Marked differences in light-switch behavior of Ru(II) complexes possessing a tridentate DNA intercalating ligand

The tridentate ligand 3-(pyrid-2'-yl)dipyrido[3,2-a:2',3'-c]phenazine (pydppz) has been prepared in two steps by elaboration of 2-(pyrid-2'-yl)-1,10-phenanthroline. Both homoleptic [Ru(pydppz)(2)](2+) and heteroleptic [Ru(tpy)(pydppz)](2+) (tpy = 2,2';6',2' '-terpyridine) complexes have been prepared and characterized by (1)H NMR. The absorption and emission spectra are consistent with low-lying MLCT excited states, which are typical of Ru(II) complexes. Femtosecond transient absorption measurements show that that the (3)MLCT excited state of the heteroleptic complex [Ru(tpy)(pydppz)](2+) (tau approximately 5 ns) is longer-lived than that of the homoleptic complex [Ru(pydppz)(2)](2+) (tau = 2.4 ns) and that these lifetimes are significantly longer than that of the (3)MLCT state of the parent complex [Ru(tpy)(2)](2+) (tau = 120 ps). These differences are explained by the lower-energy (3)MLCT excited state present in [Ru(tpy)(pydppz)](2+) and [Ru(pydppz)(2)](2+) compared to [Ru(tpy)(2)](2+), resulting in less deactivation of the former through the ligand-field state(s). DFT and TDDFT calculations are consistent with this explanation. [Ru(tpy)(pydppz)](2+) and [Ru(pydppz)(2)](2+) bind to DNA through the intercalation of the pydppz ligand; however, only the heteroleptic complex exhibits luminescence enhancement in the presence of DNA. The difference in the photophysical behavior of the complexes is explained by the inability of [Ru(pydppz)(2)](2+) to intercalate both pydppz ligands, such that one pydppz always remains exposed to the solvent. DNA photocleavage is observed for [Ru(tpy)(pydppz)](2+) in air, but not for [Ru(pydppz)(2)](2+). The DNA damage likely proceeds through the production of small amounts of (1)O(2) by the longer-lived complex. Although both complexes possess the intercalating pydppz ligand, they exhibit different photophysical properties in the presence of DNA.     

Solid-state spectroscopic properties and the geometry of binuclear rhodium(I) diisocyanoalkane complexes

A series of crystalline dinuclear rhodium complexes with different bridging diisocyano ligands and different counter ions have been studied by low-temperature crystallographic and solid-state spectroscopic techniques. The Rh-Rh distances vary from 4.5153(3) to 3.0988(7) angstroms, and the twist angles around the Rh-Rh line from 58.3(1) to 0 degree, both depending on the size and conformational rigidity of the bridging ligand. For very long distances as occur in the [Rh(2)(dimen)(4)](2+) salts the absorption is significantly blue-shifted compared to other complexes. For a given cation a shorter Rh-Rh bond gives a red shift of the phosphorescence emission band, indicating a smaller energy gap between the ground and emitting excited states. An exception occurs for the [Rh(2)(1,6-diisocyanohexane)(4)](2+) ion, in which dimer formation in the calixarate salt lengthens the Rh-Rh intramolecular bond length without affecting the emission spectrum.     

Sulfur-bridged Co(III)Pt(II)Co(III) trinuclear complexes with mixed aliphatic and aromatic thiolate ligands: effect of nonbridging ligands on the homochiral linkage of cobalt(III) octahedrons by platinum(II)

