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Conformal parallel arrays of Al-doped TiO2 nanotubes were fabricated by atomic layer deposition. TiO2/Al2O3 bilayered shells were grown on a polycarbonate template by various cyclic sequences of TiO2 and Al2O3. The doping level of Al could be tuned by the fraction of cycle number of Al2O3. From the depth profiles measured by second ion mass spectrometry, Al is uniformly distributed across the thickness, which is also supported by the analyses of X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. A uniform bulk solubility of ~7 at.% and the surface concentration of ~18 at.% were observed with the cycle ratio of Al2O3: TiO2 at 0.04. This article is protected by copyright. All rights reserved.

In this study, pristine and modified carbon cloth replaced with Al foil as current collector for lithium-rich layered oxide cathodes (Li1.2Mn0.6Ni0.2O2, LLO). The modified carbon cloths were prepared by modification of the pristine carbon cloth with phenolic resin (PR) and carbon nanotubes (CNT), followed by carbonization at 1000oC in nitrogen atmosphere. The first charge-discharge capacities of the lithium-rich layered oxide cathodes using the carbon cloth as current collector were 312 mAhg−1 and 252 mAhg−1, respectively, which was comparable with Al foil. Interestingly, an improved rate capability was obtained. After 100 cycles, the capacity of the carbon cloth was 138 mAhg−1 and 78 mAhg−1 in comparison with that of Al foil, 125 mAhg−1 and 50 mAhg−1 under 1 C and 5 C rate, respectively. In addition, after 100 cycles, no significant changes on the morphology and Id/Ig value of Raman spectra were observed. According to electrochemical impedance spectra (EIS), the charge transfer resistance of the carbon cloth, 12 ohm, was significantly lower than that of Al foil, 166 ohm. As a consequence, the enhanced rate capability was obtained. The lower resistance was associated with the increased surface area, better adhesion between the slurry and current collector interface and formation of semi-ionic C−F bonds.

A chiral nickel histidine compound, [Ni(L-his)2]×H2O (1, L-his = anion of L-histidine), was synthesized in high yield from the reaction of Ni(OAc)2×4H2O and L-histidine in the presence of 4,4′-bipyridine under mild reaction conditions. A single-crystal X-ray diffraction analysis showed that compound 1 crystallizes in the monoclinic system, space group C2, with a chemical formula of C12H18N6NiO5, cell parameters: a = 29.416(2) A, b = 8.2667(7) A, c = 6.3137(5) A, β = 90.066(2)°, V = 1535.3(2) A3 and Z = 4. Each nickel(II) ion in 1 is six coordinated, bonded to two oxygen donors and four nitrogen donors from two crystallographically independent L-his− ligands with a tridentate coordination mode to form a monomeric species. Monomeric forms of 1 undergo self-assembly to form a three-dimensional (3D) supramolecular architecture via subtle combinations of N-H···O type hydrogen bonding interactions among the adjacent L-his−ligands and π-π stacking interactions among the imidazole rings of the L-his− ligands. The supramolecular entity exhibits an unusually high thermal stability, at temperatures of up to 360 °C and shows reversible de-/re-hydration properties.

Electron density distribution of 2,2′-dipyridylamine (Hdpa) is studied by single-crystal X-ray diffraction method at 120 K. Structural determination reveals that the conformation of Hdpa molecule is the syn-anti conformation caused by the intramolecular N···H-C hydrogen bond between two pyridine rings. Two Hdpa molecules flock together via two intermolecular N···H-N hydrogen bonds to form a dimer. Bond characterization is made in terms of deformation density (Δρ), topological analysis of total electron density based on multipole model and molecular orbital (DFT) calculation. The agreement between experiment and theory is good. The topological properties of bond critical points at C-C, C-N, N-H and C-H bonds are reasonable and reveal a covalent bond character with the high ρ(rc), negative ∇2ρ(rc) and negative total energy density H((rc) values. A low ρ(rc) and positive ∇2ρ(rc) of bond critical points at N···H bonds reveal a closed-shell interaction for C-H···N and N-H···N hydrogen bonds. The π-delocalization feature around the pyridine ring is also performed by bond ellipticity (ϵ) and fermi-hole distribution.

