Versatility of azide in serendipitous assembly of Copper(II) Magnetic Polyclusters

Engineering at the molecular level is one of the most exciting new developments for the generation of functional materials. However, the concept of designing polynuclear extended structures from bottom up is still not mature. Although progress has been made with secondary building units (SBUs) in metal organic frameworks (MOFs), the control seems to be just an illusion when it comes to bridging ligands such as the azide ion. When we say that the azido ligand is versatile in its bridging capabilities, what we mean is that it would be difficult to predict or control its bridging properties. However, this kind of serendipity is not always bad news. For example, scientists have shown that the azido ligand can mediate magnetic exchanges between paramagnetic metals in a predictable fashion (usually depending upon the bonding geometries). Therefore, it is a well-respected ligand in polynuclear assemblies. Serendipitous assemblies offer new magnetic structures that we may not otherwise even think about synthesizing. The azido ligand forms a variety of complexes with copper(II) using different blocking amines or pyridine based ligands. Its structural nature changes upon changing the substitution on amine, as well as the amount of blocking ligand. In principle, if we take any of these complexes and provide more coordination sites to the bridging azido ligands by removing a fraction of the blocking ligands, we can get new complexes with intricate structural networks and therefore different magnetic properties with the same components as used for the parent complex. In this Account, we mainly discuss the development of a number of new topological and magnetic exchange systems synthesized using this concept. Not all of these new complexes can be grouped according to their basic building structures or even by the ratio of the metal to blocking ligand. Therefore, we divided the discussion by the nuclearity of the basic building structures. Some of the complexes with the same nuclearities have very similar or even almost identical basic structures. However, the way these building units are joined together (by the azido bridges) to form the overall extended structures differ almost in every case. The complexes having the Cu-6 core are particularly interesting from a structural point of view. Although they have almost identical basic structures, some of them are extended in three dimensions, but two of them are extended in two dimensions by two different bridging networks. In the complexes having linear Cu-4 basic units, we find that using similar ligands does not always give the same bridging networks even within the basic building structures. These complexes have also enriched the field of molecular magnetism. One of the complexes with a Cu-3 building unit has provided us with the opportunity to study the competing behavior of two different kinds of magnetic exchange mechanism (ferromagnetic and antiferromagnetic) acting simultaneously between two metal ions. Through density functional theory calculations, we showed how they work independently and their additive nature to produce the overall effect. The exciting methodology for the generation of copper(II) polyclusters presented in this Account will provide the opportunity to explore analogous serendipitous assembly of diverse structures with interesting magnetic behavior using other transition metal ions having more than one unpaired electrons.

The effect of multisubstitution on the thermoelectric properties of chalcogenide-based Cu2.1Zn0.9Sn1-xInxSe4 (0 <= x <= 0.1)

Quinary chalcogenide compounds Cu2.1Zn0.9Sn1-xInxSe4 (0 <= x <= 0.1) were prepared by melting (1170K) followed by annealing (773 K) for 172 h. Powder X-ray diffraction (XRD) data accompanied by electron probe microanalysis (EPMA) and Raman spectra of all the samples confirmed the formation of a tetragonal kesterite structure with Cu2FeSnS4-type. The thermoelectric properties of all the samples were measured as a function of temperature in the range of 300-780K. The electrical resistivity of all the samples exhibits metallic-like behavior. The positive values of the Seebeck coefficient and the Hall coefficient reveal that holes are the majority charge carriers. The codoping of copper and indium leads to a significant increase of the electrical resistivity and the Seebeck coefficient as a function of temperature above 650 K. The thermal conductivity of all the samples decreases with increasing temperature. Lattice thermal conductivity is not significantly modified as the doping content may infer negligible mass fluctuation scattering for copper/zinc and indium/tin substitution. Even though, the power factors (S-2/rho) of indium-doped samples Cu2.1Zn0.9Sn1-xInxSe4 (x = 0.05, 0.075) are almost the same, the maximum zT = 0.45 at 773K was obtained for Cu2.1Zn0.9Sn0.925In0.075Se4 due to its smaller value of thermal conductivity. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Transfer free suspended graphene devices on silicon using electrodeposited copper

Transfer free processes using Cu films greatly simplify the fabrication of reliable suspended graphene devices. In this paper, the authors report on the use of electrodeposited Cu films on Si for transfer free fabrication of suspended graphene devices. The quality of graphene layers on optimized electrodeposited Cu and Cu foil are found to be the same. By selectively etching the underlying Cu, the authors have realized by a transfer free process metal contacted, suspended graphene beams up to 50 mu m in length directly on Si. The suspended graphene beams do not show any increase in defect levels over the as grown state indicating the efficiency of the transfer free process. Measured room temperature electronic mobilities of up to 5200 cm(2)/V.s show that this simpler and CMOS compatible route has the potential to replace the foil based route for such suspended nano and micro electromechanical device arrays. (C) 2014 American Vacuum Society.

