New heterometallic coordination polymers self-assembled from copper(II) nitrate and (diamine)Pt(II)(pyridinecarboxylates)(2)

One-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) coordination polymers were prepared by self-assembly of binary metal complex systems, copper(II) nitrate and (en)Pt(II)(nic)(2) or (dmpda)Pt(II)(isonic)(2) (en = ethylenediamine, dmpda = 2,2'-dimethyl-1,3-propanediamine, nic = nicotinate, and isonic = isonicotinate), in aqueous solutions. Equimolar reactions of copper(II) nitrate with (dmpda)Pt(II)(isonic)(2) and (en)Pt(II)(nic)(2) resulted in 1-D ([(dmpda)Pt(isonic)(2)Cu(OH(2))(3)](NO(3))(2))(n)() (1) and 2-D ([(en)Pt(nic)(2)Cu(OH(2))](NO(3))(2))(n) (2), respectively, but the reaction of (en)Pt(II)(nic)(2) with excess copper(II) nitrate gave 3-D ([((en)Pt(nic)(2))(3)Cu(5)(OH)(2)(OH(2))(6)](NO(3))(8))(n) (3). The local structure of crystal 1 has a mononuclear copper unit, 2 has a dinuclear copper unit with a Cu-Cu distance of 2.659(5) A, and 3 has a pentanuclear copper unit. The methyl groups of the dmpda ligand are located in the space between two isonicotinate ligands of 1, which is presumed to be an important factor to determine the final structure of the crystal formed by self-assembly. Magnetic behaviors of crystals 1-3 examined in the temperature range of 4-300 K appear to be governed by the local structures around the copper(II) ions and do not indicate any significant long-range magnetic exchange interactions along the polymeric chain.     

Metallonitrosyl fragment as electron acceptor: intramolecular charge transfer, long range electronic coupling, and electrophilic reactivity in the trans-[NCRu(py)(4)(CN)Ru(py)(4)NO](3+) ion

The new complex trans-[NCRu(py)(4)(CN)Ru(py)(4)NO](PF(6))(3) (I) was synthesized. In acetonitrile solution, I shows an intense visible band (555 nm, epsilon = 5800 M(-1) cm(-1)) and other absorptions below 350 nm, associated with d(pi) --> pi(py) and pi(py) --> pi(py) transitions. The visible band is presently assigned as a donor-acceptor charge transfer (DACT) transition from the remote Ru(II) to the delocalized [Ru(II)-NO(+)] moiety. Photoinduced release of NO is observed upon irradiation at the DACT band. Application of the Hush model reveals strong electronic coupling, with H(DA) = approximately 2000 cm(-1). The difference between the optical absorption energy and redox potentials for the donor and acceptor sites (Ru(III,II), 1.40 V, and NO(+)/NO, 0.50 V, vs Ag/AgCl, 3 M KCl, respectively) (hnu - DeltaE(red)) is 1.33 eV, a large value which probably relates to the significant changes in distances and angles for the Ru-N-O moiety upon reduction. UV-vis absorptions, IR frequencies, and redox potentials are solvent-dependent. Controlled potential reduction (of NO(+)) and oxidation (of Ru(II) associated with the dicyano-chromophore) of I afford stable species, [NCRu(II)(py)(4)(CN)Ru(py)(4)NO](2+) (I(red)) and [NCRu(III)(py)(4)(CN)Ru(py)(4)NO](4+) (I(ox)), respectively, which are characterized by UV-vis and IR spectroscopies. I(red) shows an EPR spectrum characteristic of [Ru(II)-NO(*)] complexes. Compound I is electrophilically reactive in aqueous solution above pH 5: values of the equilibrium constant for the reaction [NCRu(py)(4)(CN)Ru(py)(4)NO](3+)+ 2 OH(-) <--> [NCRu(py)(4)(CN)Ru(py)(4)NO(2)](+) + H(2)O, K = 3.2 +/- 1.4 x 10(15) M(-2), and of the rate constant for the nucleophilic addition of OH(-), k = 9.2 +/- 0.2 x 10(3) M(-1) s(-1)(25 degrees C, I = 1 M), are obtained, with DeltaH = 90.7 +/- 3.8 kJ mol(-1) and DeltaS = 135 +/- 13 J K(-1) mol(-1). The oxidized complex, I(ox), shows an enhanced electrophilic reactivity toward OH(-). This addition reaction is followed by irreversible processes, which most probably lead to disproportionation of bound nitrite and other products.     