A new polymeric complex, [Fe(bpno)2(NCS)3]n (1) (bpno = 4,4′-bipyridyl-N,N′-dioxide) have been synhesized and structural characterized by single crystal X-ray diffraction. Compound 1 crystallizes in the triclinic system, space group P-1, with chemical formula C23H16FeN7O4S3, a = 9.0738(5), b = 9.7175(5), c = 15.0329(8) A, α = 97.668(1), β = 92.581(1) and γ = 102.441(1)°, V = 1279.1(1) and Z = 2. Structural determination reveals that the coordination environment of the iron(III) ion is distorted octahedral, bonded with three oxygen donors of three bpno and three nitrogen donors of three NCS− ligands. The bpno ligands adopt two different coodination modes, a monodentate coordination mode and a bis-monodentate coordination mode, which links the Fe(III) ions to form a one-dimensional (1D) zigzag chain-like coordination polymer. Neighbouring chains are mutually connected via the C-H···O type hydrogen bonds to form a 2D hydrogen-bonded layered framework and then extended to a 3D supramolecular architecture via π-π interaction between the pyridyl rings of bpno ligands and unconventional C-H···S hydrogen bonding interactions. Compound 1 exhibits moderate thermo-stability and keeps its crystalline forms up to 190 °C.

In this highlight, we have focused our attention on several examples of coordination polymers (CPs) and metal–organic frameworks (MOFs) that exhibit water-induced reversible SCSC or solid-state structural transformations under thermal conditions. Dissociation or removal of coordinated or solvated water molecules and exposure to moisture in air may cause reversible SCSC or solid-state structural transformations, which are mainly demonstrated through single-crystal X-ray diffraction, powder X-ray diffraction and cyclic TG measurement and manifested by various physical properties, such as colour, magnetism, luminescence, etc., due to changes in coordination number and geometry, structural dimensionality, interpenetration, etc.

Three coordination polymers, {[Cd(3-bpd)2(NCS)2]×C2H5OH}n (1), {[Cd(3-bpd)(dpe)(NO3)2]×(3-bpd)}2 (2), {[Cd(dpe)2(NCS)2]×3-bpd×2H2O}n (3) (3-bpd = 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene; dpe = 1,2-bis(4-pyridyl)ethane), were prepared and structurally characterized by a single-crystal X-ray diffraction method. In compound 1, each Cd(II) ion is six-coordinate bonded to six nitrogen atoms from four 3-bpd and two NCS− ligands. The 3-bpd acts as a bridging ligand connecting the Cd(II) ion to generate a 2D layered metal-organic framework (MOF) by using a rhomboidal-grid as the basic building units with the 44 topology. In compound 2, the Cd(II) ion is also six-coordinate bonded to four nitrogen atoms of two 3-bpd, two dpe and two oxygen atoms of two NO3− ligands. The 3-bpd and dpe ligands both adopt bis-monodentate coordination mode connecting the Cd(II) ions to generate a 2D layered MOF by using a rectangle-grid as the basic building units with the 44 topology. In compound 3, two crystallographically independent Cd(II) ions are both coordinated by four nitrogen atoms of dpe ligands in the basal plane and two nitrogen atom of NCS− in the axial sites. The dpe acts as a bridging ligand to connect the Cd(II) ions forming a 2D interpenetrating MOFs by using a square-grid as the basic unit with the 44 topology. All of their 2D layered MOFs in compounds 1-3 are then arranged in a parallel non-interpenetrating ABAB—packing manner in 1 and 2, and mutually interpenetrating manner in 3, respectively, to extend their 3D supramolecular architectures with their 1D pores intercalated with solvent (ethanol in 1 or H2O in 3) or free 3-bpd molecules in 2 and 3, respectively. The photoluminescence measurements of 1-3 reveal that the emission is tentatively assigned to originate from π-π* transition for 1 and 2 and probably due to ligand-center luminescence for compounds 3, respectively.

