Showing papers in "Inorganic Chemistry in 2001"

Synthesis and characterization of phosphorescent cyclometalated platinum complexes.

Abstract: The synthesis, electrochemistry, and photophysics of a series of square planar Pt(II) complexes are reported. The complexes have the general structure C∧NPt(O∧O),where C∧N is a monoanionic cyclometalating ligand (e.g., 2-phenylpyridyl, 2-(2‘-thienyl)pyridyl, 2-(4,6-difluorophenyl)pyridyl, etc.) and O∧O is a β-diketonato ligand. Reaction of K2PtCl4 with a HC∧N ligand precursor forms the chloride-bridged dimer, C∧NPt(μ-Cl)2PtC∧N, which is cleaved with β-diketones such as acetyl acetone (acacH) and dipivaloylmethane (dpmH) to give the corresponding monomeric C∧NPt(O∧O) complex. The thpyPt(dpm) (thpy = 2-(2‘-thienyl)pyridyl) complex has been characterized using X-ray crystallography. The bond lengths and angles for this complex are similar to those of related cyclometalated Pt complexes. There are two independent molecular dimers in the asymmetric unit, with intermolecular spacings of 3.45 and 3.56 A, consistent with moderate π−π interactions and no evident Pt−Pt interactions. Most of the C∧NPt(O∧O) complexes...

Cooperative spin crossover behavior in cyanide-bridged Fe(II)-M(II) bimetallic 3D Hofmann-like networks (M = Ni, Pd, and Pt).

Abstract: The three-dimensional polymeric compounds [Fe(pz)M(CN)4]·nH2O (pz = pyrazine; M = Ni(II), Pd(II), and Pt(II)) have been synthesized and characterized. They undergo strong cooperative spin transitions, large hysteresis loops, and dramatic color changes upon spin conversion. The two-dimensional homologues [Fe(py)2M(CN)4] (py = pyridine; M = Ni(II), Pd(II), and Pt(II)) also have been synthesized and characterized. In the latter case cooperativity is smaller than in the tri-dimensional derivatives, and consequently narrower hysteresis loops were observed.

Toward a Molecular Photochemical Device: A Triad for Photoinduced Charge Separation Based on a Platinum Diimine Bis(acetylide) Chromophore

Abstract: A donor−chromophore−acceptor triad (D−C−A) in which the chromophore is a Pt diimine bis(acetylide) moiety (red), the donor is phenothiazine (blue), and the acceptor is nitrophenyl (green) has been synthesized and studied spectroscopically. Irradiation leads to a charge-separated state that has a 70 ns lifetime as measured by transient absorption spectroscopy.

Photophysics of diimine platinum(II) bis-acetylide complexes

Abstract: A comprehensive photophysical investigation has been carried out on a series of eight complexes of the type (diimine)Pt(−C⋮C−Ar)2, where diimine is a series of 2,2‘-bipyridine (bpy) ligands and −C⋮C−Ar is a series of substituted aryl acetylide ligands. In one series of complexes, the energy of the Pt → bpy metal-to-ligand charge transfer (MLCT) excited state is varied by changing the substituents on the 4,4‘- and/or the 5,5‘-positions of the bpy ligand. In a second series of complexes the electronic demand of the aryl acetylide ligand is varied by changing the para substituent (X) on the aryl ring (X = −CF3, −CH3, −OCH3, and −N(CH3)2). The effect of variation of the substituents on the excited states of the complexes has been assessed by examining their UV−visible absorption, variable-temperature photoluminescence, transient absorption, and time-resolved infrared spectroscopy. In addition, the nonradiative decay rates of the series of complexes are subjected to a quantitative energy gap law analysis. The ...

Phosphonate-based bipyridine dyes for stable photovoltaic devices.

Abstract: The series of Ru(II) polypyridyl compounds shown bind to metal oxide surfaces through the phosphonic acid groups. Ground and excited state properties of the Ru(II) complexes were characterized in fluid solution and when anchored to nanocrystalline ZrO2 and TiO2 thin films. In regenerative solar cells, the complexes bound to TiO2 efficiently convert light into electricity. The position of the phosphonic acid groups on the bipyridine ligand and the introduction of a methylene spacer allow fine-tuning of the light-to-electrical energy conversion efficiencies.

