Showing papers in "Inorganic Chemistry in 2003"

Photoluminescent metal-organic polymer constructed from trimetallic clusters and mixed carboxylates.

Abstract: The solvothermal reaction of zinc acetate dihydrate with a mixture of benzene-1,4-dicarboxylic acid (H(2)BDC) and benzene-1,3,5-tricarboxylic acid (H(3)BTC) in a solution containing N,N'-dimethylformamide (DMF), absolute ethanol, and chlorobenzene gave rise to a metal-organic polymer, Zn(3).BDC.2BTC.2NH(CH(3))(2).2NH(2)(CH(3))(2). The structure of this polymer possesses a unique three-dimensional framework with tri-zinc clusters, and BDC and BTC units colinking the clusters. Moreover, this metal-organic polymer exhibits strong photoluminescence at room temperature, and the main emission band is at about 430 nm (lambda(ex) = 325 nm). Crystal data for this compound (C(17)H(20)N(2)O(8)Zn(1.5)): monoclinic, space group P2(1)/n, cell dimensions a = 11.6171(3) A, b = 14.2456(4) A, c = 12.6426(3) A, beta = 107.030(2) degrees, V = 2000.51(9) A(3), and Z = 4.

Synthesis and Characterization of Volatile, Thermally Stable, Reactive Transition Metal Amidinates

Abstract: A series of homoleptic metal amidinates of the general type [M(R-R'AMD)(n)](x) (R = (i)Pr, (t)Bu, R' = Me, (t)Bu) has been prepared and structurally characterized for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. In oxidation state 3, monomeric structures were found for the metals Ti(III), V(III), and La(III). Bridging structures were observed for the metals in oxidation state 1. Cu(I) and Ag(I) are held in bridged dimers, and Ag(I) also formed a trimer that cocrystallized with the dimer. Metals in oxidation state 2 occurred in either monomeric or dimeric form. Metals with smaller ionic radii (Co, Ni) were monomeric. Larger metals (Fe, Mn) gave monomeric structures only with the bulkier tert-butyl-substituted amidinates, while the less bulky isopropyl-substituted amidinates formed dimers. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. They have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, depositing metal oxides.

An Alternative Route to Highly Luminescent Platinum(II) Complexes: Cyclometalation with N∧C∧N-Coordinating Dipyridylbenzene Ligands

Abstract: The remarkable luminescence properties of the platinum(II) complex of 1,3-di(2-pyridyl)benzene, acting as a terdentate N∧C∧N-coordinating ligand cyclometalated at C2 of the benzene ring ([PtL1Cl]), have been investigated, together with those of two new 5-substituted analogues [PtL2Cl] and [PtL3Cl] {HL2 = methyl-3,5-di(2-pyridyl)benzoate; HL3 = 3,5-di(2-pyridyl)toluene}. All three complexes are intense emitters in degassed solution at 298 K (λmax 480−580 nm; φlum = 0.60, 0.58, and 0.68 in CH2Cl2), displaying highly structured emission spectra in dilute solution, with lifetimes in the microsecond range (7.2, 8.0, and 7.8 μs). On the basis of the very small Stokes shift, the highly structured profiles, and the relatively long lifetimes, the emission is attributed to an excited state of primarily 3π−π* character. At concentrations >1 × 10-5 M, structureless excimer emission centered at ca. 700 nm is observed. The X-ray crystal structure of [PtL2Cl] is also reported.

Incorporation of aluminum in the calcium silicate hydrate (C-S-H) of hydrated portland cements: a high-field 27Al and 29Si MAS NMR investigation.

Abstract: The calcium silicate hydrate (C-S-H) phase resulting from hydration of a white Portland cement (wPc) in water and in a 0.3 M NaAlO(2) solution has been investigated at 14 and 11 hydration times, respectively, ranging from 6 h to 1 year by (27)Al and (29)Si MAS NMR spectroscopy. (27)Al MAS NMR spectra recorded at 7.05, 9.39, 14.09, and 21.15 T have allowed a determination of the (27)Al isotropic chemical shift (delta(iso)) and quadrupolar product parameter (P(Q) = C(Q)) for tetrahedrally coordinated Al incorporated in the C-S-H phase and for a pentacoordinated Al site. The latter site may originate from Al(3+) substituting for Ca(2+) ions situated in the interlayers of the C-S-H structure. The spectral region for octahedrally coordinated Al displays resonances from ettringite, monosulfate, and a third aluminate hydrate phase (delta(iso) = 5.0 ppm and P(Q) = 1.20 MHz). The latter phase is tentatively ascribed to a less-crystalline aluminate gel or calcium aluminate hydrate. The tetrahedral Al incorporated in the C-S-H phase has been quantitatively determined from (27)Al MAS spectra at 14.09 T and indirectly observed quantitatively in (29)Si MAS NMR spectra by the Q(2)(1Al) resonance at -81.0 ppm. A linear correlation is observed between the (29)Si MAS NMR intensity for the Q(2)(1Al) resonance and the quantity of Al incorporated in the C-S-H phase from (27)Al MAS NMR for the different samples of hydrated wPc. This correlation supports the assignment of the resonance at delta(iso)((29)Si) = -81.0 ppm to a Q(2)(1Al) site in the C-S-H phase and the assignment of the (27)Al resonance at delta(iso)((27)Al) = 74.6 ppm, characterized by P(Q)((27)Al) = 4.5 MHz, to tetrahedrally coordinated Al in the C-S-H. Finally, it is shown that hydration of wPc in a NaAlO(2) solution results in a C-S-H phase with a longer mean chain length of SiO(4) tetrahedra and an increased quantity of Al incorporated in the chain structure as compared to the C-S-H phase resulting from hydration of wPc in water.