mu-Oxamido binuclear copper (II) complexes: Synthesis, crystal structure, DNA interaction and antibacterial studies

Four binuclear copper (II) complexes Cu(oxpn)Cu(B)](2+) (2-5) bridged by N, N'-bis3-(methylamino) propyl] oxamide (oxpn), where, B is N, N-donor heterocyclic bases (viz. 2,2'-bipyridine (bpy, 2), 1,10-phenathroline (phen, 3), dipyrido3,2-d:2',3'-f]quinoxaline (dpq, 4) and dipyrido3,2-a:2',3'-c]phenazine (dppz, 5) are synthesized, characterized by different spectroscopic and single crystal X-ray data technique. The phen (3) and dpq (4) complexes were structurally characterized by X-ray data analysis. Their DNA binding, oxidative cleavage and antibactirial activities were studied. The dpq (4) and dppz (5) complexes are avid binders to the Calf thymus DNA (CT-DNA). The phen (3), dpq (4) and dppz (5) complexes show efficient oxidative cleavage of supercoiled DNA (SC DNA) through hydroxyl radical ((OH)-O-center dot) pathway in the presence of Mercaptopropionic acid (MPA). (C) 2013 Elsevier Ltd. All rights reserved.

Tripodal Bile Acid Architectures Based on a Triarylphosphine Oxide Core Obtained by Copper-Catalysed 1,3]-Dipolar Cycloaddition: Synthesis and Preliminary Aggregation Studies

We report the synthesis and aggregation behaviour of new water-soluble, bile acid derived tripodal architectures based on a core derived from triphenylphosphine oxide. We employed the well-established copper-catalysed 1,3]-dipolar cycloaddition (CuAAC) for the construction of these tripodal molecules. The aggregation behaviour of these molecules in aqueous media was studied by different analytical methods such as dye solubilisation, dynamic light scattering, NMR and AFM. These molecular architectures also offer an additional advantage in aiding understanding of the influence of the nature of the bile acid backbone and of the configuration at the steroid C-3 position in these architectures; to the best of our knowledge this has not been reported in the literature. The unique gelation properties of the -derivatives were explained through molecular modelling studies and the mechanical behaviour of these gels was studied by rheology experiments.

Synthesis, crystal structure, DNA interaction and cleavage activities of mononuclear and trinuclear copper(II) complexes

Mono- and trinuclear copper(II) complexes with 2-1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL) have been synthesized and structurally characterized. The mononuclear complex Cu(L)(H2O)(ONO2)] (1) crystallizes in monoclinic space group P2(1) /n with a square pyramidal Cu(II) center coordinated by the tridentate Schiff base (L) and a water ligand in the equatorial plane and an oxygen atom from nitrate in the axial position. The trinuclear complex (CuL)(3)(mu(3)-OH)](ClO4)(2)center dot H2O (2) crystallizes in hexagonal space group P6(3); all three copper atoms are five-coordinate with square pyramidal geometries. The interactions of these complexes with calf-thymus DNA have been investigated using absorption spectrophotometry. The mononuclear complex binds more strongly than the trinuclear complex. The DNA cleavage activity of these complexes has been studied on double-stranded pBR 322 plasmid DNA by gel electrophoresis experiments in the absence and in the presence of added oxidant (H2O2). The trinuclear complex cleaves DNA more efficiently than the mononuclear complex in the presence of H2O2.

Using an Office Inkjet Printer to Define the Formation of Copper Films on Paper

A low-cost fabrication process for forming conductive copper lines on paper is presented. An office inkjet printer was used to deposit desired patterns of silver nitrate and tannic acid solutions sequentially on paper. Silver nitrate was instantaneously reduced in situ on paper by tannic acid at room temperature to form silver nanoparticles, which acted as catalysts for the subsequent electroless deposition of copper. The copper films were 1.8 mu m thick, and the sheet resistance of the copper film on paper was 9 Omega/square. A dual monopole ultrawide band antenna was fabricated on paper and its performance was equivalent to that of a similar antenna fabricated on a copper-film covered Kapton substrate using conventional lithographic processes. The paper-based conductive copper films fabricated using the facile process presented herein will aid the development of low-cost flexible circuits and sensors.

