A unique example of structural and magnetic diversity in four interconvertible copper(II)−azide complexes with the same Schiff base ligand: a monomer, a dimer, a chain, and a layer

Four new Cu(II)-azido complexes of formula [CuL(N-3)] (1), [CuL(N-3)](2) (2), [Cu7L2(N-3)(12)](n) (3), and [Cu2L(dmen)-(N-3)(3)](n) (4) (dmen = N,N-dimethylethylenediamine) have been synthesized using the same tridentate Schiff base ligand HL (2-[1-(2-dimethylaminoethylimino)ethyl]phenol, the condensation product of dmen and 2-hydroxyacetophenone). The four compounds have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 1 is mononuclear, whereas 2 is a single mu-1,1 azido-bridged dinuclear compound. The polymeric compound 3 possesses a 2D structure in which the Cu(II) ions are linked by phenoxo oxygen atoms and two different azide bridges (mu-1,1 and mu-1,1,3). The structure of complex 4 is a double helix in which two mu-1,3-azido-bridged alternating one-dimensional helical chains of CuL(N-3) and Cu(dmen)(N-3)(2) are joined together by weak mu-1,1 azido bridges and H-bonds. The complexes interconvert in solution and can be obtained in pure form by carefully controlling the conditions. The magnetic properties of compounds 1 and 2 show the presence of very weak antiferromagnetic exchange interactions mediated by a ligand pi overlap (J = -1.77) and by an asymmetric 1,1-N-3 bridge (J = -1.97 cm(-1)), respectively. Compound 3 presents, from the magnetic point of view, a decorated chain structure with both ferro- and antiferromagnetic interactions. Compound 4 is an alternating helicoidal chain with two weak antiferromagnetic exchange interactions (J -1.35 and -2.64 cm(-1)).

Asymmetric adjustment in the City of London office market

Earlier estimates of the City of London office market are extended by considering a longer time series of data, covering two cycles, and by explicitly modeling of asymmetric space market responses to employment and supply shocks. A long run structural model linking real rental levels, office-based employment and the supply of office space is estimated and then rental adjustment processes are modeled using an error correction model framework. Rental adjustment is seen to be asymmetric, depending both on the direction of the supply and demand shocks and on the state of the space market at the time of the shock. Vacancy adjustment does not display asymmetries. There is also a supply adjustment equation. Two three-equation systems, one with symmetric rental adjustment and the other with asymmetric adjustment, are subjected to positive and negative shocks to employment. These illustrate differences in the two systems.

Metal complexes with atropisomeric sulfur ligands in asymmetric hydroformylation X-ray structure of [Rh2(μ-biphes)(cod)2] (H2biphes = 4,4′-biphenanthrene-3,3′-dithiol)

The addition of the atropisomeric racemic sulfur compound 4,4′-biphenanthrene-3,3′-dithiol (H2 biphes) to a dichloromethane solution of [{M(μ-OMe)(cod)}2] (M = Rh, Ir, cod = cycloocta-1,5-diene) afforded the dithiolate-bridged complexes [{Rh2(μ-biphes)(cod)2}n] (n = 2 5 or n = 1 6) and [{Ir2(μ-biphes)(cod)2}n]·nCH2Cl27. When 1,1′-binaphthalene-2,2′-dithiol (H2 binas) reacted with [{Ir(μ-OMe)(cod)}2], complex [Ir2(μ-binas)(cod)2] 8 was obtained. Complexes 5 and 6 reacted with carbon monoxide to give the dinuclear tetracarbonyl complex [Rh2(μ-biphes)(CO)4] 9. The reaction of 9 with PR3 provided the mixed-ligand complexes [{Rh2(μ-biphes)(CO)2(PR3)2}2] · xCH2Cl2 (R = Ph, x = 2 10, C6H11, x = 1 11) and [{Rh2(μ-biphes)(CO)3(PR3)}2] · CH2Cl212 (R = OC6H4But-o). The crystal structure of 6 was determined by X-ray diffraction. Reaction of the dithioether ligand Me2biphes with [Rh(cod)2]ClO4 in CH2Cl2 solution afforded the cationic complex [Rh(cod)(Me2biphes)]ClO4 · CH2Cl213. Asymmetric hydroformylation of styrene was performed using the complexes described. The extent of aldehyde conversion ranges from 53 to 100%, with selectivities towards branched aldehydes in the range 51 to 96%. The enantioselectivities were quite low and did not exceed 20%.