Selected-control synthesis of ZnO nanowires and nanorods via a PEG-assisted route.

Abstract: Long-chain polymer-assisted growth of one-dimensional (1D) nanostructures has been investigated in previous research. This kind mild method has lots of merits such as not requiring complex procedures, without template supporting etc. Can the short-chain polymer also be used to grow long nanowires? In the present work, a short-chain polymer (PEG400) was found to promote the formation of 1D ZnO nanostructures, which cannot be obtained by long-chain polymers (such as PEG10000). Moreover, nanowires and nanorods can be selectively synthesized by using short-chain polymers. The influence factors for the formation of 1D ZnO nanostructures were also investigated in detail. The XRD, Raman spectrum, XPS, SEM, TEM, ED, HRTEM, EDXA, and PL spectra have been provided for the characterization of the as-obtained nanowires and nanorods.

Nanoscale Pt(0) particles prepared in imidazolium room temperature ionic liquids: synthesis from an organometallic precursor, characterization, and catalytic properties in hydrogenation reactions.

Abstract: The reaction of Pt2(dba)3 (dba = bis-dibenzylidene acetone) dispersed in room temperature 1-n-butyl-3-methylimidazolium (BMI) hexafluorophosphate ionic liquid with molecular hydrogen (4 atm) at 75 °C leads to stable and isolable nanometric Pt(0) particles. The X-ray diffraction analysis (XRD) of the material indicated that it is constituted of Pt(0). Transmission electron microscopy (TEM) analysis of the particles dispersed in the ionic liquid shows the formation of [Pt(0)]n nanoparticles of 2.0−2.5 nm in diameter. A detailed examination of the nanoparticles imbibed in the ionic liquid and their environment shows an interaction of the BMI·PF6 ionic liquid with the Pt(0) nanoparticles. The isolated [Pt(0)]n nanoparticles can be redispersed in the ionic liquid or in acetone or used in solventless conditions for liquid−liquid biphasic, homogeneous, or heterogeneous hydrogenation of alkenes and arenes under mild reaction conditions (75 °C and 4 atm). The recovered platinum nanoparticles can be reused as a sol...

High-dimensional architectures from the self-assembly of lanthanide ions with benzenedicarboxylates and 1,10-phenanthroline.

Abstract: Six new coordination polymers, [Eu(1,2-BDC)(1,2-HBDC)(phen)(H2O)]n (1), [Eu2(1,3-BDC)3(phen)2(H2O)2]n·4nH2O (2), [Eu(1,4-BDC)3/2(phen)(H2O)]n (3), [Yb2(1,2-BDC)3(phen)(H2O)2]n·3.5nH2O (4), [Yb2(1,3-BDC)3(phen)1/2]n (5), and [Yb2(1,4-BDC)3(phen)2(H2O)]n (6), were synthesized by hydrothermal reactions of lanthanide chlorides with three isomers of benzenedicarboxylic acid (H2BDC) and 1,10-phenanthroline (phen), and characterized by single-crystal X-ray diffraction. 1 has a 2-D herringbone architecture with a Z-shaped cavity. 2 and 5 have different 3-D networks, but both are formed by 1,3-BDC anions bridging metal centers (Eu or Yb) via carboxylate groups. 3 and 6 possess similar layer structures which are further constructed to form 3-D networks by hydrogen bonds and/or π−π aromatic interactions. 4 comprises 1-D chains that are further interlinked via hydrogen bonds, resulting in a 3-D network. In the three europium complexes, all the europium ions are eight-coordinated, while the coordination numbers of the...

Determination of ligand-field parameters and f-electronic structures of double-decker bis(phthalocyaninato)lanthanide complexes.

Abstract: The f-electronic structures of the ground states of anionic bis(phthalocyaninato)lanthanides, [Pc2Ln]- (Pc = dianion of phthalocyanine, Ln = Tb3+, Dy3+, Ho3+, Er3+, Tm3+, or Yb3+), are determined. Magnetic susceptibilities of the powder samples of [Pc2Ln]TBA (TBA = tetra-n-butylammonium cation) in the range 1.8−300 K showed characteristic temperature dependences which resulted from splittings of the ground-state multiplets. NMR signals for the two kinds of protons on the Pc rings at room temperature were shifted to lower frequency with respect to the diamagnetic Y complex in Ln = Tb, Dy, and Ho cases, and to higher frequency in Er, Tm, and Yb cases. The ratios of the paramagnetic shifts of the two positions were near constant in the six cases. This indicates that the shifts are predominantly caused by the magnetic dipolar term, which is determined by the anisotropy of the magnetic susceptibility of the lanthanide ion. Using a multidimensional nonlinear minimization algorithm, we determined a set of ligand...

Structure-dependent photophysical properties of singlet and triplet metal-to-ligand charge transfer states in copper(I) bis(diimine) compounds.

