Magnetic Properties of Linear Chain Systems: Metamagnetism of Single Crystal Co(pyridine)₂CI₂

The metamagnetic behavior of the low temperature properties of single crystal Co(pyridine)2Cl2 is discussed. At 1.25 K oriented single crystals exhibit a two-step metamagnetic transition at applied fields ~0.8 and 1.6 kG along the b-axis, a single transition at ~0.7 kG for applied fields along the a* axis, and a single transition at ~4.2 kG for an applied field along the c axis. Just above the transition fields a moment of 2µB/Co atom is measured for B0 parallel to the a* axis or b axis, and 0.4µB/Co atom is measured for the B0 parallel to the c axis. A large field dependent moment is observed at high fields. Many features of this compound closely mirror the behavior of CoCl2-2H20. However, the Co(pyridine)2Cl 2 has a much smaller interchain exchange, so that many features can be examined at lower fields. The basic features are consistent with a six-sublattice model for the ordered antiferromagnetic system. Measurements of magnetic moment versus temperature show that Co(pyridine)2Cl 2 does not obey a Curie-Weiss law even at relatively high temperatures

The dominant Anopheles vectors of human malaria in the Asia-Pacific region: occurrence data, distribution maps and bionomic précis

<p>Abstract</p> <p>Background</p> <p>The final article in a series of three publications examining the global distribution of 41 dominant vector species (DVS) of malaria is presented here. The first publication examined the DVS from the Americas, with the second covering those species present in Africa, Europe and the Middle East. Here we discuss the 19 DVS of the Asian-Pacific region. This region experiences a high diversity of vector species, many occurring sympatrically, which, combined with the occurrence of a high number of species complexes and suspected species complexes, and behavioural plasticity of many of these major vectors, adds a level of entomological complexity not comparable elsewhere globally. To try and untangle the intricacy of the vectors of this region and to increase the effectiveness of vector control interventions, an understanding of the contemporary distribution of each species, combined with a synthesis of the current knowledge of their behaviour and ecology is needed.</p> <p>Results</p> <p>Expert opinion (EO) range maps, created with the most up-to-date expert knowledge of each DVS distribution, were combined with a contemporary database of occurrence data and a suite of open access, environmental and climatic variables. Using the Boosted Regression Tree (BRT) modelling method, distribution maps of each DVS were produced. The occurrence data were abstracted from the formal, published literature, plus other relevant sources, resulting in the collation of DVS occurrence at 10116 locations across 31 countries, of which 8853 were successfully geo-referenced and 7430 were resolved to spatial areas that could be included in the BRT model. A detailed summary of the information on the bionomics of each species and species complex is also presented.</p> <p>Conclusions</p> <p>This article concludes a project aimed to establish the contemporary global distribution of the DVS of malaria. The three articles produced are intended as a detailed reference for scientists continuing research into the aspects of taxonomy, biology and ecology relevant to species-specific vector control. This research is particularly relevant to help unravel the complicated taxonomic status, ecology and epidemiology of the vectors of the Asia-Pacific region. All the occurrence data, predictive maps and EO-shape files generated during the production of these publications will be made available in the public domain. We hope that this will encourage data sharing to improve future iterations of the distribution maps.</p

Nature of the Electronic Ground State in Tris(2-chlorophenanthroline)iron(II) Perchlorate and Related Complexes

The orbital and spin ground states of [Fe(2-Cl(phen))3](ClO4)2 (phen = phenanthroline) and related high-spin ferrous complexes have been studied using Mössbauer spectroscopy. The temperature dependence of the Mössbauer spectrum of [Fe-(2-Cl(phen))3](ClO4)2 over the range 300-4.2°K indicates the system to have a ground spin quintet contrary to the results of a recent susceptibility study in which a high-spin to low-spin equilibrium is assumed. Magnetically perturbed Mössbauer spectra of the 2-Cl complex as well as the high-spin form of [Fe(phen)2(NCS)2] show these compounds to have a negative principal component (Vzz) of the electric field gradient tensor. This result is consistent with previous Mössbauer and magnetic studies of [Fe(phen)2X2] complexes (X- = Cl-, N3-) and is interpreted in terms of an electron in dz 2 corresponding to an orbital (2A) singlet ground term

