Electronic spectroscopy, photophysical properties, and emission quenching studies of an oxidatively robust perfluorinated platinum porphyrin

The highly electron-deficient, beta-octafluorinated meso-tetrakis(pentafluorophenyl)-porphyrin (H(2)F(28)TPP) was metalated with platinum to afford the oxidatively robust luminophore [PtF(28)TPP], and its X-ray structure shows that the porphyrin core exists in a slightly saddle-shaped conformation. The absorption spectrum of [PtF(28)TPP] in CH(2)Cl(2) displays a near-UV Soret band (B) at 383 nm (epsilon = 2.85 x 10(5) dm(3) mol(-1) cm(-1)) and two visible Q(1,0) and Q(0,0) bands at 501 (epsilon = 1.45 x 10(4) dm(3) mol(-1) cm(-1)) and 533 (epsilon = 1.36 x 10(4) dm(3) mol(-1) cm(-1)) nm, respectively. These absorption bands of [PtF(28)TPP] are blue-shifted from those in [PtF(20)TPP] (390, 504, and 538 nm, respectively) and [PtTPP] (401, 509, and 539 nm, respectively). Excitation of [PtF(28)TPP] (complex concentration = 1.5 x 10(-6) mol dm(-3)) in dichloromethane at the Soret or Q(1,0) or Q(0,0) band gave a phosphorescence with peak maximum at 650 nm (lifetime = 5.8 micros) and a weak shoulder at 712 nm. Both the emission lifetime and quantum yield vary with solvent polarity, and plots of tau versus E(K) and Phi versus E(K) (where E(K) is the empirical solvent polarity parameter based on the hypsochromic shift of the longest wavelength absorption of the [Mo(CO)(4)[(C(5)H(4)N)HC[double bond]NCH(2)C(6)H(5)]] complex with increasing solvent polarity; see: Kamlet, M. J.; Abboud, J. L. M.; Taft, R. W. Prog. Phys. Org. Chem. 1981, 13, pp 485-630) show linear correlation, indicating that the emission is sensitive to the local environment/medium. Electrochemical studies on [PtF(28)TPP] by cyclic voltammetry showed no porphyrin-centered oxidation at potential < or = 1.5 V versus Ag/AgNO(3), demonstrating that [PtF(28)TPP] is more resistant toward oxidation than [PtF(20)TPP] (E(1/2) = 1.33 V) and [PtTPP] (E(1/2) = 0.97 V). The porphyrin-centered reduction of [PtF(28)TPP] occurs at -0.75 and -1.18 V, which is anodically shifted from those at -1.06 and -1.55 V in [PtF(20)TPP], and -1.51 V in [PtTPP], respectively. The excited-state reduction potential of [PtF(28)TPP] is estimated to be 1.49 V versus Ag/AgNO(3). Over 97% of the emission intensity of [PtF(28)TPP] was retained after irradiation with a high power mercury arc lamp (500 W) for 14 h, compared to 90% and 12% for [PtF(20)TPP] and [PtTPP], respectively; hence, [PtF(28)TPP] exhibits superior photostability. Quenching of the emission of [PtF(28)TPP] by oxygen, alcohol, catechol, and butylamine reveals that [PtF(28)TPP] is an oxidatively robust material with medium-sensitive photoluminescence properties.     

Synthesis, structure, and luminescent and magnetic properties of novel lanthanide metal-organic frameworks with zeolite-like topology

A series of microporous lanthanide metal-organic frameworks [Ln(BTC)(DMF)(2) x H(2)O, Ln = Tb (1), Dy (2), Ho (3), Er (4), Tm (5), Yb (6); DMF = N,N'-dimethylformamide] with 4 x 4 x 4 x 6 x 6 x 8 topology, which is very common in the zeolite topologies, have been synthesized under mild conditions. The single-crystal X-ray diffraction analysis reveals that they exhibit the same three-dimensional (3D) architecture and crystallize in monoclinic symmetry space group C2/c. Organic and inorganic four-connected nodes link each other to form a 3D open framework. The framework contains approximate 13 Angstrom x 7 Angstrom rectangle channels along the [1,1,0] and [1,-1,0] directions, respectively. The luminescent properties of these complexes have been studied, and complex 1 shows a Tb(3+) characteristic emission in the range of 450-650 nm at room temperature. Complexes 1-5 exhibit antiferromagnetic interaction between Ln(3+) ions. The water sorption isotherm shows that about 15 water molecules per unit cell can be adsorbed into the micropores of dehydrated complex 4.     