Abstract: The photophysical properties of singlet and triplet metal-to-ligand charge transfer (MLCT) states of [Cu(I)(diimine)2]+, where diimine is 2,9-dimethyl-1,10-phenanthroline (dmphen), 2,9-dibutyl-1,10-phenanthroline (dbphen), or 6,6‘-dimethyl-2,2‘-bipyridine (dmbpy), were studied. On 400 nm laser excitation of [Cu(dmphen)2]+ in CH2Cl2 solution, prompt 1MLCT fluorescence with a quantum yield of (2.8 ± 0.8) ×10-5 was observed using a picosecond time-correlated single photon counting technique. The quantum yield was dependent on the excitation wavelength, suggesting that relaxation of the Franck−Condon state to the lowest 1MLCT competes with rapid intersystem crossing (ISC). The fluorescence lifetime of the copper(I) compound was 13−16 ps, unexpectedly long despite a large spin−orbit coupling constant of 3d electrons in copper (829 cm-1 ). Quantum chemical calculations using a density functional theory revealed that the structure of the lowest 1MLCT in [Cu(dmphen)2]+ (11B1) was flattened due to the Jahn−Teller ...

The remarkable reactivity of high oxidation state ruthenium and osmium polypyridyl complexes.

Abstract: There is a remarkable redox chemistry of higher oxidation state M(IV)-M(VI) polypyridyl complexes of Ru and Os. They are accessible by proton loss and formation of oxo or nitrido ligands, examples being cis-[RuIV(bpy)2(py)(O)]2+ (RuIV=O2+, bpy=2,2'-bipyridine, and py=pyridine) and trans-[OsVI(tpy)(Cl)2(N)]+ (tpy=2,2':6',2' '-terpyridine). Metal-oxo or metal-nitrido multiple bonding stabilizes the higher oxidation states and greatly influences reactivity. O-atom transfer, hydride transfer, epoxidation, C-H insertion, and proton-coupled electron-transfer mechanisms have been identified in the oxidation of organics by RuIV=O2+. The Ru-O multiple bond inhibits electron transfer and promotes complex mechanisms. Both O atoms can be used for O-atom transfer by trans-[RuVI(tpy)(O)2(S)]2+ (S=CH3CN or H2O). Four-electron, four-proton oxidation of cis,cis-[(bpy)2(H2O)RuIII-O-RuIII(H2O)(bpy)2]4+ occurs to give cis,cis-[(bpy)2(O)RuV-O-RuV(O)(bpy)2]4+ which rapidly evolves O2. Oxidation of NH3 in trans-[OsII(tpy)(Cl)2(NH3)] gives trans-[OsVI(tpy)(Cl)2(N)]+ through a series of one-electron intermediates. It and related nitrido complexes undergo formal N- transfer analogous to O-atom transfer by RuIV=O2+. With secondary amines, the products are the hydrazido complexes, cis- and trans-[OsV(L3)(Cl)2(NNR2)]+ (L3=tpy or tpm and NR2-=morpholide, piperidide, or diethylamide). Reactions with aryl thiols and secondary phosphines give the analogous adducts cis- and trans-[OsIV(tpy)(Cl)2(NS(H)(C6H4Me))]+ and fac-[OsIV(Tp)(Cl)2(NP(H)(Et2))]. In dry CH3CN, all have an extensive multiple oxidation state chemistry based on couples from Os(VI/V) to Os(III/II). In acidic solution, the OsIV adducts are protonated, e.g., trans-[OsIV(tpy)(Cl)2(N(H)N(CH2)4O)]+, and undergo proton-coupled electron transfer to quinone to give OsV, e.g., trans-[OsV(tpy)(Cl)2(NN(CH2)4O)]+ and hydroquinone. These reactions occur with giant H/D kinetic isotope effects of up to 421 based on O-H, N-H, S-H, or P-H bonds. Reaction with azide ion has provided the first example of the terminal N4(2-) ligand in mer-[OsIV(bpy)(Cl)3(NalphaNbetaNgammaNdelta)]-. With CN-, the adduct mer-[OsIV(bpy)(Cl)3(NCN)]- has an extensive, reversible redox chemistry and undergoes NCN(2-) transfer to PPh3 and olefins. Coordination to Os also promotes ligand-based reactivity. The sulfoximido complex trans-[OsIV(tpy)(Cl)2(NS(O)-p-C6H4Me)] undergoes loss of O2 with added acid and O-atom transfer to trans-stilbene and PPh3. There is a reversible two-electron/two-proton, ligand-based acetonitrilo/imino couple in cis-[OsIV(tpy)(NCCH3)(Cl)(p-NSC6H4Me)]+. It undergoes reversible reactions with aldehydes and ketones to give the corresponding alcohols.

New luminescent cyclometalated iridium(III) diimine complexes as biological labeling reagents.

