Equatorial Sites Research Articles

Carbonyl{3,3′-di-tert-butyl-5,5′-dimethoxy-2,2′-bis[(4,4,5,5-tetramethyl-1,3,2-dioxaphospholan-2-yl)oxy]biphenyl-κ2P,P′}hydrido(triphenylphosphane-κP)rhodium(I) diethyl ether trisolvate

In the title compound, [RhH(C74H68O8P2)(C18H15P)(CO)]·3C4H10O, the CHP3 coordination set at the RhI ion is arranged in a distorted trigonal–bipyramidal geometry with the P atoms adopting equatorial coordination sites and the C atom of the carbonyl ligand as well as the H atom adopting the axial sites. The asymmetric unit contains two very similar mol­ecules of the rhodium complex, two half-occupied diethyl ether mol­ecules and further diethyl ether solvent mol­ecules which could not be modelled successfully. Therefore contributions of the latter were removed from the diffraction data using the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155].

Equatorial range spread F echoes from coherent backscatter, and irregularity growth processes, from conjugate point digital ionograms

Radio wave returns from spread F plasma structures as received by ionosondes can originate from total/specular reflection, partial reflection or coherent backscattering. The dominant mechanism to account for the spread F traces in equatorial ionograms is still an open question. Depending upon the precise mechanism, ionosondes are sensitive to irregularity scale sizes of tens of meters to several tens/hundreds of kilometers. In this paper we analyze signatures of range spreading F layer traces in Digisonde ionograms, taken at Fortaleza (3.9°S, 38.45°W, dip: −9°) and Sao Luis (2.33 S, 44.2W, dip angle: −0.5°), and at a dip equatorial site Cachimbo (9.5°S, 54.8°W, dip: −4.2°) and at its two conjugate sites Bova Vista (02.8°N, 60.7°W, dip: 22.0°) and Campo Grande (20.5 S, 54.7 W, dip −22.3°) in Brazil, to determine the dominant process/mechanism of echo returns from the irregularity structures. A significant component of the ESF trace structures is found to be consistent with the echoes originating from coherent backscattering at field line perpendicular directions. The degree of range spreading of the echoes is found to increase linearly with the top frequency of the echo trace, which is shown to be a more precise indicator of the irregularity strength. Further, the irregularity strength exhibits a significant increase from the equator toward the EIA crests, as well as a strong asymmetry between the conjugate sites.

Equilibrium, Kinetic and Structural Studies of AAZTA Complexes with Ga3+, In3+ and Cu2+

AbstractA detailed study of the structures, thermodynamic stabilities and kinetics of the dissociation of Ga3+, In3+ and Cu2+ complexes formed with the heptadentate ligand AAZTA is reported. The stability constants (log KML) of the AAZTA complexes of Ga3+, In3+ and Cu2+ are 22.18, 29.58 and 22.27, respectively, which suggests that the seven‐membered‐ring skeleton is suited to the accommodation of these metal ions. The solid‐state structure of [Cu(H2AAZTA)]·H2O shows a distorted octahedral coordination. The equatorial coordination sites of Cu2+ are occupied by one of the ring N atoms, a water O atom, one of the carboxylate O atoms and the N atom of the iminodiacetate moiety. The other ring N atom and the carboxylate O atom of the iminodiacetate moiety coordinate to the Cu2+ in the axial positions. In the pH range 4.5–8.5, Ga3+ is present in the form of the highly stable [Ga(AAZTA)OH]2– (log βGaLH–1 = 17.69) The exchange reactions of [Ga(AAZTA)OH]2– with Cu2+ and transferrin are very slow and mainly occur through the spontaneous dissociation of the complex close to physiological conditions. The half‐life for the dissociation of [Ga(AAZTA)OH]2– is t1/2 = 23 h at pH = 7.5 and 25 °C in 0.025 M NaHCO3 and 0.15 M NaCl. The high conditional stability, fast formation and sufficiently slow dissociation of [Ga(AAZTA)OH]2– represent promising properties for the complexation and diagnostic applications of radioactive Ga isotopes.

(R)-2,2-Bis(diphenylphosphanyl)-1,1′-binaphthyl-κ2P,P′]{2-[(2R)-1,2-diamino-1-(4-methoxyphenyl)-3-methylbutyl]-5-methoxyphenyl-κC1}hydridoruthenium(II) benzene monosolvate

In the title complex, [Ru(C19H25N2O2)H(C44H32P2)]·C6H6, the RuII ion is in a distorted octa­hedral coordination environment with the hydride H atom trans to the tertiary carbinamine N atom, giving an H—Ru—N angle of 160.8 (12)°. The equatorial sites are occupied by two P atoms, the secondary carbinamine N atom and a coordinated C atom.

