Hexanuclear copper(II) cages built on a central {μ3-O···H···μ3-O} moiety, 1,3-bis(dimethylamino)-2-propanolato and capping R-phosphonates: crystal structures, magnetic behavior, and DFT studies

The syntheses, structural characterization, and magnetic behavior of two new hexanuclear copper(II) complexes derived from R-phosphonic acids and 1,3-bis(dimethylamino)-2-propanol (Hbdmap) with formulas [Cu(6)(μ-bdmap)(3)(μ(3)-Ph-PO(3))(2)(μ(3)-O···H···μ(3)-O)(ClO(4))(2)(H(2)O)]·5H(2)O (1) and [Cu(6)(μ-bdmap)(3)(μ(3)-t-Bu-PO(3))(2)(μ(3)-O···H···μ(3)-O)(μ(1,3)-dca)(dca)(H(2)O)]·6H(2)O (2) (Ph-H(2)PO(3) = phenylphosphonic acid, t-Bu-H(2)PO(3) = tert-butylphosphonic acid, dca = dicyanamide) are reported. Compounds 1 and 2 are hexanuclear 3.111 R-phosphonate(2-)/1,3-bis(dimethylamino)-2-propanolato(1-) cages including in the center the [μ(3)-O···H···μ(3)-O](3-) unit. The temperature dependence of the magnetic properties of 1 and 2 clearly indicates an overall strong antiferromagnetic coupling confirmed by DFT calculations.     

Helical self-organization and hierarchical self-assembly of an oligoheterocyclic pyridine-pyridazine strand into extended supramolecular fibers

The synthesis and characterization of an alternating pyridine-pyridazine strand comprising thirteen heterocycles are described. Spontaneous folding into a helical secondary structure is based on a general molecular self-organization process enforced by the conformational information encoded within the primary structure of the molecular strand itself. Conformational control based on heterocyclic "helicity codons" illustrates a strategy for designing folding properties into synthetic oligomers (foldamers). Strong intermolecular interactions of the highly ordered lock-washer subunits of compound 3 results in hierarchical supramolecular self-assembly into protofibrils and fibrils. Compound 3 also forms mechanically stable two-dimensional Langmuir-Blodgett and cast thin films.     

About the calculation of exchange coupling constants in polynuclear transition metal complexes

The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data.     

Einkristalle von A?Nd2S3, U?Ho2S3, D?Er2S3 und E?Lu2S3 durch Oxidation reduzierter Chloride der Lanthanide mit Schwefel

Single Crystals of A? Nd₂S₃, U? Ho₂S₃, D? Er₂S₃, and E? Lu₂S₃ through the Oxidation of Reduced Lanthanide Chlorides with Sulfur The oxidation of reduced chlorides (MCl₂) or chloridehydrides (MClH_x) of the lanthanides with sulfur (850°C, 7 d, tantalum ampoule) usually results in the formation of their sesquisulfides (M₂S₃) as the main product. In the presence of appropriate fluxes (e. g., NaCl), they often are obtained as single crystals, and the flux appears to decide which modification is favourized. Single crystals of Nd₂S₃ , (from NdCl₂ + NaCl + S, 2 : 2 : 1, A-type: orthorhombic, Pnma (no. 62), Z = 4; a = 743.97(5), b = 402.78(3), c = 1551.96(9) pm, V_m = 70.015(8) cm³/mol, R , = 0.026, R_w = 0.023), Ho₂S₃ , (from Na_0.25HoClH_0.75 + S, 8 : 9, U type: orthorhombic, Pnma (no. 62), Z = 4, a = 1057.24(7), b = 384.48(4), c = 1041.15(7) pm, V_m = 63.716(9) cm³/mol, R , = 0.023, R_w = 0.020), Er₂S₃ , (from ErClH_0.67 + NaCl + S, 2 : 2 : 1, D type: monoclinic, P2₁/m (no. 11), Z = 6, a = 1744.18(9), b = 398.22(3), c = 1010.13(6) pm, β = 98.688(4)°, V_m = 69.610(7) cm³/mol, R = 0.031, R_w = 0.029) and Lu₂S₃ , (from LuClH_0.67 + NaCl + S, 2 : 2 : 1, E type: trigonal, R3 c (no. 167), Z = 6, a = 672.86(2), c = 1816.84(9) pm, c/a = 2.70, V_m = 71.497(6) cm³/mol, R = 0.023, R_w = 0.020) as well as more systematic general investigations (syntheses of the lanthanide sesquisulfides from the elements in the presence of NaCl as a flux in sealed tantalum containers at 850°C) are the main topic of the work presented here.     

Chalkogenid-Disilicate der Lanthanoide vom Typ M4X3[Si2O7] (M  Ce?Er; X  S,Se)

M₄X₃[Si₂O₇]-Type Lanthanide Chalcogenide Disilicates (M ? Ce? Er; X ? S, Se) Attempts to produce single crystals of MSe₂ (or MSe^2?X) by vapour phase transport with iodine or the oxidation of MCl₂ (or MClH) with sulfur in the presence of NaCl in sealed evacuated quartz containers often yielded well-grown single crystals with the composition M₄X₃[Si₂O₇] (M ? pr, Sm, Gd, X ? Se, and M ? Nd, Er, X ? S) as by-products. The crystal structures (tetragonal, 14₁/amd (no. 141)), Z = 8, contain two crystallographically independent M₃₊ Cations that are interconnected by chalcogenide (X_2?) and disilicate anions ([Si₂O₇]^6?). (M1)³⁺ is surrounded by eight (five X^2? and three terminal O_2? of the disilicate group), (M2)³⁺ by nine (three X^2? and six terminal O^2? of the [Si₂O₇]_6? anion) chalcogenide anions. The disilicate anion itself exhibits the eclipsed conformation with non-linear Si? O? Si bridges (angles: 128 – 133°).     

Exchange coupling in halo-bridged dinuclear Cu(II) compounds: a density functional study

A density functional study of exchange coupling in halo-bridged dinuclear copper(II) compounds has been carried out. Coupling constants calculated for full unmodeled structures, as determined by X-ray diffraction, are in excellent agreement with experimental data, confirming the ability of the computational strategy used in this work to predict the magnetic behavior of such compounds. Model calculations have been used to examine the influence of several factors on the coupling constant: the nature of the bridging and terminal ligands, the coordination environment around copper atoms, and some structural distortions frequently found in this family of complexes. A ferromagnetic coupling is predicted when N-donor terminal ligands are present, especially for bromo-bridged systems, an interesting synthetic target.