High Spin-low Spin Crossover and Antiferromagnetic Interactions in Tris(1-pyrrolidinecarbodithioato)iron(III) and the 4-morpholine (FeM) and Dibutyl Analogs, Effect of Recrystallization Solvent, and Crystal Structure of FeM·nitrobenzene

High sensitivity magnetic susceptibility determinations, especially in the range 1.2-4.2 K on pure and dilute tris(pyrrolidinecarbodithioato)iron(III) (FeP) in its high spin form, show that a maximum at about 2 K is caused by antiferromagnetic interactions. The analogous chromium(III) complex does not exhibit significant antiferromagnetism compared to that of the iron complex, and it is likely that the upper e electrons possessed by the iron and not by the chromium are responsible for the bulk of the antiferromagnetism. As the iron atoms are about 9 Å apart in discrete molecules, the antiferromagnetic interactions presumably occur between unpaired spins delocalized on to the ligands of adjacent molecules. This is in keeping with NMR evidence that spin delocalization is greater in the iron(III) than in the chromium(III) complex. When diluted with large amounts of the cobalt(III) analog (CoP), FeP exhibits a spin state equilibrium. Thus, the structure of the FeP molecule is modified slightly (presumably with shortening of the Fe-S bond) to approach that of the CoP host lattice, which has a shorter metal-sulfur bond. The previous history of the samples of ferric dithiocarbamate complexes is shown to be far more important than had previously been suspected: When crystallized from benzene, FeP exhibits a high spin-low spin equilibrium, in constrast with the pure high spin behavior of the complex when not crystallized from benzene. The effect of adding 7% of benzene to the lattice is much greater than that of adding 50% of CoP. The dibutyl analog shows similar effects. The tris(4- morpholinecarbodithioato-S,S\u27)iron(III) complex FeM is shown, by single crystal x-ray data, to contain short Fe-S bond lengths (average 2.353 Å) when recrystallized from nitrobenzene. This indicates that the complex is principally low spin, in keeping with the observed magnetism and with the general strong solvent effect on the spin state. It is now proposed that the difference in Fe-S bond lengths between FeP crystallized from chloroform and FeP from benzene (the reverse of the expected differences) is due to experimental error. Crystal data for FeM-nitrobenzene: space group P21/c, Z = 4, a = 9.713(3) Å, b = 31.419(8) Å, c = 9.718(2) Å, β = 105.04(2)°, V = 2864 Å3, R = 3.3%, 2712 reflections

Hormone Anchored Metal Complexes. 1. Synthesis, Structure, Spectroscopy and In Vitro Antitumor Activity of Testosterone Acetate Thiosemicarbazone and its Metal Complexes

Testosterone acetate thiosemicarbazone (TATSC, 17-β-hydroxyandrost-4-one acetate thiosemicarbazone) was synthesized and characterized by single crystal X-ray structure determination. The copper and platinum complexes of this steroid derivative were synthesized and characterized by spectroscopy and electrochemiatry. The in vitro activity of these compounds against human breast cancer cell line MCF-7 was tested. The highest activity was found for the [Pt(TATSC)Cl1] followed by [Cu(TATSC)Cl2] and the ligand in compariosn with cisplatin

Enhanced structural correlations accelerate diffusion in charge-stabilized colloidal suspensions

Theoretical calculations for colloidal charge-stabilized and hard sphere suspensions show that hydrodynamic interactions yield a qualitatively different particle concentration dependence of the short-time self-diffusion coefficient. The effect, however, is numerically small and hardly accessible by conventional light scattering experiments. Applying multiple-scattering decorrelation equipment and a careful data analysis we show that the theoretical prediction for charged particles is in agreement with our experimental results from aqueous polystyrene latex suspensions.Comment: 1 ps-file (MS-Word), 14 page

How to Establish Successful Cooperative Student Learning Centers for STEM Courses