On the Orbital Ground State and the Magnitude of the Quadrupole Interaction in Some High-spin Iron(II) Pyridine Complexes

Mössbauer spectra of the pseudooctahedral complex trans-Fe(pyridine)4(NCS)2 have been measured at 4.2°K in applied magnetic fields of up to 60 kG. The principal component of the electric field gradient tensor is positive and consistent with a 5B2g ground electronic state in a tetragonal local site symmetry. The sign of the quadrupole interaction is discussed in relation to a number of recent investigations in which orbital ground terms are assigned solely on the basis of the magnitude and temperature of the quadrupole interaction

On the Nature of the Spin States in Some Binuclear Iron (III) Complexes

Detailed magnetic, Mössbauer, and spectroscopic studies have been made on a number of binuclear Fe(III) complexes in an effort to determine the spin state for the Fe(III) ions. The over-all data are most consistent with a spin of 5/2 for each iron. An explanation is offered for the presence of a relatively intense electronic absorption band in most of the complexes

Low-temperature Mössbauer Spectroscopy Study of Some Partially Solvated Tris(dialkyldithiocarbamato)iron(III) Complexes

The low-temperature, zero-field Mössbauer spectra of tris(morpholinecarbodithioato)iron(III), partially solvated with CHCl 3, CH 2Cl 2, or C 6H 6, and the pyrrolidyl analogue solvated with benzene are presented. Contrary to previous susceptibility studies in which limiting low-temperature magnetic moments of ∼4 μ B were used to suggest a sextet to ground quartet transition with decreasing temperature, the present Mössbauer spectra clearly indicate the presence of only spin-sextet and -doublet states; S = 3/2 is never the ground state. Slow paramagnetic relaxation spectra of the sextet fractions correspond to the expected limiting internal fields of ∼450 kG while the spin-doublet fractions exhibit no hyperfine splitting, again as expected. Previous susceptibility results are reinterpreted in terms of a combination of zero-field splitting of a “permanent” fraction of S = 5/2 state, population of the S = 1/2 state, and weak antiferromagnetic interactions of the discrete FeS 6 cores involving metal-electron spin density delocalized to the thio ligands. © 1981 American Chemical Society

Mössbauer, Electronic, and Structural Properties of Bis(pyridine)dithiocyanatoiron(II). a Ferromagnetically Ordered Polymer

An interesting example of an extended (lattice) ferromagnet containing three-atom covalent bridging has been characterized. The bis(pyridine)dithiocyanatoiron(II) complex, Fe(py)2(NCS)2, has been prepared by thermolysis of the tetrakis complex, Fe(py)4(NCS)2. A study of the X-ray, magnetic, and infrared, electronic, and Mössbauer spectral properties of the bis complex has indicated that it contains polymeric, pseudooctahedral, coordination geometry with near linear bridging thiocyanate ligands. The electronic spectrum of the bis complex shows a larger, low symmetry, ligand field than that present in Fe(py)4(NCS)2. Unperturbed Mössbauer spectra reveal a larger quadrupole splitting and a smaller isomer shift in the bis complex as compared with the tetrakis complex. The magnetically perturbed Mössbauer spectrum at room temperature shows that the principal component of the electric field gradient tensor is positive and corresponds to a dxy ground orbital. Mössbauer spectra at 4.2°K in zero and longitudinal magnetic fields of up to 80 kG confirm the presence of ferromagnetic ordering. The latter spectra, which have been computer simulated, indicate an internal hyperfine field, H, of 280 kG, a positive axially symmetric electric field gradient, Vzz, and an angle, ß, of 75° between Vzz and H

Sign of the Electric Field Gradient Tensor and the Nature of the Low Temperature Phase Transition in Fe(pyridine)₂Cl₂

Mössbauer spectra of Fe(pyridine)2Cl2 have been determined in large external magnetic fields at room temperature and 78 K. The principal component of the electric field gradient tensor is positive and consistent with an electron in the dxy orbital. The results indicate no change in orbital ground state for the low temperature phase transition of this material