The reaction of [Ni[Co(aet)(2)(pyt)](2)](2+) (aet = 2-aminoethanethiolate, pyt = 2-pyridinethiolate) with [PtCl(4)](2)(-) gave an S-bridged Co(III)Pt(II)Co(III) trinuclear complex composed of two [Co(aet)(2)(pyt)] units, [Pt[Co(aet)(2)(pyt)](2)](2+) ([1](2+)). When a 1:1 mixture of [Ni[Co(aet)(2)(pyt)](2)](2+) and [Ni[Co(aet)(2)(en)](2)](4+) was reacted with [PtCl(4)](2)(-), a mixed-type S-bridged Co(III)Pt(II)Co(III) complex composed of one [Co(aet)(2)(pyt)] and one [Co(aet)(2)(en)](+) units, [Pt[Co(aet)(2)(en)][Co(aet)(2)(pyt)]](3+) ([2](3+)), was produced, together with [1](2+) and [Pt[Co(aet)(2)(en)](2)](4+). The corresponding Co(III)Pt(II)Co(III) trinuclear complexes containing pymt (2-pyrimidinethiolate), [Pt[Co(aet)(2)(pymt)](2)](2+) ([3](2+)) and [Pt[Co(aet)(2)(en)][Co(aet)(2)(pymt)]](3+) ([4](3+)), were also obtained by similar reactions, using [Ni[Co(aet)(2)(pymt)](2)](2+) instead of [Ni[Co(aet)(2)(pyt)](2)](2+). While [Pt[Co(aet)(2)(en)](2)](4+) formed both the deltalambda (meso) and deltadelta/lambdalambda (racemic) forms in a ratio of ca. 1:1, the preferential formation of the deltadelta/lambdalambda form was observed for [1](2+) (ca. deltalambda:deltadelta/lambdalambda = 1:3) and [2](3+) (ca. delta(en)lambda(pyt)/lambda(en)delta(pyt):deltadelta/lambdalambda = 1:2). Furthermore, [3](2+) and [4](3+) predominantly formed the deltadelta/lambdalambda form. These results indicate that the homochiral selectivity for the S-bridged Co(III)Pt(II)Co(III) trinuclear complexes composed of two octahedral [Co(aet)(2)(L)](0 or +) units is enhanced in the order L = en < pyt < pymt. The isomers produced were separated and optically resolved, and the crystal structures of the meso-type deltalambda-[1]Cl(2).4H(2)O and the spontaneously resolved deltadelta-[4](ClO(4))(3).H(2)O were determined by X-ray analyses. In deltalambda-[1](2+), the delta and Lambda configurational mer(S).trans(N(aet))-[Co(aet)(2)(pyt)] units are linked by a square-planar Pt(II) ion through four aet S atoms to form a linear-type S-bridged trinuclear structure. In deltadelta-[4](3+), a similar linear-type trinuclear structure is constructed from the delta-mer(S).trans(N(aet))-[Co(aet)(2)(pymt)] and delta-C(2)-cis(S)-[Co(aet)(2)(en)](+) units that are bound by a Pt(II) ion with a slightly distorted square-planar geometry through four aet S atoms.     

Synthesis, reactivity, electrochemical behavior, and crystal structure of a family of multivalent metal carbido-carbonyl clusters based on the rh(10)(c)(2)au(4-6) framework

Six metal carbido-carbonyl clusters have been isolated and recognized as members of a multivalent family based on the dioctahedral Rh(10)(C)(2) frame, with variable numbers of CO ligands, AuPPh(3) moieties, and anionic charge: [Rh(10)(C)(2)(CO)(x)(AuPPh(3))(y)](n-) (x = 18, 20; y = 4, 5, 6; n = 0, 1, 2). Anions [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)](-) ([2](-)) and [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)](2-) ([2](2-)) have been obtained by the reduction of [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)] (2) under N(2), while [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(5)](-) ([3](-)) was obtained from [Rh(10)(C)(2)(CO)(20)(AuPPh(3))(4)] (1) by reduction under a CO atmosphere. [3](-) can be better obtained by the addition of AuPPh(3)Cl to [2](2-). [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(6)] (4) is obtained from [3](-) and 2 as well by the reduction and subsequent addition of AuPPh(3)Cl. The molecular structures of [2](2-) ([NBu(4)](+) salt), [3](-) ([NMe(4)](+) salt), and 4 have been determined by single-crystal X-ray diffraction. The redox activities of complexes 1, 2 and [3](-) have been investigated by electrochemical and electron paramagnetic resonance (EPR) techniques. The data from EPR spectroscopy have been accounted for by theoretical calculations.     

Self-assembly of D-penicillaminato M6M'8 (M = Ni(II), Pd(II), Pt(II); M' = Cu(I), Ag(I)) clusters and their organization into extended La(III)M6M'8 supramolecular structures

A series of chiral M(6)M'(8) cluster compounds having twelve free carboxylate groups, [M(6)M'(8)(D-pen-N,S)(12)X](5-) (M/M'/X = Pd(II)/Ag(I)/Cl(-) ([1](5-)), Pd(II)/Ag(I)/Br(-) ([2](5-)), Pd(II)/Ag(I)/I(-) ([3](5-)), Ni(II)/Ag(I)/Cl(-) ([4](5-)), Pt(II)/Ag(I)/Cl(-) ([5](5-)), Pd(II)/Cu(I)/Cl(-) ([6](5-)); D-H(2)pen = D-penicillamine), in which six cis-[M(D-pen-N,S)(2)](2-) square-planar units are bound to a [M'(8)X](7+) cubic core through sulfur-bridges, was synthesized by the reactions of cis-[M(D-pen-N,S)(2)](2-) with M' in water in the presence of halide ions. These M(6)M'(8) clusters readily reacted with La(3+) in aqueous buffer to form La(III)(2)M(6)M'(8) heterotrimetallic compounds, La(2)[1](CH(3)COO), La(2)[2](CH(3)COO), La(2)[3](CH(3)COO), La(2)[4](CH(3)COO), La(2)[5](CH(3)COO) and La(2)[6]Cl, in which the M(6)M'(8) cluster units are linked by La(3+) ions through carboxylate groups in a 1?:?2 ratio. While the La(III)(2)M(6)Ag(I)(8) compounds derived from [1](5-), [2](5-), [3](5-), [4](5-) and [5](5-) have a 1D helix supramolecular structure with a right-handedness, the La(III)(2)Pd(II)(6)Cu(I)(8) compound derived from [6](5-) has a 2D sheet-like structure with a triangular grid of the Pd(II)(6)Cu(I)(8) cluster units. When aqueous HCl was added to the reaction solution of [6](5-) and La(3+), another La(III)(2)Pd(II)(6)Cu(I)(8) heterotrimetallic compound, La(2)[6]Cl·HCl, in which the Pd(II)(6)Cu(I)(8) cluster units are linked by La(3+) ions to form a 2D structure with a rectangular grid, was produced. The solid-state structures of these La(III)(2)M(6)M'(8) compounds, determined by single-crystal X-ray crystallography, along with the spectroscopic properties of the M(6)M'(8) cluster compounds in solution, are described.     

