I) complex [(TMPA)CuI(MeCN)](ClO4) (1b) {TMPA = tris(2-pyridylmethyl)amine}. Complex 3 forms in preference to heme-only or copper-only binuclear products, is remarkably stable {t1/2 (RT; MeCN) approximately 20 min; lambda max = 412 (Soret), 558 nm; EPR silent}, and is formulated as a peroxo complex on the basis of manometry {1a/1b/O2 = 1:1:1}, MALDI-TOF mass spectrometry {16O2, m/z 1239 [(3 + MeCN)+]; 18O2, m/z 1243}, and resonance Raman spectroscopy {nu(O-O) = 808 cm-1; Delta16O2/18O2 = 46 cm-1; Delta16O2/16/18O2 = 23 cm-1}. Consistent with a mu-eta2:eta1 bridging peroxide ligand, two metal-O stretching frequencies are observed {nu(Fe-O) = 533 cm-1, nu(Fe-O-Cu) = 511 cm-1}, and supporting normal coordinate analysis is presented. 2H and 19F NMR spectroscopies reveal that 3 is high-spin {also muB = 5.1 +/- 0.2, Evans method} with downfield-shifted pyrrole and upfield-shifted TMPA resonances, similar to the pattern observed for the structurally characterized mu-oxo complex [(F8TPP)FeIII-O-CuII(TMPA)]+ (4) (known S = 2 system, antiferromagnetically coupled high-spin FeIII and CuII). M?ssbauer spectroscopy exhibits a sharp quadrupole doublet (zero field; delta = 0.57 mm/s, |DeltaEQ| = 1.14 mm/s) for 3, with isomer shift and magnetic field dependence data indicative of a peroxide ligand and S = 2 formulation. Both UV-visible-monitored stopped-flow kinetics and M?ssbauer spectroscopic studies reveal the formation of heme-only superoxide complex (S)(F8TPP)FeIII-(O2-) (2a) (S = solvent molecule) prior to 3. Thermal decomposition of mu-peroxo complex 3 yields mu-oxo complex 4 with concomitant release of approximately 0.5 mol O2 per mol 3. Characterization of the reaction 1a/1b + O2 --> 2 --> 3 --> 4, presented here, advances our understanding and provides new insights to heme/Cu dioxygen-binding and reduction.