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The crystal structure of the Cu(I) mixed ligand salt, [Cu(MeCN)2(PPh3)2](CF3SO3), 1, was determined using single crystal X-ray diffraction, a = 23.249(2), b = 26.665(1), c = 19.4201(9) A β = 102.614(1) A, in the P21/c space group. The packing of this complex is quite similar to the PF6 −, BF4 −, and ClO4 − analogs but contains three crystallographically unique [Cu(MeCN)2(PPh3)2](CF3SO3) complexes per asymmetric unit (instead of one). Upon dissolution and recrystallization of this salt in either toluene or tetrahydrofuran, anion (and solvent) coordination results in the formation of two new neutral species Cu(PPh3)2(CF3SO3)(MeCN) 2 and Cu(PPh3)2(CF3SO3)(THF) 3, respectively. Both 2 and 3 crystallize in the orthorhombic Pca21 space group with a = 22.533(1), b = 9.0688(5), c = 18.4689(9) A, and a = 22.434(1), b = 8.9789(5), c = 18.418(1) A, respectively. With the perchlorate anion, [Cu2(ClO4)(MeCN)(PPh3)4(THF)](ClO4) 4, is isolated, which crystallizes in the monoclinic space group C2/c with a = 27.308(1), b = 28.064(1), c = 21.448(1) A, and β = 120.342(1)°. Surprisingly, it is comprised of an analogous solvent coordinated neutral molecule, Cu(PPh3)2(THF)0.8(MeCN)0.2(ClO4) together with an anion-bridged dimeric species, [Cu2(PPh3)4(MeCN)1.6(THF)0.4(ClO4)]+, charge balanced by one additional non-coordinated ClO4 − anion. The coordinated solvent molecules are disordered in both moieties. Compounds 1–3 were further characterized using thermal gravimetric analysis.

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 .

The crystal structures of several [Cu(RCN)4]X salts (R = Me, X = SO3CF3−; R = Ph, X = BF4−, ClO4−, and PF6−) were determined using single crystal X-ray diffraction. All of the compounds contain distorted tetrahedral Cu(I) centers and noncoordinating anions, with the acetonitrile and benzonitrile structures containing three and one unique CuL4+ complex in their respective asymmetric units. One important distortion is observed in the benzonitrile-Cu bonds, which are bent up to 23° away from linearity. The result is a flattened complex that maximizes the π–π tacking of the aromatic rings and is the dominant packing interactions between the complexes.

Reaction of [Cu(MeCN)2(PPh3)2]PF6 with 1,2-bis(4-pyridyl)ethylene (bpe) produces either a layered hexagonal coordination network, [Cu(bpe)1.5(PPh3)]∞ +, if made from CH2Cl2/THF solutions, or a linear zigzag polymer, [Cu(bpe)(PPh3)2]∞ +, if crystallized using CHCl3/THF. Both compounds include significant amounts of solvent as well as the non-coordinating anions within intercrystalline channels. In the former case, the reaction to remove one PPh3 from the Cu(I) reagent complex competes effectively with the precipitation/crystallization step, whereas in the latter case, crystal growth occurs first.

The syntheses and crystal structures of four novel coordination polymers containing copper(I) and 4,7-phenanthroline (phen) are described. [Cu(phen)(MeCN)]SO3CF3, 1 and [Cu(phen)]SO3CF3·(C6H5NO2)0.75, 2 are prepared from an equimolar ratio of [Cu(MeCN)4]SO3CF3 and phen using acetonitrile (MeCN) and benzonitrile (BzCN), respectively, as solvent. Structures 3, [Cu(phen)2]SO3CF3, and 4, [Cu(phen)2)]SO3CF3·(C6H5NO2)(H2O) are also made from MeCN and BzCN, respectively, but using a tenfold excess of phen. All four compounds exhibit helical polymeric structures containing Cu(I) centers bridged by 4,7-phenanthroline ligands with a coordinated triflate counteranion completing the copper coordination sphere. In addition, 1 contains one terminal MeCN ligand, while 3 and 4 contain one terminal phenanthroline ligand in their copper(I) environments. Packing diagrams reveal π–π stacking between 4,7-phenanthrolines to be the primary intrachain interactions present. There is inclusion of noncoordinated nitrobenzene in both 2 and 4, and in each case the solvent molecules have very different influences on the chain stacking motifs.