Scrutinizing low-spin Cr(II) complexes

The oxidation state of the chromium center in the following compounds has been probed using a combination of chromium K-edge X-ray absorption spectroscopy and density functional theory: [Cr(phen)(3)][PF(6)](2) (1), [Cr(phen)(3)][PF(6)](3) (2), [CrCl(2)((t)bpy)(2)] (3), [CrCl(2)(bpy)(2)]Cl(0.38)[PF(6)](0.62) (4), [Cr(TPP)(py)(2)] (5), [Cr((t)BuNC)(6)][PF(6)](2) (6), [CrCl(2)(dmpe)(2)] (7), and [Cr(Cp)(2)] (8), where phen is 1,10-phenanthroline, (t)bpy is 4,4'-di-tert-butyl-2,2'-bipyridine, and TPP(2-) is doubly deprotonated 5,10,15,20-tetraphenylporphyrin. The X-ray crystal structures of complexes 1, [Cr(phen)(3)][OTf](2) (1'), and 3 are reported. The X-ray absorption and computational data reveal that complexes 1-5 all contain a central Cr(III) ion (S(Cr) = (3)/(2)), whereas complexes 6-8 contain a central low-spin (S = 1) Cr(II) ion. Therefore, the electronic structures of 1-8 are best described as [Cr(III)(phen(?))(phen(0))(2)][PF(6)](2), [Cr(III)(phen(0))(3)][PF(6)](3), [Cr(III)Cl(2)((t)bpy(?))((t)bpy(0))], [Cr(III)Cl(2)(bpy(0))(2)]Cl(0.38)[PF(6)](0.62), [Cr(III)(TPP(3?-))(py)(2)], [Cr(II)((t)BuNC)(6)][PF(6)](2), [Cr(II)Cl(2)(dmpe)(2)], and [Cr(II)(Cp)(2)], respectively, where (L(0)) and (L(?))(-) (L = phen, (t)bpy, or bpy) are the diamagnetic neutral and one-electron-reduced radical monoanionic forms of L, and TPP(3?-) is the one-electron-reduced doublet form of diamagnetic TPP(2-). Following our previous results that have shown [Cr((t)bpy)(3)](2+) and [Cr(tpy)(2)](2+) (tpy = 2,2':6',2"-terpyridine) to contain a central Cr(III) ion, the current results further refine the scope of compounds that may be described as low-spin Cr(II) and reveal that this is a very rare oxidation state accessible only with ligands in the strong-field extreme of the spectrochemical series.     

Hybrid cluster-cages formed via cyanometalate condensation: Cs subset Co(4)Ru(6)S(2)(CN)(12), Co(4)Ru(9)S(6)(CN)(9), and Rh(4)Ru(9)S(6)(CN)(9) frameworks

Condensation of cyanometalates and cluster building blocks leads to the formation of hybrid molecular cyanometalate cages. Specifically, the reaction of [Cs subset [CpCo(CN)(3)](4)[CpRu](3)] and [(cymene)(2)Ru(3)S(2)(NCMe)(3)]PF(6) produced [Cs subset [CpCo(CN)(3)](4)[(cymene)(2)Ru(3)S(2)][CpRu](3)](PF(6))(2), Cs subset Co(4)Ru(6)S(2)(2+). Single-crystal X-ray diffraction, NMR spectroscopy, and ESI-MS measurements show that Cs subset Co(4)Ru(6)S(2)(2+ ) consists of a Ru(4)Co(4)(CN)(12) box fused with a Ru(3)S(2) cluster via a common Ru atom. The reaction of PPN[CpCo(CN)(3)] and 0.75 equiv of [(cymene)(2)(MeCN)(3)Ru(3)S(2)](PF(6))(2) in MeCN solution produced [[CpCo(CN)(3)](4)[(cymene)(2)Ru(3)S(2)](3)](PF(6))(2), Co(4)Ru(9)S(6)(2+). Crystallographic analysis, together with NMR and ESI-MS measurements, shows that Co(4)Ru(9)S(6)(2+ ) consists of a Ru(3)Co(4)(CN)(9) "defect box" core, wherein each Ru is fused to a Ru(3)S(2) clusters. The analogous condensation using [CpRh(CN)(3)](-) in place of [CpCo(CN)(3)](-) produced the related cluster-cage Rh(4)Ru(9)S(6)(2+). Electrochemical analyses of both Co(4)Ru(9)S(6)(2+) and Rh(4)Ru(9)S(6)(2+) can be rationalized in the context of reduction at the cluster and the Co(III) subunits, the latter being affected by the presence of alkali metal cations.     