Copper-Catalyzed Oxidative Transformation of Secondary Alcohols to 1,5-Disubstituted Tetrazoles

A mild and convenient oxidative transformation of secondary alcohols to 1,5-disubstituted tetrazoles is uncovered by employing trimethylsilyl azide (TMSN3) as a nitrogen source in the presence of a catalytic amount of copper(II) perchlorate hexahydrate Cu(ClO4)(2)(.)6H(2)O] (5mol%) and 2,3-dichloro-5,6-dicyano-para-benzoquinone (DDQ) (1.2equiv.) as an oxidant. This reaction is performed under ambient conditions and proceeds through CC bond cleavage.

Conducting polymer-carbon black nanocomposite sensor for volatile organic compounds and correlating sensor response by molecular dynamics

Volatile organic compounds (VOCs) are present in our every day used products such as plastics, cosmetics, air fresheners, paint, etc. The determination of amount of VOC present in atmosphere can be carried out via various sensors. In this work a nanocomposite of a novel thiophene based conducting polymer and carbon black is used as a volatile organic compound sensor. The fabricated 2 lead chemiresistor sensor was tested for vapours of toluene, acetone, cylcohexane, and carbon tetrachloride. The sensor responds to all the vapours, however, exhibit maximum response to toluene vapours. The sensor was evaluated for various concentrations of toluene. The lower limit of detection of the sensor is 15 +/- 10 ppm. The study of the effect of humidity on senor response to toluene showed that the response decreases at higher humidity conditions. The surface morphology of the nanocomposite was characterized by scanning electron microscopy. Diffuse reflectance spectroscopy was used to investigate the absorption of vapours by the nanocomposite film. Contact angle measurements were used to present the effect of water vapour on the toluene response of nanocomposite film. Solubility parameter of the conducting polymer is predicted by molecular dynamics. The sensing behaviour of the conducting polymer is correlated with solubility parameter of the polymer. Dispersion interaction of conducting polymer with toluene is believed to be the reason for the selective response towards toluene. (C) 2014 Elsevier B.V. All rights reserved.

A Probe for the Selective and Parts-per-Billion-Level Detection of Copper(II) and Mercury(II) using a Micellar Medium and Its Utility in Cell Imaging

A novel colorimetric probe 1 based on the picolyl moiety has been designed and synthesized. Probe 1 is composed of a pyrene and a bispicolyl amine (BPA) unit, in which the BPA moiety acts as a binding unit and the binding phenomenon is sensed from the changes in the signaling subunit. The probe detects Cu2+ specifically in water and both Cu2+ and Hg2+ efficiently in neutral Brij-58 micellar media. The probe shows a color change visible to the naked eye upon addition of metal ions. Notably, in a micellar medium, probe 1 can detect both the Cu2+ and Hg2+ ions even at parts-per-billion levels. Furthermore, the probe shows ratiometric detection of both the metal ions making the sensing quantitative. The two metal ions could be discriminated both visibly under a UV lamp and with the use of fluorescence spectroscopy. The probe could be also used in biological cell lines for the detection of both Hg2+ and Cu2+ ions.

Phase Evolution in the AuCu/Sn System by Solid-State Reactive Diffusion

The interfacial reactions between several Au(Cu) alloys and pure Sn were studied experimentally at 200A degrees C. Amounts of Cu in the AuSn4 and AuSn2 phases were as low as 1 at.%. On the basis of these experimental results there is no continuous solid solution between (Au,Cu)Sn and (Cu,Au)(6)Sn-5. The copper content of (Au,Cu)Sn was determined to be approximately 7-8 at.%. Substantial amounts of Au were present in the (Cu,Au)(6)Sn-5 and (Cu,Au)(3)Sn phases. Two ternary compounds were formed, one with stoichiometry varying from (Au40.5Cu39)Sn-20.5 to (Au20.2Cu59.3)Sn-20.5 (ternary ``B''), the other with the composition Au34Cu33Sn33 (ternary ``C''). The measured phase boundary compositions of the product phases are plotted on the available Au-Cu-Sn isotherm and the phase equilibria are discussed. The complexity and average thickness of the diffusion zone decreases with increasing Cu content except for the Au(40 at.%Cu) couple.

Copper-Catalyzed Decarboxylative Sulfonylation of alpha,beta-Unsaturated Carboxylic Acids

Copper-catalyzed, ligand-promoted decarboxylative coupling of readily available a,fi-unsaturated acids with sodium aryl sulfinates is presented. This method provides a new avenue for the synthesis of vinyl sulfones via a decarboxylative radical coupling strategy by employing a catalytic amount of Cu(ClO4)(2)center dot 6H(2)O, TBHP in decane as an oxidant, and 1,10-phenanthroline as a ligand. The salient feature of this method is that it furnishes exclusively the (E)-isomer.