Highly phosphorescent iridium complexes containing both tridentate bis(benzimidazolyl)-benzene or -pyridine and bidentate phenylpyridine: synthesis, photophysical properties, and theoretical study of Ir-bis(benzimidazolyl)benzene complex

Novel mixed-ligand Ir(III) complexes, [Ir(L)(NwedgeC)X]n+ (L = N/\C/\N or N/\N/\N; X = Cl, Br, I, CN, CH3CN, or -CCPh; n = 0 or 1), were synthesized, where N/\CwedgeN = bis(N-methylbenzimidazolyl)benzene (Mebib) and bis(N-phenylbenzimidazolyl)benzene (Phbib), N/\N/\N = bis(N-methylbenzimidazolyl)pyridine (Mebip), and N/\C = phenylpyridine (ppy) derivatives. The X-ray crystal structures of [Ir(Phbib)(ppy)Cl] and [Ir(Mebib)(mppy)Cl] [mppy = 5-methyl-2-(2'-pyridyl)phenyl] indicate that the nitrogen atom of the ppy ligand is located trans to the coordinating carbon atom in Me- or Phbib, while the coordinating carbon atom in ppy occupies the trans position of Cl. [Ir(Mebip)(ppy)Cl]+ showed a quasireversible Ir(III/IV) oxidation wave at +1.05 V, while the Ir complexes, [Ir(Mebib)(ppy)Cl], were oxidized at +0.42 V versus Fc/Fc+. The introduction of an Ir-C bond in [Ir(Mebib)(ppy)Cl] induces a large potential shift of 0.63 V in a negative direction. Further, the oxidation potential of [Ir(Mebib)(Rppy)X] was altered by the substitution of R, R', and X groups. Compared to the oxidation potential, the first reduction potential revealed an almost constant value at -2.36 to -2.46 V for [Ir(L)(ppy)Cl] (L = Mebib and Phbib) and -1.52 V for [Ir(Mebip)(ppy)Cl. The UV-vis spectra of [Ir(Mebib)(R-ppy)X] show a clear singlet metal-to-ligand charge-transfer transition around 407 approximately 425 nm and a triplet metal-to-ligand charge-transfer transition at 498 approximately 523 nm. [Ir(Mebip)(ppy)Cl]+ emits at 610 nm with a luminescent quantum yield of Phi = 0.16 at room temperature. The phosphorescence of [Ir(Mebib)(ppy)X] was observed at 526 nm for X = CN and 555 nm for X = Cl with the high luminescent quantum yields, Phi = 0.77 approximately 0.86, at room temperature. [Ir(Phbib)(ppy)Cl] shows the emission at 559 nm with a luminescent quantum yield of Phi = 0.95, which is an unprecedentedly high value compared to those of other emissive metal complexes. Compared to the luminescent quantum yields of the Ir(ppy)2(L) derivatives and [Ir(Mebip)(ppy)Cl]+, the neutral Ir complexes, [Ir(L)(R-ppy)X] (L = Me- or Phbib), reveal very high quantum yields and large radiative rate constants (kr) ranging from 3.4 x 10(5) to 5.5 x 10(5) s(-1). The density functional theory calculation suggests that these Ir complexes possess dominantly metal-to-ligand charge-transfer and halide-to-ligand charge-transfer excited states. The mechanism for a high phosphorescence yield in [Ir(bib)(ppy)X] is discussed herein from the perspective of the theoretical consideration of radiative rate constants using perturbation theory and a one-center spin-orbit coupling approximation.     