Substituents dependent capability of bis(ruthenium-dioxolene-terpyridine) complexes toward water oxidation

The bridging ligand, 1,8-bis(2,2':6',2'-terpyrid-4'-yl)anthracene (btpyan) was synthesized by the Miyaura-Suzuki cross coupling reaction of anthracenyl-1,8-diboronic acid and 4'-triflyl-2,2':6'-2'-terpyridine in the presence of Pd(PPh(3))(4) (5 mol%) with 68% in yield. Three ruthenium-dioxolene dimers, [Ru(2)(OH)(2)(dioxolene)(2)(btpyan)](0) (dioxolene = 3,6-di-tert-butyl-1,2-benzosemiquinone ([1](0)), 3,5-dichloro-1,2-benzosemiquinone ([2](0)) and 4-nitro-1,2-benzosemiquinone ([3](0))) were prepared by the reaction of [Ru(2)Cl(6)(btpyan)](0) with the corresponding catechol. The electronic structure of [1](0) is approximated by [Ru(II)(2)(OH)(2)(sq)(2)(btpyan)](0) (sq = semiquinonato). On the other hand, the electronic states of [2](0) and [3](0) are close to [Ru(III)(2)(OH)(2) (cat)(2)(btpyan)](0) (cat = catecholato), indicating that a dioxolene having electron-withdrawing groups stabilizes [Ru(III)(2)(OH)(2)(cat)(2)(btpyan)](0) rather than [Ru(II)(2)(OH)(2)(sq)(2)(btpyan)](0) as resonance isomers. No sign was found of deprotonation of the hydroxo groups of [1](0), whereas [2](0) and [3](0) showed an acid-base equilibrium in treatments with t-BuOLi followed by HClO(4). Furthermore, controlled potential electrolysis of [1](0) deposited on an ITO (indium-tin oxide) electrode catalyzed the four-electron oxidation of H(2)O to evolve O(2) at potentials more positive than +1.6 V (vs. SCE) at pH 4.0. On the other hand, the electrolysis of [2](0) and [3](0) deposited on ITO electrodes did not show catalytic activity for water oxidation under similar conditions. Such a difference in the reactivity among [1](0), [2](0) and [3](0) is ascribed to the shift of the resonance equilibrium between [Ru(II)(2)(OH)(2)(sq)(2)(btpyan)](0) and [Ru(III)(2)(OH)(2)(cat)(2)(btpyan)](0).     

Characterization of low energy charge transfer transitions in (terpyridine)(bipyridine)ruthenium(II) complexes and their cyanide-bridged bi- and tri-metallic analogues

The lowest energy metal-to-ligand charge transfer (MLCT) absorption bands found in ambient solutions of a series of [Ru(tpy)(bpy)X](m+) complexes (tpy = 2,2':3',2'-terpyridine; bpy = 2,2'-bipyridine; and X = a monodentate ancillary ligand) feature one or two partly resolved weak absorptions (bands I and/or II) on the low energy side of their absorption envelopes. Similar features are found for the related cyanide-bridged bi- and trimetallic complexes. However, the weak absorption band I of [(bpy)(2)Ru{CNRu(tpy)(bpy)}(2)](4+) is missing in its [(bpy)(2)Ru{NCRu(tpy)(bpy)}(2)](4+) linkage isomer demonstrating that this feature arises from a Ru(II)/tpy MLCT absorption. The energies of the MLCT band I components of the [Ru(tpy)(bpy)X](m+) complexes are proportional to the differences between the potentials for the first oxidation and the first reduction waves of the complexes. Time-dependent density functional theory (TD-DFT) computational modeling indicates that these band I components correspond to the highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition, with the HOMO being largely ruthenium-centered and the LUMO largely tpy-centered. The most intense contribution to a lowest energy MLCT absorption envelope (band III) of these complexes corresponds to the convolution of several orbitally different components, and its absorption maximum has an energy that is about 5000 cm(-1) higher than that of band I. The multimetallic complexes that contain Ru(II) centers linked by cyanide have mixed valence excited states in which more than 10% of electronic density is delocalized between the nearest neighbor ruthenium centers, and the corresponding stabilization energy contributions in the excited states are indistinguishable from those of the corresponding ground states. Single crystal X-ray structures and computational modeling indicate that the Ru-(C≡N)-Ru linkage is quite flexible and that there is not an appreciable variation in electronic structure or energy among the conformational isomers.     