Ionic Liquids Based on FeCl3 and FeCl2. Raman Scattering and ab Initio Calculations

Abstract: We have prepared ionic liquids by mixing either iron(II) chloride or iron(III) chloride with 1-butyl-3-methylimidazolium chloride (BMIC). Iron(II) chloride forms ionic liquids from a mole ratio of 1 FeCl2/3 BMIC to almost 1 FeCl2/1 BMIC. Both Raman scattering and ab initio calculations indicate that FeCl42- is the predominant iron-containing species in these liquids. Iron(III) chloride forms ionic liquids from a mole ratio of 1 FeCl3/1.9 BMIC to 1.7 FeCl3/1 BMIC. When BMIC is in excess, Raman scattering indicates the presence of FeCl4-. When FeCl3 is in excess, Fe2Cl7- begins to appear and the amount of Fe2Cl7- increases with increasing amounts of FeCl3. Ionic liquids were also prepared from a mixture of FeCl2 and FeCl3 and are discussed. Finally, we have used both Hartree−Fock and density functional theory methods to compute the optimized structures and vibrational spectra for these species. An analysis of the results using an all-electron basis set, 6-31G*, as well as two different effective core potent...

A new inorganic-organic photoluminescent material constructed with helical Zn-3(mu(3)-OH)(mu(2)-OH) chains

Abstract: A photoluminescent inorganic−organic material formulated as [Zn3(μ3-OH)(μ2-OH)(4,4‘-bpy)0.5(4,4‘-oba)2]·0.5H2O (4,4‘-bpy = 4,4‘-bipyridine; 4,4‘-oba = 4,4‘-oxybis(benzoate)), shown by X-ray diffraction, features a novel polynuclear zinc helical chain motif. Linkage of mixed organic ligands and helical chains results in a 3-D network.

Interaction of [Ru(dmp)2(dppz)]2+ and [Ru(dmb)2(dppz)]2+ with DNA: effects of the ancillary ligands on the DNA-binding behaviors.

Abstract: By the incorporation of methyl groups on the ancillary ligand of phen and bpy, different DNA-binding behaviors of complexes 1 and 2 were characterized. Different binding rates of the isomers of 2 with CT-DNA via CD spectra were observed through dialysis experiments but not with complex 1.

Free energy of spin-crossover complexes calculated with density functional methods.

Abstract: A set of iron(II) complexes that exhibit a temperature-dependent spin-crossover between the low-spin and the high-spin state were studied by density functional methods. The total electronic energy, the zero-point vibrational energy, and the entropy were calculated in order to determine the free energy. While the calculated total energy differences between the two spin states have significant errors, qualitative agreement is achieved for the zero-point vibrational energy differences and the entropy differences.

The effect of pH on the dimensionality of coordination polymers.

