Synthesis and structural characterization of trinuclear Cu(II)-pyrazolato complexes containing mu(3)-OH, mu(3)-O, and mu(3)-Cl ligands. Magnetic susceptibility study of [PPN](2)[(mu(3)-O)Cu(3)(mu-pz)(3)Cl(3)

The nine-membered [-Cu(II)-N-N-](3) ring of trimeric copper-pyrazolato complexes provides a sturdy framework on which water is twice deprotonated in consecutive steps, forming mu(3)-OH and mu(3)-O species. In the presence of excess chlorides the mu(3)-O(H) ligand is replaced by two mu(3)-Cl ions. The interconversion of mu(3)-OH and mu(3)-O and the exchange of mu(3)-O(H) and mu(3)-Cl are reversible, and the three species involved have been structurally characterized: [PPN][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)(thf)].CH(2)Cl(2) (1a), monoclinic P2(1)/n, a = 10.055(2) A, b = 35.428(5) A, c = 15.153(2) A, beta = 93.802(3) degrees, V = 5386(1) A(3), Z = 4; [Bu(4)N][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)] (1b), triclinic P-1, a = 9.135(2) A, b = 13.631(2) A, c = 14.510(2) A, alpha = 67.393(2) degrees, beta = 87.979(2) degrees, gamma = 80.268(3) degrees, V = 1643.2(4) A(3), Z = 2; [PPN](2)[Cu(3)(mu(3)-O)(mu-pz)(3)Cl(3)] (2), monoclinic P2/c, a = 12.807(2) A, b = 13.093(2) A, c = 23.139(4) A, beta = 105.391(3) degrees, V = 3741(1) A(3), Z = 2; [PPN](2)[Cu(3)(mu(3)-Cl)(2)(mu-pz)(3)Cl(3)].0.75H(2)O.0.5CH(2)Cl(2) (3a), triclinic P-1, a = 14.042(2) A, b = 23.978(4) A, c = 25.195(4) A, alpha = 76.796(3) degrees, beta = 79.506(3) degrees, gamma = 77.629(3) degrees, V = 7988(2) A(3), Z = 4; [Bu(4)N](2)[Cu(3)(mu(3)-Cl)(2)(mu-pz)(3)Cl(3)] (3b), monoclinic C2/c, a = 17.220(2) A, b = 15.606(2) A, c = 20.133(2) A, beta = 103.057(2) degrees, V = 5270(1) A(3), Z = 4; [Et(3)NH][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)(pzH)] (4), triclinic P-1, a = 11.498(2) A, b = 11.499(2) A, c = 12.186(2) A, alpha = 66.475(3) degrees, beta = 64.279(3) degrees, gamma = 80.183(3) degrees, V = 1331.0(5) A(3), Z = 2. Magnetic susceptibility measurements show that the three copper centers of 2 are strongly antiferromagnetically coupled with J(Cu-Cu) = -500 cm(-1).     

The lattice location and hyperfine field of implanted Yb in Fe as a function of annealing temperature

A combined study has been made of the lattice location and hyperfine field of Yb implanted into Fe single crystals. The location has been determined by ion channeling and back-scattering, the hyperfine field by perturbed angular correlation (PAC) measurements on¹⁶⁹Yb (decaying to excited states in¹⁶⁹Tm). The channeling experiments indicate that initially about 60% of the Yb atoms occupy substitutional sites in the Fe lattice, while the remaining atoms are not in any specific crystallographic site. On annealing, Yb migrates from substitutional to non-substitutional sites. No Yb atoms remain substitutional after a 600°C anneal. By making PAC measurements at two temperatures for two - cascades in¹⁶⁹Tm, it is found that the PAC pattern can be described using a combined static and time-dependent magnetic interaction. The PAC results show that the average hyperfine field and relaxation parameter decrease on annealing, and that the field disappears after a 600°C anneal. The correlation between the location and the hyperfine field is discussed. A comparison of the results with previous Mössbauer results for¹⁵¹Gd implanted in Fe, together with relaxation parameter measurements on a¹⁶⁹Yb₂O₃ source, suggests that the non-substitutional Yb is internally oxidized in the Fe host.Work partly carried out while at the Clarendon Laboratory, Oxford, England and Nuclear Physics Division, AERE, Harwell, England.     

