Ru-N Bond Lengths Research Articles

Synthesis, crystal structure, electrochemical properties, and photophysical characterization of ruthenium(II) 4,4′-dimethoxy-2,2′-bipyridine polypyridine complexes

A series of ruthenium(II) polypyridine complexes of the type [Ru(tpy)((CH3O)2bpy)(4-R-py)]2+, where tpy = 2,2′;6′,2″-terpyridine, (CH3O)2bpy = 4,4′-dimethoxy-2,2′-bipyridine, and 4-R-py = pyridine (py, 2), 4-methoxypyridine (4-CH3O-py, 3), 4-aminopyridine (4-NH2-py, 4), were synthesized and their crystal structures, electronic absorption, luminescence, and electrochemical properties were investigated. The effect of adding electron-donating groups to the bidentate and monodentate ligand was investigated and compared with [Ru(tpy)(bpy)(py)]2+ (1) where bpy = 2,2′-bipyridine. While anticipated trends were not observed for the Ru-N(6) bond length as 4-R-py was varied, noticeable modifications of the measured photophysical properties were observed. A red-shift of the metal-to-ligand charge transfer (1MLCT) is observed from 466 nm in 1 to 474 nm, 478 nm, and 485 nm for 2–4, respectively. Additionally, a red-shift in the luminescence maxima is observed in 2–4 as compared to 1, with 4 exhibiting the greatest shift of more than 100 nm. Complexes 2–4 exhibited luminescence quantum yields of 2.7 × 10−4, 7.2 × 10−4, and 7.4 × 10−4, respectively, which are increased compared to the quantum yield of 2.0 × 10−4 in 1. These findings demonstrate systematic tuning of absorbance and luminescence properties of ruthenium polypyridine complexes by addition of π-donating substituents to the monodentate and bidentate ligand.

Strong metal-to-ligand π-backbonding weakens the N[sbnd]N bond in 2-pyridinealdazine coordinated to tetraammine-ruthenium(II)

A new mononuclear Ru(II) complex of formula [Ru(NH3)4(2-PCA)](PF6)2, (1), with 2-PCA=2-pyridinealdazine, has been synthesized and characterized by spectroscopic and electrochemical techniques. The complete structure of (1) was determined by X-ray diffraction. A strong π-backbonding effect dπ(Ru)→π *(2-PCA) is disclosed in (1) by the high value of the RuIII/RuII redox potential and the short Ru-N(imine) bond length, which leads to a weakened NN bond in coordinated 2-PCA compared to that of the free ligand and thus to an enhanced reactivity in acidic media. In effect, the product of the reaction of excess Ru with 2-PCA is not the dinuclear species bridged by 2-PCA, but the already known 2-iminopyridine complex of tetraammineruthenium(II). DFT and TD-DFT calculations of (1) were consistent with experimental results and allowed the complete assignment of its UV–Visible bands.

Ruthenium dihydroxybipyridine complexes are tumor activated prodrugs due to low pH and blue light induced ligand release

Ruthenium drugs are potent anti-cancer agents, but inducing drug selectivity and enhancing their modest activity remain challenging. Slow Ru ligand loss limits the formation of free sites and subsequent binding to DNA base pairs. Herein, we designed a ligand that rapidly dissociates upon irradiation at low pH. Activation at low pH can lead to cancer selectivity, since many cancer cells have higher metabolism (and thus lower pH) than non-cancerous cells. We have used the pH sensitive ligand, 6,6′-dihydroxy-2,2′-bipyridine (66′bpy(OH)2), to generate [Ru(bpy)2(66′(bpy(OH)2)]2+, which contains two acidic hydroxyl groups with pKa1=5.26 and pKa2=7.27. Irradiation when protonated leads to photo-dissociation of the 66′bpy(OH)2 ligand. An in-depth study of the structural and electronic properties of the complex was carried out using X-ray crystallography, electrochemistry, UV/visible spectroscopy, and computational techniques. Notably, RuN bond lengths in the 66′bpy(OH)2 complex are longer (by ~0.3Å) than in polypyridyl complexes that lack 6 and 6′ substitution. Thus, the longer bond length predisposes the complex for photo-dissociation and leads to the anti-cancer activity. When the complex is deprotonated, the 66′bpy(O−)2 ligand molecular orbitals mix heavily with the ruthenium orbitals, making new mixed metal–ligand orbitals that lead to a higher bond order. We investigated the anti-cancer activities of [Ru(bpy)2(66′(bpy(OH)2)]2+, [Ru(bpy)2(44′(bpy(OH)2)]2+, and [Ru(bpy)3]2+ (44′(bpy(OH)2=4,4′-dihydroxy-2,2′-bipyridine) in HeLa cells, which have a relatively low pH. It is found that [Ru(bpy)2(66′(bpy(OH)2)]2+ is more cytotoxic than the other ruthenium complexes studied. Thus, we have identified a pH sensitive ruthenium scaffold that can be exploited for photo-induced anti-cancer activity.

