Nazario Lopez

Lanthanide–3d cyanometalate chains Ln(III)–M(III) (Ln = Pr, Nd, Sm, Eu, Gd, Tb; M = Fe) with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz): evidence of ferromagnetic interactions for the Sm(III)–M(III) compounds (M = Fe, Cr)

A series of cyanide-bridged chain mixed Fe(III)/Ln(III) (Ln=Pr, Nd, Sm, Eu, Gd, Tb) complexes with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) used as a capping group has been prepared. Reactions of tptz and LnCl3 with K3Fe(CN)6 yield a family of air-stable 1-D compounds {[Pr(tptz)(H2O)4Fe(CN)6].8H2O}infinity, {[Nd(tptz)(H2O)4Fe(CN)6].8H2O}infinity, {[Sm(tptz)(H2O)4Fe(CN)6].8H2O}, {[Eu(tptz)(H2O)4Fe(CN)6].6H2O}infinity, {[Gd(tptz)(H2O)4Fe(CN)6].6H2O}infinity, and {[Tb(tptz)(H2O)4Fe(CN)6].8H2O}infinity. Temperature dependent magnetic susceptibility studies of reveal that in , the Sm(III) and Fe(III) ions are ferromagnetically coupled with 3-D ordering occurring below 3.5 K. The appearance of the frequency dependent out-of-phase signal is explained in terms of an ordering with a spin glass-like behavior. To compare the magnetic behavior of with related compounds, {[Sm(tptz)(H2O)4Co(CN)6].8H2O}infinity and {[La(tptz)(DMF)(H2O)3Fe(CN)6].5H2O}infinity, {[Sm(tmphen)(DMF)3(H2O)Fe(CN)6].2H2O}infinity, {[Sm(tmphen)2(H2O)2Fe(CN)6].MeOH.13H2O}infinity and {[Sm(tmphen)2(H2O)2Cr(CN)6].MeOH.9H2O}infinity with 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) were also prepared.

Reversible Reduction of Oxygen to Peroxide Facilitated by Molecular Recognition

Boxing in Peroxide Hydrogen peroxide (H2O2) is a powerful oxidant, and its reactivity is exploited in numerous biological, as well as synthetic, contexts. Lopez et al. (p. 450) have now managed to capture its dianion (O22-) in a cryptand—essentially a molecular box assembled from benzamide derivatives—keeping the dianion stable in organic solution for days through a net of well-placed internal hydrogen-bond donors. The encapsulated dianion exhibited clean oxidative reactivity back to O2 either by chemical or by electrochemical means. The highly reactive peroxide dianion (O22–) can be captured and stabilized by hydrogen bonding in a molecular box. Generation of soluble sources of peroxide dianion (O22–) is a challenge in dioxygen chemistry. The oxidizing nature of this anion renders its stabilization in organic media difficult. This Report describes the chemically reversible reduction of oxygen (O2) to cryptand-encapsulated O22–. The dianion is stabilized by strong hydrogen bonds to N-H groups from the hexacarboxamide cryptand. Analogous stabilization of peroxide by hydrogen bonding has been invoked recently in crystalline saccharide and protein systems. The present peroxide adducts are stable at room temperature in dimethyl sulfoxide (DMSO) and N,N′-dimethylformamide (DMF). These adducts can be obtained in gram quantities from the cryptand-driven disproportionation reaction of potassium superoxide (KO2) at room temperature.

Unprecedented Binary Semiconductors Based on TCNQ: Single‐Crystal X‐ray Studies and Physical Properties of Cu(TCNQX2) X=Cl, Br