Determination of sulfur dioxide in vitriol plant wastewater by using a polyNiMe4TAA electrochemically modified Pt microelectrode

A Pt microelectrode modified with nickel(II) polytetramethyldibenzo[b,i]tetraaza[14]annulene was prepared by electropolymerization of nickel(II) tetramethyldibenzo[b,i]tetraaza[14]annulene monomers and applied to determine sulfur dioxide in vitriol plant wastewater. For determination of SO2 with this electrochemically modified Pt microelectrode, the linear range was from 9.6 x 10(-6) to 2.4 x 10(-4) mol L-1, the sensitivity was 1.8 x 10(-4) A L mol-1, the detection limit was calculated to be 4.8 x 10(-6) mol L-1 (S/N = 3), the response time was less than 20 s and the relative standard deviation was found to be 2.1% on analyzing 4.8 x 10(-5) mol L-1 SO2 solution repeatedly (n = 7). These results demonstrated good accuracy compared with those obtained by the conventional iodimetric method.     

超分子化合物[H3N(CH2)3NH3]•[Pb2(SIP)2]•6H2O的水热合成与表征

在水热条件下, 用NaH2SIP与Pb(Ⅱ)盐, 以1,3-丙二胺(1,3-PDA)作为结构导向剂进行反应, 得到化合物[H3N(CH2)3NH3]•[Pb2(SIP)2]•6H2O(1). 同时采用单晶X射线衍射、X射线粉末衍射、元素分析、红外光谱和荧光光谱对化合物1进行了表征.     

具有新结构类型的化合物Csln[PO3(OH)]2的合成与结构

水热法合成了新结构类型化合物CsIn[P03(0H)]2,并通过单晶X-射线衍射表征结构.标题化合物空间群为P121/c1(No.14),晶体学参数为:M=439.69,mP56,a=0.532 86(6)nm,b=0.91653(7)nm,c=1.478 39(14)nm,β=93.849(9).,V=0.7204(1)nm3,Z=4,Dx=4.054 g·cm-3,μ=8.713 mm-1,F(000)=800,R1= 0.0325,wR2=0.0874.在该化合物中,2个In06八面体和4个PO4四面体形成交连的六元环柱,并沿a轴方向形成近六方密堆积并连接成Cs+离子占据的十二元环结构隧道,六元环和十二元环连接构筑了三维网络结构.与类似化学计量比化合物Na2In2[PO3(0H)]4·H2O比较,标题化合物中十二元环的形成明显取决于隧道阳离子的大小,其拓扑构造可看作扩展的6,3-网格连接,化合物RbIn[PO3(0H)]2与之同构.     

Synthesis, structure and luminescent properties of rare earth coordination polymers constructed from paddle-wheel building blocks

A series of three-dimensional (3D) novel coordination polymers M(bpdc)1.5(H2O) x 0.5DMF (M = Tb (1), Ho (2), Er (3), or Y (4)) have been synthesized by reaction of the rare earth ions (M3+) with 4,4'-biphenyldicarboxylic acid (H2bpdc) in a mixed solution of DMF and C2H5OH. They possess the same 3D architectures and crystallize in monoclinic space group C2/c. Two seven-coordinated metal centers and four dimonodentate bpdc groups construct a paddle-wheel building block. These building blocks connect with two carboxyl groups to lead to a one-dimensional inorganic chain, ---M-O-C-O-M---, along the [001] direction. The inorganic chains are linked with two biphenyl groups to form 25.15 A x 17.09 A rhombic channels along the c axis without interpenetration. These complexes exhibit strong fluorescence in the visible region, and complex 3 shows Er3+ characteristic emission in the range of 1450-1650 nm at room temperature. These complexes could be anticipated as potential fluorescent probes and an IR-emitter, respectively.     