Abstract: Hydrothermal reactions of simple alkaline salts or their hydroxides with 3,5-pyrazoledicarboxylic acid (H 3pdc) yielded seven new compounds. At a lower pH level three one-dimeinsional structures [Ca(Hpdc)(H2O)4]‚2H2O (1), [Ca(Hpdc)(H2O)4]‚H2 O( 2), and [Ba(H2pdc)2(H2O)4]‚2H2 O( 6) were obtained by evaporation of the solutions resulting from hydro(solvo)thermal reactions of MCl2 (M ) Ca, Ba) with H3pdc in water (1, 6) or in water/Et3N (2 )a t 150°C for 3 days. Crystal structures of 1 and 2 contain zigzag chains of metal centers bridged by a single Hpdc 2- ligand, whereas structure 6 consists of linear chains of metal centers bridged by two H2pdc - ligands. A dimer molecule [Sr(H3pdc)(H2pdc)2(H2O)3]2‚2(H3pdc)‚4H2 O( 4) was obtained from a similar hydrothermal reaction using Sr(ClO4)2‚6H2O instead of MCl2. This compound contains [2+2] metallomacrocycles. At higher pH levels (pH ) 4-6), the three-dimensional polymers [M(Hpdc)(H2O)] (Ca 3 ,S r5 ,B a7 ) were isolated by reactions of MCl2 (M ) Ca, Sr, Ba) with H3pdc in water/Et3N or in M(OH)2 (M ) Ca, Sr, Ba) with H3pdc in water under hydro(solvo)thermal conditions (150 °C, 3 days). Calcium and strontium are seven- and nine-coordinated in 3 and 5, respectively; barium is nine- and ten-coordinated in 7. It was observed that the increase in pH resulted in a higher connectivity level of ligands, which in turn leads to a higher dimensionality of the crystal structures. The correlation between the structures and pH values will be discussed. Crystal data: for 1, monoclinic, space group P21/n (No. 14), with a ) 8.382(2), b ) 12.621(3), c ) 11.767(2) A,‚ ) 98.91(3)°, Z ) 4; for 2, 3, and 5, monoclinic, space group P21/c (No. 14), Z ) 4, a ) 7.711(2), b ) 15.574(3), c ) 9.341(2) A,‚ ) 96.73(3)°, Z ) 4( 2), a ) 6.616(1), b ) 12.654(3), c ) 8.782(2) A,‚ ) 103.65(3)°, Z ) 4( 3), a ) 9.213(2), b ) 12.088(3), c ) 6.196(2) A,‚ ) 98.96(3)° (5); for 4 and 7, triclinic, space group P 1 h (No. 2), with a ) 11.263(2), b ) 11.460(3), c ) 12.904(2) A, R) 71.54(3), ‚ ) 98.96(3), A ) 89.03(3)°, Z ) 1( 4), a ) 7.107(1), b ) 9.780(2), c ) 11.431(2) A, R) 74.69(3), ‚ ) 73.39(3), A ) 85.29(3)°, Z ) 2( 7); for 6, monoclinic, space group C2/c (No. 15), with a ) 20.493(4), b ) 6.708(1), c ) 15.939(3) A,‚ ) 123.56(3)°, Z ) 4.

Synthesis and characterization of copper-, zinc-, manganese-, and cobalt-substituted dimeric heteropolyanions, [(alpha-XW9O33)2M3(H2O)3](n-) (n = 12, X =As(III), Sb(III), M = Cu(2+), Zn(2+); n = 10, X = Se(IV), Te(IV), M = Cu(2+) and [(alpha-AsW9O33)2WO(H2O)M2(H2O)2](10-) (M = Zn(2+), Mn(2+), Co(2+).

Abstract: Interaction of the lacunary [α-XW9O33]9- (X = AsIII, SbIII) with Cu2+ and Zn2+ ions in neutral, aqueous medium leads to the formation of dimeric polyoxoanions, [(α-XW9O33)2M3(H2O)3]12- (M = Cu2+, Zn2+; X = AsIII, SbIII), in high yield. The selenium and tellurium analogues of the copper-containing heteropolyanions are also reported: [(α-XW9O33)2Cu3(H2O)3]10- (X = SeIV, TeIV). The polyanions consist of two [α-XW9O33] units joined by three equivalent Cu2+ (X = As, Sb, Se, Te) or Zn2+ (X = As, Sb) ions. All copper and zinc ions have one terminal water molecule resulting in square-pyramidal coordination geometry. Therefore, the title anions have idealized D3h symmetry. The space between the three transition metal ions is occupied by three sodium ions (M = Cu2+, Zn2+; X = AsIII, SbIII) or potassium ions (M = Cu2+; X = SeIV, TeIV) leading to a central belt of six metal atoms alternating in position. Reaction of [α-AsW9O33]9- with Zn2+, Co2+, and Mn2+ ions in acidic medium (pH = 4−5) results in the same structur...

Computed Ligand Electronic Parameters from Quantum Chemistry and Their Relation to Tolman Parameters, Lever Parameters, and Hammett Constants

Abstract: The calculated (DFT, B3PW91) A(1) nu(CO) frequency in LNi(CO)(3) defines an electronic parameter that reliably predicts the relative donor powers of a wide variety of cationic, neutral, and negatively charged ligands. These calculated parameters correlate very well with the available Tolman and Lever parameters, and also with Hammett's sigma(m), where available. The method avoids any experimental limitations and, in particular, can be used for proposed ligands not yet experimentally available.

