Oxygen atom transfer from a trans-dioxoruthenium(VI) complex to nitric oxide

In aqueous acidic solutions trans-[Ru(VI)(L)(O)(2)](2+) (L=1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) is rapidly reduced by excess NO to give trans-[Ru(L)(NO)(OH)](2+). When ≤1 mol equiv NO is used, the intermediate Ru(IV) species, trans-[Ru(IV)(L)(O)(OH(2))](2+), can be detected. The reaction of [Ru(VI)(L)(O)(2)](2+) with NO is first order with respect to [Ru(VI)] and [NO], k(2)=(4.13±0.21)×10(1) M(-1) s(-1) at 298.0 K. ΔH(≠) and ΔS(≠) are (12.0±0.3) kcal mol(-1) and -(11±1) cal mol(-1) K(-1), respectively. In CH(3)CN, ΔH(≠) and ΔS(≠) have the same values as in H(2)O; this suggests that the mechanism is the same in both solvents. In CH(3)CN, the reaction of [Ru(VI)(L)(O)(2)](2+) with NO produces a blue-green species with λ(max) at approximately 650 nm, which is characteristic of N(2)O(3). N(2)O(3) is formed by coupling of NO(2) with excess NO; it is relatively stable in CH(3)CN, but undergoes rapid hydrolysis in H(2)O. A mechanism that involves oxygen atom transfer from [Ru(VI)(L)(O)(2)](2+) to NO to produce NO(2) is proposed. The kinetics of the reaction of [Ru(IV)(L)(O)(OH(2))](2+) with NO has also been investigated. In this case, the data are consistent with initial one-electron O(-) transfer from Ru(IV) to NO to produce the nitrito species [Ru(III)(L)(ONO)(OH(2))](2+) (k(2)>10(6) M(-1) s(-1)), followed by a reaction with another molecule of NO to give [Ru(L)(NO)(OH)](2+) and NO(2)(-) (k(2)=54.7 M(-1) s(-1)).     

Encapsulation of cyanometalates by a tris-macrocyclic ligand tricopper(II) complex: syntheses, structural variation, and magnetic exchange coupling pathways

The reaction of [M(CN)(6)](3-) (M = Cr(3+), Mn(3+), Fe(3+), Co(3+)) and [M(CN)(8)](4-/3-) (M = Mo(4+/5+), W(4+/5+)) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu(3)(L)](6+)) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu(3)(L)](6+) forms the isostructural host-guest complexes [[[Cu(3)(L)(OH(2))(2)][M(CN)(6)](2)][M(CN)(6)]][M(CN)(6)]30 H(2)O with one bridging, two partially encapsulated, and one isolated [M(CN)(6)](3-) unit. The octacyanometalates of Mo(4+/5+) and W(4+/5+) are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)(8)](4-) were obtained. The Mo(4+) and W(4+) complexes were crystallized in two different structural forms: [[Cu(3)(L)(OH(2))](2)[Mo(CN)(8)]](NO(3))(8)15 H(2)O with a structural motif that involves isolated spherical [[Cu(3)(L)(OH(2))](2)[M(CN)(8)]](8+) ions and a "string-of-pearls" type of structure [[[Cu(3)(L)](2)[M(CN)(8)]][M(CN)(8)]](NO(3))(4) 20 H(2)O, with [M(CN)(8)](4-) ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the CuCu pairs in the [Cu(3)(L)](6+) "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr(3+), exchange coupling of Mn(3+) and Fe(3+) is very small, and the octacoordinate Mo(4+) and W(4+) systems have a closed-shell ground state.     