Synthesis,Crystal Structure,Vibrational Spectroscopy,and Thermal Behavior of Y[B_2O_3（OH）]_3

The hydroxy yttrium hexaborate,Y[B2O3(OH)]3,has been synthesized under mild hydrothermal conditions at 458 K.The crystal structure was solved and refined from single-crystal X-ray diffraction.It adopts a trigonal space group R3c(No.161) with a = 8.3942(4),c = 20.6484(12) ,V = 1260.03(12) 3,YB6H3O12,Mr = 348.79,Z = 6,Dc = 2.758 g/cm3,F(000) = 1008,μ = 7.015 mm-1,R = 0.0321 and wR = 0.0772.Its crystal structure is made up of six-membered rings,alternating three-connected [BO3(OH)] tetrahedra and planar [BO3] trigonal groups,which are interconnected with each other by sharing their common oxygen corners to form a three-dimensional framework structure with six-membered ring channels that are occupied by the yttrium atoms and run along the c axis.FT-IR,Raman,and TG-DTA results are also presented.     

Preparation of single-crystalline NdVO4 nanorods, and their emissions in the ultraviolet and blue under ultraviolet excitation

This paper describes a facile sacrifical (NH4)0.5V2O5 nanowires approach to single-crystalline NdVO4 nanorods. The nanorods have a rectangular cross section of about 30 x 30 nm2 to 100 x 200 nm2, and length ranging from 400 to 700 nm. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) show that the nanorods grew respectively along the [312] and [101] direction on the (NH4)0.5V2O5 nanowires. Ultraviolet (362 nm) and blue (467 nm) emissions can be observed under excitation of 310 nm at room temperature, suggesting that the nanorods should be good candidates for fabricating UV and blue nanodevices.     

Amine-templated open-framework zinc arsenates of varying dimensionalities: synthesis, structure, polymorphism, and transformation reactions

Eight new open-framework zinc arsenates, encompassing the entire hierarchy of open-framework structures, have been prepared hydrothermally. The structures include zero-dimensional, one-dimensional chains, two-dimensional layers, and three-dimensional structures formed through the transformation of the molecular zinc arsenates. The structure of [C6N4H21][Zn(HAsO4)2(H2AsO4)], I, is composed of ZnO4 and H2AsO4 units connected through the vertices forming four-membered rings with HAsO4 units hanging from the Zn center. The four-membered rings are connected through the corners forming the one-dimensional chain structures in [C4N2H12][Zn(HAsO4)2] x H2O, II, and [C5N2H14][Zn(HAsO4)2] x H2O, III. ZnO4 and AsO4 units form a fully four-connected two-dimensional structure in [C4N2H12][Zn(AsO4)]2, IV. One-dimensional zigzag ladders are connected through HAsO4 units forming two-dimensional layers in [C4N2H12]1.5[Zn2(AsO4)(HAsO4)2] x H2O, V, while the similar building units form a layer with hanging HAsO4 units in the layered arsenate [C6N4H21]6[Zn12(HAsO4)21], VI. Hanging HAsO4 units are also observed in the polymorphic structures of [C6N3H20][Zn2(AsO4)(HAsO4)2] x 2H2O, VII and VIII. Formation of zero-dimensional monomer, I, a fully four-connected layer, IV, and the polymorphic structures, VII and VIII, are important and noteworthy. The transformation reactions of I indicate that the monomer is reactive and gives rise to structures of higher dimensionalities, indicating a possible Aufbau-type building-up process in these structures.     

Analysis of thiocyanate in biological fluids by capillary zone electrophoresis

A new sensitive and simple method has been developed for the determination of thiocyanate in human serum, urine and saliva. The determinations were performed in a fused-silica capillary [64.5 cm (56 cm effective length) x 75 microm] using 0.1 M beta-alanine-HCl (pH 3.50) as a background electrolyte, separation voltage 18 kV (negative polarity), temperature of capillary 25 degrees C and direct detection at 200 nm. Serum samples were 10-times diluted with deionised water and deproteinised with acetonitrile in the ratio 1:2. Urine and saliva samples need only 20-fold dilution with deionised water. The proposed method was successfully applied to the determination of thiocyanate in various human serum, saliva and urine samples.     