Synthesis, characterization, and chiral behavior of S-bridged Co(III)Pt(II)Co(III) trinuclear complexes composed of bis(thiolato)-type octahedral units cis(S)-[Co(aet)(2)(en)](+) and/or trans(N)-[Co(D-pen- N,O,S)(2)](-) (aet = 2-aminoethanethiolate, D-pen = D-penicillaminate)

A series of linear-type Co(III)Pt(II)Co(III) trinuclear complexes composed of C(2)-cis(S)-[Co(aet)(2)(en)](+) (aet = 2-aminoethanethiolate) and/or Lambda(D)-trans(N)-[Co(D-pen-N,O,S)(2)](-) (D-pen = D-penicillaminate) were newly prepared, and their chiral behavior, which is markedly different from that of the corresponding Co(III)Pd(II)Co(III) complexes, is reported. The 1:1 reaction of an S-bridged Co(III)Ni(II)Co(III) trinuclear complex, [Ni[Co(aet)(2)(en)](2)]Cl(4), with K(2)[PtCl(4)] in water gave an S-bridged Co(III)Pt(II)Co(III) trinuclear complex, [Pt[Co(aet)(2)(en)](2)]Cl(4) ([1]Cl(4)), while the corresponding 1:2 reaction produced an S-bridged Co(III)Pt(II) dinuclear complex, [PtCl(2)[Co(aet)(2)(en)]]Cl ([2]Cl). Complex [1](4+) formed both racemic (DeltaDelta/LambdaLambda) and meso (DeltaLambda) forms, which were separated and optically resolved by cation-exchange column chromatography. An optically active S-bridged Co(III)Pt(II)Co(III) trinuclear complex having the pseudo LambdaLambda configuration, Lambda(D)Lambda(D)-[Pt[Co(D-pen-N,O,S)(2)](2)](0) (Lambda(D)Lambda(D)-[3]), was also prepared by reacting Lambda(D)-trans(N)-K[Co(D-pen-N,O,S)(2)] with K(2)[PtCl(4)] in a ratio of 2:1 in water. Treatment of the racemic Delta/Lambda-[2]Cl with Lambda(D)-trans(N)-K[Co(D-pen-N,O,S)(2)] in a ratio of 1:1 in water led to the formation of LambdaLambda(D)- and DeltaLambda(D)-[Pt[Co(aet)(2)(en)][Co(D-pen-N,O,S)(2)]](2+) (LambdaLambda(D)- and DeltaLambda(D)-[4](2+)) and DeltaDelta(D)-[Pt[Co(aet)(2)(en)][Co(D-pen-N,S)(2)(H(2)O)(2)]](2+) (DeltaDelta(D)-[4'](2+)), besides trace amounts of Lambda(D)Lambda(D)-[3] and DeltaDelta- and DeltaLambda-[1](4+). These Co(III)Pt(II)Co(III) complexes were characterized on the basis of electronic absorption, CD, and NMR spectra, along with single-crystal X-ray analyses for DeltaDelta/LambdaLambda-[1]Cl(4), DeltaLambda-[1]Cl(4), and DeltaLambda(D)-[4]Cl(2). Crystal data: DeltaDelta/LambdaLambda-[1]Cl(4).6H(2)O, monoclinic, space group C2/c with a = 14.983(3) A, b = 19.857(4) A, c = 12.949(3) A, beta = 113.51(2) degrees, V = 3532(1) A(3), Z = 4; DeltaLambda-[1]Cl(4).3H(2)O, orthorhombic, space group Pbca with a = 14.872(3) A, b = 14.533(3) A, c = 14.347(2) A, V = 3100(1) A(3), Z = 4; DeltaLambda(D)-[4]Cl(2).6H(2)O, monoclinic, space group P2(1) with a = 7.3836(2) A, b = 20.214(1) A, c = 10.622(2) A, beta = 91.45(1) degrees V = 1682.0(4) A(3), Z = 2.     

A very large Rh-Rh bond shortening on excitation of the [Rh2(1,8-diisocyano-p-menthane)4]2+ ion by time-resolved synchrotron X-ray diffraction

A very large Rh-Rh contraction of approximately 0.85 A occurs on excitation of the [Rh(2)(1,8-diisocyano-p-menthane)(4)](2+) ion to its triplet state.     