The Dinitramide Anion, N(NO(2))(2)(-)

The infrared and Raman spectra of the NH(4)(+), K(+), and Cs(+) salts of N(NO(2))(2)(-) in the solid state and in solution have been measured and are assigned with the help of ab initio calculations at the HF/6-31G and MP2/6-31+G levels of theory. In agreement with the variations observed in the crystal structures, the vibrational spectra of the N(NO(2))(2)(-) anion are also strongly influenced by the counterions and the physical state. Whereas the ab initio calculations for the free N(NO(2))(2)(-) ion indicate a minimum energy structure of C(2) symmetry, Raman polarization measurements on solutions of the N(NO(2))(2)(-) anion suggest point group C(1) (i.e., no symmetry). This is attributed to the very small (<3 kcal/mol) N-NO(2) rotational barrier in N(NO(2))(2)(-) which allows for easy deformation.     

Use of HNO(3) as the source of NO to prepare a nitric oxide complex of ruthenium

Reaction of cis-Ru(bisox)(2)Cl(2), where bisox is 4,4,4',4'-tetramethyl-2,2'-bisoxazoline, with HNO(3) in 1 : 4 molar proportion in boiling water under N(2) atmosphere and subsequent addition of an excess of NaClO(4).H(2)O yields [Ru(bisox)(HL)(NO)](ClO(4))(NO(3)) (1). HL is a hydrolysed form of bisox where one of the oxazoline rings opens up. X-Ray crystallography shows that 1 contains an octahedral RuN(5)O core. HL binds the metal through an imino N, an amide N and an alcoholic O atom. Reaction of cis-Ru(bisox)(2)Cl(2) with an excess of NaNO(2) in water gives cis-Ru(bisox)(2)(NO(2))(2) (2). On acidification by HClO(4) in methanol, is smoothly converted to cis-[Ru(bisox)(2)(NO(2))(NO)](ClO(4))(2) (3) due to equilibrium (1). [formula: see text] (1) The X-ray crystal structures of 2 and 3 have also been determined. NO binds Ru in 1 and 3 linearly. The Ru-NO bond length in 1 is 1.764(13) A and that in 3 is approximately 1.78 A. All the three complexes have been characterised by FTIR, NMR and ESIMS. The NO stretching frequencies in 1 and 3 are 1897 and 1936 cm(-1) respectively. While 3 reverts back to 2 readily in presence of OH(-) [equilibrium (1)], 1 does not react with OH(-). It is concluded that while in the reaction of cis-Ru(bisox)(2)Cl(2) with HNO(3), bisox is hydrolysed following abstraction of NO from HNO(3), generation of the nitrosyl complex 3 via reaction (1) is not accompanied with such hydrolysis.     

Highly electrophilic, 16-electron [Ru(P(OMe)(OH)(2))(dppe)(2)](2+) complex turns H(2)(g) into a strong acid and splits a Si-H bond heterolytically. Synthesis and structure of the novel phosphorous acid complex [Ru(P(OH)(3))(dppe)(2)](2+)

The highly electrophilic, 16-electron, coordinatively unsaturated [Ru(P(OMe)(OH)(2))(dppe)(2)][OTf](2) complex brings about the heterolytic activation of H(2)(g) and spontaneously generates HOTf. In addition, trans-[Ru(H)(P(OMe)(OH)(2))(dppe)(2)](+) and an unprecedented example of a phosphorous acid complex, [Ru(P(OH)(3))(dppe)(2)](2+), are formed. The [Ru(P(OMe)(OH)(2))(dppe)(2)][OTf](2) complex also cleaves the Si-H bond in EtMe(2)SiH in a heterolytic fashion, resulting in the trans-[Ru(H)(P(OMe)(OH)(2))(dppe)(2)](+) derivative.     