Tuning of luminescence spectra of neutral ruthenium(II) complexes by crystal waters

Neutral ruthenium(II) complexes [RuLL'(CN)2] (L, L' = bpy, dmb, dbb; bpy = 2,2'-bipyridine, dmb = 4,4'-dimethyl-2,2'-bipyridine, dbb = 4,4'-tert-butyl-2,2'-bipyridine) were prepared, and the luminescence characteristics of the complexes in the solid state were measured. The luminescence was tuned by crystal waters included in the crystals; for example, [Ru(dbb)2(CN)2] x 2H2O, [Ru(dbb)2(CN)2] x H2O, and [Ru(dbb)2(CN)2] emit luminescence at 640, 685, and 740 nm, respectively.     

A layered tungstic acid H2W2O7 x nH2O with a double-octahedral sheet structure: conversion process from an aurivillius phase Bi2W2O9 and structural characterization

The conversion process of an Aurivillius phase, Bi(2)W(2)O(9), into a layered tungstic acid by hydrochloric acid treatment has been investigated, and resultant H(2)W(2)O(7) x nH(2)O has been fully characterized. The c parameter of Bi(2)W(2)O(9) [2.37063(5) nm] decreases to 2.21(1) nm in an acid-treated product dried at ambient temperature. The a and b parameters of Bi(2)W(2)O(9) [a = 0.54377(1) nm and b = 0.54166(1) nm] also decrease slightly to a = 0.524(1) nm and b = 0.513(1) nm in the acid-treated product dried at ambient temperature, indicating structural changes in the ReO(3)-like slabs in Bi(2)W(2)O(9) upon acid treatment. Drying at 120 degrees C leads to a further decrease in the c parameter [1.86(1) nm] with no notable change in the a and b parameters [a = 0.5249(2) nm and b = 0.513(2) nm]. The formation of an expandable layered structure is demonstrated by the successful intercalation of n-octylamine [interlayer distance 2.597(9) nm] and n-dodecylamine [interlayer distance 3.56(2) nm]. The compositions of the acid-treated products are determined to be H(2)W(2)O(7) x nH(2)O typically with n = 0.58 for the air-dried product and n = 0 for the product dried at 120 degrees C. As a consequence, the composition of the layer is H(2)W(2)O(7), and the decrease in the c parameter upon drying is ascribable to the loss of interlayer water. Scanning electron microscopy reveals no morphological change during acid treatment, which strongly suggests a selective leaching of the bismuth oxide sheets as a reaction mechanism. High-resolution transmission electron microscopy (HREM) observation of the acid-treated product shows consistency with a structural model for H(2)W(2)O(7), derived from Bi(2)W(2)O(9) through removal of the bismuth oxide sheets and contraction along the c axis. HREM observation also reveals that the WO(6) octahedra arrangement changes slightly with acid treatment. A one-dimensional electron density map projected on the c axis for the product dried at 120 degrees C, H(2)W(2)O(7), shows good consistency with that calculated for the structural model.     

Photoluminescence and Raman scattering from catalytically grown Zn(x)Cd(1-x)Se alloy nanowires