Lanthanide(III) and group 13 metal ion complexes of tripodal amino phosphinate ligands

The tripodal amino-phosphinate ligands, tris(4-(phenylphosphinato)-3-benzyl-3-azabutyl)amine (H(3)ppba.2HCl.H(2)O) and tris(4-(phenylphosphinato)-3-azabutyl)amine (H(3)ppa.HCl.H(2)O) were synthesized and reacted with Al(3+), Ga(3+), In(3+) and the lanthanides (Ln(3+)). At 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(3)ppba)(2)](3+)(M = Al(3+), Ga(3+), In(3+), Ho(3+)-Lu(3+)) were isolated. The bicapped [Ga(H(3)ppba)(2)](NO(3))(2)Cl.3CH(3)OH was structurally characterized and was shown indirectly by various techniques to be isostructural with the other [M(H(3)ppba)(2)](3+) complexes. Also, at 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)(2)](5+)(M = La(3+)-Tb(3+)) were characterized, and the X-ray structure of [Gd(H(4)ppba)(2)](NO(3))(4)Cl.3CH(3)OH was determined. At 1 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)](4+)(M = La(3+)-Er(3+)) were isolated and characterized. Elemental analysis and spectroscopic evidence supported the formation of a 1 : 1 monocapped complex. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+), complex of the type [Ga(ppa)].3H(2)O was obtained. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+) a neutral complex [Ga(ppa)].3H(2)O was obtained. The formation of an encapsulated 1 : 1 complex is supported by elemental analysis and spectroscopic evidence.     

Hydrocarbon oxidation by Bis-mu-oxo manganese dimers: electron transfer,hydride transfer,and hydrogen atom transfer mechanisms

Described here are oxidations of alkylaromatic compounds by dimanganese mu-oxo and mu-hydroxo dimers [(phen)(2)Mn(IV)(mu-O)(2)Mn(IV)(phen)(2)](4+) ([Mn(2)(O)(2)](4+)), [(phen)(2)Mn(IV)(mu-O)(2)Mn(III)(phen)(2)](3+) ([Mn(2)(O)(2)](3+)), and [(phen)(2)Mn(III)(mu-O)(mu-OH)Mn(III)(phen)(2)](3+) ([Mn(2)(O)(OH)](3+)). Dihydroanthracene, xanthene, and fluorene are oxidized by [Mn(2)(O)(2)](3+) to give anthracene, bixanthenyl, and bifluorenyl, respectively. The manganese product is the bis(hydroxide) dimer, [(phen)(2)Mn(III)(mu-OH)(2)Mn(II)(phen)(2)](3+) ([Mn(2)(OH)(2)](3+)). Global analysis of the UV/vis spectral kinetic data shows a consecutive reaction with buildup and decay of [Mn(2)(O)(OH)](3+) as an intermediate. The kinetics and products indicate a mechanism of hydrogen atom transfers from the substrates to oxo groups of [Mn(2)(O)(2)](3+) and [Mn(2)(O)(OH)](3+). [Mn(2)(O)(2)](4+) is a much stronger oxidant, converting toluene to tolyl-phenylmethanes and naphthalene to binaphthyl. Kinetic and mechanistic data indicate a mechanism of initial preequilibrium electron transfer for p-methoxytoluene and naphthalenes because, for instance, the reactions are inhibited by addition of [Mn(2)(O)(2)](3+). The oxidation of toluene by [Mn(2)(O)(2)](4+), however, is not inhibited by [Mn(2)(O)(2)](3+). Oxidation of a mixture of C(6)H(5)CH(3) and C(6)H(5)CD(3) shows a kinetic isotope effect of 4.3 +/- 0.8, consistent with C-H bond cleavage in the rate-determining step. The data indicate a mechanism of initial hydride transfer from toluene to [Mn(2)(O)(2)](4+). Thus, oxidations by manganese oxo dimers occur by three different mechanisms: hydrogen atom transfer, electron transfer, and hydride transfer. The thermodynamics of e(-), H(*), and H(-) transfers have been determined from redox potential and pK(a) measurements. For a particular oxidant and a particular substrate, the choice of mechanism is influenced both by the thermochemistry and by the intrinsic barriers. Rate constants for hydrogen atom abstraction by [Mn(2)(O)(2)](3+) and [Mn(2)(O)(OH)](3+) are consistent with their 79 and 75 kcal mol(-)(1) affinities for H(*). In the oxidation of p-methoxytoluene by [Mn(2)(O)(2)](4+), hydride transfer is thermochemically 24 kcal mol(-)(1) more facile than electron transfer; yet the latter mechanism is preferred. Thus, electron transfer has a substantially smaller intrinsic barrier than does hydride transfer in this system.     