Two versatile N,N'-bipyridine-type ligands for preparing organic-inorganic coordination polymers: new cobalt- and nickel-containing framework materials.

Abstract: The Schiff base ligands 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (L1, monoclinic, P2(1)/c, a = 3.856(1) A, b = 11.032(2) A, c = 12.738(3) A, beta = 92.21(3) degrees, Z = 2) and 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (L2, monoclinic, P2(1)/c, a = 10.885(2) A, b = 4.613(1) A, c = 14.978(3) A, beta = 92.827(4) degrees, Z = 2) were used in the synthesis of four new organic-inorganic coordination polymers, each of them adopting a different structural motif. Synthesis, X-ray structural determinations, and spectroscopic and thermogravimetric analyses are presented. The reaction between Co(NO(3))(2).6H(2)O and L1 afforded a two-dimensional noninterpenetrating brick-wall structure, [Co(C(12)N(4)H(10))(1.5)(NO(3))(2)(H(2)O)(CH(2)Cl(2))(2)](n)() (1, triclinic, P1; a = 10.242(7) A, b = 10.802(7) A, c = 15.100(1) A, alpha = 70.031(1), beta = 75.168(11), gamma = 76.155(11), Z = 2), while Ni(NO(3))(2).6H(2)O combined with L1 yielded an interpenetrating three-dimensional rhombus-grid polymer, [Ni(C(12)N(4)H(10))(2)(NO(3))(2)(OC(4)H(8))(1.66)(H(2)O)(0.33)](n) (2, monoclinic, C2/c; a = 20.815(8) A, b = 23.427(8) A, c = 17.291(6) A, beta = 116.148(6), Z = 8). The reaction of Co(NO(3))(2).6H(2)O and L2 was found to be solvent-sensitive and resulted in the formation of two different noninterpenetrating compounds: [Co(C(14)N(4)H(14))(2)(NO(3))(2)(C(6)H(6))(1.5)](n)() (3, monoclinic, C2/c; a = 22.760(2) A, b = 21.010(3) A, c = 25.521(2) A, beta = 97.151(2), Z = 8), which adopts a two-dimensional square-grid motif formed by propeller-type modules, and [Co(C(14)N(4)H(14))(1.5)(NO(3))(2)(CH(2)Cl(2))(2)](n)() (4, monoclinic, P2(1)/n; a = 14.432(2) A, b = 14.543(8) A, c = 15.448(4) A, beta = 96.968(0), Z = 4), consisting of T-shaped building blocks assembled into a one-dimensional ladder-type structure. These four coordination polymers all exhibit impressive thermal stability. Thermogravimetric studies showed that after complete removal of the solvents, the frameworks are stable to temperatures between 234 degrees C and 260 degrees C.

Dye sensitization of nanocrystalline titanium dioxide with square planar platinum(II) diimine dithiolate complexes.

Abstract: A series of platinum-based sensitizers of the general type Pt(NN)(SS), where NN is 4,4‘-dicarboxy-2,2‘-bipyridine (dcbpy) or 4,7-dicarboxy-1,10-phenanthroline (dcphen) and SS is ethyl-2-cyano-3,3-dimercaptoacrylate (ecda), quinoxaline-2,3-dithiolate (qdt), 1,2-benzenedithiolate (bdt), or 3,4-toluenedithiolate (tdt), that have various ground-state oxidation potentials has been synthesized and anchored to nanocrystalline titanium dioxide electrodes for light-to-electricity conversion in regenerative photoelectrochemical cells with an I-/I-3 acetonitrile electrolyte. The intense mixed-Pt/dithiolate-to-diimine charge-transfer absorption bands in this series could be tuned from 440 to 580 nm by choosing appropriate dithiolate ligands, and the highest occupied molecular orbitals varied by more than 500 mV. Spectrophotometric titration of the Pt(dcphen)(bdt) complex exhibits a ground-state pKa value of 3.2 ± 0.1, which can be assigned to the protonation of the carboxylate group of the dcphen ligand. Binding of P...