Abstract: We report the synthesis, characterization, and photophysical and electrochemical properties of thirty luminescent cyclometalated iridium(III) diimine complexes [Ir(N-C)(2)(N-N)](PF(6)) (HN-C = 2-phenylpyridine, Hppy; 2-(4-methylphenyl)pyridine, Hmppy; 3-methyl-1-phenylpyrazole, Hmppz; 7,8-benzoquinoline, Hbzq; 2-phenylquinoline, Hpq; N-N = 4-amino-2,2'-bipyridine, bpy-NH(2); 4-isothiocyanato-2,2'-bipyridine, bpy-ITC; 4-iodoacetamido-2,2'-bipyridine, bpy-IAA; 5-amino-1,10-phenanthroline, phen-NH(2); 5-isothiocyanato-1,10-phenanthroline, phen-ITC; 5-iodoacetamido-1,10-phenanthroline, phen-IAA). The X-ray crystal structure of [Ir(mppz)(2)(bpy-NH(2))](PF(6)) has also been investigated. Upon irradiation, all the complexes display intense and long-lived luminescence under ambient conditions and in 77-K glass. On the basis of the photophysical and electrochemical data, the emission of most of these complexes is assigned to an excited state of predominantly triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi(Ir) --> pi(N-N)) character. In some cases, triplet intraligand ((3)IL) (pi --> pi)(N-N or N-C(-)) excited states have also been identified. In view of the specific reactivity of the isothiocyanate and iodoacetamide moieties toward the primary amine and sulfhydryl groups, respectively, we have labeled various biological molecules with a selection of these luminescent iridium(III) complexes. The photophysical properties of the luminescent conjugates have been investigated. In addition, a heterogeneous assay for digoxin has also been designed on the basis of the recognition of biotinylated anti-digoxin by avidin labeled with one of the luminescent iridium(III) complexes.

Realizing Green Phosphorescent Light-Emitting Materials from Rhenium(I) Pyrazolato Diimine Complexes

Abstract: Two neutral pyrazolato diimine rhenium(I) carbonyl complexes with formula [Re(CO)3(N-N)(btpz)] where N-N = 2,2‘-bipyridine (1) and 1,10-phenanathroline (2), and btpz = 3,5-bis(trifluoromethyl) pyrazolate, were synthesized and characterized by elemental analysis, routine spectroscopic methods, and single-crystal X-ray diffraction study. Ground and excited state properties of these complexes were investigated by steady-state and time-resolved spectroscopies. Complexes 1 and 2 show photoluminescent emission in both solution and solid-state at room temperature, arising from metal to ligand charge-transfer (MLCT) transition with strong overlapping of intraligand π → π* transitions. The long-lived excited state lifetimes of complexes 1 and 2, which are on the order of microseconds, indicate the presence of phosphorescent emission. As these complexes hold the potential to serve as phosphors for organic light-emitting diodes (OLEDs), their electroluminescent performances were evaluated by employing them as dopant...

Coexistence of water dimer and hexamer clusters in 3D metal-organic framework structures of Ce(III) and Pr(III) with pyridine-2,6-dicarboxylic acid.

Abstract: Ce(NO3)3·6H2O or Pr(NO3)3·6H2O and pyridine-2,6-dicarboxylic acid form a linear coordination polymeric structure under hydrothermal conditions. Hexameric water clusters join these linear chains through bonding to the metal ions. Other coordinated water and the carboxylate oxygen form an intricate array of hydrogen bonding resulting in a 3D network where each metal ion shows 9-coordination with an approximate D3 symmetry. Dimeric water clusters are also located in the void spaces. In the structure containing Pr(III), the water dimers are hydrogen-bonded to the hexamers, whereas in the Ce(III) structure, the dimers and the hexamers are far apart.

A Porous Supramolecular Architecture from a Copper(II) Coordination Polymer with a 3D Four-Connected 86 Net

Abstract: A novel coordination polymer {[Cu(L1)(L2)(H2O)]·5H2O}n (1), where L1 =1,1‘-(1,4-butanediyl)bis(imidazole) and L2 = m-phthalate anion, has been obtained by using an unusual crystallization process. ...

End-on and side-on peroxo derivatives of non-heme iron complexes with pentadentate ligands: models for putative intermediates in biological iron/dioxygen chemistry.

Abstract: Mononuclear iron(III) species with end-on and side-on peroxide have been proposed or identified in the catalytic cycles of the antitumor drug bleomycin and a variety of enzymes, such as cytochrome P450 and Rieske dioxygenases. Only recently have biomimetic analogues of such reactive species been generated and characterized at low temperatures. We report the synthesis and characterization of a series of iron(II) complexes with pentadentate N5 ligands that react with H2O2 to generate transient low-spin FeIII−OOH intermediates. These intermediates have low-spin iron(III) centers exhibiting hydroperoxo-to-iron(III) charge-transfer bands in the 500−600-nm region. Their resonance Raman frequencies, νO-O, near 800 cm-1 are significantly lower than those observed for high-spin counterparts. The hydroperoxo-to-iron(III) charge-transfer transition blue-shifts and the νO-O of the Fe−OOH unit decreases as the N5 ligand becomes more electron donating. Thus, increasing electron density at the low-spin Fe(III) center we...

[Ni(Et2PCH2NMeCH2PEt2)2]2+ as a Functional Model for Hydrogenases

Abstract: The reaction of Et2PCH2N(Me)CH2PEt2 (PNP) with [Ni(CH3CN)6](BF4)2 results in the formation of [Ni(PNP)2](BF4)2, which possesses both hydride- and proton-acceptor sites. This complex is an electrocatalyst for the oxidation of hydrogen to protons, and stoichiometric reaction with hydrogen forms [HNi(PNP)(PNHP)](BF4)2, in which a hydride ligand is bound to Ni and a proton is bound to a pendant N atom of one PNP ligand. The free energy associated with this reaction has been calculated to be −5 kcal/mol using a thermodynamic cycle. The hydride ligand and the NH proton undergo rapid intramolecular exchange with each other and intermolecular exchange with protons in solution. [HNi(PNP)(PNHP)](BF4)2 undergoes reversible deprotonation to form [HNi(PNP)2](BF4) in acetonitrile solutions (pKa = 10.6). A convenient synthetic route to the PF6- salt of this hydride involves the reaction of PNP with Ni(COD)2 to form Ni(PNP)2, followed by protonation with NH4PF6. A pKa of value of 22.2 was measured for this hydride. This ...