Reactions of [Ru(H(2)O)(6)](2+) with water-soluble tertiary phosphines

In aqueous solutions under mild conditions, [Ru(H(2)O)(6)](2+) was reacted with various water-soluble tertiary phosphines. As determined by multinuclear NMR spectroscopy, reactions with the sulfonated arylphosphines L =mtppms, ptppms and mtppts yielded only the mono- and bisphosphine complexes, [Ru(H(2)O)(5)L](2+), cis-[Ru(H(2)O)(4)L(2)](2+), and trans-[Ru(H(2)O)(4)L(2)](2+) even in a high ligand excess. With the small aliphatic phosphine L = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1(3,7)]decane (pta) at [L]:[Ru]= 12:1, the tris- and tetrakisphosphino species, [Ru(H(2)O)(3)(pta)(3)](2+), [Ru(H(2)O)(2)(pta)(4)](2+), [Ru(H(2)O)(OH)(pta)(4)](+), and [Ru(OH)(2)(pta)(4)] were also detected, albeit in minor quantities. These results have significance for the in situ preparation of Ru(II)-tertiary phosphine catalysts. The structures of the complexes trans-[Ru(H(2)O)(4)(ptaMe)(2)](tos)(4)x2H(2)O, trans-[Ru(H(2)O)(4)(ptaH)(2)](tos)(4)[middle dot]2H(2)O, and trans-mer-[RuI(2)(H(2)O)(ptaMe)(3)]I(3)x2H(2)O, containing protonated or methylated pta ligands (ptaH and ptaMe, respectively) were determined by single crystal X-ray diffraction.     

C-H activation by a mononuclear manganese(III) hydroxide complex: synthesis and characterization of a manganese-lipoxygenase mimic?

Lipoxygenases are mononuclear non-heme metalloenzymes that regio- and stereospecifically convert 1,4-pentadiene subunit-containing fatty acids into alkyl peroxides. The rate-determining step is generally accepted to be hydrogen atom abstraction from the pentadiene subunit of the substrate by an active metal(III)-hydroxide species to give a metal(II)-water species and an organic radical. All known plant and animal lipoxygenases contain iron as the active metal; recently, however, manganese was found to be the active metal in a fungal lipoxygenase. Reported here are the synthesis and characterization of a mononuclear Mn(III) complex, [Mn(III)(PY5)(OH)](CF(3)SO(3))(2) (PY5 = 2,6-bis(bis(2-pyridyl)methoxymethane)pyridine), that reacts with hydrocarbon substrates in a manner most consistent with hydrogen atom abstraction and provides chemical precedence for the proposed reaction mechanism. The neutral penta-pyridyl ligation of PY5 endows a strong Lewis acidic character to the metal center allowing the Mn(III) compound to perform this oxidation chemistry. Thermodynamic analysis of [Mn(III)(PY5)(OH)](2+) and the reduced product, [Mn(II)(PY5)(H(2)O)](2+), estimates the strength of the O-H bond in the metal-bound water in the Mn(II) complex to be 82 (+/-2) kcal mol(-)(1), slightly less than that of the O-H bond in the related reduced iron complex, [Fe(II)(PY5)(MeOH)](2+). [Mn(III)(PY5)(OH)](2+) reacts with hydrocarbon substrates at rates comparable to those of the analogous [Fe(III)(PY5)(OMe)](2+) at 323 K. The crystal structure of [Mn(III)(PY5)(OH)](2+) displays Jahn-Teller distortions that are absent in [Mn(II)(PY5)(H(2)O)](2+), notably a compression along the Mn(III)-OH axis. Consequently, a large internal structural reorganization is anticipated for hydrogen atom transfer, which may be correlated to the lessened dependence of the rate of substrate oxidation on the substrate bond dissociation energy as compared to other metal complexes. The results presented here suggest that manganese is a viable metal for lipoxygenase activity and that, with similar coordination spheres, iron and manganese can oxidize substrates through a similar mechanism.     

