Application of sampled-d.c. anodic stripping voltammetry to metal/fulvic acid equilibria

The use of anodic stripping voltammetry (ASV) to determine the labile metal fraction in metal/ fulvic acid equilibrium systems is discussed. A method is described for distinguishing between the contributions of processes in the reduction and oxidation steps to the observed anodic (stripping) current. This method, which facilitates separate examination of the two processes, is based on timed addition of fulvic acids during the deposition step, on pH control, and on measurement of sampled-d.c. ASV peak areas (Faradaic charge) for metal/fulvic acid solutions. Results are presented for copper(Il) and lead(Il) complexes with six colloid-free soil-derived fulvic acids. In contrast to differential-pulse ASV, the stripping current measured by sampled-d.c. ASV showed no measurable contribution from ligand adsorption on the mercury drop. For heterogeneous ligand systems, such as fulvic acid, use of stripping peak heights over-estimates the fraction of non-labile metal complex because peak broadening results from the range of complexes formed in the anodic step.     

From the {FeIII2Ln2} Butterfly's Perspective: the Magnetic Benefits and Challenges of Cooperativity within 3 d–4 f Based Coordination Clusters

In this Review we discuss the tuning handles which can be used to steer the magnetic properties of Fe^III-4 f “butterfly” compounds. The majority of presented compounds were produced in the context of project A3 “Di- to tetranuclear compounds incorporating highly anisotropic paramagnetic metal ions” within the SFB/TRR88 “3MET”. These contain {Fe^III₂Ln₂} cores encapsulated in ligand shells which are easy to tune in a “test-bed” system. We identify the following advantages and variables in such systems: (i) the complexes are structurally simple usually with one crystallographically independent Fe^III and Ln^III, respectively. This simplifies theory and anaylsis; (ii) choosing Fe allows ⁵⁷Fe Mössbauer spectroscopy to be used as an additional technique which can give information about oxidation levels and spin states, local moments at the iron nuclei and spin-relaxation and, more importantly, about the anisotropy not only of the studied isotope, but also of elements interacting with this isotope; (iii) isostructural analogues with all the available (i. e. not Pm) 4 f ions can be synthesised, enabling a systematic survey of the influence of the 4 f ion on the electronic structure; (iv) this cluster type is obtained by reacting [Fe^III₃O(O₂CR)₆(L)₃](X) (X=anion, L=solvent such as H₂O, py) with an ethanolamine-based ligand L′ and lanthanide salts. This allows to study analogues of [Fe^III₂Ln₂(μ₃-OH)₂(L′)₂(O₂CR)₆] using the appropriate iron trinuclear starting materials. (v) the organic main ligand can be readily functionalised, facilitating a systematic investigation of the effect of organic substituents on the ligands on the magnetic properties of the complexes. We describe and discuss 34 {M^III₂Ln₂} (M=Fe or in one case Al) butterfly compounds which have been reported up to 2020. The analysis of these gives perspectives for designing new SMM systems with specific electronic and magnetic signatures     

A Novel Synthesis of 5-Aryltropoxe Derivatives

The reaction of substituted arylboronic acids with 5-bromo-2-methoxytropone catalyzed by palladium(0) complex furnished 5-arylated tropone derivatives in good yield.     

Neutron diffraction study of the plastic phases of polycrystalline SF6 and CBr4

An investigation of the plastic phases of polycrystalline specimens of sulphur hexafluoride (SF₆) and carbon tetrabromide (CBr₄) by neutron elastic scattering and neutron diffraction experiments is reported. A theory of neutron diffraction in plastic crystals, which treats the Bragg scattering and the diffuse scattering from a unified point of view, is developed and applied in the interpretation of the neutron results. The Debye-Scherrer peaks are analysed, both by a cumulant expansion technique and a cubic harmonic analysis, to determine the crystal structures of the plastic phase which are found to be body-centred cubic (space group Im3_m) for SF₆ and face-centred cubic (space group Fm3m) for CBr₄. The bond-orientation distribution function, f(Ω), has maxima in the <100> directions for SF₆ and in the <110> directions for CBr₄. Since, in both cases, f(Ω) is appreciably different from zero for all orientations, it is apparent that significant thermal reorientation takes place in both these crystals. The translational and librational displacements in CBr₄ are exceptionally large and give rise to extensive diffuse scattering which is analysed on the basis of a simple Einstein model. The model predicts that the centre-of-mass thermal vibration and the orientational disorder give approximately equal contributions to the total diffuse scattering. The calculated scattering is in good agreement with experiment for all wave vector transfers outside the range 2 to 3 Å^-1. Inside this range discrepancies occur which are interpreted as evidence for the existence of orientational short-range order in CBr₄.