(2,2′-Bipyridine)chlorido[diethyl (2,2′:6′,2′′-terpyridin-4-yl)phosphonate]ruthenium(II) hexafluoridophosphate acetonitrile/water solvate

The cationic complex in the title compound, [RuCl(C10H8N2)(C19H20N3O3P)]PF6·0.83CH3CN·0.17H2O, is a water-oxidation precatalyst functionalized for TiO2 attachment via terpyridine phospho­nate. The The RuII atom in the complex has a distorted octa­hedral geometry due to the restricted bite angle [159.50 (18)°] of the terpyridyl ligand. The dihedral angle between the least-squares planes of the terpyridyl and bipyridyl moieties is 86.04 (14)°. The mean Ru—N bond length for bi­pyridine is 2.064 (5) Å, with the bond opposite to Ru—Cl being 0.068 Å shorter. For the substituted terpyridine, the mean Ru—N distance involving the outer N atoms trans to each other is 2.057 (6) Å, whereas the bond length involving the central N atom is 1.944 (5) Å. The Ru—Cl distance is 2.4073 (15) Å. The P atom of the phospho­nate group lies in the same plane as its adjacent pyridyl ring, with the ordinary character of the bond between P and Ctpy [1.801 (6) Å] allowing for free rotation of the terpyridine substituent around the P—Ctpy axis. The aceto­nitrile solvent mol­ecule was refined to be disordered with two water mol­ecules; occupancies for the acetontrile and water mol­ecules were 0.831 (9) and 0.169 (9), respectively. Also disordered was the PF6 − counter-ion (over three positions) and one of the eth­oxy substituents (with two positions). The crystal structure shows significant intra- and inter­molecular H⋯X contacts, especially some involving the Cl− ligand.

Strong metal–metal coupling in mixed-valent intermediates [Cl(L)Ru(μ-tppz)Ru(L)Cl]+, L = β-diketonato ligands, tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine

Five diruthenium(II) complexes [Cl(L)Ru(μ-tppz)Ru(L)Cl] (1-5) containing differently substituted β-diketonato derivatives (1: L = 2,4-pentanedionato; 2: L = 3,5-heptanedionato; 3: L = 2,2,6,6-tetramethyl-3,5-heptanedionato; 4: L = 3-methyl-2,4-pentanedionato; 5: L = 3-ethyl-2,4-pentanedionato) as ancillary ligands (L) were synthesized and studied by spectroelectrochemistry (UV-Vis-NIR, electron paramagnetic resonance (EPR)). X-ray structural characterisation revealed anti (1, 2, 5) or syn (3) configuration as well as non-planarity of the bis-tridentate tppz bridge and strong dπ(Ru(II)) → π*(pyrazine, tppz) back-bonding. The widely separated one-electron oxidation steps, Ru(II)Ru(II)/Ru(II)Ru(III) and Ru(II)Ru(III)/Ru(III)Ru(III), result in large comproportionation constants (K(c)) of ≥10(10) for the mixed-valent intermediates. The syn-configurated (n) exhibits a particularly high K(c) of 10(12) for n = 1+, accompanied by density functional theory (DFT)-calculated minimum Ru-N bond lengths for this Ru(II)Ru(III) intermediate. The electrogenerated mixed-valent states 1(+)-5(+) exhibit anisotropic EPR spectra at 110 K with average values <g> of 2.304-2.234 and g anisotropies Δg = g(1)-g(3) of 0.82-0.99. Metal-to-metal charge transfer (MMCT) absorptions occur for 1(+)-5(+) in the NIR region at 1660 nm-1750 nm (ε ≈ 2700 dm(3) mol(-1) cm(-1), Δν(1/2) ≈ 1800 cm(-1)). DFT calculations of 1(+) and 3(+) yield comparable Mulliken spin densities of about 0.60 for the metal ions, corresponding to valence-delocalised situations (Ru(2.5))(2). Rather large spin densities of about -0.4 were calculated for the tppz bridges in 1(+) and 3(+). The calculated electronic interaction values (V(AB)) for 1(+)-5(+) are about 3000 cm(-1), comparable to that for the Creutz-Taube ion at 3185 cm(-1). The DFT calculations predict that the Ru(III)Ru(III) forms in 1(2+)-5(2+) prefer a triplet (S = 1) ground state with ΔE (S = 0 - S = 1) ∼5000 cm(-1). One-electron reduction takes place at the tppz bridge which results in species [Cl(L)Ru(II)(μ-tppz˙(-))Ru(II)(L)Cl](-) (1˙(-)-3˙(-), 5˙(-)) which exhibit free radical-type EPR signals and NIR transitions typical of the tppz radical anion. The system 4(n) is distinguished by lability of the Ru-Cl bonds.