(3-Acetyl-5-carboxylato-4-methyl-1H-pyrazol-1-ido-κ2N1,O5)aqua[(pyridin-2-yl)methanamine-κ2N,N′]copper(II)

In the title compound, [Cu(C7H6N2O3)(C6H8N2)(H2O)], the CuII ion is in a distorted square-pyramidal N3O2 environment formed by two bidentate chelating ligands in the equatorial coordination sites and one water mol­ecule in the apical direction. In the crystal, O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds link the complex mol­ecules into a three-dimensional supra­molecular network.

A deep Eastern Equatorial Pacific thermocline during the early Pliocene warm period

During the early Pliocene warm period (∼4.6–4.2Ma) in the Eastern Equatorial Pacific upwelling region, sea surface temperatures were warm in comparison to modern conditions. Warm upwelling regions have global effects on the heat budget and atmospheric circulation, and are argued to have contributed to Pliocene warmth. Though warm upwelling regions could be explained by weak winds and/or a deep thermocline, the temporal and spatial evolution of the equatorial thermocline is poorly understood. Here we reconstruct temporal and spatial changes in subsurface temperature to monitor thermocline depth and show the thermocline was deeper during the early Pliocene warm period than it is today. We measured subsurface temperature records from Eastern Equatorial Pacific ODP transect Sites 848, 849, and 853 using Mg/Ca records from Globorotalia tumida, which has a depth habitat of ∼50–100m. In the early Pliocene, subsurface temperatures were ∼4–5°C warmer than modern temperatures, indicating the thermocline was relatively deep. Subsurface temperatures steeply cooled ∼2–3°C from 4.8 to 4.0Ma and continued to cool an additional 2–3°C from 4.0Ma to present. Compared to records from other regions, the data suggests the pronounced subsurface cooling between 4.8 and 4.0Ma was a regional signal related to restriction of the Isthmus of Panama, while continued cooling from 4.0Ma to present was likely related to global processes that changed global thermocline structure. Additionally, the spatial evolution of the equatorial thermocline along a N–S transect across ODP Sites 853, 849 and 848 suggests an intensification of the southeast trades from the Pliocene to present. Large-scale atmospheric and oceanographic circulation processes link high and low latitude climate through their influence on equatorial thermocline source water regions and consequently the equatorial thermocline. Through these low latitude/high latitude linkages, changes in the equatorial thermocline and thermocline source water played an important role in the transition from the warm Pliocene to the cold Pleistocene.

A Dimorphic Os(IV) Complex with Pyramidal Sulfur Inversion in a Sulfanyl Chelating Ligand

Coordination compound [Os(SC6F4H-4)2(SC6F3H-4(SC6F4H)-2)(C6H5)] is obtained during the thermolysis of [Os(SC6F4H-4)4(PPh3)] in non-dried toluene, as a product of C–F bond cleavage. The complex presents the expected trigonal–bipyramidal coordination geometry, with a thiolate-sulfanyl κ2 S,S’-ligand chelating the metal center in axial and equatorial sites. The complex was crystallized in the centrosymmetric space group C2/c and in the non-centrosymmetric space group Pna21. In both forms, the crystal is a RS racemate, with the chiral center being the axially coordinated sulfanyl S atom. In the case of the non centrosymmetric space group, the asymmetric unit retained for the refinement consists of two independent molecules related by a pyramidal sulfur inversion at the stereogenic center. Cell parameters: form I, C2/c, a = 20.8459(14) A, b = 12.2646(12) A, c = 25.253(3) A, β = 91.582(7)°; form II, Pna21, a = 16.208(2) A, b = 16.500(3) A, c = 23.604(3) A. An Os(IV) coordination complex bearing a thiolate-sulfanyl κ2 S,S’-ligand was crystallized in two spaces groups, C2/c with one molecule in the asymmetric unit, and Pna21 with two enantiomeric molecules in the asymmetric unit.