The inducing NO-vasodilation by chemical reduction of coordinated nitrite ion in cis-[Ru(NO(2))L(bpy)(2)](+) complex

The synthesis of [Ru(NO(2))L(bpy)(2)](+) (bpy = 2,2'-bipyridine and L = pyridine (py) and pyrazine (pz)) can be accomplished by addition of [Ru(NO)L(bpy)(2)](PF(6))(3) to aqueous solutions of physiological pH. The electrochemical processes of [Ru(NO(2))L(bpy)(2)](+) in aqueous solution were studied by cyclic voltammetry and differential pulse voltammetry. The anodic scan shows a peak around 1.00 V vs. Ag/AgCl attributed to the oxidation process centered on the metal ion. However, in the cathodic scan a second peak around -0.60 V vs. Ag/AgCl was observed and attributed to the reduction process centered on the nitrite ligand. The controlled reduction potential electrolysis at -0.80 V vs. Ag/AgCl shows NO release characteristics as judged by NO measurement with a NO-sensor. This assumption was confirmed by ESI/MS(+) and spectroelectrochemical experiment where cis-[Ru(bpy)(2)L(H(2)O)](2+) was obtained as a product of the reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The vasorelaxation observed in denuded aortic rings pre-contracted with 0.1 mumol L(-1) phenylephrine responded with relaxation in the presence of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The potential of rat aorta cells to metabolize cis-[Ru(II)(NO(2))L(bpy)(2)](+) was also followed by confocal analysis. The obtained results suggest that NO release happens by reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+) inside the cell. The maximum vasorelaxation was achieved with 1 x 10(-5) mol L(-1) of cis-[Ru(II)(NO(2))L(bpy)(2)](+) complex.     

Syntheses, structural determination, and electrochemistry of Ru(2)(Fap)(4)Cl and Ru(2)(Fap)(4)(NO)Cl

Ru(2)(Fap)(4)Cl and Ru(2)(Fap)(4)(NO)Cl, where Fap is the 2-(2-fluoroanilino)pyridinate anion, were synthesized, and their structural, electrochemical, and spectroscopic properties were characterized. Ru(2)(Fap)(4)Cl, which was obtained by reaction between Ru(2)(O(2)CCH(3))(4)Cl and molten HFap, crystallizes in the monoclinic space group P2(1)/c, with a = 11.2365(4) A, b = 19.9298(8) A, c = 19.0368(7) A, beta = 90.905(1) degrees, and Z = 4. The presence of three unpaired electrons on the Ru(2)(5+) core and the 2.2862(3) A Ru-Ru bond length for Ru(2)(Fap)(4)Cl are consistent with the electronic configuration (sigma)(2)(pi)(4)(delta)(2)(pi*)(2)(delta*)(1). The reaction between Ru(2)(Fap)(4)Cl and NO gas yields Ru(2)(Fap)(4)(NO)Cl, which crystallizes in the orthorhombic space group Pbca, with a = 10.0468(6) A, b = 18.8091(10) A, c = 41.7615(23) A, and Z = 8. The Ru-Ru bond length of Ru(2)(Fap)(4)(NO)Cl is 2.4203(8) A, while its N-O bond length and Ru-N-O bond angle are 1.164(8) A and 155.8(6) degrees, respectively. Ru(2)(Fap)(4)(NO)Cl can be formulated as a formal Ru(2)(II,II)(NO(+)) complex with a linear Ru-N-O group, and the proposed electronic configuration for this compound is (sigma)(2)(pi)(4)(delta)(2)(pi*)(3)(delta*)(1). The binding of NO to Ru(2)(Fap)(4)Cl leads to some structural changes of the Ru(2)(Fap)(4) framework and a stabilization of the lower oxidation states of the diruthenium unit. Also, IR spectroelectrochemical studies of Ru(2)(Fap)(4)(NO)Cl show that NO remains bound to the complex upon reduction and that the first reduction involves the addition of an electron on the diruthenium core and not on the NO axial ligand.     