2010 WILEY-VCH Verlag Gm Much current research in science is being directed at the synthesis and fabrication of nanoscale materials for new types of electronic and magnetic devices. Pressure to reduce the size and improve the response times of electronic components has always existed in information technology, but as we approach the miniaturization limits of traditional charge storage estimated to occur by 2016, the global quest for faster andmore efficient data storage and processing is heightening. One strategy that is being explored for the development of new device components is the pursuit of materials whose bistability is based on a resistance change rather than current flow. Such ‘‘nonvolatile’’ memory devices are capable of operating at increased speeds with reduced energy expenditure. Gigantic nonlinear responses (or switching phenomena) of materials have been observed in molecule-based organiccontaining materials in response to short pulses of low-power external stimuli. In this vein, materials are being vigorously pursued that respond to the application of an electric field, light, pressure, or temperature as the basis for electronic devices with ultrafast operating speeds. In terms of electric-field-induced behavior, one of the most extensively studied examples is Cu(TCNQ) where TCNQ is 7,7,8,8-tetracyanoquinodimethane. One phase of this material exhibits reversible switching from a high resistive state to a conducting state promoted by the application of an electric field or upon irradiation, which makes it an excellent candidate for nonvolatile memory. The promise for commercial applications is sufficiently high such that researchers have fabricated devices with nanowires, nanorods, and nanoribbons of Cu(TCNQ) as well as Ag(TCNQ). Although a vast amount of research has been directed at understanding the Cu(TCNQ) system, analogous materials based on TCNQ derivatives are surprisingly scarce. Given this situation, we recently initiated a broad survey of binary metal-containing TCNQ derivatives in order to probe the steric and electronic influences of the substituent on the structure and properties of these materials. Herein we report large high-quality crystals of two new isostructural semiconductors based on Cu ions. The materials are Cu(TCNQCl2) (1) and Cu(TCNQBr2) (2), where TCNQCl2 is 2,5-dichloro-7,7,8,8-tetracyanoquinodimethane and TCNQBr2 is 2,5-dibromo-7,7,8,8-tetracyanoquinodimethane. The conductivity of compound 1 is the highest in the family of 1:1 Mþ:(TCNQ) salts whereas the conductivity of 2 is comparable to that of Cu(TCNQ) phase I (3). The 3D architecture of the Cu ions coordinated to the m4-TCNQX2 (X1⁄4Cl, Br) ligands is unprecedented among the widely studied Cu(TCNQ) and Ag(TCNQ) compounds and derivatives. The extraordinary properties observed for Cu(TCNQ) have spurred the exploration of numerous strategies to obtain crystalline phases of Cu(TCNQ); these efforts include spontaneous electrolysis, reduction of TCNQ with CuI, vapor deposition of TCNQ on Cu, photocrystallization, electrocrystallization, physical chemical vapor combined deposition and vacuum co-deposition. The only known instance wherein crystals sufficiently large for single-crystal data collection were obtained is the work from our laboratories a number of years ago in which we reported marginal structures obtained from very tiny crystals of Cu(TCNQ). In this study, we discovered the previously unrecognized existence of polymorphism in Cu(TCNQ). The materials, which we dubbed phase I and phase II, exhibit marked differences involving not only the arrangements of TCNQ ligands, but also the infrared spectral, conducting, andmagnetic properties. It was noted in this study that Cu(TCNQ) phase I and the only other previously analogue that had been structurally characterized, namely Ag(TCNQ), adopt a common structure, referred to hereafter as type A. The structure involves metal ions in a highly distorted tetrahedral environment with m4-TCNQ ligands arranged in segregated stacks of TCNQ along the short axis; the adjacent stacks of TCNQ are rotated by 908 with respect to each other (Fig. 1c). Cu(TCNQ) phase II, defined as structure type B, differs from phase I in that the TCNQ ligands are parallel to each other throughout the extended framework and do not form close contacts that signify p-stacking of the TCNQ ligands. Crystals of 1 and 2 were obtained by slow diffusion of acetonitrile solutions of CuI and the respective TCNQX2 derivative (X1⁄4Cl (1), Br (2)), in a manner akin to the method used to prepare Cu(TCNQ) phase I. The X-ray crystal structures of 1 and 2 at 110K revealed that they also crystallize as 3D frameworks with Cu ions coordinated to four different [TCNQX2] anions (Fig. 1a). The Cu ions are in a highly distorted tetrahedral environment as evidenced by the N Cu N angles of 1: 94.738, 101.778, 130.898, and 139.688; and of 2: 93.218,

Anion-Receptor Mediated Oxidation of Carbon Monoxide to Carbonate by Peroxide Dianion

The reactivity of peroxide dianion O2(2-) has been scarcely explored in organic media due to the lack of soluble sources of this reduced oxygen species. We now report the finding that the encapsulated peroxide cryptate, [O2⊂mBDCA-5t-H6](2-) (1), reacts with carbon monoxide in organic solvents at 40 °C to cleanly form an encapsulated carbonate. Characterization of the resulting hexacarboxamide carbonate cryptate by single crystal X-ray diffraction reveals that carbonate dianion forms nine complementary hydrogen bonds with the hexacarboxamide cryptand, [CO3⊂mBDCA-5t-H6](2-) (2), a conclusion that is supported by spectroscopic data. Labeling studies and (17)O solid-state NMR data confirm that two-thirds of the oxygen atoms in the encapsulated carbonate derive from peroxide dianion, while the carbon is derived from CO. Further evidence for the formation of a carbonate cryptate was obtained by three methods of independent synthesis: treatment of (i) free cryptand with K2CO3; (ii) monodeprotonated cryptand with PPN[HCO3]; and (iii) free cryptand with TBA[OH] and atmospheric CO2. This work demonstrates CO oxidation mediated by a hydrogen-bonding anion receptor, constituting an alternative to transition-metal catalysis.

Ultrafast Photoinduced Electron Transfer from Peroxide Dianion

The encapsulation of peroxide dianion by hexacarboxamide cryptand provides a platform for the study of electron transfer of isolated peroxide anion. Photoinitiated electron transfer (ET) between freely diffusing Ru(bpy)3(2+) and the peroxide dianion occurs with a rate constant of 2.0 × 10(10) M(-1) s(-1). A competing electron transfer quenching pathway is observed within an ion pair. Picosecond transient spectroscopy furnishes a rate constant of 1.1 × 10(10) s(-1) for this first-order process. A driving force dependence for the ET rate within the ion pair using a series of Ru(bpy)3(2+) derivatives allows for the electronic coupling and reorganization energies to be assessed. The ET reaction is nonadiabatic and dominated by a large inner-sphere reorganization energy, in accordance with that expected for the change in bond distance accompanying the conversion of peroxide dianion to superoxide anion.

Electron-Transfer Studies of a Peroxide Dianion

A peroxide dianion (O2(2-)) can be isolated within the cavity of hexacarboxamide cryptand, [(O2)⊂mBDCA-5t-H6](2-), stabilized by hydrogen bonding but otherwise free of proton or metal-ion association. This feature has allowed the electron-transfer (ET) kinetics of isolated peroxide to be examined chemically and electrochemically. The ET of [(O2)⊂mBDCA-5t-H6](2-) with a series of seven quinones, with reduction potentials spanning 1 V, has been examined by stopped-flow spectroscopy. The kinetics of the homogeneous ET reaction has been correlated to heterogeneous ET kinetics as measured electrochemically to provide a unified description of ET between the Butler-Volmer and Marcus models. The chemical and electrochemical oxidation kinetics together indicate that the oxidative ET of O2(2-) occurs by an outer-sphere mechanism that exhibits significant nonadiabatic character, suggesting that the highest occupied molecular orbital of O2(2-) within the cryptand is sterically shielded from the oxidizing species. An understanding of the ET chemistry of a free peroxide dianion will be useful in studies of metal-air batteries and the use of [(O2)⊂mBDCA-5t-H6](2-) as a chemical reagent.