A new coordination polymer, [Zn(dpe)(bdc)]·4H(2)O (ZndB; dpe=1,2-bis(4-pyridyl)ethane, bdc(2-)=dianion of benzenedicarboxylic acid), which possesses a 3D metal-organic framework (MOF) has been synthesized and structurally characterized. This 3D MOF is constructed by the assembly of helical channels filled with guest water molecules in both inner and outer regions of the channel. The resulting network also creates a 2D water layer containing hydrogen-bonded (H(2)O)(16) rings as the basic building units. Thermogravimetric and powder X-ray diffraction measurements of ZndB revealed a two-step weight loss of water molecules with a reversible water adsorption/desorption process in the inner channel for the first stage, and irreversible water desorption in the outer channel for the second stage. This spongelike property is manifested by the excimer emission originating from interaction between dpe (π*) and the other dpe (π) of the proximal helical channel, which is highly sensitive to the environmental perturbation. Powder X-ray analyses reveal that the dehydration process induces the readjustment of dpe π-π stacking distance/orientation, which results in dramatic luminescence changes from dim pale blue (λ(em)≈470 nm) upon hydration to bright white-light generation (broad, λ(em)≈500-550 nm) upon water depletion, accompanied by a ≈100-fold increase in the emission intensity.

A new polymeric complex, [Cd(bpym) 0.5 (N 3 ) 2 ] n (bpym = 2,2'-bipyrimidine) has been synthesized and characterized by spectroscopic, elemental analyses and single crystal X-ray diffraction. The title compound crystallizes in the monoclinic system, space group P2 1 /c, with chemical formula C 4 H 3 CdN 8 , a = 7.6763(5), b = 13.1539(9), c = 7.9693(5) A, β = 109.988(1)°, and Z = 4. Structural determination reveals that the coordination environment of the cadmium atoms is distorted octahedral, consisting of two nitrogen donors of one bpym and four nitrogen donors of four azide ligands. The azide ligand acts as a bridging ligand with two different bridging modes, an end-on (μ 1,1 -) and an end-to-end (μ 1,3 -) coordination mode, linking the Cd" ions to form a two-dimensional layer metal-organic framework (MOF), which get crosslinked by the bridges of bis-bidentate bpym ligands to form a novel 3D network.

Two extended coordination frameworks of CdII–squarate complexes with the formulas [Cd2(C4O4)2.5(H2O)4](dpaH)·1.5(H2O) (1) and [Cd(C4O4)(dpa)(H2O)] (2) (dpa = 2,2′-dipyridylamine) have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction studies. Structural determination reveals that compound 1 consists of a free monoprotonated 2,2′-dipyridylamine ion (dpaH+) and a two-dimensional (2D) anionic, layered framework, {[Cd2(C4O4)2.5(H2O)4]–}, which is formed with two antiprismatic square-boxes as the fundamental building unit through the connection between CdII ions and hybrid μ1,2,3-, μ1,2,3,4-squarates. Each square-box acts as a host for the inclusion of one pyridine ring of dpaH+. Adjacent dpaH+ cations are then self-assembled by the parallel alignment of the other pyridine ring of dpaH+ to complete a 3D network with one-dimensional (1D) channels intercalated by water molecules. Compound 2 contains a distorted octahedral CdII center coordinated by two squarates, two waters and one dpa ligand to form a 1D 2-legged, ladder-like framework by the connection of a [Cd(dpa)(μ2-H2O)]24+ dimeric unit and a μ1,2-squarate. Weak π–π stacking interaction and hydrogen bonds of N–H···O, O–H···O and C–H···O among the squarate, water and dpa ligands provide additional intra- and intermolecular interactions on the stabilization of these two polymeric frameworks. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Two metal coordination polymers with general formula [M(dpa)(C4O4)(H2O)] [M = Co (1), Ni (2), Zn (3); dpa = 2,2'-dipyridylamine] and [Cu(dpa)(C4O4)(H2O)]2·H2O (4) have been synthesized under hydrothermal conditions. The single-crystal X-ray analyses reveal that compounds 1–3 are isostructural and possess distorted octahedral metal centers coordinated by two squarates, one dpa, and two water molecules. A 1D two-legged ladder-like framework is formed by interconnection of the water-bridged [M(dpa)(μ2-OH2)]24+ dimeric fragments and μ1,2-squarate ligands. Intra- and intermolecular hydrogen bonds between squarate, water, and dpa ligands, as well as the π-π stacking interaction of the pyridyl ring in the dpa ligands, provide extra forces to stabilize the extended network. Conversely, the molecular structure of compound 4 contains two distorted square-pyramidal CuII centers coordinated by two squarates, one dpa ligand, and one water molecule. The squarates adopt a μ1,2-binding mode to link the Cu centers and form a 1D helical chain. For compound 2, the magnetic exchange couplings between metal centers are analyzed with a binuclear magnetic model. The resulting negative magnetic exchange coupling constant indicates an antiferromagnetic interaction within the dimers. The magnetic behavior of compound 4 is typical of paramagnetic CuII ions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