Synthesis and characterization of the dimercury(I)-linked compound [PPn]4[(Re7C(CO)21Hg)2]. Oxidative cleavage of the mercury-mercury bond leading to carbidoheptarhenate complexes of mercury(II), including [PPN][Re7C(CO)21Hg(S=C(NME2)2)

The reaction of [PPN](3)[Re(7)C(CO)(21)] with Hg(2)(NO(3))(2).2H(2)O in dichloromethane formed the complex [PPN](4)[(Re(7)C(CO)(21)Hg)(2)] ([PPN](4)[1]), isolated in 60% yield. Analogous salts of [1](4-) with [PPh(4)](+) and [NEt(4)](+) were also prepared. The crystal structure of [PPN](4)[1] showed that two carbidoheptarhenate cores are linked by a dimercury(I) unit (d(Hg-Hg) = 2.610(4) A), with each individual mercury atom face-bridging. Oxidative cleavage of the Hg-Hg bond in [1](4-) was effected by 4-bromophenyl disulfide to form [Re(7)C(CO)(21)HgSC(6)H(4)Br](2-) ([4](2-)), by I(2) to form [Re(7)C(CO)(21)HgI](2-) ([5](2-)), and by Br(2) to form [Re(7)C(CO)(21)HgBr](2-) ([6](2-)). Oxidation of [1](4-) by ferrocenium ion (2 equiv) in the presence of tetramethylthiourea resulted in the derivative [Re(7)C(CO)(21)HgSC(NMe(2))(2)](-) ([7](-)). The molecular structure of [PPN][7] was determined by X-ray crystallography. This is the first example of a carbidoheptarhenate-mercury complex with a neutral ligand on mercury, and ligand exchange was demonstrated by displacement with triethylphosphine. Complex [7](-) can also be prepared by protonating [Re(7)C(CO)(21)HgO(2)CCH(3)](2-) in the presence of tetramethylthiourea. Cyclic voltammetry data to calibrate and compare the redox properties of compounds [1](4-) and [7](-) have been measured.     

M-M bond-stretching energy landscapes for M2(dimen)4(2+) (M = Rh, Ir; dimen = 1,8-diisocyanomenthane) complexes

Isomers of Ir(2)(dimen)(4)(2+) (dimen = 1,8-diisocyanomenthane) exhibit different Ir-Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir-Ir distance is favored at room temperature [K = ～8; ΔH° = -0.8 kcal/mol; ΔS° = 1.44 cal mol(-1) K(-1)]. We report calculations that shed light on M(2)(dimen)(4)(2+) (M = Rh, Ir) structural differences: (1) metal-metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A(2u)) distortion promotes twisting of the ligand backbone at short metal-metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir(2)(dimen)(4)(2+) (～4.1 ? Ir-Ir with 0° twist angle and ～3.6 ? Ir-Ir with ±12° twist angle) but not for the rhodium analogue (～4.5 ? Rh-Rh with no twisting). Because both the ligand strain and A(2u) distortional energy are virtually identical for the two complexes, the strength of the metal-metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir-Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir(2)(dimen)(4)(2+) (R(e,Ir-Ir) = 2.87 ?; F(Ir-Ir) = 0.99 mdyn ?(-1)); (2) a single-minimum, anharmonic surface for the ground state of Rh(2)(dimen)(4)(2+) (R(e,Rh-Rh) = 3.23 ?; F(Rh-Rh) = 0.09 mdyn ?(-1)); (3) a double-minimum (along the Ir-Ir coordinate) surface for the ground state of Ir(2)(dimen)(4)(2+) (R(e,Ir-Ir) = 3.23 ?; F(Ir-Ir) = 0.16 mdyn ?(-1)).     

Cationic carbonyl complexes of rhodium(I) and rhodium(III): syntheses,vibrational spectra,NMR studies,and molecular structures of tetrakis(carbonyl)rhodium(I) heptachlorodialuminate and -gallate, [Rh(CO)4][Al2Cl7] and [Rh(CO)4][Ga2Cl7