Formation, reactivity, and photorelease of metal bound nitrosyl in [Ru(trpy)(L)(NO)](n+) (trpy = 2,2':6',2'-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline)

Nitrosyl complexes with {Ru-NO} (6) and {Ru-NO} (7) configurations have been isolated in the framework of [Ru(trpy)(L)(NO)] ( n+ ) [trpy = 2,2':6',2'-terpyridine, L = 2-phenylimidazo[4,5- f]1,10-phenanthroline] as the perchlorate salts [ 4](ClO 4) 3 and [ 4](ClO 4) 2, respectively. Single crystals of protonated material [ 4-H (+)](ClO 4) 4.2H 2O reveal a Ru-N-O bond angle of 176.1(7) degrees and triply bonded N-O with a 1.127(9) A bond length. Structures were also determined for precursor compounds of [ 4] (3+) in the form of [Ru(trpy)(L)(Cl)](ClO 4).4.5H 2O and [Ru(trpy)(L-H)(CH 3CN)](ClO 4) 3.H 2O. In agreement with largely NO centered reduction, a sizable shift in nu(NO) frequency was observed on moving from [ 4] (3+) (1953 cm (-1)) to [ 4] (2+) (1654 cm (-1)). The Ru (II)-NO* in isolated or electrogenerated [ 4] (2+) exhibits an EPR spectrum with g 1 = 2.020, g 2 = 1.995, and g 3 = 1.884 in CH 3CN at 110 K, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); (14)N (NO) hyperfine splitting ( A 2 = 30 G) was also observed. The plot of nu(NO) versus E degrees ({RuNO} (6) --> {RuNO} (7)) for 12 analogous complexes [Ru(trpy)(L')(NO)] ( n+ ) exhibits a linear trend. The electrophilic Ru-NO (+) species [ 4] (3+) is transformed to the corresponding Ru-NO 2 (-) system in the presence of OH (-) with k = 2.02 x 10 (-4) s (-1) at 303 K. In the presence of a steady flow of dioxygen gas, the Ru (II)-NO* state in [ 4] (2+) oxidizes to [ 4] (3+) through an associatively activated pathway (Delta S++ = -190.4 J K (-1) M (-1)) with a rate constant ( k [s (-1)]) of 5.33 x 10 (-3). On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic [Ru(trpy)(L)(NO)] (2+) ([ 4] (2+)) undergoes facile photorelease of NO ( k NO = 2.0 x 10 (-1) min (-1) and t 1/2 approximately 3.5 min) with the concomitant formation of the solvate [Ru (II)(trpy)(L)(CH 3CN)] (2+) [ 2'] (2+). The photoreleased NO can be trapped as an Mb-NO adduct.     

Reactions of acetonitrile coordinated to a nitrosylruthenium complex with H2O or CH(3)OH under mild conditions: structural characterization of imido-type complexes

The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) (bpy = 2,2'-bipyridine) in H(2)O at room temperature proceeded to afford two new nitrosylruthenium complexes. These complexes have been identified as nitrosylruthenium complexes containing the N-bound methylcarboxyimidato ligand, cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+), and methylcarboxyimido acid ligand, cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+), formed by an electrophilic reaction at the nitrile carbon of the acetonitrile coordinated to the ruthenium ion. The X-ray structure analysis on a single crystal obtained from CH(3)CN-H(2)O solution of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](PF(6))(3) has been performed: C(22)H(20.5)N(6)O(2)P(2.5)F(15)Ru, orthorhombic, Pccn, a = 15.966(1) A, b = 31.839(1) A, c = 11.707(1) A, V = 5950.8(4) A(3), and Z = 8. The structural results revealed that the single crystal consisted of 1:1 mixture of cis-[Ru(NO)(NH=C(O)CH(3))(bpy)(2)](2+) and cis-[Ru(NO)(NH=C(OH)CH(3))(bpy)(2)](3+) and the structural formula of this single crystal was thus [Ru(NO)(NH=C(OH(0.5))CH(3))(bpy)(2)](PF(6))(2.5). The reaction of cis-[Ru(NO)(CH(3)CN)(bpy)(2)](3+) in dry CH(3)OH-CH(3)CN at room temperature afforded a nitrosylruthenium complex containing the methyl methylcarboxyimidate ligand, cis-[Ru(NO)(NH=C(OCH(3))CH(3))(bpy)(2)](3+). The structure has been determined by X-ray structure analysis: C(25)H(29)N(8)O(18)Cl(3)Ru, monoclinic, P2(1)/c, a = 13.129(1) A, b = 17.053(1) A, c = 15.711(1) A, beta = 90.876(5) degrees, V = 3517.3(4) A(3), and Z = 4.     