Two novel Dy8 and Dy11 clusters with cubane [Dy4(μ3-OH)4]8+ units exhibiting slow magnetic relaxation behaviour

Two unique octa- and hendeca-nuclear dysprosium(III) clusters incorporating [Dy(4)(μ(3)-OH)(4)](8+) cubane units have been synthesized with the 1,10-phenanthroline-2,9-dicarbaldehyde dioxime (H(2)phendox) ligand and DyCl(3)·6H(2)O or Dy(OAc)(3)·4H(2)O. They are [Dy(8)(OH)(8)(phendox)(6)(H(2)O)(8)]Cl(2)(OH)(2)·18H(2)O·18MeOH (1) and [Dy(11)(OH)(11)(phendox)(6)(phenda)(3)(OAc)(3)](OH)·40H(2)O·7MeOH (2). Adjacent Dy(8) in 1 or Dy(11) in 2 motifs are packed by off-set π-π interactions of the aromatic rings on phendox(2-) to generate a 3D supramolecular architecture in the honeycomb topology and with 1D or 3D channels along the c-axis. Adsorption research shows that complex 1 has selective adsorption ability for H(2)O over small gas molecules (H(2), N(2), CO(2)). Complex 2 is stable upon the removal of guest molecules and the desolvated compound absorbed a considerable amount of CO(2). Furthermore, the oximes underwent hydrolysis to carboxylic acid and the resulting 1,10-phenanthroline-2,9-dicarboxylate link the dysprosium atoms to form a hendecanuclear cluster of 2. Magnetic studies reveal that both clusters exhibit slow magnetic relaxation behavior, expanding upon the recent reports of the pure 4f type single-molecule magnets (SMMs).     

Simplest homoleptic metal-centered tetrahedrons, [M(OH2)4]2+, in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (M = Co, Ni, Cu)

Dissolution of a tetrafluoroborate or perchlorate salt of [M(OH(2))(6)](2+) (M = Co, Ni, Cu) in 1-ethyl-3-methylimidazolium tetraluforoborate ionic liquid ([emim]BF(4)) results in significant solvatochromism and increasing intensity of color. These observations arise from partial dehydration from the octahedral [M(OH(2))(6)](2+) and formation of the tetrahedral [M(OH(2))(4)](2+). This reaction was monitored by the intense absorption band due to the d-d transition in the UV-vis absorption spectrum. The EXAFS investigation clarified the coordination structures around M(2+) {[Co(OH(2))(4)](2+), R(Co-O) = 2.17 ?, N = 4.2; [Cu(OH(2))(4)](2+), R(Cu-O) = 2.09 ?, N = 3.8}. (1)H and (19)F NMR study suggested that both [emim](+) and BF(4)(-) are randomly arranged in the second-coordination sphere of [M(OH(2))(4)](2+).     

Molecular view of the anomalous acidities of Sn2+, Pb2+, and Hg2+

Experimental results taken from both the condensed and gaseous phase show that, when associated with water, the three dications Sn(2+), Pb(2+), and Hg(2+) exhibit a facile proton-transfer reaction. In the gas phase, no stable [M.(H(2)O)(n)](2+) ions are observed; but instead the cations appear to undergo rapid hydrolysis to give ions of the form M(+)OH(H(2)O)(n-1). A series of ab initio calculations have been undertaken on the structures and proton-transfer reaction profiles associated with the complexes [M.(H(2)O)(2,4)](2+), where M is one of Sn, Pb, Hg, and Ca. The latter has been used as a reference point both in terms of comparisons with previous calculations, and the fact that Ca(2+) is a very weak acid. The calculations show that for Sn(2+), Pb(2+), and Hg(2+), the only barriers to proton transfer are those associated with the movement of water molecules. In the gas phase, these barriers could be overcome through energy gained during ion formation, and in the condensed phase the thermal motion of water molecules would be sufficient. In contrast, the calculations show that for Ca(2+) it is the proton-transfer step that provides the most significant reaction barrier. Proton transfer in Sn(2+) and Pb(2+) is further assisted by distortions in the geometries of [M.(H(2)O)(2,4)](2+) complexes due to voids created by the 5s(2) (6s(2)) inert lone pair. For Hg(2+), ease of proton transfer is derived partly from the high degree of covalent bonding found in both the reactants and products.     