Reversible guest exchange and ferrimagnetism (T(C) = 60.5 K) in a porous cobalt(II)-hydroxide layer structure pillared with trans-1,4-cyclohexanedicarboxylate.

Abstract: The synthesis, characterization, and reversible guest-exchange chemistry of a new porous magnetic material that orders ferrimagnetically at 60.5 K are described. The material, Co5(OH)8(chdc)·4H2O (chdc = trans-1,4-cyclohexanedicarboxylate), contains tetrahedral−octahedral−tetrahedral Co(II)−hydroxide layers of composition Co(oct)3Co(tet)2(OH)8 that are linked together by bis(unidentate) chdc pillars. Noncoordinated water molecules occupy 1-D channels situated between the chdc pillars. The material remains monocrystalline during dehydration from Co5(OH)8(chdc)·4H2O (CDCC·4H2O) to Co5(OH)8(chdc) (CDCC) via an intermediate Co5(OH)8(chdc)·2H2O (CDCC·2H2O) upon heating or evacuation. In-situ single crystal and powder X-ray diffraction analyses indicate that the interlayer spacing decreases in two steps, each corresponding to the loss of two water molecules per formula unit as determined by thermogravimetry. The single crystal structure of the fully dehydrated material, CDCC, has no void volume due to a tilting...

Controlled Reactions on a Copper Surface: Synthesis and Characterization of Nanostructured Copper Compound Films

Abstract: We report the synthesis of nanostructured copper compound films on a copper surface under mild conditions. A series of low-dimensional structures including Cu(OH)2 fibers and scrolls, CuO sheets and whiskers, and Cu2(OH)2CO3 rods have been successfully grown on the copper surfaces at ambient temperature and pressure. Most of the structures are phase-pure single crystallites. The films were formed by the direct oxidation of copper in aqueous solutions of NaOH with an oxidant (NH4)2S2O8. The evolution of the ultrafine structures as a function of the reaction conditions has been revealed, from fibers of Cu(OH)2 to scrolls of Cu(OH)2 to sheets or whiskers of CuO. By replacing NaOH with NaHCO3 in the synthesis, square/rectangular rod arrays of Cu2(OH)2CO3 were obtained. The controlled reactions allow the large-scale, template-free, cost-effective synthesis of copper compound films with ordered, uniform, stable, ultrafine structures.

Separating innocence and non-innocence of ligands and metals in complexes [(L)Ru(acac)2](n) (n = -1, 0, +1; L = o-iminoquinone or o-iminothioquinone).

Abstract: The diamagnetic title complexes were obtained from Ru(acac)2(CH3CN)2 and 2-aminophenol or 2-aminothiophenol. X-ray structure analysis of (L1)Ru(acac)2 (L1 = o-iminoquinone) revealed C−C intra-ring, C−O, and C−N distances which suggest a RuIII-iminosemiquinone oxidation state distribution with antiparallel spin−spin coupling. One-electron oxidation and reduction of both title compounds to paramagnetic monocations [(L)Ru(acac)2]+ or monoanions [(L)Ru(acac)2]- occurs reversibly at widely separated potentials (ΔE > 1.3 V) and leads to low-energy shifted charge transfer bands. In comparison with clearly established RuII-semiquinone or RuIII-catecholate systems the g tensor components 2.23 > g1 > 2.09, 2.16 > g2 > 2.07, and 1.97 > g3 > 1.88 point to considerable metal contributions to the singly occupied MO, corresponding to RuIII complexes with either o-quinonoid (→ cations) or catecholate-type ligands (→ anions) and only minor inclusion of RuIV- or RuII-iminosemiquinone formulations, respectively. The prefere...

Excited-state energy-transfer dynamics in self-assembled triads composed of two porphyrins and an intervening Bis(dipyrrinato)metal complex.

Abstract: The synthesis and characterization of various triads composed of a linear array of two zinc porphyrins joined via an intervening bis(dipyrrinato)metal(II) complex are reported. The preparation exploits the facile complexation of dipyrrins with divalent metal ions to give bis(dipyrrinato)metal(II) complexes [abbreviated (dp)(2)M]. Copper(II) and palladium(II) chelates of dipyrrins (available by oxidation of dipyrromethanes) were prepared in 50-80% yield. A one-flask synthesis of bis(dipyrrinato)zinc(II) complexes was developed by oxidation of a dipyrromethane with DDQ or p-chloranil in the presence of Zn(OAc)(2).2H(2)O in THF ( approximately 80% yield). Three routes were developed for preparing porphyrin-dipyrrins: (1). Suzuki coupling of a boronate-substituted zinc porphyrin (ZnP) and bis[5-(4-iodophenyl)dipyrrinato]Pd(II) to give the (ZnP-dp)(2)Pd triad (50% yield), followed by selective demetalation of the (dp)(2)Pd unit by treatment with 1,4-dithiothreitol under neutral conditions (71% yield); (2). oxidation of a porphyrin-dipyrromethane with p-chloranil in the presence of Zn(OAc)(2).2H(2)O followed by chromatography on silica gel (71% yield); and (3). condensation of a dipyrrin-dipyrromethane and a dipyrromethane-dicarbinol under InCl(3) catalysis followed by oxidation with DDQ (10-16% yield). Four triads of form (ZnP-dp)(2)Zn were prepared in 83-97% yield by treatment of a porphyrin-dipyrrin with Zn(OAc)(2).2H(2)O at room temperature. Free base dipyrrins typically absorb at 430-440 nm, while the bis(dipyrrinato)metal complexes absorb at 460-490 nm. The fluorescence spectra/yields and excited-state lifetimes of the (ZnP-dp)(2)Zn triad in toluene show (1). efficient energy transfer from the bis(dipyrrinato)zinc(II) chromophore to the zinc porphyrins (98.5% yield), and (2). little or no quenching of the resulting excited zinc porphyrin relative to the isolated chromophore. Taken together, these results indicate that bis(dipyrrinato)zinc(II) complexes can serve as self-assembling linkers that further function as secondary light-collection elements in porphyrin-based light-harvesting arrays.