Asymmetric oligopoly and foreign direct investment: implications for host-country tax-setting

We present a duopoly model with heterogeneous firms that vary in cost-efficiency, each of which can choose to serve a foreign market by either exporting or local production. We do so to analyse the effects of a host-country corporate profit tax on both the scale and composition of FDI, and find that: strategic interaction between oligopolistic firms provides for a pattern of FDI that favours cost-inefficiency to the detriment of host-country welfare; and the host-country tax rate can be optimally used to avoid such patterns of FDI and instead promote direct investment by a relatively cost-efficient firm.

Asymmetric space market adjustment in the London office market

Models of the City of London office market are extended by considering a longer time series of data, covering two cycles, and by explicit modeling of asymmetric rental response to supply and demand model. A long run structural model linking demand for office space, real rental levels and office-based employment is estimated and then rental adjustment processes are modeled using an error correction model framework. Adjustment processes are seen to be asymmetric, dependent both on the direction of the supply and demand shock and on the state of the rental market at the time of the shock. A complete system of equations is estimated: unit shocks produce oscillations but there is a return to a steady equilibrium state in the long run.

Asymmetric response of demand-supply mismatch to investor's sentiment

We look through both the demand and supply side information to understand dynamics of price determination in the real estate market and examine how accurately investors’ attitudes predict the market returns and thereby flagging off extent of any demand-supply mismatch. Our hypothesis is based on the possibility that investors’ call for action in terms of their buy/sell decision and adjustment in reservation/offer prices may indicate impending demand-supply imbalances in the market. In the process, we study several real estate sectors to inform our analysis. The timeframe of our analysis (1995-2010) allows us to observe market dynamics over several economic cycles and in various stages of those cycles. Additionally, we also seek to understand how investors’ attitude or the sentiment affects the market activity over the cycles through asymmetric responses. We test our hypothesis variously using a number of measures of market activity and attitude indicators within several model specifications. The empirical models are estimated using Vector Error Correction framework. Our analysis suggests that investors’ attitude exert strong and statistically significant feedback effects in price determination. Moreover, these effects do reveal heterogeneous responses across the real estate sectors. Interestingly, our results indicate the asymmetric responses during boom, normal and recessionary periods. These results are consistent with the theoretical underpinnings.

An unusual axial–axial combination of alternating cyclic rings in the chair conformations of hexameric water and chlorine-water clusters

An alternating hexameric water (H2O)(6) cluster and a chlorine-water cluster [Cl-2(H2O)(4)](2-) in the chair forms combine axially to each other to form a 1D chain [{Cl-2(H2O)(6)}(2-)](n) in complex [FeL2]Cl center dot(H2O)(3) (L=2-[(2-methylaminoethylimino)-methyl]-phenol)]. The water molecules display extensive H-bonding interactions with monomeric iron-organic units to form a hydrogen-bonded 2D supramolecular assembly.

Spin-canted antiferromagnetic phase transitions in alternating phenoxo- and carboxylato-bridged Mn(III)-salen complexes

Three new MnIII complexes, {[Mn-2(salen)(2)(OCn)](ClO4)}(n) (1), {[Mn-2(salen)(2)(OPh)](ClO4)}(n) (2) and {[Mn-2(salen)(2)(OBz)](ClO4)}(2) (3) (where salen = N,N'-bis(salicylidene)-1,2-diaminoethane dianion, OCn = cinnamate, OPh = phenylacetate and OBz = benzoate), have been synthesized and characterized structurally and magnetically. The crystal structures reveal that all three structures contain syn-anti carboxylatebridged dimeric [Mn-2(salen)(2)(OOCR)](+) cations (OOCR = bridging carboxylate) that are joined together by weak Mn center dot center dot center dot O(phenoxo) interactions to form infinite alternating chain structures in 1 and 2, but the relatively long Mn center dot center dot center dot O(phenoxo) distance [3.621(2)angstrom] in 3 restricts this structure to tetranuclear units. Magnetic studies showed that 1 and 2 exhibited magnetic long-range order at T-N = 4.0 and 4.6 K (T-N = Neel transition temperature), respectively, to give spin-canted antiferromagnetic structures. Antiferromagnetic coupling was also observed in 3 but no peaks were recorded in the field-cooled magnetization (FCM) or zero-field-cooled magnetization (ZFCM) data, indicating that 3 remained paramagnetic down to 2 K. This dominant antiferromagnetic coupling is attributed to the carboxylate bridges. The ferromagnetic coupling expected due to the Mn-O(phenoxo)center dot center dot center dot Mn bridge plays an auxiliary role in the magnetic chain, but is an essential component of the bulk magnetic properties of the material.