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.

In this paper we demonstrate that photoluminescence (PL) from GaAs exposed to (3-mercaptopropyl)trimethoxysilane (MPT) exhibits a 10-fold enhancement over that of an oxidized sample. The PL enhancement is attributed to the formation of sulfur−surface bonds. We demonstrate that the MPT surface film that results from the treatment described herein is a monolayer thick by ellipsometry, and we examine the composition of the GaAs/MPT interfacial region using X-ray photoelectron spectroscopy (XPS). The XPS results indicate that the native oxide is removed by the etching procedure, and reoxidation of the surface is minimal during the subsequent deposition of MPT. The nature of the sulfur−surface bond is discussed in view of the XPS results reported here and those of previous measurements by other researchers. The self-assembled monolayers of MPT that forms on the GaAs surface leave a trimethoxy-silyl terminated surface that can be polymerized by exposure to weak acid. We demonstrate that the polymerized overlaye...

Monolayer and multilayer thin films consisting of anionic α-zirconium phosphate (α-ZrP) sheets and polycations (poly(allylamine hydrochloride) (PAH), cytochrome c) were characterized by transmission electron microscopy (TEM), ellipsometry, UV−visible absorbance spectroscopy, reflectance FT-IR, XPS, and X-ray diffraction. Titration and powder X-ray diffraction experiments confirm that exfoliation of α-ZrP begins to occur when enough tetra(n-butylammonium) hydroxide (TBA+OH-) has been added to exceed single-layer packing of TBA+ ions (x ≈ 0.50) in the intercalation compound Zr(HPO4)2-x(TBA+PO4-)x·nH2O. The identical contrast of many sheets in TEM micrographs suggests that the suspension is unilamellar. Alternately dipping cationic substrates into α-ZrP-containing suspensions and aqueous PAH gives a multilayer film that resembles the corresponding bulk intercalation compound. X-ray photoelectron spectra of multilayer films show that they are Zr-rich, relative to α-ZrP, consistent with some corrosion during t...

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...

Coordination chemistry represents an attractive means for forming well-ordered surface multilayer films and crystalline three-dimensional networks. The preferred bonding geometries of metals and ligands dictate the structures of these layered and framework solids. Ligand substitution rates of metal ions vary over some 15 orders of magnitude, and this property can be used to make bond formation irreversible (in layered films) or reversible (in framework solids, allowing ‘annealing’ of the lattice). The lamellar Hofmann clathrates, M(BL)M'(CN)4, where M and M' are divalent metal ions (Ru2+ and Ni2+, respectively) and BL is a bridging ligand, such as 4,4′-bipyridine, can be grown layer-by-layer oh surfaces using a three-step adsorption sequence. Bulk solids that resemble ‘expanded’ perovskite can be grown from octahedrally coordinated ions such as Cd2+ and a bridging phenylenediamine ligand. Preliminary structural data on solids prepared from tetrahedral Cu+ cations in combination with bent bridging ligands, intended to mimic the coordination of oxygen in silicate structures, are also described.

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.

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.

Solid-state compounds have historically been prepared through high-temperature solid-solid reactions. New mechanistic understanding of these reactions suggests possible routes to metastable compositions and structures as well as to thermodynamically stable, low-temperature phases that decompose at higher temperatures. Intermediate-temperature synthetic techniques, including flux and hydrothermal methods, as well as low-temperature intercalation and coordination reactions, have recently been developed and have been used to prepare unprecedented materials with interesting electronic, optical, and catalytic properties. The trend in modern solid-state synthesis resembles increasingly the approach used in small-molecule chemistry, in the sense that attention to reaction mechanism and the use of molecular building blocks result in an ability to prepare new materials of designed structure.