Reactions of beryllium halides in liquid ammonia: the tetraammineberyllium cation [Be(NH3)4]2+, its hydrolysis products, and the action of Be2+ as a fluoride-ion acceptor

The first structural characterization of the text-book tetraammineberyllium(II) cation [Be(NH(3))(4)](2+), obtained in the compounds [Be(NH(3))(4)](2)Cl(4)?17NH(3) and [Be(NH(3))(4)]Cl(2), is reported. Through NMR spectroscopic and quantum chemical studies, its hydrolysis products in liquid ammonia were identified. These are the dinuclear [Be(2)(μ-OH)(NH(3))(6)](3+) and the cyclic [Be(2)(μ-OH)(2)(NH(3))(4)](2+) and [Be(3)(μ-OH)(3)(NH(3))(6)](3+) cations. The latter species was isolated as the compound [Be(3)(μ-OH)(3)(NH(3))(6)]Cl(3)?7NH(3). NMR analysis of solutions of BeF(2) in liquid ammonia showed that the [BeF(2)(NH(3))(2)] molecule was the only dissolved species. It acts as a strong fluoride-ion acceptor and forms the [BeF(3)(NH(3))](-) anion in the compound [N(2)H(7)][BeF(3)(NH(3))]. The compounds presented herein were characterized by single-crystal X-ray structure analysis, (9)Be, (17)O, and (19)F?NMR, IR, and Raman spectroscopy, deuteration studies, and quantum chemical calculations. The extension of beryllium chemistry to the ammine system shows similarities but also decisive differences to the aquo system.     

X-ray absorption spectroscopic and computational investigation of a possible S···S interaction in the [Cu3S2]3+ core

The electronic structure of the [Cu(3)S(2)](3+) core of [(LCu)(3)(S)(2)](3+) (L = N,N,N',N'-tetramethyl-2R,3R-cyclohexanediamine) is investigated using a combination of Cu and S K-edge X-ray absorption spectroscopy and calculations at the density functional and multireference second-order perturbation levels of theory. The results show that the [Cu(3)S(2)](3+) core is best described as having all copper centers close to but more oxidized than Cu(2+), while the charge on the S(2) fragment is between that of a sulfide (S(2-)) and a subsulfide (S(2)(3-)) species. The [Cu(3)S(2)](3+) core thus is different from a previously described, analogous [Cu(3)O(2)](3+) core, which has a localized [(Cu(3+)Cu(2+)Cu(2+))(O(2-))(2)](3+) electronic structure. The difference in electronic structure between the two analogues is attributed to increased covalent overlap between the Cu 3d and S 3p orbitals and the increased radial distribution function of the S 3p orbital (relative to O 2p). These features result in donation of electron density from the S-S σ* to the Cu and result in some bonding interaction between the two S atoms at ~2.69 ? in [Cu(3)S(2)](3+), stabilizing a delocalized S = 1 ground state.     

Synthesis, characterization, and stereochemistry of S-bridged Co(III)MCo(III)(M = Pd(II), Pt(II)) trinuclear complexes containing two non-bridging thiolato groups: building blocks for the construction of chiral heterometallic aggregates