Trans-Dichlorido(2,2-dimethylpropane-1,3-diamine)bis(triphenylphosphane)ruthenium(II)

In the title compound, [RuCl2(C5H14N2)(C18H15P)2], the RuII atom is six-coordinated, forming a slightly distorted octa­hedral geometry, with two chloride ions in an axial arrangement, and two P atoms of two triphenyl­phosphane and two chelating N atoms of the bidentate 2,2-dimethyl­propane-1,3-diamine ligand located in the equatorial plane. The average Ru—P, Ru—N and Ru—Cl bond lengths are 2.325 (18), 2.1845 (7) and 2.4123 (12) Å, respectively.

Structural Properties of Ruthenium Biimidazole Complexes Determining the Stability of their Supramolecular Aggregates

The results of a detailed investigation of the influence of substituents in a variety of ruthenium biimidazole-type complexes [Ru(R-bpy)2(R´-bi(bz)imH2)]2+ (R = H, tBu; R´ = H,Me; bi(bz)imH2 = 2,2´-bi(benz)imidazole) on selected structural and photophysical properties is reported. The photophysical properties are only marginally influenced by the substituents at the bipyridine and the biimidazole core. All complexes show intense absorptions in the visible range of the spectrum with maxima around 475 nm, and emission from the formed excited state occurs at wavelengths between 650 and 670 nm. The comparison of structural properties determined by X-ray analysis within a series of related complexes shows that the Ru-N bond lengths to the coordinated bipyridines are not significantly influenced by the substituents, but slight differences in the Ru-N bond lengths to the biimidazole-type ligands can be detected. The reactions between ruthenium complexes containing different biimidazole-type ligands with the sulfate dianion, however, show a strong correlation between the substituents at the biimidazole core and the solubility of the product. The bibenzimidazolecontaining complexes precipitate from aqueous solution whereas the ruthenium complex containing unsubstituted biimidazole stays in solution. The solid-state structure of one example of the sulfatecontaining products (2b) shows that strong hydrogen bonds between the secondary amine function of the bibenzimidazole and the oxygen functionalities of the sulfate contribute to this unexpected behavior.

(Benzophenone imine-κN)chlorido(hydridotripyrazolylborato)(triphenylphosphine)ruthenium(II) diethyl ether solvate

The reaction of RuCl(Tp)(Ph3P)2, where Tp is [(CH)3N2]3BH, with benzophenone imine leads to the formation of the title compound, [Ru(C9H10BN6)Cl(C13H11N)(C18H15P)]·C4H10O. The environment about the Ru atom corresponds to a slightly distorted octa­hedron and the bite angle of the Tp ligand produces an average N—Ru—N angle of 86.3 (9)°. The three Ru—N(Tp) bond lengths [2.117 (2), 2.079 (2) and 2.084 (2) Å] are slightly longer than the average distance (2.038 Å) in other ruthenium–Tp complexes.