Asymmetric synthesis of peptides

The present invention provides a process comprising substitution of an acceptor molecule comprising a group -XC(O)- wherein X is O, S or NR8, where R8 is C1-6 alkyl, C6-12 aryl or hydrogen, with a nucleophile, wherein the acceptor molecule is cyclised such that said nucleophilic substitution at -XC (O)- occurs without racemisation. This process has particular application for the production of a peptide by extension from the activated carboxy-terminus of an acyl amino acid residue without epimerisation.

Asymmetric synthesis of peptides

The present invention provides a process comprising substitution of an acceptor molecule comprising a group -XC(O)- wherein X is O, S or NR8, where R8 is C1-6 alkyl, C6-12 aryl or hydrogen, with a nucleophile, wherein the acceptor molecule is cyclised such that said nucleophilic substitution at -XC (O)- occurs without racemisation. This process has particular application for the production of a peptide by extension from the activated carboxy-terminus of an acyl amino acid residue without epimerisation.

Alternating sums of binomial coefficients with unit fraction arithmetic sequence coefficients

Expressions for finite sums involving the binomial coefficients with unit fraction coefficients whose denominators form an arithmetic sequence are determined.

Asymmetric organocatalysis and the nitro group functionality

The nitro group is an exceptionally versatile functional group, not only because it is essentially a masked amine, but also because its chemistry can be exploited in a number of useful ways. Asymmetric organocatalysis in particular has capitalized on the use of the nitro group towards the synthesis of a variety of nitrogen- containing targets. Perhaps of greatest interest is that this functional group has been shown to be invaluable within the rapidly expanding field of organocatalytic domino reactions. This review features selected examples of nitro group reactivity in organocatalysis to demonstrate its dynamism and utility.

Asymmetric forcing from stratospheric aerosols impacts Sahelian rainfall

The Sahelian drought of the 1970s–1990s was one of the largest humanitarian disasters of the past 50 years, causing up to 250,000 deaths and creating 10 million refugees1. It has been attributed to natural variability2–5, overgrazing6 and the impact of industrial emissions of sulphur dioxide7,8. Each mechanism can influence the Atlantic sea surface temperature gradient, which is strongly coupled to Sahelian precipitation2,3. We suggest that sporadic volcanic eruptions in the Northern Hemisphere also strongly influence this gradient and cause Sahelian drought. Using de-trended observations from 1900 to 2010, we show that three of the four driest Sahelian summers were preceded by substantial Northern Hemisphere volcanic eruptions. We use a state-ofthe- art coupled global atmosphere–ocean model to simulate both episodic volcanic eruptions and geoengineering by continuous deliberate injection into the stratosphere. In either case, large asymmetric stratospheric aerosol loadings concentrated in the Northern Hemisphere are a harbinger of Sahelian drought whereas those concentrated in the Southern Hemisphere induce a greening of the Sahel. Further studies of the detailed regional impacts on the Sahel and other vulnerable areas are required to inform policymakers in developing careful consensual global governance before any practical solar radiation management geoengineering scheme is implemented.

Asymmetric output gap effects in Phillips Curve and mark-up pricing models: evidence for the US and the UK

A number of studies have found an asymmetric response of consumer price index inflation to the output gap in the US in simple Phillips curve models. We consider whether there are similar asymmetries in mark-up pricing models, that is, whether the mark-up over producers' costs also depends upon the sign of the (adjusted) output gap. The robustness of our findings to the price series is assessed, and also whether price-output responses in the UK are asymmetric.