Crystal structures and magnetic properties of two octacyanotungstate(IV) and (V)-cobalt(II) three-dimensional bimetallic frameworks.

Abstract: The synthesis, X-ray structures, and magnetic behavior of two new, three-dimensional compounds [WIV{(μ-CN)4CoII(H2O)2}2·4H2O]n (1) and [{WV(CN)2}2{(μ-CN)4CoII(H2O)2}3·4H2O]n (2) are presented. Compound 1 crystallizes in the tetragonal system, space group I4/m with cell constants a = b = 11.710(3) A, c = 13.003(2) A, and Z = 4, whereas 2 crystallizes in the orthorhombic system, space group Cmca with cell constants a = 13.543(5) A, b = 16.054(6) A, c = 15.6301(9) A, and Z = 4. The structure of 1 shows alternating eight-coordinated W(IV) and six-coordinated Co(II) ions bridged by single cyanides in a three-dimensional network. The geometry of each [WIV(CN)8]4- entity in 1 is close to a square antiprism. Its eight cyanide groups are coordinated to Co(II) ions which have two coordinated water molecules in trans position. The structure of 2 consists of alternating eight-coordinated W(V) and six-coordinated Co(II) ions linked by single cyanide bridges in a three-dimensional network. Each [WV(CN)8]3- unit shows a...

[Mn2(saltmen)2Ni(pao)2(L)2](A)2 with L=pyridine, 4-picoline, 4-tert-butylpyridine, N-methylimidazole and A=ClO4-, BF4-, PF6-, ReO4-: a family of single-chain magnets.

Abstract: A series of single-chain magnets, [Mn2(saltmen)2Ni(pao)2(L)2](A)2 (saltmen(2-)=N,N'-(1,1,2,2-tetramethylethylene) bis(salicylideneiminate), pao-=pyridine-2-aldoximate; A-=ClO4- with L=4-picoline; 2, 4-tert-butylpyridine; 3, N-methylimidazole; 4, and L=pyridine with A-=BF4-; 5, PF6-; 6, ReO4-; 7), was prepared by reactions between MnIII dimer units, i.e., [Mn2(saltmen)2(H2O)2](A)2 (A-=ClO4-, BF4-, PF6-) or Mn2(saltmen)2(ReO4)2, and NiII monomeric units, i.e., Ni(pao)2(L)2, in methanol/water media. The crystal structures of 4, 6, and 7 were established by single-crystal X-ray crystallography. These three compounds are isostructural with [Mn2(saltmen)2Ni(pao)2(py)2](ClO4)2 (1) (Clerac, R.; Miyasaka, H.; Yamashita, M.; Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837) and crystallize in monoclinic space group C2/c. The linear arrangement of MnIII dimer units and NiII building blocks leads to an alternating chain having a repeating unit, [-(O)2-Mn-ON-Ni-NO-Mn-]. The chains are well separated with the nearest interchain intermetallic distance of 10.36 A for 4, 10.51 A for 6, and 10.30 A for 7, and there is no significant pi-pi interchain interaction between ligands. The void space between the chains is occupied by counteranions, which control the three-dimensional organization of the chains. The X-ray diffraction analysis (XRD) on a powder sample was also performed for all compounds. The XRD patterns for 1, 2, and 4-7 are very similar, emphasizing the isostructural nature of these materials although they have individually slight different interchain distances. Inversely, the XRD pattern for 3 reveals a completely different shape being indicative of the peculiar crystal packing compared to the others. Nevertheless, the one-dimensional nature of the structure is also kept in 3 as indicated by magnetic measurements. The whole family of compounds exhibits quasi-identical magnetic behavior compared to that described for 1. Above 30 K, the heterometallic chain can be described as an assembly of antiferromagnetically coupled Mn...Ni....Mn trimers (via oximate bridge, -24.2 K

Novel pb and zn coordination polymers: synthesis, molecular structures, and third-order nonlinear optical properties.

Abstract: Three novel coordination polymers [Pb(bbbm)2(NO3)2]n (bbbm = 1,1‘-(1,4-butanediyl)bis-1H-benzimidazole) 1, [Zn(bbbt)(NCS)2]n (bbbt = 1,1‘-(1,4-butanediyl)bis-1H-benzotriazole) 2, and [Zn(pbbt)(NCS)2]n (pbbt = 1,1‘-(1,3-propylene)bis-1H-benzotriazole) 3 were synthesized and structurally characterized. Polymer 1 exhibits a two-dimensional rhombohedral grid network structure, the dimensions of the grid are 14.274 × 14.274 A, and the diagonal-to-diagonal distances are 24.809 × 14.125 A. Polymer 2 possesses a concavo-convex chain structure different from those of the known one-dimensional polymers, which are linear chain, zigzag chain, helical chain, double-stranded chain, and ladder chain. Polymer 3 exhibits a one-dimensional zigzag chain structure, and these chains were packed as an ...ABAB... layered structure. The third-order nonlinear optical (NLO) properties of polymers 1, 2, and 3 were determined with a 7-ns pulsed laser at 532 nm. 1 shows strong third-order NLO absorptive and refractive properties, and...

