C3-symmetric ligands carrying a rigid triaminoguanidinium backbone are important building blocks for the preparation of supramolecular coordination cages as tetrahedra or trigonal bipyramides. Coordination of Eu(III)- or Gd(III)-ions leads to 1,2,4-triazole formation, which has been reported only rarely. Using Pd(II)-complexes as a model system, this triazole formation could be analyzed in more detail. The preparation of Pd(II)-coordination compounds can be easily done under stoichiometric control. These complexes could be transformed into 1,2,4-triazoles using O2 or H2O2 as an oxidation reagent. The steric demand of the PR3-coligand seems to play a key role in the cyclisation reaction.
The quasibinary section of the intermetallic phases MAl and MGa with M=Sr and Ba have been characterised by means of X-ray diffraction (XRD) studies and differential thermal analysis. The binary phases show complete miscibility and form solid solutions M(Al Ga ) with M=Sr and Ba. These structures crystallise in the BaAl structure type with four- and five-bonded Al and/or Ga atoms (denoted as Al(4b), Al(5b), Ga(4b), and Ga(5b), respectively) that form a polyanionic Al/Ga sublattice. Solid state Al NMR spectroscopic analysis and quantum mechanical (QM) calculations were applied to study the bonding of the Al centres and the influence of Al/Ga substitution, especially in the regimes with low degrees of substitution. M(Al Ga ) with M=Sr and Ba and 0.925≤x≤0.975 can be described as a matrix of the binary majority compound in which a low amount of the Ga atoms has been substituted by Al atoms. In good agreement with the QM calculations, Al NMR investigations and single crystal XRD studies prove a preferred occupancy of Al(4b) for these substitution regimes. Furthermore, two different local Al environments were found, namely isolated Al(4b1) atoms and Al(4b2), due to the formation of Al(4b)-Al(4b) pairs besides isolated Al(4b) atoms within the polyanionic sublattice. QM calculations of the electric field gradient (EFG) using superlattice structures under periodic boundary conditions are in good agreement with the NMR spectroscopic results.
The gold-rich intermetallic compounds Sr2Au6Zn3, Eu2Au6Zn3, Sr2Au6Ga3, and Eu2Au6Ga3 were synthesized from the elements in sealed tantalum ampoules in induction or muffle furnaces. The europium compounds are reported for the first time and their structures were refined from single crystal X-ray diffractometer data: Sr2Au6Zn3 type, R3̅c, a = 837.7(1), c = 2184.5(4) pm, wR2 = 0.0293, 572 F2 values for Eu2Au6.04Zn2.96 and a = 838.1(2), c = 2191.7(5) pm, wR2 = 0.0443, 513 F2 values for Eu2Au6.07Ga2.93 with 20 variables per refinement. The structures consist of a three-dimensional gold network with a 6R stacking sequence, similar to the respective diamond polytype. The cavities of the network are filled in a ratio of 2:1 by strontium (europium) atoms and Ga3 (Zn3) triangles in an ordered manner. Sr2Au6Zn3 and Sr2Au6Ga3 are diamagnetic with room temperature susceptibilities of –3.5 × 10−4 emu mol–1. Temperature dependent susceptibility and 151Eu Mössbauer spectroscopic measurements show a stable divalent ground state for both europium compounds. Eu2Au6Zn3 and Eu2Au6Ga3 order antiferromagnetically below Néel temperatures of 16.3 and 12.1 K, respectively. Anisotropic electrical conductivity of Sr2Au6Ga3 is proven by an alignment of the crystallites in the magnetic field. Orientation-dependent 69;71Ga NMR experiments combined with quantum mechanical calculations (QM) give evidence for a highly anisotropic charge distribution of the Ga atoms.
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