New Ruthenium Nitrosyl Complexes with Tris(1-pyrazolyl)methane (tpm) and 2,2‘-Bipyridine (bpy) Coligands. Structure, Spectroscopy, and Electrophilic and Nucleophilic Reactivities of Bound Nitrosyl

The new compound [Ru(bpy)(tpm)NO](ClO4)3 [tpm = tris(1-pyrazolyl)methane; bpy = 2,2'-bipyridine] has been prepared in a stepwise procedure that involves the conversion of [Ru(bpy)(tpm)Cl]+ into the aqua and nitro intermediates, followed by acidification. The diamagnetic complex crystallizes to exhibit distorted octahedral geometry around the metal, with the Ru-N(O) bond length 1.774(12) A and the RuNO angle 179.1(12) degrees , typical for a {RuNO}6 description. The [Ru(bpy)(tpm)NO]3+ ion (I) has been characterized by 1H NMR and IR spectroscopies (nu(NO) = 1959 cm(-1)) and through density functional theory calculations. Intense electronic transitions in the 300-350-nm region are assigned through time-dependent (TD)DFT as intraligand pi --> pi for bpy and tpm. The dpi --> pi(bpy) metal-to-ligand charge-transfer transitions appear at higher energies. Aqueous cyclic voltammetric studies show a reversible wave at 0.31 V (vs Ag/AgCl, 3 M Cl-), which shifts to 0.60 V in MeCN, along with the onset of a wave of an irreversible process at -0.2 V. The waves are assigned to the one- and two-electron reductions centered at the NO ligand, leading to species with {RuNO}(7) and {RuNO}(8) configurations, respectively. Controlled potential reduction of I in MeCN led to the [Ru(bpy)(tpm)NO]2+ ion (II), revealing a significant downward shift of nu(NO) to 1660 cm(-1) as well as changes in the electronic absorption bands. II was also characterized by electron paramagnetic resonance, showing an anisotropic signal at 110 K that arises from an S = 1/2 electronic ground state; the g-matrix components and hyperfine coupling tensor resemble the behavior of related {RuNO}7 complexes. Both I and II were characterized through their main reactivity modes, electrophilic and nucleophilic, respectively. The addition of OH- into I generated the nitro complex, with k(OH) = 3.05 x 10(6) M(-1) s(-1) (25 degrees C). This value is among the highest obtained for related nitrosyl complexes and correlates with ENO+/NO, the one-electron redox potential. Complex II is a robust species toward NO release, although a conversion to I was observed in the presence of O2. This reaction afforded a second-order rate law with k = 3.5 M(-1) s(-1) (25 degrees C). The stabilization of the NO radical complex is attributed to the high positive charge of the precursor and to the geometrical and electronic structure as determined by the neutral tpm ligand.

A ruthenium complex with 1,5-diphenyl-3-thiocarbazone (dithizone) as monodentate ligands: bis(2,2'-bipyridyl-kappa(2)N,N')bis(dithizonato-kappaS)ruthenium(II).

The title compound, [Ru(C(13)H(11)N(4)S)(2)(C(15)H(8)N(2))(2)], has C(2) symmetry, with bidentate 2,2'-bipyridyl ligands dictating a cis geometry around the Ru(II) center. The monodentate S-bonded dithizone ligands are almost planar, except for one of the phenyl rings, which is twisted by 34.2 (4) degrees from the N/N/C(S)/N/N plane. The Ru-S bond length is 2.4140 (13) A, and the Ru-N bond lengths are 2.048 (4) and 2.074 (4) A.

Interaction between dioxoruthenium(VI) porphyrins and hydroxylamines: coordination of N-substituted hydroxylamine to ruthenium and X-ray crystal structures of ruthenium complexes with a unidentate nitrosoarene ligand.

The interactions between dioxoruthenium(VI) porphyrins 1 with N-phenylhydroxylamine or unsubstituted hydroxylamine are described. Reaction of complexes 1 with excess PhNHOH leads to isolation of bis(nitrosobenzene)ruthenium(II) porphyrins 3 and mono(nitrosobenzene)ruthenium(II) porphyrins 4. Both the types of ruthenium complexes are characterized by 1H NMR, IR, and UV/Vis spectroscopy, and mass spectrometry. The X-ray structure determinations on [Ru(II)(TPP)(PhNO)2] (3a), [Ru(II)(2,6-Cl-TPP)(PhNO)2] (3e), and [Ru(II)(4-MeO-TPP)(PhNO)(PhNH2)] (4d) (TPP tetraarylporphyrin) disclose a unidentate nitrosoarene coordination in all these complexes, with Ru-N(PhNO) bond lengths of 2.003(3) (3a, average), 1.991(3) (3e, average), and 2.042(2) A (4d). In the case of 4d, the Ru-N(PhNH2) bond length is found to be 2.075(3) A. Mechanistic investigations reveal the formation of intermediates [Ru(II)(Por)(PhNO)(PhNHOH)] (5; Por=porphyrin), a ruthenium complex with N-substituted hydroxylamine ligand, in the "1 + PhNHOH" system. The Ru-NH(OH)Ph moiety in 5 undergoes no rapid exchange with free PhNHOH in solution at room temperature, as revealed by 1H NMR spectroscopy. Unlike the interaction between complexes 1 and PhNHOH, reaction of such complexes with NH2OH affords nitrosylruthenium(II) porphyrins [Ru(II)(Por)(NO)(OH)] (6).