Molecule-based magnets formed by bimetallic three-dimensional oxalate networks and chiral tris(bipyridyl) complex cations. The series [ZII(bpy)3][ClO4][MIICrIII(ox)3] (ZII = Ru, Fe, Co, and Ni; MII = Mn, Fe, Co, Ni, Cu, and Zn; ox = oxalate dianion).

Abstract: The synthesis, structure, and physical properties of the series of molecular magnets formulated as [ZII(bpy)3][ClO4][MIICrIII(ox)3] (ZII = Ru, Fe, Co, and Ni; MII = Mn, Fe, Co, Ni, Cu, and Zn; ox = oxalate dianion) are presented. All the compounds are isostructural to the [Ru(bpy)3][ClO4][MnCr(ox)3] member whose structure (cubic space group P4(1)32 with a = 15.506(2) A, Z = 4) consists of a three-dimensional bimetallic network formed by alternating MII and CrIII ions connected by oxalate anions. The identical chirality (lambda in the solved crystal) of all the metallic centers determines the 3D chiral structure adopted by these compounds. The anionic 3D sublattice leaves some holes where the chiral [Z(bpy)3]2+ and ClO4- counterions are located. These compounds behave as soft ferromagnets with ordering temperatures up to 6.6 K and coercive fields up to 8 mT.

Three-coordinated boron-11 chemical shifts in borates.

Abstract: Despite the importance of 11B nuclear magnetic resonance (NMR) in structural studies of borate glasses, no clear means of correlating NMR parameters with the number of nonbridging oxygens on three-coordinate boron has been demonstrated. In this work, a series of anhydrous, polycrystalline, binary borates has been examined by 11B magic-angle spinning (MAS) NMR to obtain precise measurements of their three-coordinate boron isotropic chemical shifts. The shifts generally increase with the replacement of bridging oxygens by nonbridging oxygens, ranging from 14.6 ppm in crystalline B2O3 to 22.5 ppm in magnesium orthoborate. The underlying physical basis for this trend is satisfactorily accounted for by considering second neighbor effects using bond valence sums. These data are supportive of a structural model for B2O3 glass in which 72% of the boron atoms are in rings. High-field MAS NMR experiments (B0 = 18.8 T) indicate that the boron shielding is anisotropic, with greater anisotropy measured for three-coord...

2.4 angstrom crystal structure of an oxaliplatin 1,2-d(GpG) intrastrand cross-link in a DNA dodecamer duplex

Abstract: (1R,2R-Diaminocyclohexane)oxalatoplatinum(II) (oxaliplatin) is a third-generation platinum anticancer compound that produces the same type of inter- and intrastrand DNA cross-links as cisplatin. In combination with 5-fluorouracil, oxaliplatin has been recently approved in Europe, Asia, and Latin America for the treatment of metastatic colorectal cancer. We present here the crystal structure of an oxaliplatin adduct of a DNA dodecanucleotide duplex having the same sequence as that previously reported for cisplatin (Takahara, P. M.; Rosenzweig, A. C.; Frederick, C. A.; Lippard, S. J. Nature 1995, 377, 649−652). Pt-MAD data were used to solve this first X-ray structure of a platinated DNA duplex derived from an active platinum anticancer drug other than cisplatin. The overall geometry and crystal packing of the complex, refined to 2.4 A resolution, are similar to those of the cisplatin structure, despite the fact that the two molecules crystallize in different space groups. The platinum atom of the {Pt(R,R-D...

