A small methanoato ligand in the structural differentiation of copper(II) complexes

Several copper(II) methanoato complexes, namely mononuclear [Cu(O₂CH)₂(2-mpy)₂] (1) (2-mpy = 2-methylpyridine), binuclear [Cu₂(μ-O₂CH)₄(2-mpy)₂] (2), and the polynuclear {[Cu(μ-O₂CH)₂(2-mpy)₂][Cu₂(μ-O₂CH)₄]}_n (3) and {Na₂[Cu(μ-O₂CH)₂(O₂CH)₂][Cu₂(μ-O₂CH)₄]}_n (4), have been synthesized. The mononuclear complex 1 is formed by two asymmetric chelate methanoate anions and two 2-methylpyridine molecules, giving a highly distorted ‘elongated octahedral’ coordination sphere. Complex 1 decomposes outside the mother-liquid, transforming into a regular isolated binuclear paddle-wheel complex 2 with four intra-binuclear bridging methanoates and two axial 2-mpy ligands. The polynuclear complex 3 is formed of alternate mononuclear and binuclear building blocks resembling the central cores of 1 and 2, but with significant differences, especially for the methanoates of the mononuclear units. The oxygen atom of the mononuclear unit in the octahedral axial position in 3 is simultaneously coordinated to the axial position of the binuclear paddle-wheel central core, thus enabling a chain type of structure. A chain of alternate mononuclear and binuclear building blocks, as in the neutral compound 3, are found as well in the ionic polymeric compound 4, though two types of bridges are found in 4, while there is only one type in 3. Namely, the axial position of the octahedral mononuclear unit in 4 is occupied by the methanoate oxygen atom that is already a part of the binuclear paddle-wheel unit, while one equatorial methanoate from the mononuclear unit serves as a triatomic bridge to the axial position of the binuclear building block. A very strong antiferromagnetic interaction is found for all the complexes with the paddle-wheel building blocks [Cu₂(μ-O₂CH)₄] 2–4 (−2J = 444–482 cm⁻¹), attributed to the methanoate intra-binuclear bridges. On the other hand, this strong antiferromagnetism, found already at room temperature, reduces the intensity of the EPR S = 1 spin signals reported for the isolated paddle-wheel complex 2. For the polymeric 3, only the spin S = ½ signals are found in the EPR spectra, and they are assigned to the mononuclear building blocks. No signals with a clear origin are however seen in the room temperature EPR spectrum of the polymeric analogue 4, only the S = ½ signals in the low temperature spectra. This feature is suggested to be due to a specific influence between the adjacent S = 1 (binuclear) and S = ½ (mononuclear) species via their bridges.     

Exact adaptive pointwise drift estimation for multidimensional ergodic diffusions

The problem of pointwise adaptive estimation of the drift coefficient of a multivariate diffusion process is investigated. We propose an estimator which is sharp adaptive on scales of Sobolev smoothness classes. The analysis of the exact risk asymptotics allows to identify the impact of the dimension and other influencing values—such as the geometry of the diffusion coefficient—of the prototypical drift estimation problem for a large class of multidimensional diffusion processes. We further sketch generalizations of our results to arbitrary diffusions satisfying suitable Bernstein-type inequalities.     

Dosimetry on the Spacelab missions IML1 and IML2, and D2 and on MIR

Detector packages consisting of plastic nuclear track detectors, nuclear emissions, and thermoluminescence detectors were exposed inside BIORACK during the Spacelab missions IML1 and IML2, in different sections of the MIR space station, and inside the Spacelab module at rack front panels or stowage lockers and in the Spacelab tunnel during D2. In addition, during D2, each Payload Specialist (PS) has worn three permanent detector packages; one at the neck; one at the waist; and one at the ankle. Total dose measurements, particle fluence rate and LET spectra, number of nuclear disintegrations and neutron dose from this exposure are given in this report. The results are compared to theoretical calculations and to previous missions results. The dose equivalent (total radiation exposure) received by the PSs were calculated from the measurements and range from 190 to 770 μSv d⁻¹. Finally, a cursory investigation of results from a particle telescope from two silicon detectors, first used in the last BIORACK mission on STS76, is reported.     

EPR on bis(1,2-dithiosquarato)cuprate(II) in the bis(1,2-dithiosquarato)nickelate(II) host lattice — structure and spectroscopy‡

EPR spectroscopy is a well suited analytical tool to monitor the electronic situation around paramagnetic metal centres as copper(II) and therefore the structural influences on the paramagnetic ion. 1,2-Dithiosquaratometalates are available by direct synthesis from metal salts with dipotassium-1,2-dithiosquarate and the appropriate counter cations. Synthesis and characterisation of bis(benzyltributylammonium)1,2-dithiosquaratonickelate(II), (BzlBu₃N)₂[Ni(dtsq)₂], and bis(benzyltributylammonium)1,2-dithiosquaratocuprate(II), (BzlBu₃N)₂[Cu(dtsq)₂], with benzyltributylammonium as the counter ion is reported and the X-ray structures of two complexes, (BzlBu₃N)₂[Ni(dtsq)₂] and (BzlBu₃N)₂[Cu(dtsq)₂], are presented. Both complexes, crystallising in the monoclinic space group P2₁/c, are isostructural with only small differences in the coordination sphere due to the different metal ions. The diamagnetic nickel complex is therefore well suited as a host lattice for the paramagnetic Cu(II) complex to measure EPR for additional structural information.     

On the interaction of ascorbic acid and the tetrachlorocuprate ion [CuCl4]2- in CuCl nanoplatelet formation from an ionic liquid precursor (ILP)

The formation of CuCl nanoplatelets from the ionic liquid precursor (ILP) butylpyridinium tetrachlorocuprate [C(4)Py](2)[CuCl(4)] using ascorbic acid as a reducing agent was investigated. In particular, electron paramagnetic resonance (EPR) spectroscopy was used to evaluate the interaction between ascorbic acid and the Cu(II) ion before reduction to Cu(I). EPR spectroscopy suggests that the [CuCl(4)](2-) ion in the neat IL is a distorted tetrahedron, consistent with DFT calculations. Addition of ascorbic acid leads to the removal of one chloride from the [CuCl(4)](2-) anion, as shown by DFT and the loss of symmetry by EPR. DFT furthermore suggests that the most stable adduct is formed when only one hydroxyl group of the ascorbic acid coordinates to the Cu(II) ion.