A new unsymmetrical bisdithiolene nickel complex Ni(Et 2 dazdt)(mnt) was synthesized and structurally characterized, where Et 2 dazdt and mnt denote 1,4-diethyl-perhydrodiazepine-2,3-dithione and maleonitrildithiolate, respectively. Its crystal structure and absorption spectrum were determined and compared to those of Ni(Et 2 pipdt)(mnt), where Et 2 pipdt is 1,4-diethyl-piperazine-2,3-dithione. X-ray diffraction analysis reveals that the Ni(S 2 C 2 ) 2 moiety of Ni(Et 2 dazdt)(mnt) is not planar due to the twist conformation of a seven-member ring of Et 2 dazdt ligand. The twisting of Et 2 pipdt is less severe and NiS 4 center of Ni(Et 2 pipdt)-(mnt) possesses a closer to planar conformation than that of Ni(Et2dazdt)(mnt). Unlike Ni(Et 2 pipdt)(mnt), Ni(dazdt)(mnt) shows two major separated absorption bands in the visible and near-IR region, although both absorption bands show negative solvatochromism similar to that of Ni(Et2pipdt)(mnt).

Two new linear tri-nickel(II) complexes with an infinite polymeric chain, [Ni 3 (μ 3 -dpa) 4 (C 4 O 4 Me)](BF4) 1 and [Ni 3 (μ 3 -dpa)4(N3)](PF6) 2, [dpa - = di(α-pyridyl)amido anion], have been synthesized and their structures were determined by X-ray diffraction. Compound 1 crystallizes in the monoclinic system, space group C 2/c, with a = 19.9078(3), b = 13.2986(2), c = 37.6622(5) A, β = 94.091(1)°, Z = 8. Compound 2 crystallizes in the monoclinic system, space group P 2 1 /n, with a = 13.323(4), b = 23.217(3), c = 17.528(5) A, β = 94.42(3)°, Z = 4. The two complexes are described as one-dimensional systems with the (C 4 O 4 Me) - , 1, or N 3 - , 2, serving as a μ-(1,3) bridged ligand at the two axial sites of each [Ni 3 (μ 3 -dpa) 4 ] 2 + fragment. The Ni-Ni distances of 2.400(1) and 2.402(1) in 1 and 2.389(2), 2.385(2) in 2 are obviously shorter than those of 2.4325(7), 2.4356(7) in the monomeric complex [Ni 3 (μ 3 -dpa) 4 (N 3 ) 2 ] 3. The magnetic properties of complexes 2 and 3 were studied by susceptibility measurements vs temperature. The Χ M vs T plots of both complexes show a strong antiferromagnetic behavior. The simulated J 1 3 values are -95 cm - 1 and -97 cm - 1 for 2 and 3, respectively.