Late Quaternary productivity changes from offshore Southeastern Australia: A biomarker approach

Reconstructions of primary productivity at low latitudes have been the focus of several studies to better understand how the export of nutrient-rich, intermediate Southern Ocean (SO) waters influences productivity at these latitudes. This was triggered by the general observation of minima in the planktonic foraminiferal δ13C values during deglaciations, which was interpreted as an isotopic signal of intermediate SO waters, together with a concomitant increase in diatom productivity at some equatorial sites. However, the impact of these SO waters on productivity at higher latitudes is not well constrained. Here, we compare a high-resolution planktonic foraminiferal δ13C record with total organic carbon and biomarker records for Proboscia diatoms and haptophytes in marine sediments from offshore Southeastern Australia. The planktonic foraminiferal δ13C record shows distinct minima during deglaciations and the Marine Isotope Stage 4/3 transition, tentatively suggesting that 13C-depleted SO waters reached the coast of Southeastern Australia. However, it did not result in increased productivity during these periods. Instead, the highest primary productivity period, as indicated by total organic carbon and alkenone accumulation rates, occurred during the Last Glacial Maximum while Proboscia diatoms mainly proliferated during interglacials and Marine Isotope Stage 3 matching periods of increased diatom productivity in some sites of the Eastern Equatorial Pacific. Our study suggests that increased primary productivity offshore Southeastern Australia was mainly due to stronger westerly winds during glacial periods while Proboscia diatom productivity was probably controlled by the transport of silicic acid to this area.

Obliquity forcing of organic matter accumulation during Oceanic Anoxic Event 2

An analysis of orbitally influenced climate‐sensitive sedimentation is conducted across a meridional transect of the proto‐North Atlantic, to reconstruct the behavior of the carbon cycle and climate during Oceanic Anoxic Event 2 (OAE 2; ∼94 Ma). Midlatitude to near equatorial sites spanning deep‐ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata. The results yield consistent independent astrochronologies at each location—compatible with the recently published radioisotopic/astrochronologic time scale at the Cenomanian‐Turonian GSSP—and thus provide a unified high‐resolution temporal context for evaluation of the event. The proto‐North Atlantic astrochronologies document an amplification of obliquity power during OAE 2, indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event. The strong obliquity signal suggests an influence of high‐latitude climate processes across midlatitude deep‐ocean to tropical shelf environments. Changes in oceanic circulation during OAE 2 represent a likely mechanism for the propagation of a high latitude signal, and proxy data from Demerara Rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification. We hypothesize that a dense high‐latitude water mass displaced a pre‐existing nutrient‐rich anoxic deep‐water layer in the proto‐North Atlantic (augmented by enhanced volcanism), driving an episode of high productivity that lasted 700–800 ka. The development and intensification of the new intermediate/deep water source was potentially driven by eustatic sea level rise, which created expansive seaways in mid to high latitudes.

One-Step Orthogonal-Bonding Approach to the Self-Assembly of Neutral Rhenium-Based Metallacycles: Synthesis, Structures, Photophysics, and Sensing Applications

Self-assembled metallacycles offer structural diversity and interesting properties based on their unique frameworks and host-guest chemistry. As a result, the design and synthesis of these materials has attracted significant research interest. This Account describes our comprehensive investigations of an effective orthogonal-bonding approach for the self-assembly of neutral Re-based metallacycles. We discuss the various types of assemblies that can be created based on the nuclearity of the luminophore, including bimetallic materials, rectangles, cages, and calixarenes. This approach permits the preparation of a rectangular molecule, rather than two molecular squares, in excellent yields. We extended this strategy to the high yield synthesis of a series of Re-based metallacycles with different shapes. With the rich spectroscopic and luminescence properties, Re(I) metallacycles provide an excellent platform for studies of host-guest interactions. When possible, we also present potential applications of the luminescent Re-based metallosupramolecular assemblies. The orthogonal-bonding approach involves the simultaneous introduction of two ligands: a bis-chelating ligand to coordinate to two equatorial sites of two fac-(CO)(3)Re cores and a monotopic or ditopic nitrogen-donor ligand to the remaining orthogonal axial site. Furthermore, by the appropriate choice of the predesigned organic ligands with various backbones and connectivity information and fac-Re(CO)(3) metal centers, we could also design other novel functional metallacycles including rotors, gondolas, cages, triangles, and metallacalixarenes in high yields. The incorporation of flexible ligands into the Re(I) metallacycles allows us to introduce various conformation states and novel structures. As a result, these structures acquire new functions, such as adaptive recognition properties. For example, we assembled Re(I)-based metallacyclic rotors via a one-step process. These rotors, which contain a para-phenylene unit that rapidly rotates within the metallacycles, are prototypes of a neutral altitudinal rotor. Most of the metallacycles are luminescent. The ability to chemically modify the organic ligands offers opportunities to create structural diversity and to tune the photophysical properties of these Re(I) metallacycles efficiently. Several strategies for increasing emission quantum yields and excited-state lifetimes and tuning the colors in Re(I) metallacycles are available. The cyclometalated ligands in Re(I) metallacycles improve excited state lifetimes and quantum yields, and these C-H bond-activated metallacycles are considerably more emissive than their non-C-H bond-activated analogues. The introduction of crown-ether-like recognition sites into neutral gondola-shaped metallacycles that selectively recognize metal ions also enhanced emission. Rhenium-based rectangular boxes, synthesized via a simple one-step route, contain a large and tunable hydrophobic inner cavity, which selectively recognizes benzene molecules. Such structures were the best host for benzene reported to date. In addition, we designed and synthesized novel neutral metallacalixarenes with tunable size, cavity, color, and functionality. These structures are efficient hosts for the recognition of planar aromatic guests.