Ruthenium(II) ammine and hydrazine complexes with [N(Ph2PQ)2]- (Q = S, Se) ligands.

Reactions of coordinatively unsaturated Ru[N(Ph2PQ)2]2(PPh3) (Q = S (1), Se (2)) with pyridine (py), SO2, and NH3 afford the corresponding 18e adducts Ru[N(Ph2PQ)2]2(PPh3)(L) (Q = S, L = NH3 (5); Q = Se, L = py (3), SO2 (4), NH3 (6)). The molecular structures of complexes 2 and 6 are determined. The geometry around Ru in 2 is pseudo square pyramidal with PPh3 occupying the apical position, while that in 6 is pseudooctahedral with PPh3 and NH3 mutually cis. The Ru-P distances in 2 and 6 are 2.2025(11) and 2.2778(11) A, respectively. The Ru-N bond length in 6 is 2.185(3) A. Treatment of 1 or 2 with substituted hydrazines L or NH2OH yields the respective adducts Ru[N(Ph2PQ)2]2(PPh3)(L) (Q = S, L = NH2NH2 (12), t-BuNHNH2 (14), l-aminopiperidine (C5H10NNH2) (15); Q = Se, L = PhCONHNH2 (7), PhNHNH2 (8), NH2OH (9), t-BuNHNH2 (10), C5H10NNH2 (11), NH2NH2 (13)), which are isolated as mixtures of their trans and cis isomers. The structures of cis-14 and cis-15 are characterized by X-ray crystallography. In both molecular structures, the ruthenium adopts a pseudooctahedral arrangement with PPh3 and hydrazine mutually cis. The Ru-N bond lengths in cis-14.CH2Cl2 and cis-15 are 2.152(3) and 2.101(3) A, respectively. The Ru-N-N bond angles in cis-14.CH2Cl2 and cis-15 are 120.5(4) and 129.0(2) degrees, respectively. Treatment of 1 with hydrazine monohydrate leads to the isolation of yellow 5 and red trans-Ru[N(Ph2PS)2]2(NH3)(H2O) (16), which are characterized by mass spectrometry, 1H NMR spectroscopy, and elemental analyses. The geometry around ruthenium in 16 is pseudooctahedral with the NH3 and H2O ligands mutually trans. The Ru-O and Ru-N bond distances are 2.118(4) and 2.142(6) A, respectively. Oxidation reactions of the above ruthenium hydrazine complexes are also studied.

Bis Axial Ligation of Simple Imine and Methyleneamido Groups by Ruthenium Porphyrins

Bis(N-ethylideneethanamine)ruthenium(ii) porphyrins, [Ru11(Por)(N(Et)=CHMe)2] (Por=TTP, 4-Cl-TPP), were prepared by the reaction of dioxoruthenium(VI) porphyrins with triethylamine in approximately 85% yields. The reaction between dioxoruthenium(VI) porphyrins and benzophenone imine afforded bis(diphenylmethyleneamido)ruthenium(IV) porphyrins, [Ru(IV)(Por)(N=CPh2)2] (Por=TTP, 3,4,5-MeO-TPP), in approximately 65% yields. These new classes of metalloporphyrins were characterized by 1H NMR, UV/Vis, and IR spectroscopy as well as by mass spectrometry and elemental analysis. The X-ray crystallographic structures of [Ru(II)(TTP)(N(Et)=CHMe)2] and [Ru(IV)(3,4,5-MeO-TPP)(N=CPh2)2] revealed an axial Ru-N bond length of 2.115(6) A for the imine complex and 1.896(8) A for the methyleneamido complex. Each of the N=CPh2 axial groups in [Ru(IV)(3,4,5-MeO-TPP)(N=CPh2)2] adopts a linear coordination mode with a corresponding Ru-N-C angle of 175.9(9)degrees. Spectral and structural studies revealed essentially single bonding character for the bis(imine) complexes but a multiple bonding character for the bis(methyleneamido) complexes with respect to their axial Ru-N bonds.

