RESUMEN
A series of luminescent Cu4I4 clusters with stair-step, cubane, and octahedral geometries supported by a novel type of cyclic As,N-ligand, pyridyl-containing 10-phenoxarsines, were synthesized and characterized by NMR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction analysis. An unusual arrangement of As,N-bidentate and µ2-iodo ligands was found in the octahedral cluster. The structural diversity of the Cu(I) complexes is reflected in their photophysical properties: the phosphorescence spectra of the compounds display emission in a broad spectral range of 495-597 nm. The complex with the Cu4I4L2 stoichiometry bearing a stair-step Cu4I4 core demonstrates temperature-dependent dual emission. The luminescence properties of all complexes were rationalized by DFT calculations.
RESUMEN
The interaction of the pivalate complexes of iron(iii), [Fe3O(Piv)6(H2O)3]·HPiv, and cadmium(ii), [Cd(Piv)2], in Et2O resulted in one more type of "ferric wheel" family complex, namely [Fe8(Piv)16{Cd(Piv)2}(µ-OH)8]·Et2O (1). The complex is an octanuclear iron(iii) wheel with a {Cd(Piv)2} moiety asymmetrically incorporated into the ring.
RESUMEN
A combination of detailed magnetisation studies and electronic-structure analysis using broken-symmetry DFT is used to explore the electronic structure of a trigonal prismatic Cu(II)(6) cluster. The presence of six paramagnetic metal centres with S = 1/2 gives rise to a maximum multiplicity of S = 3 and a total of 31 broken-symmetry states with M(S) < 3. Computed differences in energy between the high-spin and broken-symmetry states are expressed in terms of the 15 distinct Heisenberg exchange coupling parameters, J(ij), and the equations are solved by a least-squares fitting procedure. By inspection of the errors introduced by progressive symmetrisation of the Hamiltonian to reduce the number of independent J(ij), we arrive at a minimal model containing only four distinct J(ij) (three intra- and one inter-triangular). The computed values then guide the fitting of the magnetisation data. The computed trends in J(ij) can only be reproduced when antisymmetric exchange is included in the model Hamiltonian. The use of this Hamiltonian provides a reasonable description of the magnetic behaviour at all temperatures and fields. If a simpler isotropic model Hamiltonian is used instead, the best fit values of J(ij) are compromised by the need to fit the low-temperature region where antisymmetric exchange dominates the shape of the curve.