The Crystal Structure of Ba3Cu2Al2F16: a Relative of Ba4Cu2Al3F21

Ba₃Cu₂Al₂F₁₆ is monoclinic: a = 7.334(1)Å, b = 5.320(2)Å, c = 16.022(1)Å, β = 96.34(1)°, Z = 2. Its crystal structure was solved in the space group P2₁ (No. 4) from synchrotron X‐ray single crystal data using 2685 unique reflections (2639 with F_o/σ(F_o) > 4). The final R factor is 0.044. The structure consists of a succession along the c‐axis of the cell of three layers of two different kinds of sheets developing in the (a, b) plane. The first one, formulated [(AlF₅)₂]_∞^4— and hereafter named A, is built up from infinite cis‐chains of aluminium‐fluorine octahedra [AlF₆], linked by two vertices and distanced by a. The second one, formulated [Cu₂AlF₁₁]_∞^4— and named B, is bidimensional. It is constituted of distorted copper‐fluorine octahedra [CuF₆], linked by edges, which form infinite chains interconnected by three vertices of isolated [AlF₆] octahedra. The stacking sequence of the sheets is (A, B, B)_∞. The barium ions, 12‐coordinated, are inserted between the sheets. The crystal structure of Ba₃Cu₂Al₂F₁₆ is closely related to that of Ba₄Cu₂Al₃F₂₁. Only the proportion and the stacking sequence of the two kinds of sheets in the c‐direction differ, according to two different compositions and two different symmetries.     

P and H NMR studies of the transesterification polymerization of polyphosphonate oligomers

Polymeric phosphonate esters are an interesting class of organophosphorus polymers because both the polymer backbone and phosphorus substituents can be modified. These polymers have been prepared by ring-opening polymerizations of cyclic phosphites, stoichiometric polycondensations of dimethyl phosphonate with diols in conjunction with diazomethane treatment and by transesterification of polyphosphonate oligomers. Our initial attempts to prepare high molecular weight polymeric phosphonate esters by the transesterification methods were unsuccessful. Results indicate that the reactions of dimethyl phosphonate with diols to form polyphosphonate oligomers with only methyl phosphonate end groups are plagued by a serious side reaction that forms phosphonic acid end groups. These end groups do not participate in the transesterification reaction and limit the molecular weights of the polymers that can be obtained. The phosphonic acid end groups can be converted into reactive methyl phosphonate end groups by treatment with diazomethane, however diazomethane is explosive and the polymerization is slow. An alternative route for the production of high molecular weight polymers is the transesterification of the 1,12-bis(methyl phosphonato)dodecane, formed by the reaction of excess dimethyl phosphonate and 1,12-dodecanediol, with a Na₂CO₃ promoter. This allows polymers with molecular weights of up to 4.5×10⁴ to be prepared, and no phosphonic acid end groups are observed in these polymers. Thermal analyses of the poly(1,12-dodecamethylene phosphonate) have shown that this polymer has reasonable thermal stability (onset of thermal decomposition at 273 °C). This polymer also undergoes a cold crystallization process at 15 °C similar to that which has been observed in some polyesters, polyamides and elastomers.     

Exo-metal coordination by a tricyclic [(P(mu-N-2-NC5H4))2(mu-O)]2 dimer in [(P(mu-N-2-NC5H4))2(mu-O)]2(CuCl x (C5H5N)2)4 (2-NC5H4 = 2-pyridyl, C5H5N = pyridine)

The in situ reaction of the phosphazane dimer [CIP(mu-N-2-NC5H4)]2 (2) with CuCl in the presence of CsH5N/H2O gives the title complex [(P(mu-N-2-NC5H4))2(mu-O)]2(CuCl x (C5H5N)2)4 (1), containing a tricyclic [(P(mu-N-2-NC5H4))2(mu-O)]2 ligand which is isoelectronic with species of the type [(P(mu-NR))2NR]2.     

Synthesis and structure of [(Sn(mu-PCy))3(Na x PMDETA)2], containing an electron-deficient [(Sn(mu-PCy))3]2- dianion

The reaction of CyPHNa with Sn(NMe2)2 in the presence of PMDETA (= (Me2NCH2CH2)2NMe) gives the title compound [(Sn(mu-PCy))3(Na x PMDETA)2] (1), containing an electron-deficient [(Sn(mu-PCy))]3(2-) dianion with a novel two-electron, three centre (2e-3c) bonding arrangement.     