Dimeric rhodium(I) bis(carbonyl) chloride, [Rh(CO)(2)(mu-Cl)](2), is found to be a useful and convenient starting material for the syntheses of new cationic carbonyl complexes of both rhodium(I) and rhodium(III). Its reaction with the Lewis acids AlCl(3) or GaCl(3) produces in a CO atmosphere at room temperature the salts [Rh(CO)(4)][M(2)Cl(7)] (M = Al, Ga), which are characterized by Raman spectroscopy and single-crystal X-ray diffraction. Crystal data for [Rh(CO)(4)][Al(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.705(3), b = 9.800(2), c = 10.268(2) A; alpha = 76.52(2), beta = 76.05(2), gamma = 66.15(2) degrees; V = 856.7(5) A(3); Z = 2; T = 293 K; R(1) [I > 2sigma(I)] = 0.0524, wR(2) = 0.1586. Crystal data for [Rh(CO)(4)][Ga(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.649(1), b = 9.624(1), c = 10.133(1) A; alpha = 77.38(1), beta = 76.13(1), gamma = 65.61(1) degrees; V = 824.4(2) A(3); Z = 2; T = 143 K; R(1) [I > 2sigma(I)] = 0.0358, wR(2) = 0.0792. Structural parameters for the square planar cation [Rh(CO)(4)](+) are compared to those of isoelectronic [Pd(CO)(4)](2+) and of [Pt(CO)(4)](2+). Dissolution of [Rh(CO)(2)Cl](2) in HSO(3)F in a CO atmosphere allows formation of [Rh(CO)(4)](+)((solv)). Oxidation of [Rh(CO)(2)Cl](2) by S(2)O(6)F(2) in HSO(3)F results in the formation of ClOSO(2)F and two seemingly oligomeric Rh(III) carbonyl fluorosulfato intermediates, which are easily reduced by CO addition to [Rh(CO)(4)](+)((solv)). Controlled oxidation of this solution with S(2)O(6)F(2) produces fac-Rh(CO)(3)(SO(3)F)(3) in about 95% yield. This Rh(III) complex can be reduced by CO at 25 degrees C in anhydrous HF to give [Rh(CO)(4)](+)((solv)); addition of SbF(5) at -40 degrees C to the resulting solution allows isolation of [Rh(CO)(4)][Sb(2)F(11)], which is found to have a highly symmetrical (D(4)(h)()) [Sb(2)F(11)](-) anion. Oxidation of [Rh(CO)(2)Cl](2) in anhydrous HF by F(2), followed in a second step by carbonylation in the presence of SbF(5), is found to be a simple, straightforward route to pure [Rh(CO)(5)Cl][Sb(2)F(11)](2), which has previously been structurally characterized by us. All new complexes are characterized by vibrational and NMR spectroscopy. Assignment of the vibrational spectra and interpretation of the structural data are supported by DFT calculations.     

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.     

Separation and optical resolution of a pair of atrop diastereomers of the octahedral rhodium(III) complex with a nine-membered S,S-chelate ring

Treatment of fac-[Rh(aet) 3] (aet = 2-aminoethanethiolate) with 2,2'-bis(bromomethyl)-1,1'-biphenyl gave a mononuclear rhodium(III) complex with a nine-membered S, S-chelate ring, fac-[Rh(aet)(L)] (2+) ([ 1] (2+), L = 2,2'-bis(2-aminoethylthiomethyl)-1,1'-biphenyl). Complex [ 1] (2+) afforded a pair of atrop diastereomers, Delta SS( S ax)/Lambda RR( R ax)-[ 1] (2+) ([ 1a] (2+)) and Delta SS( R ax)/Lambda RR( S ax)-[ 1] (2+) ([ 1b] (2+)), which involves the axial chirality ( R ax/ S ax) about a biphenyl moiety of L, besides the central chirality (Delta/Lambda) about a Rh (III) ion bound by two asymmetric ( R/ S) thioether donors. The atrop diastereomers ([ 1a] (2+) and [ 1b] (2+)) were successfully separated, isolated, and optically resolved, and the circular dichroism (CD) contribution from the axial chirality was evaluated by CD spectral analyses.     

Redox-switched complexation/decomplexation of K(+) and Cs(+) by molecular cyanometalate boxes

The reaction of [N(PPh(3))(2)][CpCo(CN)(3)] and [Cb*Co(NCMe)(3)]PF(6) (Cb* = C(4)Me(4)) in the presence of K(+) afforded {K subset[CpCo(CN)(3)](4)[Cb*Co](4)}PF(6), [KCo(8)]PF(6). IR, NMR, ESI-MS indicate that [KCo(8)]PF(6) is a high-symmetry molecular box containing a potassium ion at its interior. The analogous heterometallic cage {K subset[Cp*Rh(CN)(3)](4)[Cb*Co](4)}PF(6) ([KRh(4)Co(4)]PF(6)) was prepared similarly via the condensation of K[Cp*Rh(CN)(3)] and [Cb*Co(NCMe)(3)]PF(6). Crystallographic analysis confirmed the structure of [KCo(8)]PF(6). The cyanide ligands are ordered, implying that no Co-CN bonds are broken upon cage formation and ion complexation. Eight Co-CN-Co edges of the box bow inward toward the encapsulated K(+), and the remaining four mu-CN ligands bow outward. MeCN solutions of [KCo(8)](+) and [KRh(4)Co(4)](+) were found to undergo ion exchange with Cs(+) to give [CsCo(8)](+) and [CsRh(4)Co(4)](+), both in quantitative yields. Labeling experiments involving [(MeC5H4)Co(CN)(3)]- demonstrated that Cs(+)-for-K(+) ion exchange is accompanied by significant fragmentation. Ion exchange of NH(4+) with [KCo(8)](+) proceeds to completion in THF solution, but in MeCN solution, the exclusive products were [Cb*Co(NCMe)(3)]PF(6) and the poorly soluble salt NH(4)CpCo(CN)(3). The lability of the NH(4+)-containing cage was also indicated by the rapid exchange of the acidic protons in [NH(4)Co(8)](+). Oxidation of [MCo(8)](+) with 4 equiv of FcPF(6) produced paramagnetic (S = 4/2) [Co(8)](4+), releasing Cs(+) or K(+). The oxidation-induced dissociation of M(+) from the cages is chemically reversed by treatment of [Co(8)](4+) and CsOTf with 4 equiv of Cp(2)Co. Cation recognition by [Co(8)] and [Rh(4)Co(4)] cages was investigated. Electrochemical measurements indicated that E(1/2)(Cs(+))--E(1/2)(K(+)) approximately 0.08 V for [MCo(8)](+).     