The reaction of fac(S)-[Co(aet)(3)](aet = aminoethanethiolate) with [PdCl(4)](2-) in a 2:1 ratio in water gave an S-bridged Co(III)Pd(II)Co(III) trinuclear complex composed of two mer(S)-[Co(aet)(3)] units, [Pd[Co(aet)(3)](2)](2+)([1](2+)). In [1](2+), each of the two mer(S)-[Co(aet)(3)] units is bound to a square-planar Pd(II) ion through two of three thiolato groups, leaving two non-bridging thiolato groups at the terminal. Of two geometrical forms, syn and anti, possible for [Pd[Co(aet)(3)](2)](2+), which arise from the difference in arrangement of two terminal non-bridging thiolato groups, [1](2+) afforded only the syn form. A similar reaction of fac(S)-[Co(aet)(3)] with [PtCl(4)](2-) or trans-[PtCl(2)(NH(3))(2)] produced an analogous Co(III)Pt(II)Co(III) trinuclear complex, [Pt[Co(aet)(3)](2)](2+)([2](2+)), but both the syn and anti forms were formed for [2](2+). Complexes [1](2+) and syn- and anti-[2](2+), which exclusively exist as a racemic(DeltaDelta/LambdaLambda) form, were successfully optically resolved with use of [Sb(2)(R,R-tartrato)(2)](2-) as the resolving agent. The reaction of syn-[2](2+) with [AuCl[S(CH(2)CH(2)OH)(2)]] led to the formation of an S-bridged Co(III)(4)Pt(II)(2)Au(I)(2) octanuclear metallacycle, [Au(2)[Pt[Co(aet)(3)](2)](2)](6+)([3](6+)), while the corresponding reaction of anti-[2](2+) afforded a different product ([[4](3+)](n)) that is assumed to have a polymeric structure in [[Au[Pt[Co(aet)(3)](2)]](3+)](n).     

General synthesis and structural evolution of a layered family of Ln8(OH)20Cl4 x nH2O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y)

The synthesis process and crystal structure evolution for a family of stoichiometric layered rare-earth hydroxides with general formula Ln(8)(OH)(20)Cl(4) x nH(2)O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y; n approximately 6-7) are described. Synthesis was accomplished through homogeneous precipitation of LnCl(3) x xH(2)O with hexamethylenetetramine to yield a single-phase product for Sm-Er and Y. Some minor coexisting phases were observed for Nd(3+) and Tm(3+), indicating a size limit for this layered series. Light lanthanides (Nd, Sm, Eu) crystallized into rectangular platelets, whereas platelets of heavy lanthanides from Gd tended to be of quasi-hexagonal morphology. Rietveld profile analysis revealed that all phases were isostructural in an orthorhombic layered structure featuring a positively charged layer, [Ln(8)(OH)(20)(H(2)O)(n)](4+), and interlayer charge-balancing Cl(-) ions. In-plane lattice parameters a and b decreased nearly linearly with a decrease in the rare-earth cation size. The interlamellar distance, c, was almost constant (approximately 8.70 A) for rare-earth elements Nd(3+), Sm(3+), and Eu(3+), but it suddenly decreased to approximately 8.45 A for Tb(3+), Dy(3+), Ho(3+), and Er(3+), which can be ascribed to two different degrees of hydration. Nd(3+) typically adopted a phase with high hydration, whereas a low-hydration phase was preferred for Tb(3+), Dy(3+), Ho(3+), Er(3+), and Tm(3+). Sm(3+), Eu(3+), and Gd(3+) samples were sensitive to humidity conditions because high- and low-hydration phases were interconvertible at a critical humidity of 10%, 20%, and 50%, respectively, as supported by both X-ray diffraction and gravimetry as a function of the relative humidity. In the phase conversion process, interlayer expansion or contraction of approximately 0.2 A also occurred as a possible consequence of absorption/desorption of H(2)O molecules. The hydration difference was also evidenced by refinement results. The number of coordinated water molecules per formula weight, n, changed from 6.6 for the high-hydration Gd sample to 6.0 for the low-hydration Gd sample. Also, the hydration number usually decreased with increasing atomic number; e.g., n = 7.4, 6.3, 7.2, and 6.6 for high-hydration Nd, Sm, Eu, and Gd, and n = 6.0, 5.8, 5.6, 5.4, and 4.9 for low-hydration Gd, Tb, Dy, Ho, and Er. The variation in the average Ln-O bond length with decreasing size of the lanthanide ions is also discussed. This family of layered lanthanide compounds highlights a novel chemistry of interplay between crystal structure stability and coordination geometry with water molecules.     

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.     

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).     