Students learn more if they are actively involved in the learning process, particularly in a cooperative manner. Several UMR faculty have operated course-based learning centers (LCs) as part of the campus-wide Learning Enhancement Across Disciplines (LEAD) Program of student learning assistance and enhancement. LCs are designed to assist large numbers of students in a cost- and time-efficient manner that promotes student engagement without requiring undue amounts of faculty time. Course instructors spend time in the open learning environment of the LC, in lieu of office hours, guiding students to master course material and skills in their evolution from novice to expert techniques. The goals are to build student self-confidence through direct interaction with role models and to develop teamwork skills. LCs can be much more attractive to students than faculty office hours or traditional tutoring because they satisfy the social elements of student learning communities. However, there are a few simple practical elements instructors should orchestrate to generate high-volume LC usage. We will discuss practical issues of establishing and operating successful learning centers for STEM (science, technology, engineering, mathematics) courses

Soft X-ray Photochemistry at the L₂,₃-edges in K₃[Fe(CN)₆], [Co(acac)₃] and [Cp₂Fe][BF₄]

Soft X-ray photoreduction has been observed in K3[Fe(CN)6], [Co(acac)3] and [Cp2Fe][BF4]

Cu(ii) complexes of a tridentate N,N,O-donor Schiff base of pyridoxal: synthesis, X-ray structures, DNA-binding properties and catecholase activity

Two new Cu(II) complexes [Cu(L1)(N3)](1) and [Cu(L1)(NCS)]n(2), where HL1 ((E)-4-((2(dimethylamino)ethylimino)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol) is a N,N,O-donor Schiff base ligand, have been synthesized. These complexes were characterized on the basis of spectroscopic, electrochemical, and other physicochemical properties. X-ray crystal structure determination reveals that in complex 1, Cu(II) is in a square planar geometry with the N,N,O-donor ligand and a terminally coordinated azide ion. In complex 2, however, Cu(II) assumes a square pyramidal geometry, and apart from the tridentate Schiff base ligand there is a thiocyanate ion, which acts in a μ1,3-bridging mode, connecting adjacent Cu(II) atoms in an axial-equatorial fashion forming an one dimensional chain. Cyclic voltammetry shows that complexes undergo Cu(II)/Cu(I) reductions at −0.40 to −0.55V followed by imine reduction at around −0.7V. Cu(I)/Cu(0) reduction is observed at approximately −0.9V. Complex 1 also shows appreciable catalytic activity for the aerial oxidation of 3,5 DTBCH2 to DTBQ (catecholase activity). Both the complexes also show strong binding affinity towards calf-thymus DNA

Автоматический выпуск конструкторской документации в PDM-системе

BaFe12O19 powders were prepared by coprecipitation and by glass crystallization. Electron microscopic investigations revealed that the particles of the glass crystallized powder exhibit excellent uniform shapes and narrow size distribution in comparison to the coprecipitated one consisting of irregularly shaped, polycrystalline particles with a broad and inhomogeneous size distribution. The crystallites of the coprecipitated powder particles, however, are smaller (mean diameter D = 0.11 μm) and the size distribution is narrower than that of the particles of the glass crystallized powder with a mean diameter of D = 0.42 μm. The lattice perfection of the particles and the crystallites of both ensembles is quite good. In order to determine the magnetic properties - above all the effective anisotropy field - we used six different methods: transverse susceptibility χt, singular point detection (SPD), ferromagnetic resonance (FMR), torsion pendulum (TP), rotational hysteresis losses (RHL), remanence curves (RC). It has been found that differences in coercivity values HcJ are not dramatic (about ±3%). Effective anisotropy fields Ha measured with “switching” methods (RHL, RC) are smaller than those measured with “stiffness” ones (FMR, TP, SPD, χt), by about 1700 Oe for the coprecipitated powder and about 2500 Oe for the glass crystallized one. The glass crystallized particle assemblies used for the present investigations do not exhibit pure Stoner-Wohlfarth behaviour, because of their relatively large particle diameters. The ratio HcJ/Ha ≈ 0.39 of the coprecipitated powder is relatively near the ideal value of 0.48, although the particles are considerably mechanically aggregated. © 1992