Triangular,ferromagnetically-coupled CuII 3-pyrazolato complexes as possible models of particulate methane monooxygenase (pMMO)

Magnetic susceptibility and EPR studies show that trinuclear Cu(II)-pyrazolato complexes with a Cu(3)(mu3-X)2 core (X = Cl, Br) are ferromagnetically coupled: J(Cu-Cu) = +28.6 cm(-1) (X = Cl), +3.1 cm(-1) (X = Br). The orderly transition from an antiferromagnetic to a ferromagnetic exchange among the Cu centers of Cu(3)(mu3-X) complexes, X = O, OH, Cl, Br, follows the change of the Cu-X-Cu angle from 120 degrees to approximately 80 degrees. The crystal structures of [Bu4N]2"[Cu3(mu3-Br)2(mu-pz*)3Br3] (pz* = pz (1a) or 4-O2N-pz (1b), pz = pyrazolato anion, C(3)H(3)N(2)(1-)) are presented.     

Doubling the Carbonate-Binding Capacity of Nanojars by the Formation of Expanded Nanojars

Anion binding and extraction from solutions is currently a dynamic research topic in the field of supramolecular chemistry. A particularly challenging task is the extraction of anions with large hydration energies, such as the carbonate ion. Carbonate-binding complexes are also receiving increased interest due to their relevance to atmospheric CO₂ fixation. Nanojars are a class of self-assembled, supramolecular coordination complexes that have been shown to bind highly hydrophilic anions and to extract even the most hydrophilic ones, including carbonate, from water into aliphatic solvents. Here we present an expanded nanojar that is able to bind two carbonate ions, thus doubling the previously reported carbonate-binding capacity of nanojars. The new nanojar is characterized by detailed single-crystal X-ray crystallographic studies in the solid state and electrospray ionization mass spectrometric (including tandem MS/MS) studies in solution.     

Lowering of magnetic field intensity at the surfaces of α-Fe2O3 and FeBO3 single crystals

Depth-selective conversion electron Mössbauer spectroscopy was used to study magnetic properties of the thin surface layers of the α-Fe₂O₃ and FeBO₃ single crystals. An analysis of the experimental spectra indicates that the magnetic properties of the layers at a depth of more than ～100 nm from the surface are similar to the properties of crystal bulk, and the corresponding spectra consist of narrow lines. The lines gradually broaden as the crystal surface is approached. The spectra of the ～10-nm-thick surface layers consist of broad lines, indicating a wide distribution δ=2.1 T of the effective magnetic field about its mean value of 32.2(4) T. The experimental spectra were used to determine the effective magnetic fields (H _eff) for the iron ions situated in the surface layers of thickness ～100 nm. The effective fields in these layers were found to gradually decrease at room temperature (291 K) as the crystal surface was approached. The H _eff values in the 2.4(9)-nm-thick surface layer of the α-Fe₂O₃ crystal and 4.9(9)-nm layer of FeBO₃ are 0.7(2) and 1.2(3)%, respectively, smaller than for the nuclei of the ions in the bulk of these crystals.     

Investigation of stimulated Brillouin scattering under well-defined interaction conditions

Ruby-laser light scattering was used to gain spatially and temporally resolved information about plasma parameters for nanosecond CO₂ laser-plasma interaction studies. The results confirm a heating model, where heat conduction in dense model plasmas can be described classically. CO₂-laser excited stimulated Brillouin scattering could directly be shown to arise from near thermal level by simultaneous Thomson scattering with a ruby-laser, and turbulence enhanced density fluctuations could be excluded.     

Magnetic phase in the near-surface region of an FeBO3 single crystal

An FeBO3 single crystal was studied from 291 K up to the Neel temperature T(N) = 348.35 K by depth selective conversion electron Mossbauer spectroscopy in ultrahigh vacuum (10(-9) mbar). A new magnetic near-surface phase was found. Its thickness D diverges on approaching T(N) and gives a critical exponent for the correlation length of nu = 0.59(4). The phase boundary between the bulk and near-surface phase could be identified.     

The structure of 9-methyladenine salicylate

Crystals of 9-methyladenine salicylate (C₆H₈N ₅ ⁺ ·C₇H₅O ₃ ^? ), mp 126°C, are orthorhombic, space groupPbcn (D _2h ¹⁴ , No. 60) witha=25.305(3),b=8.066(1),c=12.928(2) Å,d _c=1.446 g cm^?3,d _m=1.43 g cm^?3 (CCl₄/ cyclohexane) forZ=8. The 9-methyladenine, protonated at N(1), and salicylate form a pair of strong hydrogen bonds with N?O distances of 2.617 and 2.858 Å. In addition, a hydrogen bond is formed between two adenine moieties using the amino group and imidazole nitrogen, N(7), with N?N separation of 3.114 Å. As in salicylic acid, an intermolecular hydrogen bond of 2.560 Å is formed between the hydroxyl and a carboxyl oxygen atoms.