2-(2-Chlorophenyl)-5-methyl-1,3-dioxane-5-carboxylic acid

In the title compound, C12H13ClO4, the 1,3-dioxane ring adopts a chair conformation and the 2-chloro­benzene and methyl substituents occupy equatorial sites. The carboxyl group is in an axial inclination. In the crystal, carb­oxy­lic acid inversion dimers linked by pairs of O—H⋯O hydrogen bonds generate R 2 2(8) loops.

Substitution mechanism and structural study of MnO-doped Bi2VO5.5-δ

The Aurivillius-type Bi2VO5.5-δ series doped by magnetic cations may have a significant electronic contribution to their total conductivity and special magnetoelectric properties which extend potential applications to magnetoelectronic and spintronic fields. Bi2(V1-xMnx)O5.5-δ and (Bi2-xMnx)VO5.5-δ (x=0.10–0.30) compounds with nominal composition doped by manganese cation on the Bi- or V-site were prepared via a solid-state reaction. Results show that partial substitution of Mn on the V-site stabilizes Bi2(V1-xMnx)O5.5-δ in the high-temperature tetragonal structure of Bi2VO5.5-δ for compositions in the range 0.10≤x<0.25. The geometric magnetic frustration was observed through magnetic susceptibility analysis. The crystal structure was refined by the Rietveld method based on a four-oxygen-site model. The resulting solid-solution limit confirms the equatorial vacancy model which assumes that all vacancies are located on the equatorial oxygen sites. The possible substitution mechanism is determined which supports V↔Mn, rather than Bi↔Mn in the MnO-doped Bi2VO5.5-δ series.

Catena-Poly[[[bis-(nitrato-κO)copper(II)]-bis-[μ-1,3-bis-(imidazol-1-yl)-5-methyl-benzene-κ(2)N(3):N(3')]] dihydrate

In the title complex, {[Cu(NO3)2(C13H12N4)2]·2H2O}n, the CuII atom is located on a crystallographic center of symmetry and adopts an N4O2 octa­hedral coordination geometry with four imidazole N atoms in the equatorial sites and two O atoms in the axial sites. The dihedral angles between the central benzene ring and the imidazole rings are 4.93 (11) and 46.08 (12)°. The 1,3-bis­(imidazol-1-yl)-5-methyl­benzene ligand is bis-monodentate, linking symmetry-related CuII atoms into sheets in the bc plane. These sheets are further bridged into a three-dimensional supra­molecular structure by O—H⋯O and C—H⋯O hydrogen bonds.

Catena-Poly[[[bis(acetato-κ2 O,O′)aquacadmium]-μ-[(pyridin-3-yl)(pyridin-4-yl)methanone]-κ2 N:N′] dihydrate

In the title complex, {[Cd(CH3COO)2(C11H8N2O)(H2O)]·2H2O}n, the CdII ion adopts an O5N2 penta­gonal–bipyramidal coordination geometry with four acetate O atoms and one water O atom at the equatorial sites and two pyridine N atoms at the axial sites. The (pyridin-3-yl)(pyridin-4-yl)methanone ligand acts in a μ2-bridging mode, linking the metal atoms, leading to an infinite chain along [-110]. O—H⋯O hydrogen bonds involving the lattice water mol­ecules connect these chains into a three-dimensional network.

Comparison of Rhizon Sampling and Whole Round Squeezing for Marine Sediment Porewater

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Effects of oxygen vacancy location on the electronic structure and spin density of Co-doped rutile TiO2 dilute magnetic semiconductors

According to density functional theory (DFT) using the plane wave base and pseudo-potential, we investigate the effects of the specific location of oxygen vacancy (VO) in a (Ti,Co)O6 distorted octahedron on the spin density and magnetic properties of Co-doped rutile TiO2 dilute magnetic semiconductors. Our calculations suggest that the VO location has a significant influence on the magnetic moment of individual Co cations. In the case where two Co atoms are separated far away from each other, when the VO is located at the equatorial site of a Co-contained octahedron, the ground state of the two Co cations is d6(t32g ↑,t32g ↓) without any magnetic moment. However, if the VO is located at the apical site, these two Co sites have different ground states and magnetic moments. The spin densities are also observed to be modified by the exchange coupling between the Co cations and the location of VO. Some positive spin polarization is induced around the adjacent O ions.