Titanium alkoxides as initiators for the controlled polymerization of lactide.

Abstract: Fourteen titanium alkoxides were synthesized for comparison of their catalytic properties in the bulk and solution polymerization of lactide (LA). In bulk polymerizations, they are effective catalysts in terms of polymer yield and molecular weight. Titanatranes gave polylactides with significantly increased molecular weight over more extended polymerization times, and those with five-membered rings afforded polymers in higher yields and with larger molecular weights than their six-membered ring counterparts. Steric hindrance of the rings was found to significantly affect polymer yields. Increased heterotactic-biased poly(rac-LA) was formed as the number of chlorine atoms increased in TiCl(x)(O-i-Pr)(4)(-)(x). In solution polymerizations, titanium alkoxides catalyzed controlled polymerizations of LA, and end group analysis demonstrated that an alkoxide substituent on the titanium atom acted as the initiator. That polymerization is controlled under our conditions was shown by the linearity of molecular weight versus conversion. A tendency toward formation of heterotactic-biased poly(rac-LA) was observed in the solution polymerizations. The rate of ring-opening polymerization (ROP) and the molecular weight of the polymers are greatly influenced by the substituents on the catalyst, as well as by factors such as the polymerization temperature, polymerization time, and concentration of monomer and catalyst.

Room temperature phosphorescence from a platinum(II) diimine bis(pyrenylacetylide) complex.

Abstract: Room temperature phosphorescence has been observed in a synthetically facile Pt(II) complex, Pt(dbbpy)(C⋮C-pyrene)2 (dbbpy = 4,4‘-di(tert-butyl)-2,2‘-bipyridine; C⋮C-pyrene = 1-ethynylpyrene), in fluid solution. The static and time-resolved absorption and luminescence data are consistent with phosphorescence emerging from the appended C⋮C-pyrenyl units following excitation into the low energy dπ Pt → π* dbbpy metal-to-ligand charge transfer absorption bands.

Uranyl Coordination Environment in Hydrophobic Ionic Liquids: An in Situ Investigation

Abstract: Different inner-sphere coordination environments are observed for the uranyl nitrate complexes formed with octyl-phenyl-N,N-diisobutylcarbamoylmethylphosphine oxide and tributyl phosphate in dodecane and in the hydrophobic ionic liquids (ILs) [C4mim][PF6] and [C8mim][N(SO2CF3)2]. Qualitative differences in the coordination environment of the extracted uranyl species are implied by changes in peak intensity patterns and locations for uranyl UV−visible spectral bands when the solvent is changed. EXAFS data for uranyl complexes in dodecane solutions is consistent with hexagonal bipyramidal coordination and the existence of UO2(NO3)2(CMPO)2. In contrast, the complexes formed when uranyl is transferred from aqueous nitric acid solutions into the ILs exhibit an average equatorial coordination number of approximately 4.5. Liquid/liquid extraction results for uranyl in both ILs indicate a net stoichiometry of UO2(NO3)(CMPO)+. The concentration of the IL cation in the aqueous phase increases in proportion to the a...

Modified Polyoxometalates: Hydrothermal Syntheses and Crystal Structures of Three Novel Reduced and Capped Keggin Derivatives Decorated by Transition Metal Complexes

Abstract: Three novel polyoxometalate derivatives decorated by transition metal complexes have been hydrothermally synthesized. Compound 1 consists of [PMoVI6MoV2VIV8O44{Co (2,2‘-bipy)2(H2O)}4]3+ polyoxocations and [PMoVI4MoV4VIV8O44{Co(2,2‘-bipy)2(H2O)}2]3- polyoxoanions, which are both built on mixed-metal tetracapped [PMo8V8O44] subunits covalently bonded to four or two {Co(2,2‘-bpy)2(H2O)}2+ clusters via terminal oxo groups of the capping V atoms. Compound 2 is built on [PMoVI8VIV6O42{CuI(phen)}2]5- clusters constructed from mixed-metal bicapped [PMoVI8VIV6O42]7- subunits covalently bonded to two {Cu(phen)}+ fragments in the similar way to 1. The structure of 3 is composed of [PMoVI9MoV3O40]6- units capped by two divalent Ni atoms via four bridging oxo groups. The crystal data for these are the following: C120H126Co6Mo16N24O103P2V16 (1), triclinic P1, a = 15.6727(2) A, b = 17.3155(3) A, c = 19.5445(2) A, α = 86.1520(1)°, β = 81.2010(1)°, γ = 63.5970(1)°, Z = 1; C120H85Cu6Mo8N20O44PV6 (2), triclinic P1, a = 1...

Synthesis and characterization of heterodinuclear Ln(3+)-Fe3+ and Ln(3+)-Co3+ complexes, bridged by cyanide ligand (Ln3+ = lanthanide ions). Nature of the magnetic interaction in the Ln(3+)-Fe3+ complexes.