Steric control in the oligomerisation of phosphazane dimers; towards new phosphorus-nitrogen macrocycles

The reaction of [ClP(mu-NtBu)]2 (1) with H2O (1 : 2 equivalents) in the presence of excess Et3N gives the new chain compound [(mu-O)[P(mu-NtBu)2P(H)=O]2] (3), consisting of two P2N2 rings linked by a mu-O atom and terminating in P(V)(H)=O groups. A similar chain species is obtained from the reaction of the lithiate of [(tBuNH)P(mu-NtBu)2P(H)=O] (5) with [ClP(mu-NtBu)2P(NHtBu)] (2), the product being [(mu-O)[P(mu-NtBu)2P(NHtBu)]2] (6). Compounds 3 and 6 are the first examples of O-bridged chain phosphazanes and potential precursors to new phosphorus-nitrogen macrocycles. The syntheses and X-ray structures of 3, 5 and 6 are reported.     

Elucidation of the pore structure of SBA-2 using Monte Carlo simulation to interpret experimental data for the adsorption of light hydrocarbons

We have measured the adsorption of methane and ethane to high pressure on SBA-2, a structured mesoporous silica composed of spheres connected by narrow channels. The experimental data were analyzed by carrying out Monte Carlo simulations of adsorption in pore structure models of different complexity and then adjusting the parameters of the models to match the Monte Carlo results to the experimental data. We found that a model based on single-sized spherical cavities was inadequate and that it is necessary to explicitly account for the interconnecting channels. Further, we found that despite the basic regularity of the SBA-2 structure, it is necessary to allow for a distribution of the sizes of both the cavities and the channels. These size distributions were obtained by fitting the parameters of the model to the experimental adsorption data, revealing detailed structural information not previously known for this material. The channels were found to be 5-15 A in diameter, while the cavities were 40-50 A in diameter. There is some evidence that the distribution of channel sizes leads to a percolation effect whereby the pore structure is not equally accessible to all adsorptives.     

Solvent-free low-dimensional polymer electrolytes for lithium-polymer batteries

The development of solvent-free low-dimensional polymer electrolytes intended for use in solvent-free lithium batteries operating at ambient or sub-ambient temperatures is described. The synthetic routes to the amphiphilic polymers I having 5-alkoxy-3,4-phenylene units connected with oligoethoxy segments via polyester-ether or pure polyether links (abbrev. CmOn, m = 12, 16, 18, n = 1-5) and to the copolymers CmO1-CmOn are described. The structures, thermal properties and SAXS long spacings of their complexes with lithium salts (type A) and with long chain n-alkane or alkyl side chain intercalation (type B) are discussed. However, high ambient conductivities (10(-4)-10(-3) S cm(-1)) are observed in type C systems when a second copolymer based on polytetramethylene oxide segments (II) is incorporated as a microphase between the lamellae of I and serving as an ion bridge or "glue". DC polarization between Li electrodes also gives ambient conductivities >/=ca.10(-3) S cm(-1). In type D systems the I/II interface is stabilized by including a copolymer III, promoting high reproducibility in performance. Copolymers I of CmO1-CmO5 having CmO1 in excess give optimum conductivities with low temperature-dependence. This, together with molecular modeling, suggests uncoupled ion mobilities by hopping between small aggregates in the interlamellar spaces.     

Formation of ti(28) ln cages, the highest nuclearity polyoxotitanates (ln=la, ce)

The solvothermal reactions of Ti(OEt)(4) with LnCl(3) (Ln=La, Ce) produced new Ti(28) Ln cages, in which the Ln(3+) ions are coordinated within a metallocrown arrangement, which represents the highest nuclearity cages of this type.     

Near-infrared spectroscopy of LiNH3: first observation of the electronic spectrum

Electronic spectra of LiNH(3) and its partially and fully deuterated analogues are reported for the first time. The spectra have been recorded in the near-infrared and are consistent with two electronic transitions in close proximity, the ?(2)E-X(2)A(1) and B(2)A(1)-X(2)A(1) systems. Vibrational structure is seen in both systems, with the Li-N-H bending vibration (ν(6)) dominant in the ?(2)E-X(2)A(1) system and the Li-N stretch (ν(3)) in the B(2)A(1)-X(2)A(1) system. The prominence of the 6(0)(1) band in the ?(2)E-X(2)A(1) spectrum is attributed to Herzberg-Teller coupling. The proximity of the B(2)A(1) state, which lies a little more than 200 cm(-1) above the ?(2)E state, is likely to be the primary contributor to this strong vibronic coupling.     

Synthesis of Sialyl Lewis X Analogues

Abstract

Sialyl Lewis X (SLe^x) analogs 2a and 2b were synthesised, where the N-acetyl-D-glucose and the D-galactose units of SLe^x 1 were replaced with an alkyl and a heteroalkyl spacer. Sulphate ester 6i was also synthesised from alcohol 6b and chlorosulphonic acid. A novel promoter, silver mercaptoethanesulphonate, was used to synthesise α-sialosides 2c. 7b and 7c.