X-ray absorption spectroscopic studies of chromium nitroso complexes. Crystal and molecular structure of (Ph4P)3[Cr(NO)(NCS)5].2.4(CH3)2CO

X-ray absorption spectroscopy (XAS) provides a direct means of solving the controversy on Cr oxidation states in nitroso complexes. The first XAS studies of four known Cr-NO complexes, [Cr(NO)(OH(2))(5)](2+), [Cr(NO)(acac)(2)(OH(2))], [Cr(NO)(CN)(5)](3)(-), and [Cr(NO)(NCS)(5)](3)(-), have been performed, in comparison with the related Cr(III) complexes, [Cr(OH(2))(6)](3+), [Cr(acac)(3)], [Cr(CN)(6)](3)(-), and [Cr(NCS)(6)](3)(-). The X-ray absorption near-edge structure (XANES) spectra of the Cr-NO complexes are distinguished from those of the corresponding Cr(III) complexes by increased intensities of pre-edge absorbancies due to the 1s --> 3d transition, as well as with slight shifts (by 0.2-1.0 eV) of the edge positions to lower energies, with no major changes in the edge shape. These features, together with the available structural data on Cr-NO complexes, show that the effective Cr oxidation states in such complexes are close to Cr(III), due to the pi-back-bonding within the Cr-NO moiety. Multiple-scattering fitting of X-ray absorption fine structure (XAFS) spectra of [Cr(NO)(acac)(2)(OH(2))] supported the assignment of this complex as a trans-isomer (Keller, A.; Jezovska-Trzebiatowska, B. Polyhedron 1985, 4, 1847-1852). The first crystal structure of a Cr nitroso-isothiocyanato complex, (Ph(4)P)(3)[Cr(NO)(NCS)(5)].2.4(CH(3))(2)CO, has been determined.     

Nitrosyl induces phosphorous-acid dissociation in ruthenium(II)

The trans-[Ru(NO)(NH(3))(4)(P(OH)(3))]Cl(3) complex was synthesized by reacting [Ru(H(2)O)(NH(3))(5)](2+) with H(3)PO(3) and characterized by spectroscopic ((31)P-NMR, δ = 68 ppm) and spectrophotometric techniques (λ = 525 nm, ε = 20 L mol(-1) cm(-1); λ = 319 nm, ε = 773 L mol(-1) cm(-1); λ = 241 nm, ε = 1385 L mol(-1) cm(-1); ν(NO(+)) = 1879 cm(-1)). A pK(a) of 0.74 was determined from infrared measurements as a function of pH for the reaction: trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) + H(2)O ? trans-[Ru(NO)(NH(3))(4)(P(O(-))(OH)(2))](2+) + H(3)O(+). According to (31)P-NMR, IR, UV-vis, cyclic voltammetry and ab initio calculation data, upon deprotonation, trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) yields the O-bonded linkage isomer trans- [Ru(NO)(NH(3))(4)(OP(OH)(2))](2+), then the trans-[Ru(NO)(NH(3))(4)(OP(H)(OH)(2))](3+) decays to give the final products H(3)PO(3) and trans-[Ru(NO)(NH(3))(4)(H(2)O)](3+). The dissociation of phosphorous acid from the [Ru(NO)(NH(3))(4)](3+) moiety is pH dependent (k(obs) = 2.1 × 10(-4) s(-1) at pH 3.0, 25 °C).     