Bis axial ligation of simple imine and methyleneamido groups by ruthenium porphyrins

Bis(N-ethylideneethanamine)ruthenium(ii) porphyrins, [Ru11(Por)(N(Et)=CHMe)2] (Por=TTP, 4-Cl-TPP), were prepared by the reaction of dioxoruthenium(VI) porphyrins with triethylamine in approximately 85% yields. The reaction between dioxoruthenium(VI) porphyrins and benzophenone imine afforded bis(diphenylmethyleneamido)ruthenium(IV) porphyrins, [Ru(IV)(Por)(N=CPh2)2] (Por=TTP, 3,4,5-MeO-TPP), in approximately 65% yields. These new classes of metalloporphyrins were characterized by 1H NMR, UV/Vis, and IR spectroscopy as well as by mass spectrometry and elemental analysis. The X-ray crystallographic structures of [Ru(II)(TTP)(N(Et)=CHMe)2] and [Ru(IV)(3,4,5-MeO-TPP)(N=CPh2)2] revealed an axial Ru-N bond length of 2.115(6) A for the imine complex and 1.896(8) A for the methyleneamido complex. Each of the N=CPh2 axial groups in [Ru(IV)(3,4,5-MeO-TPP)(N=CPh2)2] adopts a linear coordination mode with a corresponding Ru-N-C angle of 175.9(9)degrees. Spectral and structural studies revealed essentially single bonding character for the bis(imine) complexes but a multiple bonding character for the bis(methyleneamido) complexes with respect to their axial Ru-N bonds.

Reactivity of dioxoruthenium(VI) porphyrins toward amines. Synthesis and characterization of bis(arylamine)ruthenium(II), bis(arylamido)- and bis(diphenylamido)ruthenium(IV), and oxo(tert-butylimido)ruthenium(VI) porphyrins.

Reactions of dioxoruthenium(VI) porphyrins, [Ru(VI)O2(Por)], with p-chloroaniline, trimethylamine, tert-butylamine, p-nitroaniline, and diphenylamine afforded bis(amine)ruthenium(II) porphyrins, [Ru(II)(Por)(L)2] (L-p-ClC6H4NH2, Me3N, Por=TTP, 4-Cl-TPP; L=tBuNH2, Por = TPP, 3,4,5-MeO-TPP, TTP, 4-Cl-TPP, 3,5-Cl-TPP) and bis(amido)ruthenium(IV) porphyrins, [Ru(IV)(Por)(X)2] (X=p-NO2C6H4NH, Por=TTP, 4-Cl-TPP; X = Ph2N, Por = 3,4,5-MeO-TPP, 3,5-Cl-TPP), respectively. Oxidative deprotonation of [Ru(II)(Por)(NH2-p-C6H4Cl)2] in chloroform by air generated bis(arylamido)ruthenium(IV) porphyrins, [RuIV(Por)(NH-p-C6H4Cl)2] (Por=TTP. 4-Cl-TPP). Oxidation of [RuII(Por)-(NH2tBu)2] by bromine in dichloromethane in the presence of tert-butylamine and traces of water produced oxo(imido)ruthenium(VI) porphyrins, [RuVI-O(Por)(NtBu)] (Por=TPP, 3,4,5-MeO-TPP, TTP, 4-Cl-TPP, 3,5-Cl-TPP). These new classes of ruthenium complexes were characterized by 1H NMR, IR, and UV/visible spectroscopy, mass spectrometry, and elemental analysis. The structure of [Ru(IV)(TTP)(NH-p-C6H4Cl)2 . CH2Cl2 was determined by X-ray crystallography. The Ru-N bond length and the Ru-N-C angle of the Ru-NHAr moiety are 1.956(7) A and 135.8(6) degrees, respectively.