The linear pentanuclear chromium complexes [CrII5(μ5-tpda)4Cl2] (1), [CrII5(μ5-tpda)4(NCS)2] (2), [CrIIICrII4(μ5-tpda)4F2](BF4) (3), and [CrIIICrII4(μ5-tpda)4F(OTf)](OTf) (4), with four all-syn tri(α-pyridyl)diamido dianion (tpda2–) ligands, have been prepared and structurally characterized. Compounds 1 and 2 possess a delocalized Cr(II)–Cr(II)–Cr(II)–Cr(II)–Cr(II) five-centred metal–metal bond of order 1.5. In both 1 and 2 two values for CrII–CrII bond lengths are found both; the outer ones connected with axial ligands are 2.284(1) and 2.285(2) A, and the inner ones are 2.2405(8) and 2.246(1) A, for 1 and 2, respectively. When compound 1 reacts with 2 equiv. of AgBF4 or Ag(OTf), a oxidation reaction takes place and one of the terminal chromium(II) ions is oxidized to produce [CrIIICrII4(μ5-tpda)4F2]BF4 (3) or [CrIIICrII4(μ5-tpda)4F(OTf)](OTf) (4). Two short Cr–Cr distances [1.969(2) and 2.138(2) A for 3, 1.846(1) and 1.922(1) A for 4] are found, with the presence of two quadruple bonds among four adjacent CrII ions. The fifth CrIII ion, which is separated from the neighboring CrII ion by 2.487(2) A for 3 and 2.610(1) A for 4, is simply a square pyramidal unit with no metal–metal bonding interaction.

The electron density distribution of a chromium(IV)-oxo complex, [CrIV(O)(TMP)] (TMP = 5,10,15,20-tetrakis-p-methoxyphenyl porphyrin), is investigated by molecular orbital calculation. The molecular and crystal structure of the compound is studied by x-ray diffraction. It belongs to the space group 1 2, Z = 2, a = 14.979(4) A, b = 9.752(3), c = 15.605(3) A, β = 100.97(2)°, V = 2238(1) A3, Mo Kα radiation λ = 0.7107 A, R = 4.9%, Rw = 3.5% for 3575 observed reflections. Cr is five-coordinated in a square pyramidal fashion with the Cr atom located 0.42 A toward the oxo-ligand. Deformation density maps are derived from the single point molecular orbital calculation on the basis of HF and DFT(density functional theory) calculations. The accumulation of deformation density along the C-H, C-C, C-N and C-O bonds in the porphyrin ligand is well represented. The asphericity in electron density around the Cr ion is clearly demonstrated. Natural bond orbital analysis (NBO) reveals that the Cr-Ooxo is actually a triple-bond character (σ2π4) and the four N of pyrrole serves as a σ-donor to Cr. The Cr-Npyrrole bond is essentially a dative bond d-Orbital populations of Cr derived from both calculations are in good agreement with each other. Planar dπ-orbital is the most populated, which is in accord with the prediction from crystal field theory. Detail bond characterization of the Cr-L, multiple bond is discussed.