Addition of Pt(PBu(t)(3)) groups to Ru(5)(CO)(12)(eta(6)-C(6)H(6))(mu(5)-C). Synthesis, structures, and dynamical activity

The reaction of Ru(5)(CO)(12)(eta(6)-C(6)H(6))(mu(5)-C), 7, with Pt(PBu(t)(3))(2) yielded two products Ru(5)(CO)(12)(eta(6)-C(6)H(6))(mu(6)-C)[Pt(PBu(t)(3))], 8, and Ru(5)(CO)(12)(eta(6)-C(6)H(6))(mu(6)-C)[Pt(PBu(t)(3))](2), 9. Compound 8 contains a Ru(5)Pt metal core in an open octahedral structure. In solution, 8 exists as a mixture of two isomers that interconvert rapidly on the NMR time scale at 20 degrees C, DeltaH() = 7.1(1) kcal mol(-1), DeltaS() = -5.1(6) cal mol(-)(1) K(-)(1), and DeltaG(298)(#) = 8.6(3) kcal mol(-1). Compound 9 is structurally similar to 8, but has an additional Pt(PBu(t)(3)) group bridging an Ru-Ru edge of the cluster. The two Pt(PBu(t)(3)) groups in 9 rapidly exchange on the NMR time scale at 70 degrees C, DeltaH(#) = 9.2(3) kcal mol(-)(1), DeltaS(#) = -5(1) cal mol(-)(1) K(-)(1), and DeltaG(298)(#) = 10.7(7) kcal mol(-1). Compound 8 reacts with hydrogen to give the dihydrido complex Ru(5)(CO)(11)(eta(6)-C(6)H(6))(mu(6)-C)[Pt(PBu(t)(3))](mu-H)(2), 10, in 59% yield. This compound consists of a closed Ru(5)Pt octahedron with two hydride ligands bridging two of the four Pt-Ru bonds.     

Tuning the electronic structure of octahedral iron complexes [FeL(X)] (L = 1-alkyl-4,7-bis(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane,X = Cl,CH(3)O,CN, NO). The S = 1/2 <==>3/2 Spin equilibrium of [FeL(Pr)(NO)

Two new pentadentate, pendent arm macrocyclic ligands of the type 1-alkyl-4,7-bis(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane where alkyl represents an isopropyl, (L(Pr))(2-), or an ethyl group, (L(Et))(2-), have been synthesized. It is shown that they bind strongly to ferric ions generating six-coordinate species of the type [Fe(L(alk))X]. The ground state of these complexes is governed by the nature of the sixth ligand, X: [Fe(III)(L(Et))Cl] (2) possesses an S = 5/2 ground state as do [Fe(III)(L(Et))(OCH(3))] (3) and [Fe(III)(L(Pr))(OCH(3))] (4). In contrast, the cyano complexes [Fe(III)(L(Et))(CN)] (5) and [Fe(III)(L(Pr))(CN)] (6) are low spin ferric species (S = 1/2). The octahedral [FeNO](7) nitrosyl complex [Fe(L(Pr))(NO)] (7) displays spin equilibrium behavior S = 1/2<==>S = (3)/(2) in the solid state. Complexes [Zn(L(Pr))] (1), 4.CH(3)OH, 5.0.5toluene.CH(2)Cl(2), and 7.2.5CH(2)Cl(2) have been structurally characterized by low-temperature (100 K) X-ray crystallography. All iron complexes have been carefully studied by zero- and applied-field M?ssbauer spectroscopy. In addition, Sellmann's complexes [Fe(pyS(4))(NO)](0/1+) and [Fe(pyS(4))X] (X = PR(3), CO, SR(2)) have been studied by EPR and M?ssbauer spectroscopies and DFT calculations (pyS(4) = 2,6-bis(2-mercaptophenylthiomethyl)pyridine(2-)). It is concluded that the electronic structure of 7 with an S = 1/2 ground state is low spin ferrous (S(Fe) = 0) with a coordinated neutral NO radical (Fe(II)-NO) whereas the S = 3/2 state corresponds to a high spin ferric (S(Fe) = 5/2) antiferromagnetically coupled to an NO(-) anion (S = 1). The S = 1/2<==>S = 3/2 equilibrium is then that of valence tautomers rather than that of a simple high spin<==>low spin crossover.     