Kinetics and Mechanisms of Aqueous Ozone Reactions with Bromide, Sulfite, Hydrogen Sulfite, Iodide, and Nitrite Ions

Abstract: Reactions of ozone with Br-, SO32-, HSO3-, I-, and NO2-, studied by stopped-flow and pulsed-accelerated-flow techniques, are first order in the concentration of O3(aq) and first order in the concentration of each anion. The rate constants increase by a factor of 5 × 106 as the nucleophilicities of the anions increase from Br- to SO32-. Ozone adducts with the nucleophiles are proposed as steady-state intermediates prior to oxygen atom transfer with release of O2. Ab initio calculations show possible structures for the intermediates. The reaction between Br- and O3 is accelerated by H+ but exhibits a kinetic saturation effect as the acidity increases. The kinetics indicate formation of BrOOO- as a steady-state intermediate with an acid-assisted step to give BrOH and O2. Temperature dependencies of the reactions of Br- and HSO3- with O3 in acidic solutions are determined from 1 to 25 °C. These kinetics are important in studies of annual ozone depletion in the Arctic troposphere at polar sunrise.

[N2H5]+2[N4C−NN−CN4]2-: A New High-Nitrogen High-Energetic Material

Abstract: The reaction of [N2H5]+2[SO4]2- with barium 5,5‘-azotetrazolate gave new high-energy-density materials (HEDM) based on the 5,5‘-azotetrazolate dianion. The dihydrazinium salt of [N4C−NN−CN4]2- 1, i...

Multiple hydrogen bond stabilization of a sandwich complex of sulfate between two macrocyclic tetraamides.

Abstract: A tetraamide macrocycle derived from isophthaloyl dichloride and diethylenetriamine shows extremely high affinities for phosphate and sulfate ions in CDCl3, with log K = 4.66 and 4.50, respectively. Crystallographic findings in the case of sulfate indicate an unusual sulfate sandwich complex, in which a single sulfate ion is held between two macrocyclic amides by hydrogen bonds to eight amides. Two tetra-n-butylammonium ions serve to balance the charge.

Three-coordinate zinc amide and phenoxide complexes supported by a bulky Schiff base ligand.

Abstract: Three-coordinate zinc complexes are potential catalysts for the ring-opening of cyclic monomers such as lactide and oxiranes. By use of a bulky Schiff base ligand, monomeric zinc amide and phenoxide are prepared and characterized by X-ray crystallography.

Molecular and electronic structure of octahedral o-aminophenolato and o-iminobenzosemiquinonato complexes of V(V), Cr(III), Fe(III), and Co(III). Experimental determination of oxidation levels of ligands and metal ions.

Abstract: The coordination chemistry of the ligands 2-anilino-4,6-di-tert-butylphenol, H[LAP], and N,N‘‘‘-bis{2-(4,6-di-tert-butylphenol}diethylenetriamine, H2[(LAP)N(LAP)], has been studied with the first-row transition metal ions V, Cr, Fe, and Co. The ligands are noninnocent in the sense that the aminophenolato parts, [LAP]- and [LAP−H]2-, can be readily oxidized to their o-iminobenzosemiquinonato, [LISQ]-, and o-iminobenzoquinone, [LISB], forms. The following neutral octahedral complexes have been isolated as crystalline materials, and their crystal structures have been determined by X-ray crystallography at 100 K: [CrIII(LISQ)3] (1), [FeIII(LISQ)3] (2), [CoIII(LISQ)3] (3), [VV(LISQ)(LAP−H)2] (4), [VV(LAP−H)2(LAP)] (5), and [VVO{(LAP)N(LAP−H)}] (6). From variable-temperature magnetic susceptibility measurements and X-band EPR spectroscopy it has been established that they possess the ground states: 1, S = 0; 2, S = 1; 3, S = 3/2; 4, S = 1/2; 5, S = 0; 6, S = 0. The o-iminobenzosemiquinonato radicals (Srad = 1...

Synthesis, Characterization and Structural Transformation of A Condensed Rare Earth Metal Coordination Polymer

Abstract: A new condensed three-dimensional structure Er4(bdc)6·6H2O was synthesized by the hydro(solvo)thermal method. A probable explanation of the structure change was also investigated.

Long-lived emissions from 4'-substituted Pt(trpy)Cl+ complexes bearing aryl groups. Influence of orbital parentage.