Abstract: The reaction of Ln(NO3)3.aq with K3[Fe(CN)6] or K3[Co(CN)6] in N,N'-dimethylformamide (DMF) led to 25 heterodinuclear [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O and [Ln(DMF)4(H2O)3(mu-CN)Co(CN)5].nH2O complexes (with Ln = all the lanthanide(III) ions, except promethium and lutetium). Five complexes (Pr(3+)-Fe3+), (Tm(3+)-Fe3+), (Ce(3+)-Co3+), (Sm(3+)-Co3+), and (Yb(3+)-Co3+) have been structurally characterized; they crystallize in the equivalent monoclinic space groups P21/c or P21/n. Structural studies of these two families show that they are isomorphous. This relationship in conjunction with the diamagnetism of the Co3+ allows an approximation to the nature of coupling between the iron(III) and the lanthanide(III) ions in the [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O complexes. The Ln(3+)-Fe3+ interaction is antiferromagnetic for Ln = Ce, Nd, Gd, and Dy and ferromagnetic for Ln = Tb, Ho, and Tm. For Ln = Pr, Eu, Er, Sm, and Yb, there is no sign of any significant interaction. The isotropic nature of Gd3+ helps to evaluate the value of the exchange interaction.

Solid-State and solution studies of [Ln(n)(SiW11O39)] polyoxoanions: an example of building block condensation dependent on the nature of the rare earth.

Abstract: The reactivity of the [α-SiW 1 1 O 3 9 ] 8 - monovacant polyoxometalate with lanthanide has been investigated for four different trivalent rare-earth cations (Ln = Nd I I I , Eu I I I , Gd I I I , Yb I I I ). The crystal structures of KCs 4 [Yb(α-SiW 1 1 O 3 9 )-(H 2 O) 2 ].24H 2 O (1), K 0 . 5 Nd 0 . 5 [Nd 2 (α-SiW 1 1 O 3 9 )(H 2 O) 1 1 ].17H 2 O (2a), and Na 0 . 5 Cs 4 . 5 [Eu(α-SiW 1 1 O 3 9 )(H 2 O) 2 ].23H 2 O (3a) are reported. The solid-state structure of compound 1 consists of linear wires built up of [α-SiW 1 1 O 3 9 ] 8 - anions connected by Yb 3 + cations, while the linkage of the building blocks by Eu 3 + centers in 3a leads to the formation of zigzag chains. In 2a, dimeric [Nd 2 (α-SiW 1 1 O 3 9 ) 2 (H 2 O) 8 ] 1 0 - entities are linked by four Nd 3 + cations. The resulting chains are connected by lanthanide ions, leading to a bidimensional arrangement. Thus, the dimensionality, the organization of the polyoxometalate building units, and the Ln/[α-SiW 1 1 O 3 9 ] 8 - ratio in the solid state can be tuned by choosing the appropriate lanthanide. The luminescent properties of compound 3a have been studied, showing that, in solution, the polymer decomposes to give the monomeric complex [Eu(α-SiW 1 1 O 3 9 )(H H O) 4 ] 5 - . The lability of the four exogenous ligands connected to the rare earth must allow the functionalization of this lanthanide polyanion.

Magneto-structural xorrelations in 2D and 3D extended structures of manganese(II)-malonate systems.

Abstract: Two polymeric malonato-bridged manganese(II) complexes of formula [Mn(mal)(H(2)O)(2)](n)() (1) and [Mn(2)(mal)(2)(4,4'-bipy)(H(2)O)(2)](n)() (2) have been synthesized and characterized (mal = malonate dianion; 4,4'-bipy = 4,4'-bipyridine). The crystal structure of complex 1 was already known. Complex 2 crystallizes in monoclinic space group P2(1)/n, Z = 2, with unit cell parameters of a = 7.2974(10) A, b = 18.7715(10) A, c = 7.514(3) A, and beta = 91.743(12) degrees. The structure determination reveals that the complex [Mn(2)(mal)(2)(4,4'-bipy)(H(2)O)(2)](n)() (2) is a 3D network being composed of Mn-malonate sheets which are pillared by bidentate 4,4'-bipy spacer forming small voids. The Mn-Mn distances through Mn-mu-(O3-C8-O4)-Mn, Mn-mu(O1-C6-O2)-Mn, and Mn-mu-4,4'-bipy-Mn bridges are 5.561, 5.410, and 11.723 A, respectively. The magnetic behaviors of complexes 1 and 2 in the temperature range 300-2 K are very close, corresponding to a weak antiferromagnetic coupling. The magnetic pathways of complex 1 are through two Mn-O-C-O-Mn with anti-anti conformation and two Mn-O-C-O-Mn with syn-anti conformations and in complex 2 through all Mn-O-C-O-Mn with syn-anti conformations. Both syn-anti and anti-anti conformations create weak antiferromagnetic coupling, and the susceptibility data are fitted by the expansion series of Lines and the Curely formula for an S = 5/2 antiferromagnetic quadratic layer, based on the exchange Hamiltonian H = -Sigma(nn)()JS(i)()S(j)(). The best fit is given by the superexchange parameters J = -0.32 cm(-)(1) and g = 2.00 for complex 1 and J = -0.14 cm(-)(1), J(inter) = -0.031 cm(-)(1), and g = 2.00 for complex 2. Finally, in both the complexes there is a magnetic pathway Mn-O-C-C-C-O-Mn, and this pathway through the three carbon atoms of the malonato-bridging ligand could be considered negligible.