Photodriven electron and energy transfer from a light-harvesting metallodendrimer

Intermolecular electron and energy transfer from a light-harvesting metallodendrimer [Ru[bpy(C-450)(4)](3)](2+), where bpy(C-450)(4) is a 2,2'-bipyridine derivative containing 4 coumarin-450 units connected together through aryl ether linkages, is observed in acetonitrile solutions at room temperature. The model complex [Ru(dmb)(3)](2+), where dmb is 4,4'-dimethyl-2,2'-bipyridine, is included for quantitative comparison. The excited states of both compounds are metal-to-ligand charge transfer in nature and participate in excited-state electron and triplet energy transfer processes. Quenching constants were determined from luminescence and time-resolved absorption experiments at constant ionic strength. [Ru[bpy(C-450)(4)](3)](2+) displays significantly slower quenching rates to molecular oxygen and methyl viologen relative to the other processes investigated. Triplet energy transfer from [Ru[bpy(C-450)(4)](3)](2+) to 9-methylanthracene is quantitatively indistinguishable from [Ru(dmb)(3)](2+) while reductive electron transfer from phenothiazine was slightly faster in the former. With the exception of dioxygen quenching, our results indicate that the current dendritic structure is ineffective in shielding the core from bimolecular electron and triplet energy transfer reactions. Electrochemical measurements of [Ru[bpy(C-450)(4)](3)](2+) reveal irreversible oxidative processes at potentials slightly negative to the Ru(III/II) potential that are assigned to oxidations in the dendritic structure. Excited-state oxidative electron-transfer reactions facilitate this process resulting in the reduction of ground-state Ru(III) to Ru(II) and the trapping of the methyl viologen radical cation (MV(*+)) when methyl viologen serves as the quencher. This process generates a minimum of 9 MV(*+)'s for every [Ru[bpy(C-450)(4)](3)](2+) molecule and disassembles the metallodendrimer, resulting in the production of a [Ru(dmb)(3)](2+)-like species and "free" C-450-like dyes.     

Gas-phase coordination complexes of dipositive plutonyl, PuO2(2+): chemical diversity across the actinyl series

We report the first transmission of solvent-coordinated dipositive plutonyl ion, Pu(VI)O(2)(2+), from solution to the gas phase by electrospray ionization (ESI) of plutonyl solutions in water/acetone and water/acetonitrile. ESI of plutonyl and uranyl solutions produced the isolable gas-phase complexes, [An(VI)O(2)(CH(3)COCH(3))(4,5,6)](2+), [An(VI)O(2)(CH(3)COCH(3))(3)(H(2)O)](2+), and [An(VI)O(2)(CH(3)CN)(4)](2+); additional complex compositions were observed for uranyl. In accord with relative actinyl stabilities, U(VI)O(2)(2+) > Pu(VI)O(2)(2+) > Np(VI)O(2)(2+), the yields of plutonyl complexes were about an order of magnitude less than those of uranyl, and dipositive neptunyl complexes were not observed. Collision-induced dissociation (CID) of the dipositive coordination complexes in a quadrupole ion trap produced doubly- and singly-charged fragment ions; the fragmentation products reveal differences in underlying chemistries of plutonyl and uranyl, including the lower stability of Pu(VI) as compared with U(VI). Particularly notable was the distinctive CID fragment ion, [Pu(IV)(OH)(3)](+) from [Pu(VI)O(2)(CH(3)COCH(3))(6)](2+), where the plutonyl structure has been disrupted and the tetravalent plutonium hydroxide produced; this process was not observed for uranyl.     