Abstract: Pt(trpy)Cl+, where trpy denotes 2,2‘:6‘,2‘ ‘-terpyridine, is a versatile binding agent but has a limited photochemistry due to a short excited-state lifetime. However, this work shows that the introduction of aryl substituents at the 4‘ position of the trpy ligand drastically alters the picture. For the substituents phenyl, p-methoxyphenyl, 1-naphthyl, 2-naphthyl, 9-phenanthrenyl, and 1-pyrenyl, the ligand abbrevations are 4‘-Ph-T, 4‘-pMeOPh-T, 4‘-Npl-T, 4‘-Np2-T, 4‘-Phe9-T, and 4‘-Pyre1-T, respectively. Techniques utilized include electrochemistry as well as absorption and emission spectroscopies. While the lowest energy excited states of Pt(4‘-Ph-T)Cl+ and the parent complex Pt(trpy)Cl+ exhibit mainly metal-to-ligand charge-transfer (MLCT) character, the emitting state takes on aryl-to-trpy intraligand charge-transfer (ILCT) character as the substituents become more electron-donating. Studies of Zn(trpy)Cl2, its aryl-substituted analogues, and the free ligands themselves provide information about the re...

Syntheses and redox properties of bis(hydroxoruthenium) complexes with quinone and bipyridine ligands. Water-oxidation catalysis.

Abstract: The novel bridging ligand 1,8-bis(2,2':6',2"-terpyridyl)anthracene (btpyan) is synthesized by three reactions from 1,8-diformylanthracene to connect two [Ru(L)(OH)]+ units (L = 3,6-di-tert-butyl-1,2-benzoquinone (3,6-tBu2qui) and 2,2'-bipyridine (bpy)). An addition of tBuOK (2.0 equiv) to a methanolic solution of [RuII2(OH)2(3,6-tBu2qui)2(btpyan)](SbF6)2 ([1](SbF6)2) results in the generation of [RuII2(O)2(3,6-tBu2sq)2(btpyan)]0 (3,6-tBu2sq = 3,6-di-tert-butyl-1,2-semiquinone) due to the reduction of quinone coupled with the dissociation of the hydroxo protons. The resultant complex [RuII2(O)2(3,6-tBu2sq)2(btpyan)]0 undergoes ligand-localized oxidation at E1/2 = +0.40 V (vs Ag/AgCl) to give [RuII2(O)2(3,6-tBu2qui)2(btpyan)]2+ in MeOH solution. Furthermore, metal-localized oxidation of [RuII2(O)2(3,6-tBu2qui)2(btpyan)]2+ at Ep = +1.2 V in CF3CH2OH/ether or water gives [RuIII2(O)2(3,6-tBu2qui)2(btpyan)]4+, which catalyzes water oxidation. Controlled-potential electrolysis of [1](SbF6)2 at +1.70 V in the presence of H2O in CF3CH2OH evolves dioxygen with a current efficiency of 91% (21 turnovers). The turnover number of O2 evolution increases to 33,500 when the electrolysis is conducted in water (pH 4.0) by using a [1](SbF6)2-modified ITO electrode. On the other hand, the analogous complex [RuII2(OH)2(bpy)2(btpyan)](SbF6)2 ([2](SbF6)2) shows neither dissociation of the hydroxo protons, even in the presence of a large excess of tBuOK, nor activity for the oxidation of H2O under similar conditions.

Complex Magnetism and Magnetic Structures of the Metastable HoMnO3 Perovskite

Abstract: The magnetic properties and the low-temperature magnetic structures of the orthorhombic perovskite HoMnO3 (space group Pnma) have been studied on polycrystalline samples by magnetization, specific ...

2D molecular square grid with strong blue fluorescent emission: a complex of norfloxacin with zinc(II).

Abstract: The hydrothermal reactions of norfloxacin (H-Norf) with Zn(OH)2 and Zn(NO3)2·6H2O respectively, afford two different products, Zn(Norf)2·4H2O (1) and Zn(H-Norf)2.(NO3)2·2H2O(2). 1 represents, to our knowledge, an unprecedented neutral metal-based molecular square grid with strong blue fluorescent emission.

