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Two new coordination polymers containing Cu(I) and 4,7-phenanthroline (phen) have been synthesized and structurally characterized. 1a , [Cu 3 (phen) 4 (PPh 3 )](BF 4 ) 3 · 2(THF), crystallizes in the triclinic space group P 1 with a =11.5407(6) A, b =14.5687(7) A, c =23.579(1) A, α =74.203(1)°, β =80.530(1)°, γ =83.998(1)°, and Z =2. 1b (isostructural with 1a ), [Cu 3 (phen) 4 (PPh 3 )](BF 4 ) 3 · Et 2 O, also crystallizes in the triclinic, space group P 1 , with a =11.4920(6) A, b =14.5074(8) A, c =23.749(1) A, α =73.599(1)°, β =79.871(1)°, γ =83.814(1)°, and Z =2. 2 , [Cu 5 (phen) 7 ](BF 4 ) 3 · 4(NO 2 Ph), crystallizes in the triclinic space group P 1 , with a =11.7867(9) A, b =14.5076(1) A, c =15.946(1) A, α =100.076(1)°, β =106.637(1)°, γ =95.612(1)°, and Z =1. Three unique copper atoms reside in the asymmetric units of all three compounds; each display trigonal Y-shaped coordination environments. For 1 , (Cu 3 phen 3 ) +3 bowl shaped triangles are linked through a phen bridge into one-dimensional chains. In 2 , two Cu(I) cations have similar coordination environments containing three bridging phen ligands, but the third Cu(I) cation is coordinated by two fully occupied phen ligands, as well as a one-half occupied phen ligand, or a one half-occupied BF 4 − anion which sit roughly on the same general position. The Cu(I) centers are linked through the phen ligands to form a ladder-like structure composed of two disordered chains (similar to those seen in 1 ) fused together. Extensive π–π stacking interactions are observed in both 1 and 2 .

Three new linear coordination polymers containing Cu(I) and 4,7-phenanthroline (phen) have been synthesized and structurally characterized by single-crystal X-ray diffraction. [Cu(phen)(MeCN)(2)]PF(6) (3) and [Cu(phen)(MeCN)]BF(4) (4) are prepared from acetonitrile, and [Cu(phen)(BzCN)]BF(4) (5) is made from benzonitrile (MeCN = acetonitrile; BzCN = benzonitrile). All of the compounds have linear polymeric structures containing Cu(I) centers coordinated by two bridging 4,7-phenanthroline ligands, with additional coordinated solvent molecules completing the copper coordination sphere. In 3 and 4, when acetonitrile is used, two and one MeCN solvent molecules coordinate to each Cu atom, resulting in a distorted tetrahedral and distorted trigonal geometry, respectively. The major interchain interactions are phenanthroline pi-pi stacks. When benzonitrile is used in 5, the chain-packing motif changes to allow the coordinated benzonitrile ligands to participate in the interchain pi-pi stacking. Crystal data: for [Cu(phen)(MeCN)(2)]PF(6) (3), monoclinic, space group P2(1)/c (No. 14), with a = 11.4303(6) Å, b = 11.4954(6) Å, c = 14.0444(7) Å, beta = 99.948(1) degrees, and Z = 4; for [Cu(phen)(MeCN)]BF(4) (4), monoclinic, space group P2(1)/c (No. 14), with a = 8.7677(5) Å, b = 11.5140(7) Å, c = 14.8858(9) Å, beta = 96.548(1) degrees, and Z = 4; for [Cu(phen)(BzCN)](2)2BF(4) (5), triclinic, space group Ponemacr; (No. 2), with a = 11.338(1) Å, b = 12.461(1) Å, c = 13.904(1) Å, alpha = 115.909(2) degrees, beta = 100.870(2) degrees, gamma = 92.052(2) degrees, and Z = 2.

A new tetrameric copper species is formed from the reaction of 3-aminopyridine and [Cu(MeCN)4]BF4. Four molecules per unit cell crystallize in the monoclinic space group P21/c, having a = 13.2552(7) A, b = 17.8202(9) A, c = 28.527(2) A, β = 91.105(1), and a volume of 6737.1 A [3], giving a calculated density of 1.482 g/mol. 22315 reflections were observed and the structure was refined to a final R 1 = 0.063 [I > 2σ(I)]. The distorted cubic core is composed of four copper(II) cations and four μ3-OH− ions. Two pyridine nitrogen atoms from the 3-aminopyridine ligands complete the Jahn-Teller distorted square-pyramidal coordination sphere around each copper. Longer, sixth bonds on two of the copper centers are made to a bridging MeCN. Three of the BF− 4 anions participate in intramolecular O[sbnd]H … F hydrogen bonding with the bridging hydroxide ions and N[sbnd]H … F with the free amino groups, while the remaining (disordered) BF4 forms intermolecular hydrogen bonds between tetramers.

The crystal structure of [Cu(pyrimidine)4]2BF4 was determined using single crystal X-ray diffraction. The compound crystallizes in the monoclinic space groupP21/n, with lattice parametersa=9.9736(8),b=13.872(1),c=16.568(1) A. β=98.002(1), andZ=8, yielding a calculated density of 1.857 g/cm3. The Jahn-Teller distorted copper coordination sphere is composed of the four pyrimidine ligands in the equatorial positions (ave. Cu−N=2.02 A) and the longer axial bonds from the copper to one fluorine (ave Cu−F=2.39 A) on each of the BF 4 − anions. The crystal structure features layers of molecules having interleaved pyrimidine rings: the layers are connected through intermolecular H … F hydrogen bonds.