Scandium ion-enhanced oxidative dimerization and N-demethylation of N,N-dimethylanilines by a non-heme iron(IV)-oxo complex

Oxidative dimerization of N,N-dimethylaniline (DMA) occurs with a nonheme iron(IV)-oxo complex, [Fe(IV)(O)(N4Py)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), to yield the corresponding dimer, tetramethylbenzidine (TMB), in acetonitrile. The rate of the oxidative dimerization of DMA by [Fe(IV)(O)(N4Py)](2+) is markedly enhanced by the presence of scandium triflate, Sc(OTf)(3) (OTf = CF(3)SO(3)(-)), when TMB is further oxidized to the radical cation (TMB(?+)). In contrast, we have observed the oxidative N-demethylation with para-substituted DMA substrates, since the position of the C-C bond formation to yield the dimer is blocked. The rate of the oxidative N-demethylation of para-substituted DMA by [Fe(IV)(O)(N4Py)](2+) is also markedly enhanced by the presence of Sc(OTf)(3). In the case of para-substituted DMA derivatives with electron-donating substituents, radical cations of DMA derivatives are initially formed by Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), giving demethylated products. Binding of Sc(3+) to [Fe(IV)(O)(N4Py)](2+) enhances the Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), whereas binding of Sc(3+) to DMA derivatives retards the electron-transfer reaction. The complicated kinetics of the Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+) are analyzed by competition between binding of Sc(3+) to DMA derivatives and to [Fe(IV)(O)(N4Py)](2+). The binding constants of Sc(3+) to DMA derivatives increase with the increase of the electron-donating ability of the para-substituent. The rate constants of Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), which are estimated from the binding constants of Sc(3+) to DMA derivatives, agree well with those predicted from the driving force dependence of the rate constants of Sc(3+) ion-coupled electron transfer from one-electron reductants to [Fe(IV)(O)(N4Py)](2+). Thus, oxidative dimerization of DMA and N-demethylation of para-substituted DMA derivatives proceed via Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+).     

Ge(7)O(13)(OH)(2)F(3)](3)(-).Cl(-).2[Ni(dien)(2)](2+): the first chainlike germanate templated by a transition metal complex

The first chainlike germanate, [Ge(7)O(13)(OH)(2)F(3)](3)(-).Cl(-).2[Ni(dien)(2)](2+), has been solvothermally synthesized by using Ni(dien)(2)(2+) cations as the template and characterized by IR, SEM, TGA, powder X-ray diffraction (PXRD), energy-dispersive X-ray analysis (EDXA), elemental analysis, and single-crystal X-ray diffraction, respectively. This compound crystallized in the monoclinic space group P2/nwith a = 8.8904(2) A, b = 17.4374(3) A, c = 13.2110(3) A, beta = 101.352(1) degrees, V = 2007.97(7) A(3), and Z = 2. Interestingly, the structure contains two types of chiral mer-[Ni(dien)(2)](2+) cations and two types of chiral chains, one left-handed and the other right-handed, which lead to a racemic compound. The orderly separation of achiral s-fac-[Ni(dien)(2)](2+) and chiral mer-[Ni(dien)(2)](2+) isomers was found in the structure. The structure is stabilized by N-H.O(F, Cl) hydrogen bonds.     

Thermodynamics of formation of urea complexes with manganese(II), nickel(II) and zinc(II) ions in N,N-dimethylformamide

The complexation of urea (ur) with manganese(II), nickel(II) and zinc(II) ions has been studied by titration calorimetry in N,N-dimethylformamide (DMF) containing 0.4M (C(2)H(5))(4) NBF(4) as a constant ionic medium at 25 degrees C. The calorimetric data were well explained in terms of the formation of [Mn(ur)](2+), [Mn(ur)(2)](2+) and [Mn(ur)(4)](2+) for manganese(II), [Ni(ur)](2+) for nickel(II) and [Zn(ur)](2+) and [Zn(ur)(2)](2+) for zinc(II), and their formation constants, reaction enthalpies and entropies were determined. The complexation of the nickel(II)-urea system in DMF has also been studied by means of spectrophotometric titration and electronic spectra of individual nickel(II) complexes were determined. On the basis of the stepwise thermodynamic quantities and the individual electronic spectra of the complexes, it is revealed that the [Mn(ur)](2+), [Mn(ur)(2)](2+), [Ni(ur)](2+), [Zn(ur)](2+) and [Zn(ur)(2)](2+) complexes have a six-coordinate octahedral structure, while the [Mn(ur)(4)](2+) complex has a four-coordinate tetrahedral structure.