Nd isotope systematics on ODP Sites 756 and 762 sediments reveal major volcanic, oceanic and climatic changes in South Indian Ocean over the last 35 Ma

We have analyzed the Nd isotopic composition of both ancient seawater and detrital material from long sequences of carbonated oozes of the South Indian Ocean which are ODP Site 756 (Ninety East Ridge (−30°S), 1518m water depth) and ODP Site 762 (Northwest Australian margin, 1360m water depth). The measurements indicate that the εNd changes in Indian seawater over the last 35Ma result from changes in the oceanic circulation, large volcanic and continental weathering Nd inputs. This highlights the diverse nature of those controls and their interconnections in a small area of the ocean.These new records combined with those previously obtained at the equatorial ODP Sites 757 and 707 in the Indian Ocean (Gourlan et al., 2008) established that the distribution of intermediate seawater εNd was uniform over most of the Indian Ocean from 35Ma to 10Ma within a geographical area extending from 40°S to the equator and from −60°E to 120°E. However, the εNd value of Indian Ocean seawater which kept an almost constant value (at about −7 to −8) from 35 to 15Ma rose by 3 εNd units from 15 to 10Ma. This sharp increase has been caused by a radiogenic Nd enrichment of the water mass originating from the Pacific flowing through the Indonesian Passage. Using a two end-members model we calculated that the Nd transported to the Indian Ocean through the Indonesian Pathway was 1.7 times larger at 10Ma than at 15Ma.The Nd isotopic composition of ancient seawater and that of the sediment detrital component appear to be strongly correlated for some specific events. A first evidence occurs between 20 and 15Ma with two positive spikes recorded in both εNd signals that are clearly induced by a volcanic crisis of, most likely, the St. Paul hot-spot. A second evidence is the very large εNd decrease recorded at ODP Sites 756 and 762 during the past 10Ma which has never been previously observed. The synchronism between the εNd decrease in seawater from 10 to 5Ma and evidences of desertification in the western part of the nearly Australian continent suggests enhanced weathering inputs in this ocean from this continent as a result of climatic changes.

Poly[[(μ2-di-3-pyridylmethanone-κ2N:N′)(μ2-hexafluorosilicato-κ2F:F′)copper(II)] dihydrate

In the title complex, {[Cu(SiF6)(C11H8N2O)2]·2H2O}n, the CuII atom adopts an N4F2-octa­hedral coordination geometry with four pyridine N atoms in the equatorial sites and two F atoms in the axial sites. The di-3-pyridyl­methanone and hexa­fluoro­silicate ligands act as bidentate ligands, linking symmetry-related CuII atoms. Water mol­ecules form O—H⋯O and O—H⋯F hydrogen bonds with the di-3-pyridyl­methanone and hexa­fluoro­silicate ligands. The Cu2+ and SiF6 2− ions are each located on a twofold axis.

Ethyl 4-{[3-(adamantan-1-yl)-4-phenyl-5-sulfanylidene-4,5-dihydro-1H-1,2,4-triazol-1-yl]methyl}piperazine-1-carboxylate

The title mol­ecule, C26H35N5O2S, displays a chair-shaped piperazine ring, as well as a planar triazole ring whose phenyl substituent is perpendicular to the mean plane of the five-membered ring [dihedral angle = 90.00 (13)°]. The methyl­ene substituent on the piperazine ring occupies an equatorial site. Weak inter­molecular C—H⋯O hydrogen bonding is present in the crystal structure. The crystal studied was a non-merohedral twin, with a 33.9 (3)% minor component.

Butyl-bis-(dimethyl-glyoximato-κN,N')(pyridine-κN)cobalt(III).

In the title compound, [Co(C4H9)(C4H7N2O2)2(C5H5N)], which was prepared as a model complex of vitamin B12, the CoIII atom is coordinated by a butyl group, a pyridine and two N,N′-bidentate dimethyl­glyoximate ligands in a distorted octa­hedral geometry. The bis-chelating dimethyl­glyoximate ligands, which occupy equatorial sites, are linked by strong intra­molecular O—H⋯O hydrogen bonds.