Zn(x)Cd(1-x)Se alloy nanowires, with composition x = 0, 0.2, 0.5, 0.7, and 1, have been successfully synthesized by a chemical vapor deposition (CVD) method assisted with laser ablation. The as-synthesized alloy nanowires, 60-150 nm in diameter and several tens of micrometers in length, complied with a typical vapor-liquid-solid (VLS) growth mechanism. The Zn(x)Cd(1-x)Se nanowires are single crystalline revealed from high-resolution transmission electron microscopic (HRTEM) images, selected area electron diffraction (SAED) patterns, and X-ray diffraction (XRD) measurement. Compositions of the alloy nanowires can be adjusted by varying the precursor ratios of the laser ablated target and the CVD deposition temperature. Crystalline structures of the Zn(x)Cd(1-x)Se nanowires are hexagonal wurtzite at x = 0, 0.2, and 0.5 with the [0 1 -1 0] growth direction and zinc blende at x = 0.7 and 1 with the [1 -1 1] growth direction. Energy gaps of the Zn(x)Cd(1-x)Se nanowires, determined from micro-photoluminescence (PL) measurements, change nonlinearly as a quadratic function of x with a bowing parameter of approximately 0.45 eV. Strong PL from the Zn(x)Cd(1-x)Se nanowires can be tuned from red (712 nm) to blue (463 nm) with x varying from 0 to 1 and has demonstrated that the alloy nanowires have potential applications in optical and sensory nanotechnology. Micro-Raman shifts of the longitudinal optical (LO) phonon mode observed in the Zn(x)Cd(1-x)Se nanowires show a one-mode behavior pattern following the prediction of a modified random element isodisplacement (MREI) model.     

一个新的三维配位聚合物Na[Cu2(malonate)2]·(ClO4)·(H2O)2的合成与表征(英)

通过Cu(ClO₄)₂和丙二酸在水溶液中的自组装合成了一个新的3D配位聚合物：Na[Cu₂(malonate)₂]·(ClO₄)·(H₂O)₂。X-射线结构分析表明该化合物晶体属于正交晶系Pnma空间群(a=1.256 5(3)，b=1.0594 3(2)，c=1.0755 6(14) nm，V=1.431 7(4) nm³，Z=4)。该聚合物的空间堆积在沿b轴和c轴方向分别形成大小为0.98 nm × 0.83 nm和0.40 nm × 0.40 nm的方形孔洞，在沿a轴方向形成大小为0.85 nm × 0.40 nm的砖墙形孔洞。磁性测试结果表明该化合物显示出铁磁性。导电性能测试实验表明它是一个半导体，经拟合得到其活化能为0.80 eV。     

NC4H12]2[(UO2)6(H2O)2(SO4)7]: the first organically templated actinide sulfate with a three-dimensional framework structure

[NC4H12][(UO2)6(H2O)2(SO4)7] is the first organically templated actinide sulfate with a three-dimensional framework structure; it has channels of dimensions 8.5 A x 8.5 A, running along the [001] direction, containing tetramethylammonium cations.     

两种具有三维孔道结构有机模板稀土硫酸盐的合成、表征及性质研究

本文分别采用水热和溶剂热的方法,以乙二胺和哌嗪为有机模板剂分别合成了两种新的三维孔道结构的稀土硫酸盐[Gd2(SO4)5(H2O)2][C2N2H10]2(1),[Eu2(SO4)5(H2O)2][C4N2H12]2(2),并且通过单晶X射线衍射、元素分析、红外、热重对两种化合物进行了表征。化合物1和2都属于单斜晶系,P21/c空间群。化合物1:a=0.652 1(4)nm,b=1.692 0(9)nm,c=2.023 3(11)nm,β=95.168(7)°,Z=4。化合物2:a=1.972 1(2)nm,b=1.927 1(2)nm,c=1.323 20(14)nm,β=92.307 0(10)°,Z=8。单晶结构分析表明,这两种化合物的无机骨架都是由SO4连接具有交替十六元环与八元环二维层形成的三维孔道结构。化合物2的固体荧光分析表明,在396 nm的激发波长下表现出Eu3+的特有发光性质。     

Mixed-metal sandwich complexes [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14- (M(II) = Co, Mn): synthesis and stability. The molecular structure of [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14-

Two new mixed-metal sandwich complexes [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14- (abbreviated [M2Fe2P4W30], M(II) = Co(II), Mn(II)) were obtained at pH 3 by addition of M2+ to [Na2(H2O)2Fe(III)2(P2W15O56)2]16- (abbreviated [Na2Fe2P4W30]) without substitution in the alpha-[P2W15O56]12- (abbreviated [P2W15]) units. Their X-ray structures are reported. At lower pH, back conversion to [Na2Fe2P4W30] was followed by 31P NMR, electrochemistry and UV-visible spectroscopy. The preparation and the characterization in solution of the lacunary intermediate [NaCo(II)(H2O)2Fe(III)2(P2W15O56)2]15- (abbreviated [NaCoFe2P4W30]) is also described.     