Stepwise Crystallization: Illustrative Examples of the Use of Metalloligands Cu-6(mna)(6)](6-) and (Ag-6(Hmna)(2)(mna)(4)](4-) (H(2)mna=2-Mercapto Nicotinic Acid) in the Formation of Heterometallic Two- and Three-Dimensional Assemblies with brucite, pcu, and sql Topologies

Three new inorganic coordination polymers, {Mn(H2O)(6)]-Mn-2(H2O)(6)](Cu-6(mna)(6)]center dot 6H(2)O}, 1, {Mn-4(OH)(2)(H2O)(10)] (Cu-6(mna)6]center dot 8H(2)O}, 2, and {Mn-2(H2O)(5)]Ag-6(Hmna)(2)(mna)(4)]center dot 20H(2)O}, 3, have been synthesized at room temperature through a sequential crystallization route. In addition, we have also prepared and characterized the molecular precursor Cu-6(Hmna)(6)]. Compounds 1 and 3 have a two-dimensional structure, whereas 2 has a three-dimensional structure. The formation of 2 has been achieved by minor modification in the synthetic composition, suggesting the subtle relationship between the reactant composition and the structure. The hexanudear copper and silver duster cores have Cu center dot center dot center dot Cu and Ag center dot center dot center dot Ag distances close to the sum of the van der Waals radii of Cu1+ and Ag1+, respectively. The connectivity between Cu-6(mna)(6)](6-) cluster units and Mn2+ ions gives rise to a brucite related layer in 1 and a pcu-net in 2. The Ag-6(Hmna)(2)(mna)(4)](4-) cluster in 3, on the other hand, forms a sql-net with Mn2+. Compound 1 exhibits an interesting and reversible hydrochromic behavior, changing from pale yellow to red, on heating at 70 degrees C or treatment under a vacuum. Electron paramagnetic resonance studies indicate no change in the valence states, suggesting the color change could be due to changes in the coordination environment only. The magnetic studies indicate weak antiferromagnetic behavior. Proton conductivity studies indicate moderate proton migrations in 1 and 3. The present study dearly establishes sequential crystallization as an important pathway for the synthesis of heterometallic coordination polymers.

Hetero-tri-spin 2p-3d-4f] Chain Compounds Based on Nitronyl Nitroxide Lanthanide Metallo-Ligands: Synthesis, Structure, and Magnetic Properties

Employing nitronyl nitroxide lanthanide(III) complexes as metallo-ligands allowed the efficient and highly selective preparation of three series of unprecedented heterotri-spin (Cu Ln-radical) one-dimensional compounds. These 2p-3d-4f spin systems, namely Ln(3)Cu(hfac)II(NitPhOAII)41 (Ln(III)=Gd 1(Gd), Tb 1(Tb), Dy 1(Dy); NitPhOAII=2-(4'-allyloxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3- oxide), Ln(3)Cu(hfac)II(NitPhOPO4] (1-nrn=Gd 2Gd, Tb 2Tb, Dy 2(Dy), Ho 2HOf Yb 2yb; NitPhOPr= 2-(4'-propoxyphenyI)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) and Ln3Cu(hfac)II(NitPhOB441 (LnIm=Gd 3Gd, Tb 3Tb, Dy 3(Dy); NitPhOBz=2-(4'-benzyloxy- phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) involve O-bound nitronyl nitroxide radicals as bridging ligands in chain structures with a Cu-Nit-Ln-Nit-Ln-Nit-Ln-Nit] repeating unit. The dc magnetic studies show that ferromagnetic metal radical interactions take place in these heterotri-spin chain complexes, these and the next-neighbor interactions have been quantified for the Gd derivatives. Complexes 1Tb and 2Tb exhibit frequency dependence of ac magnetic susceptibilities, indicating single-chain magnet behavior.

Simultaneous co-ordination of three cytosine ligands displaying different binding sites around the copper centres

We report the synthesis and structural characterization of a polymeric ternary copper-cytosine-phenanthroline complex, Cu-4(phen)(3)-(mu(3)-cyt)(2)(mu-OH)(cyt)(OH)Cl-3](n)center dot 16H(2)O, where three cytosine ligands with different binding sites have simultaneously complexed to the four copper metal centres. Interestingly, the complex exhibits two different coordination geometries around the metal centres.