The synthesis, crystal structures and magnetic properties of linear heptanuclear nickel(II) complexes [Ni7(μ7-teptra)4X2], (teptra = tetrapyridyltriamido), with the axial ligand X = Cl− (1), NCS− (2), are reported. The hepta-nuclear metal chain is helically wrapped by four syn-syn-syn-syn-syn-syn teptra3− ligands. Both of the [Ni7(μ7-teptra)4]2+ moiety are isostructural involving a Ni7 linear chain unit with all of the ∠Ni-Ni-Ni being 180°, terminated by two axial ligands. Three types of NiNi distances are found in these complexes. The longest ones bonded with the axial ligands are 2.383(1), 2.374(2) and 2.375(2), 2.354(2), and the intermediate ones are 2.310(1), 2.304(1) and 2.300(2), 2.303(2) A for (1) and (2), respectively. The innermost NiNi distances are the shortest ones with the distances of 2.226(2), 2.214(2) and 2.194(2), 2.206(2) A for (1) and (2), respectively. Two terminal Ni(II) ions bonded with the axial ligands are in a square-pyramidal (NiN4X) environment and exhibit long NiN bonds (−2.10 A) which are consistent with a high-spin Ni(II) configuration. The inner five Ni(II) ions displayed short NiN (∼1.90 A) bond distances which are consistent with a square-planar (NiN4), diamagnetic arrangement of a low-spin Ni(II) configuration. The magnetic measurement of (1) shows an antiferromagnetic interaction of two terminal high-spin Ni(II) ions with the coupling constant J = −3.8 cm−1. The NiNi, NiN distances and magnetic behavior among tri-, penta-, and hepta-nickel(II) complexes are compared and discussed.

Heptasulfur imide, S7NH, was studied by X-ray diffraction at both 100 and 300 K: space group Pnma, Z= 4, Mr= 239, a= 7.842(2), b= 13.115(2), c= 7.6219(7)A, at 100 K; R= 0.028 and 0.029 for 2517 and 994 reflections at 100 and 300 K respectively. The crown shape of the compound is similar to that of cyclooctasulfur, with one sulfur atom replaced by an NH group. The experimental deformation density distribution reveals a large positive accumulation between the sulfur and nitrogen atoms; small accumulations were found between the sulfur atoms. A multipole refinement shows much clearer features in the bonding and lone-pair electron regions. The results of theoretical calculations by the extended-Huckel molecular orbital, AM1 and ab initio methods are compared with experimental results. There is evidence of bent S–N bonds with endocyclic maxima in the deformation density distribution. The electrondensity distribution may be affected by the packing of molecules in the solid so that it differs from that of the isolated molecule. The net atomic charges from the multipole refinement indicate that N is negative, H is positive and S are neutral. However, those obtained from the ab initio method show a positive charge on the sulfur atom attached to the NH group.

Analysis of the theoretical electron deformation density based on EHMO and ab initio calculations has been applied to the simple molecules F2, H2O and SO2 The effects from varied basis sets for such deformation density were sought. The accumulation of electron density between the bonded atoms calculated from EHMO and ab initio methods with STO-3G is generally under-estimated. Such phenomena are significantly improved by using split-valence basis sets e.g. 3–21G and 4–31G. The addition of d polarization functions is apparently important for the sulfur atom in sulfur-related bonding. 3–21G or 3–21G* basis sets were found to provide not only valuable deformation density distributions of molecules but also comparable orbital energy states with respect to the experimental values.

1,3,5,7-Tetra-t-butyl-s-indacene is a twelve-membered fused-ring compound; the stabilization of the compound by bulky t-butyl groups is discussed. The distribution of bonding electron density is depicted in terms of deformation density using the experimental X-X method, a multipole expansion model and a calculation according to the extended Huckel molecular orbital method (EHMO). The molecules crystallize according to the space group P21/n with cell parameters a = 9.700(3), b = 11.746(3), c = 10.858(2)A, β = 107.67(2)°, Z=2 at 100K. The molecule has a center of inversion( ) and belongs to the symmetry point group Ci. The packing of two unique t-butyl groups in the asymmetric unit appears significantly different. However, the map of deformation density in the plane of the ring shows pseudo D2h symmetry. The accumulation of density at the midpoint of the bonds is observed as expected. The theoretical deformation densities agree with the experimental ones. Analyses of the molecular-orbital wavefunctions provide a good illustration of the aromatic π-electron system. A theoretical study of a series of substituents (-H, - CH3, -t-butyl ) on s-indacene illustrates the stabilization effect of the t-butyl group on the 12-π-electron ring system.