Tandem mass spectrometry of metal nitrate negative ions produced by electrospray ionization

M(NO(3))(x)(-) ions are generated by electrospray ionization (ESI) of metal solutions in nitric acid in negative ion mode. Collision-induced reactions of these ions are monitored in a tandem mass spectrometer (MS) of quadrupole-octopole-quadrupole (QoQ) geometry. For Group 1 and 2 elements, the M(NO(3))(x)(-) ions dissociate into NO(3)(-) and neutral metal nitrate molecules. These elements also form some M(x)(NO(3))x+1- clusters, especially Li(+). Metal nitrate ions from transition elements and Group 13 elements fragment into oxo products and also undergo internal electron transfer to leave the M atom in a lower oxidation state. To calibrate the collision energy, the dissociation energy of O-NO(2)(-) is found to be 5.55 eV, about 0.76 eV lower than a value derived from thermochemistry. The product ions from Fe(NO(3))(4)(-) ions have low formation thresholds of only 0.5 to 2 eV.     

Germanium-rich pentaruthenium carbonyl clusters including Ru(5)(CO)(11)(mu-GePh(2))(4)(mu(5)-C) and its reactions with hydrogen

The reaction of Ru(5)(CO)(15)(mu(5)-C), 1, with Ph(3)GeH at 150 degrees C has yielded two new germanium-rich pentaruthenium cluster complexes: Ru(5)(CO)(11)(mu-CO)(mu-GePh(2))(3)(mu(5)-C), 2; Ru(5)(CO)(11)(mu;-GePh(2))(4)(mu(5)-C), 3. Both compounds contain square pyramidal Ru(5) clusters with GePh(2) groups bridging three and four of the edges of the Ru(5) square base, respectively. When treated with 1 equiv of Ph(3)GeH at 150 degrees C compound 2 is converted to 3. Reaction of 3 with H(2) at 150 degrees C yielded Ru(5)(CO)(10)(mu-GePh(2))(4)(mu(5)-C)(mu-H)(2), 4, containing two hydride ligands and one less CO ligand. Reaction of 4 with hydrogen at 150 degrees C yielded the compound Ru(5)(CO)(10)(mu-GePh(2))(2)(mu(3)-GePh)(2)(mu(3)-H)(mu(4)-CH), 5, by loss of benzene and conversion of two of the bridging GePh(2) groups into triply bridging GePh groups. Compound 5 contains one triply bridging hydride ligand and a quadruply bridging methylidyne ligand formed by addition of one hydrogen atom to the carbido carbon atom.     

Excited-state properties of Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF, PPh(3), py)

The photophysical properties of Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF = tetrahydrofuran, PPh(3) = triphenylphosphine, py = pyridine) were explored upon excitation with visible light. Time-resolved absorption shows that all the complexes possess a long-lived transient (3.5-5.0 micros) assigned as an electronic excited state of the molecules, and they exhibit an optical transition at approximately 760 nm whose position is independent of axial ligand. No emission from the Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF, PPh(3), py) systems was detected, but energy transfer from Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) to the (3)pipi excited state of perylene is observed. Electron transfer from Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) to 4,4'-dimethyl viologen (MV(2+)) and chloro-p-benzoquinone (Cl-BQ) takes place with quenching rate constants (k(q)) of 8.0 x 10(6) and 1.2 x 10(6) M(-1) s(-1) in methanol, respectively. A k(q) value of 2 x 10(8) M(-1) s(-1) was measured for the quenching of the excited state of Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) by O(2) in methanol. The observations are consistent with the production of an excited state with excited-state energy, E(00), between 1.34 and 1.77 eV.     

Reactions of nitrogen oxides with heme models. Characterization of NO and NO2 dissociation from Fe(TPP)(NO2)(NO) by flash photolysis and rapid dilution techniques: Fe(TPP)(NO2) as an unstable intermediate