Novel acetate polyoxomolybdate "host" accommodating a zigzag-chainlike "guest" of five edge-shared sodium cations: Na(21)[[Na(5)(H(2)O)(14)]within[Mo(46)O(134)(OH)(10)(mu-CH(3)COO)(4)]].CH(3)COONa. approximately equal to 95H(2)O

A novel ESR-silent polyoxomolybdate Na(21)([Na(5)(H(2)O)(14)][Mo(46)O(134)(OH)(10)(mu-CH(3)COO)(4)]).CH(3)COONa.approximately equal to 90H(2)O (3) was simply synthesized in high yield by reducing an acidified aqueous solution of Na(2)MoO(4).2H(2)O and CH(3)COONa.3H(2)O. The structure of 3 is constructed by a 46-member crown-shaped anion, [Na(5)(H(2)O)(14)]within[Mo(V)(20)Mo(VI)(26)O(134)(OH)(10)(mu-CH(3)COO)(4)](21-), 3a, which is built up by three different but related building blocks in a new mode and further connected into layers via Na(+) and hydrogen bonds. Crystal data of compound 3: triclinic space group P(-1); a = 16.4065(3), b = 17.4236(2), c = 20.8247(3) A; alpha= 87.57, beta= 67.9810(10), gamma= 80.6970(10)o; V = 5445.08(14) A(3); Z = 1; D(calcd) = 2.902. Structure solution and refinement are based on 19014 reflections, R = 0.0750.     

Synthesis and characterization of a twin Cubane-type molybdenum-rhodium-sulfur cluster, [{Mo3RhCp*S4(H2O)7(O)}2]8+. X-ray structure of [{Mo3RhCpS4(H2O7O}2](CH3C6H4SO3)(8).14H2O

The reaction of [Mo(3)S(4)(H(2)O)(9)](4+) (1) with [(CpRhCl(2))(2)] afforded a novel rhodium-molybdenum cluster, [{Mo(3)RhCpS(4)(H(2)O)(7)(O)}(2)](8+) (2). X-ray structure analysis of [2](pts)(8).14H(2)O (pts(-) = CH(3)C(6)H(4)SO(3)(-)) has revealed the existence of a new oxo-bridged twin cubane-type core, (Mo(3)RhCpS(4))(2)(O)(2). The high affinity of the CpRh group for sulfur atoms in 1 seems to be the main driving force for this reaction. The strong Lewis acidity of the CpRh group in intermediate A, [Mo(3)RhCpS(4)(H(2)O)(9)](6+), caused a release of proton from one of the water molecules attached to the molybdenum atoms to give intermediate B, [Mo(3)RhCpS(4)(H(2)O)(8)(OH)](5+). The elimination of two water molecules from two intermediate B molecules, followed by the deprotonation reaction of hydroxo bridges, generated the twin cubane-type cluster 2. The formal oxidation states of rhodium and molybdenum atoms are the same before and after the reaction (i.e., Mo(IV)(3), Rh(III)). The Mo-O-Mo moieties in [2](pts)(8).14H(2)O are nearly linear with a bond angle of 164.3(3) degrees, and the basicity of the bridging oxygen atoms seems to be weak. For this reason, protonation at the bridging oxygen atoms does not occur even in a strongly acidic aqueous solution. The binding energy values of Mo 3d(5/2), Rh 3d(5/2), and C 1s obtained from X-ray photoelectron spectroscopy measurements for [2](pts)(8).14H(2)O are 229.8, 309.3, and 285 eV, respectively. The XPS measurements on the Rh 3d(5/2) binding energy indicate that the oxidation state of Rh is 3+. The binding energy of Mo 3d(5/2) (229.8 eV) compares with that observed for [1](pts)(4).7H(2)O (230.7 eV, Mo 3d(5/2)). A lower energy shift (0.9 eV) is observed in the binding energy of Mo 3d(5/2) for [2](pts)(8).14H(2)O. This energy shift may correspond to the coordination of an oxygen atom having a negative charge to the molybdenum atom.