Ruthenium Complexes Containing "Noninnocent" o-Benzoquinone Diimine/o-Phenylenediamide(2-) Ligands. Synthesis and Crystal Structure of the Nitrido-Bridged Complex [{LRu(o-C(6)H(4)(NH)(2))}(2)(&mgr;-N)](PF(6))(2).3CH(3)CN.C(6)H(5)CH(3).

Reaction of LRu(III)Cl(3) (L = 1,4,7-trimethyl-1,4,7-triazacyclononane) with 1,2-phenylenediamine (opdaH(2)) in H(2)O in the presence of air affords [LRu(II)(bqdi)(OH(2))](PF(6)) (1), where (bqdi) represents the neutral ligand o-benzoquinone diimine. From an alkaline methanol/water mixture of 1 was obtained the dinuclear species [{LRu(II)(bqdi)}(2)(&mgr;-H(3)O(2))](PF(6))(3) (1a). The coordinated water molecule in 1 is labile and can be readily substituted under appropriate reaction conditions by acetonitrile, yielding [LRu(II)(bqdi)(CH(3)CN)](PF(6))(2) (2), and by iodide and azide anions, affording [LRu(II)(bqdi)I](PF(6)).0.5H(2)O (3) and [LRu(bqdi)(N(3))](PF(6)).H(2)O (4), respectively. Heating of solid 4 in vacuum at 160 degrees C generates N(2) and the dinuclear, nitrido-bridged complex [{LRu(o-C(6)H(4)(NH)(2))}(2)(&mgr;-N)](PF(6))(2) (5). Complex 5 is a mixed-valent, paramagnetic species containing one unpaired electron per dinuclear unit whereas complexes 1-4 are diamagnetic. The crystal structures of 1, 1a.3CH(3)CN, 3, 4.H(2)O, and 5.3CH(3)CN.0.5(toluene) have been determined by X-ray crystallography: 1 crystallizes in the monoclinic space group P2(1)/m, Z = 2, with a = 8.412(2) Å, b = 15.562(3) Å, c = 10.025 Å, and beta = 109.89(2) degrees; 1a.3CH(3)CN, in the monoclinic space group C2/c, Z = 4, with a = 19.858(3) Å, b = 15.483(2) Å, c = 18.192(3) Å, and beta = 95.95(2) degrees; 3, in the orthorhombic space group Pnma, Z = 4, with a = 18.399(4) Å, b = 9.287(2) Å, and c = 12.052(2) Å, 4.H(2)O, in the monoclinic space group P2(1)/c, Z = 4, with a = 8.586(1) Å, b = 15.617(3) Å, c = 16.388(5) Å, and beta = 90.84(2) degrees; and 5.3CH(3)CN.0.5(toluene), in the monoclinic space group P2(1)/c, Z = 4, with a = 15.003(3) Å, b = 16.253(3) Å, c = 21.196(4) Å, and beta = 96.78(3) degrees. The structural data indicate that in complexes 1-4 the neutral o-benzoquinone diimine ligand prevails. In contrast, in 5 this ligand has predominantly o-phenylenediamide character, which would render 5 formally a mixed-valent Ru(IV)Ru(V) species. On the other hand, the Ru-N bond lengths of the Ru-N-Ru moiety at 1.805(5) and 1.767(5) Å are significantly longer than those in other crystallographically characterized Ru(IV)=N=Ru(IV) units (1.72-1.74 Å). It appears that the C(6)H(4)(NH)(2) ligand in 5 is noninnocent and that formal oxidation state assignments to the ligands or metal centers are not possible.