Described are studies directed toward elucidating the controversial chemistry relating to the solution phase reactions of nitric oxide with the iron(II) porphyrin complex Fe(TPP)(NO) (1, TPP = meso-tetraphenylporphinato2-). The only reaction observable with clean NO is the formation of the diamagnetic dinitrosyl species Fe(TPP)(NO)2 (2), and this is seen only at low temperatures (K(1) < 3 M(-1) at ambient temperature). However, 1 does readily react reversibly with N2O3 in the presence of excess NO to give the nitro nitrosyl complex Fe(TPP)(NO2)(NO) (3), suggesting that previous claims that 1 promotes NO disproportionation to give 3 may have been compromised by traces of air in the nitric oxide sources. It is also noted that 3 undergoes reversible loss of NO to give the elusive nitro species Fe(TPP)(NO2) (4), which has been implicated as a powerful oxygen atom transfer agent in reactions with various substrates. Furthermore, in the presence of excess NO2, the latter undergoes oxidation to the stable nitrato analogue Fe(TPP)(NO3) (5). Owing to such reactivity of Fe(TPP)(NO2), flash photolysis and stopped-flow kinetics rather than static techniques were necessary for the accurate measurement of dissociation equilibria characteristic of Fe(TPP)(NO2)(NO) in 298 K toluene solution. Flash photolysis of 3 resulted in competitive NO2 and NO dissociation to give Fe(TPP)(NO) and Fe(TPP)(NO2), respectively. The rate constant for the reaction of 1 with N2O3 to generate Fe(TPP)(NO2)(NO) was determined to be 1.8 x 10(6) M(-1) s(-1), and that for the NO reaction with 4 was similarly determined to be 4.2 x 10(5) M(-1) s(-1). Stopped-flow rapid dilution techniques were used to determine the rate constant for NO dissociation from 3 as 2.6 s(-1). The rapid dilution experiments also demonstrated that Fe(TPP)(NO2) readily undergoes further oxidation to give Fe(TPP)(NO3). The mechanistic implications of these observations are discussed, and it is suggested that NO2 liberated spontaneously from Fe(P)(NO2) may play a role in an important oxidative process involving this elusive species.     

Reactivity of radicals generated on irradiation of trans-[Ru(NH3)4(NO2)P(OEt)3](PF6)

The electronic absorption spectrum of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in aqueous solution is characterized by a strong absorption band at 334 nm (lambda(max) = 1800 mol(-1) L cm(-1)). On the basis of quantum mechanics calculations, this band has been assigned to a MLCT transition from the metal to the nitro ligand. Molecular orbital calculations also predict an LF transition at 406 nm, which is obscured by the intense MLCT transition. When trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in acetonitrile is irradiated with a 355 nm pulsed laser light, the absorption features are gradually shifted to represent those of the solventocomplex trans-[Ru(NH(3))(4)(solv)(P(OEt)(3)](2+) (lambda(max) = 316 nm, epsilon = 650 mol(-1) L cm(-1)), which was also detected by (31)P NMR spectroscopy. The net photoreaction under these conditions is a photoaquation of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+), although, after photolysis, the presence of the nitric oxide was detected by differential pulse polarography. In phosphate buffer pH 9.0, after 15 min of photolysis, a thermal reaction resulted in the formation of a hydroxyl radical and a small amount of a paramagnetic species as detected by EPR spectroscopy. In the presence of trans-[Ru(NH(3))(4)(solv)P(OEt)(3)](2+), the hydroxyl radical initiated a chain reaction. On the basis of spectroscopic and electrochemical data, the role of the radicals produced is analyzed and a reaction sequence consistent with the experimental results is proposed. The 355 nm laser photolysis of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in phosphate buffer pH 7.4 also gives nitric oxide, which is readily trapped by ferrihemeproteins (myoglobin, hemoglobin, and cytochrome C), giving rise to the formation of their nitrosylhemeproteins(II), (NO)Fe(II)hem.     

Spectroscopic and density functional studies of the dinitrosyl metalloporphyrin complexes Fe(P)(NO)2 and Ru(P)(NO)2

Experimental evidence including infrared spectra for the formation of the dinitrosyl metalloporphyrin complexes M(P)(NO)(2) (M = Ru or Fe, P = tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), or tetra-m-tolylporphryin (TmTP)) is described. Although observation of a single NO stretching band in the IR spectrum of each M(P)(NO)(2) complex first suggested a centrosymmetric (D(4)(h)() or C(2)(h)()) structure, DFT geometry optimizations and frequency calculations of model complexes indicate that the trans-syn (C(2)(v)()) conformation should be more stable. The frequency calculations resolve the apparent ambiguity in the IR spectra in terms of the relative oscillator strengths of the predicted IR bands.