Two integrated systems for light-induced vectorial electron transfer are described. Both utilize photosensitized semiconductor particles grown in linear channel zeolites as components of the electron transfer chain. One system consists of internally platinized zeolites L and mordenite containing TiO2 particles and methylviologen ions, with a size-excluded photosensitizer, tris(2,2‘-bipyridyl-4,4‘-dicarboxylate)ruthenium (RuL32+), adsorbed on the external surface of the zeolite/TiO2 composite. In the other system, Nb2O5 replaces TiO2. The kinetics of photochemical electron transfer reactions and charge separation were studied by diffuse reflectance flash photolysis. Despite very efficient initial charge separation, the TiO2 system does not generate hydrogen photochemically in the presence of an electrochemically reversible, anionic electron donor, methoxyaniline N,N‘-bis(ethyl sulfonate). Only the Nb2O5-containing composites evolved hydrogen photochemically under these conditions. These results are interpr...

The superconducting, orthorhombic form of RBa[sub 2]Cu[sub 3]O[sub 7[minus][partial derivative]] for R = Nd, Sm, Eu, and Gd has been synthesized by direct precipitation from molten NaOH and KOH at 450[degrees]C. In contrast to materials prepared by standard ceramic methods, the products obtained are relatively large, plates with rectangular rather than square faces and are free of the a-b twin boundaries associated with the uptake of oxygen at the orthorhombic-to-tetragonal phase transformation. It is notable that these materials do not contain alkali metals. 19 refs., 4 figs.

Energy Dispersive X-ray Spectroscopy (EDS) was used to show that the elemental homogeneity of YBa2Cu3O7 powders can be improved substantially by heating the powder in a nitrogen dioxide-containing atmosphere (e.g., 950°C), followed by annealing in oxygen at 950°C, and slow-cooling to room temperature. The improved homogeneity results in a substantially larger flux exclusion signal for the NO2-treated powder, as measured by both ac and dc techniques. The experimental results suggest a mechanism which involves the formation of a small amount of molten Ba(NO3)2, which acts as a flux that dissolves the constituents and reprecipitates them as high purity YBa2Cu3O7.

Linking tetrahedral Cu(I) centers with bent, bridging, nonchelating 3,3‘-bipyridine ligands results in the formation of a three-dimensional extended structure. Interestingly, there is sufficient void space within this coordination framework to allow the interpenetration of a second, identical network, as indicated by the diagram (copper atoms are spheres, and the bent cylinders represent bipyridine ligands). The only interactions between the dark and light “adamantane-like” cages are aromatic stacking contacts between twisted bipyridine rings on different networks.

Reaction of [Cu(MeCN)4]BF4 with 1,3-dithiane results in the formation of four novel coordination networks depending on metal-to- ligand ratio and solvent conditions used. 1 and 2, both [Cu(1,3-dithiane)(MeCN)2]+∞, and 3, [Cu(1,3-dithiane)2(MeCN)]+∞, are one-dimensional chains, but due to the different bonding modes of the dithiane sulfur atoms all three networks are unique. In 4, [Cu(1,3-dithiane)(MeCN)]+∞, one–dimensional ribbons are formed where each dithiane is bonding to three copper(I) centers, and one of the S-atoms on each ligand acts as a μ2 4-electron donor.

The possibility of site-selective substitution of 18O into YBa2Cu3O7 was explored. Samples containing various quantities of 18O were prepared by processing in 18O2 both at 950 °C and at 400 °C. The samples were characterized by secondary ion mass spectroscopy (SIMS), temperature programmed desorption (TPD) and reduction (TPR), Raman spectroscopy, and magnetization measurements. Measurements of the shifts in the Raman active modes with 18O substitution and of the ratios of 18O to 16O by TPD, TPR, and SIMS show that even for temperatures as low as 400 °C and times as short as 2 h. 18O is not substituted exclusively into the chain site (O1) in YBa2Cu3O7. In addition, there is no consistent variation in the shifts in Tc with the degree of substitution; therefore, the isotope effect for a sample with 100% 18O cannot be predicted by a linear extrapolation of data obtained for samples with partial 18O substitution. The mechanism of oxygen substitution, the difficulties of measuring the true magnitude of the oxygen isotope shift, and the meaning of the small isotope shift are discussed.

An interesting property of the new YBa 2 Cu 3 O 7 superconductor is that oxygen can be removed from this material at temperatures as low as 400°C. In this paper, temperature programmed desorption (TPD) is used to study the removal of oxygen as well as other impurities. During heating in flowing helium, 0.25 moles of O 2 per mole of YBa 2 Cu 3 O 7 desorb in a peak centered near 815 K. This peak is associated with the reduction of the sample to YBa 2 Cu 3 O 6.5 ; the reduced material does not superconduct. In addition, YBa 2 Cu 3 O 7 incorporates a considerable amount of H 2 O, CO 2 , and CO during exposure to air.

The effect of oxygen isotope substitution on the superconducting transition temperature, T(c), has been measured for BaBi(0.25)Pb(0.75)O(3) (T(c), approximately 11 K) and Lal(1.85) Ca(0.15)CuO(4) (T(c) approximately 20 K), and is compared to the shifts observed for La(1.85)Sr(0.15)CuO(4) (T(c) approximately 37 K) and YBa(2)Cu(3)O(7) (T(c) approximately 92 K). For all four materials, the transition temperature is shifted to lower temperature upon substitution of oxygen-18 for oxygen-16. The observed shifts demonstrate that phonons are involved in the electron-pairing mechanism in these oxide superconductors.