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(PPh(3))(2)(MeCN)(2)]PF(6) and trans-1,2-bis(4-pyridyl)ethylene (bpe) results in the trans-cis isomerization of the bpe and subsequent formation of a mixed-isomer linear coordination polymer over the course of several days or weeks depending on solvent. The one unique copper atom in the structure is coordinated to two bridging cis-bpe ligands, one bridging trans-bpe ligand, and one terminal triphenylphoshine ligand to create [Cu(trans-bpe)(0.5)(cis-bpe)(PPh(3))](+)( infinity ) zigzag chains. The reaction requires both visible light and Cu(I), and the crystallization of this particular coordination polymer is insensitive to the ratio of trans:cis isomers in solution, occurring both from trans-rich and cis-rich solutions.

The spherical phosphotungstate ion, PW12O403−, has been used as a non-coordinating anionic template for the construction of a novel, three-dimensional Cu(I) coordination polymer.

Solid-state compounds have historically been prepared through high-temperature solid-solid reactions. New mechanistic understanding of these reactions suggests possible routes to metastable compositions and structures as well as to thermodynamically stable, low-temperature phases that decompose at higher temperatures. Intermediate-temperature synthetic techniques, including flux and hydrothermal methods, as well as low-temperature intercalation and coordination reactions, have recently been developed and have been used to prepare unprecedented materials with interesting electronic, optical, and catalytic properties. The trend in modern solid-state synthesis resembles increasingly the approach used in small-molecule chemistry, in the sense that attention to reaction mechanism and the use of molecular building blocks result in an ability to prepare new materials of designed structure.

The intercalation/exfoliation reactions of MoS2 and SnS2 yield lamellar colloids, which may be grown layer-by-layer on cationic surfaces by alternate adsorption of cationic clusters or polymers.

An interactive classroom activity is described that allows visualization of microscopic reaction mechanisms via the macroscopic process of unwrapping and eating chocolate candies.

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.

Experiments and demonstrations to expose undergraduate students to electronic properties of solids.

An oxygen isotope shift is observed in superconducting ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ when $^{18}\mathrm{O}$ is substituted partially for $^{16}\mathrm{O}$; the superconducting transition temperature ${T}_{c}$ is lowered by 0.3 to 1.0 K in different samples. We examine these results using conventioanl phonon-mediated BCS theory and conclude that, for ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$, phonons play an important role in the pairing mechanism.

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.

A small decrease in T/sub c/ of 0.3 K to 0.5 K is observed when as much as 90% of the /sup 16/O in YBa/sub 2/Cu/sub 3/O/sub 7/ is substituted with /sup 18/O. This result is consistent with our observation that there is an oxygen isotope effect in La/sub 1.85/Sr/sub 0.15/CuO/sub 4/, but in contrast with previous reports that there is no isotope effect for YBa/sub 2/Cu/sub 3/O/sub 7/. This new result suggests that phonons play an important role in the electron-pairing mechanism in YBa/sub 2/Cu/sub 3/O/sub 7/.

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.

For the past 15 years, advances in superconductivity have come about only slowly and even a 0.5 K increase in transition temperature was noteworthy. Until April 1986, the highest transition temperatures were near 23 K. At that time, Bednorz and Mueller reported superconductivity in La-Ba-Cu-O compounds above 30 K. The authors report here the composition and properties of a superconducting phase containing Y, Ba, Cu, and O which is copper-rich compared with Y/sub 1.2/Ba/sub 0.8/CuO/sub 4/. This phase show 10-20% Meissner effect, with T/sub 0/ = 90 K. Further the most exciting aspect of this phase is that it is near a low melting (below 1200 /sup 0/C) eutectic; if the phase metals congruently it will be possible to fashion wires.

An isotope effect has been searched for in the high-T/sub c/ superconductor YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ through substitution of /sup 18/O for /sup 16/O. No shift in the superconducting transition temperature T/sub c/ is observed by electrical resistivity or magnetic susceptibility measurements. We discuss the implications of this result for mechanisms of superconductivity in the high-T/sub c/ oxides.

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.