New Ru(II) Chromophores with Extended Excited-State Lifetimes

Abstract: We describe the synthesis, electrochemical, and photophysical properties of two new luminescent Ru(II) diimine complexes covalently attached to one and three 4-piperidinyl-1,8-naphthalimide (PNI) chromophores, [Ru(bpy)2(PNI−phen)](PF6)2 and [Ru(PNI−phen)3](PF6)2, respectively. These compounds represent a new class of visible light-harvesting Ru(II) chromophores that exhibit greatly enhanced room-temperature metal-to-ligand charge transfer (MLCT) emission lifetimes as a result of intervening intraligand triplet states (3IL) present on the pendant naphthalimide chromophore(s). In both Ru(II) complexes, the intense singlet fluorescence of the pendant PNI chromophore(s) is nearly quantitatively quenched and was found to sensitize the MLCT-based photoluminescence. Excitation into either the 1IL or 1MLCT absorption bands results in the formation of both 3MLCT and 3IL excited states, conveniently monitored by transient absorption and fluorescence spectroscopy. The relative energy ordering of these triplet states...

Rational Design of Three-Dimensional (3D) Optically Active Molecule-Based Magnets: Synthesis, Structure, Optical and Magnetic Properties of {[Ru(bpy)3]2+, ClO4-, [MnIICrIII(ox)3]-}n and {[Ru(bpy)2ppy]+, [MIICrIII(ox)3]-}n, with MII = MnII, NiII. X-ray Structure of {[ΔRu(bpy)3]2+, ClO4-, [ΔMnIIΔCrIII(ox)3]-}n and {[ΛRu(bpy)2ppy]+, [ΛMnIIΛCrIII(ox)3]-}n

Abstract: To elucidate the relation between structural and magnetic properties, we have synthesized molecular materials having both Cotton effects and a ferromagnetic long range order. Such optically active 3D molecule-based magnets were rationally designed using the enantioselective template effect of optically active cations, namely Δ or Λ [Ru(bpy)3, ClO4]+ or Δ or Λ [Ru(bpy)3ppy]+ (bpy = bipyridine; ppy = phenylpyridine). Such cations are able to template the formation of optically active 3D anionic networks in which transition metal ions (Cr−Mn) and (Cr−Ni) are connected by oxalate ligands (ox). Following this strategy, we described the synthesis of {[Ru(bpy)3]2+, ClO4-, [MnIICrIII(ox)3]-}n and {[Ru(bpy)2ppy]+, [MIICrIII(ox)3]-}n with MII = MnII, NiII in their optically active forms. In these 3D networks, all of the metallic centers have the same configuration, Δ or Λ, as the template cation. We have determined the structure of {[ΔRu(bpy)3][ClO4][ΔMnΔCr(ox)3]}n and {[ΛRu(bpy)2ppy]+, [ΛMnIIΛCrIII(ox)3]-}n by X-r...

Mixed-valence tetranuclear manganese single-molecule magnets.

Abstract: The preparations, X-ray structures, and detailed physical characterizations are presented for two new mixed-valence tetranuclear manganese complexes that function as single-molecule magnets (SMM’s): [Mn4(hmp)6Br2(H2O)2]Br2·4H2O (2) and [Mn4(6-me-hmp)6Cl4]·4H2O (3), where hmp- is the anion of 2-hydroxymethylpyridine and 6-me-hmp- is the anion of 6-methyl-2-hydroxymethylpyridine Complex 2·4H2O crystallizes in the space group P21/c, with cell dimensions at −160 °C of a = 10907(0) A, b = 15788(0) A, c = 13941(0) A, β = 10121(0)°, and Z = 2 The cation lies on an inversion center and consists of a planar Mn4 rhombus that is mixed-valence, Mn2IIIMn2II The hmp- ligands function as bidentate ligands and as the only bridging ligands in 2·4H2O Complex 3·4H2O crystallizes in the monoclinic space group C2/c, with cell dimensions at −160 °C of a = 170852(4) A, b = 208781(5) A, c = 14835(3) A, β = 905485(8)°, and Z = 4 This neutral complex also has a mixed-valence Mn2IIIMn2II composition and is best descri