Perpendicularly Arranged Ruthenium Porphyrin Dimers and Trimers

A series of ruthenium(II) porphyrin dimers and trimers (carbonyl dimers, 1-4; carbonyl trimers, 5-7, bis(pyridyl) trimers, 8-10), having axial or bridging porphyrin ligands, were synthesized and characterized by (1)H NMR and IR spectroscopy and mass spectrometry. An X-ray structural determination of Ru(II)(OEP)(CO)(H(2)PyP(3)P) (1) (OEP = octaethylporphyrinato dianion, H(2)PyP(3)P = 5-pyridyl-10,15,20-triphenylporphyrinato dianion) was carried out. The axial porphyrin ligand is coordinated to the ruthenium porphyrin subunit obliquely. The Ru-N(Py) bond length is 2.237(4) Å, and the angle between the ruthenium porphyrin macrocycle and the pyridyl ring is 63.23(35) degrees. Crystallographic data for 1 are as follows: chemical formula C(80)H(73)N(9)ORu.CH(2)Cl(2), triclinic, P&onemacr;, a = 14.954(5) Å, b = 25.792(5) Å, c = 10.124(3) Å, alpha = 90.21(2) degrees, beta = 108.43(2) degrees, gamma = 73.39(2) degrees, Z = 2, R(F) = 0.0674. (1)H NMR signals of 2,6- and 3,5-pyridyl protons of the axial ligand porphyrins of the oligomers 1-10 showed significant upfield shifts, indicating that the axial porphyrin subunits are coordinated to the ruthenium porphyrin subunits through the pyridyl group in solution. UV-vis spectra revealed the presence of excitonic interaction between two axial ligand porphyrin subunits in the trimers 8-10. The MLCT bands from the central ruthenium(II) ions to the octaethylporphyrin rings were observed around 450 nm in 8 and 9. Cyclic voltammograms of the carbonyl dimers and trimers showed no redox waves of the ruthenium(II) ions, because the ruthenium(II) oxidation state of these complexes was significantly stabilized by the coordination of the axial CO ligands. On the other hand, bis(pyridyl) trimers exhibit the Ru(III/II) waves in the region of -0.12 to +0.15 V vs Ag/Ag(+) reference electrode.

The adsorption of atomic nitrogen on Ru(0001): geometry and energetics

The local adsoprtion geometries of the (2 × 2)-N and (✓3 × ✓3)R30°-N phases on the Ru(0001) surface are determined by analyzing low-energy electron diffraction intensity data. For both phases, nitrogen occupies the threefold hcp site. The nitrogen sinks deeply into the top Ru layer resulting in a N-Ru interlayer distance of 1.05 and 1.10 Å in the (2 × 2) and the (✓3 × ✓3)R30° unit cell, respectively. This result is attributed to a strong N binding to the Ru surface (Ru-N bond length = 1.93 A ̊ ) in both phases as also evidenced by an initio calculations which revealed binding energies of 5.82 and 5.59 eV, respectively.

Synthesis and crystal structures of lithium and potassium hexanitroruthenates (II)

A procedure for preparing Li4[Ru(NO2)6]…12H2O and K4[Ru(NO2)6] is described. We have carried out an X-ray diffraction study of polycrystals (DRON-UM1 diffractometer, R=192mm, CuKα radiation, Ni filter) and single crystals (CAD-4 automatic diffractometer, MoKα radiation, graphite monochromator, ω/2ϕ scan mode). Crystal data for Li4[Ru(NO2)6]…12H2O are a=11.749(9), c=16.807(12) A, space group\(I\bar 4\), V=2320.0 A3, Z=4, dcalc=1.778 g/cm3; for K4 [Ru(NO2)6]: a=8.595(1) A, α=53.23 (2)o, space group\(R\bar 3\), V=367.0 A3, Z=1, dcalc=2.414 g/cm3. The structures are composed of [Ru(NO2)6]4− comple anions, alkaline metal cations, and crystallization water molecules. In both compounds, the coordination polyhedra of Ru are nearly regular octahedra formed by nitrite nitrogen atoms. The Ru-N bond lengths are 2.054–2.102 A. The NO2 groups have virtually the same geometric characteristics: the N−O distances are within 1.196–1.316 A and the O−N−O angles are 112.9–117.4o. The coordination environment of alkaline metals by oxygen atoms is discussed.

Crystal and molecular structure of the photocatalyst tris(2,2?-bipyrazine)ruthenium(II) hexafluorophosphate

The X-ray structure determination of the complex tris(2,2′-bipyrazine)ruthenium(II) hexafluorophosphate, [Ru(C8N4H6)3](PF6)2, has shown that the compound crystallizes in the monoclinic space group P21/c witha=13.459(5),b=23.486(8),c=17.913(10) A,β=139.85(1)°, andZ=4. Each asymmetric unit also contains one dimethylformamide and one water molecule. Least-squares refinement led to an R factor of 0.074 based on 3463 reflections for which I>2σ(I). The [Ru(C8N4H6)3]2+ cation has no crystallographic symmetry, but the requirements for point symmetry 32 are nearly met. The six Ru-N bond lengths agree within experimental error and have an average length of 2.05(1) A.