Raman spectroscopy of the mixtures (x)1-butyl-1-methylpyrrolidinium chloride-(1 - x)TaCl5 in solid and molten states

A series of novel ionic liquids consisting of 1-butyl-1-methylpyrrolidinium chloride (Pyr14Cl) and TaCl5 were obtained in a wide range of molar compositions for electrochemical application. Raman spectroscopy was used to investigate the complex formation of tantalum(V) in the mixtures of (x)Pyr14Cl-(1 - x)TaCl5 (x = 0.80-0.30) over the temperature range 20-160 degrees C. Depending on the molar composition, different species of tantalum (V) were identified. In the basic and neutral mixtures of (x)Pyr14Cl-(1 - x)TaCl5 (x = 0.80-0.50), tantalum(V) exists in the form of octahedral [TaCl6](-) in both solid and molten states. In acidic ionic liquids (x = 0.45-0.30), [Ta2Cl10] units are the main species of tantalum(V) identified in the solid state. As the temperature rose, the gradual degradation of [Ta2Cl10] units was observed in the solid state, accompanied by the formation of [TaCl6](-) and [Ta2Cl11](-) anions. In the molten state, in the range between 130 and 160 degrees C, the latter two species exist in equilibrium and are the dominant species of tantalum(V). The formation of oxochloride species of tantalum(V) was investigated in mixtures of Pyr14Cl-TaCl5-Na2O (x = 0.65) at various O/Ta mole ratios, and the formation of the oligomeric species with Ta-O-Ta bridging bonds was determined.     

Syntheses, structures and properties of cadmium benzenedicarboxylate metal-organic frameworks

The products isolated from the reaction between Cd(NO3)2 x 4H2O and 1,4-benzenedicarboxylic acid (H2bdc) in DMF are very dependent on the conditions. At 115 degrees C, the reaction gives [Cd(bdc)(DMF)]infinity, which has a three-dimensional network structure, whereas at 95 degrees C, 1 is formed alongside [Cd3(bdc)3(DMF)4]infinity 2, which has a two-dimensional network structure. When the reaction is carried out under pressure, it yields [Cd3(bdc)3(DMF)4]infinity 3, which is a supramolecular isomer of 2. The structure of 3 differs from that of 2 regarding the way the Cd3(O2CR)6 units are interlinked to form layers. When the reaction was carried out in DMF that had undergone partial hydrolysis, the only isolated product was [(NMe2H2)2[Cd(bdc)2] x 2DMF]infinity 4. Compound 4 has a three-dimensional triply-interpenetrated diamondoid structure, with dimethylammonium cations and DMF molecules included within the pores. The reaction between Cd(NO3)2 x 4H2O and H2bdc in DEF gave [Cd(bdc)(DEF)]infinity 5, regardless of the solvent quality. Compound 5 has a three-dimensional network structure. The reaction of Cd(NO3)2 x 4H2O and 1,3-benzenedicarboxylic acid (H2mbdc) in DMF gave [Cd(mbdc)(DMF)]infinity 6 which has a bilayer structure. The thermal properties of the new materials have been investigated, and the coordinated DEF molecules from 5 can be removed on heating to 400 degrees C without any change in the powder X-ray diffraction pattern. The H2 sorption isotherm for the desolvated material shows marked hysteresis between adsorption and desorption, and less adsorption than predicted by simulations. Kinetic data indicate that the hysteresis is not due to mass transfer limitations, and the most likely explanation for this behaviour lies in partial collapse of the framework to an amorphous phase under the conditions of activation.