A photoluminescent six-coordinated zinc(ii) complex with hydroxides as axial ligands, [Zn(Hhpa)2(OH)2] (Hhpa = 3-hydroxypicolinamide)

Structure and NMR properties of the dinuclear complex di-μ-azido-κ4 N 1:N 1-bis-[(azido-κN)(pyridine-2-carboxamide-κ2 N 1,O)zinc(II)]

The new diamagnetic complex, [Zn2(N3)4(C6H6N2O)2] or [Zn2(pca)2(μ1,1-N3)2(N3)2] was synthesized using pyridine-2-carboxamide (pca) and azido ligands, and characterized using various techniques: IR spectroscopy and single-crystal X-ray diffraction in the solid state, and nuclear magnetic resonance (NMR) in solution. The mol-ecule is placed on an inversion centre in space group P . The pca ligand chelates the metal centre via the pyridine N atom and the carbonyl O atom. One azido ligand bridges the two symmetry-related Zn2+ cations in the end-on coordination mode, while the other independent azido anion occupies the fifth coordination site, as a terminal ligand. The resulting five-coordinate Zn centres have a coordination geometry inter-mediate between trigonal bipyramidal and square pyramidal. The behaviour of the title complex in DMSO solution suggests that it is a suitable NMR probe for similar or isostructural complexes including other transition-metal ions. The diamagnetic nature of the complex is reflected in similar 1H and 13C NMR chemical shifts for the free ligand pca as for the Zn complex.

Novel primary amide-based cationic metal complexes: green synthesis, crystal structures, Hirshfeld surface analysis and solvent-free cyanosilylation reaction

A new symmetrical and flexible primary amide functionalized ligand, 2,2'-(ethane-1,2-diylbis((pyridin-2-ylmethyl)azanediyl))diacetamide (2-BPEG), has been synthesized and structurally characterized. Using this multidentate ligand, four novel metal complexes, namely [Cu(2-BPEG)](ClO4)2·0.5H2O (1), [Zn(2-BPEG)](ClO4)2 (2), [Zn(2-BPEG)](ZnCl4)·H2O (3) and [Cd(2-BPEG)(H2O)](ClO4)2·H2O (4), have been synthesized under ambient conditions and characterized by elemental, spectroscopic and thermal analysis, and single and powder X-ray diffraction. Complexes 1-3 are hexacoordinated with an N4O2 donor set (provided by the hexadentate 2-BPEG ligand), while complex 4 is heptacoordinated with an additional coordinated water molecule. In all cases, the 2-BPEG ligand acts as a hexadentate ligand. A change in the starting metal salt has resulted in the formation of 2 and 3 with different tetrahedral anions, ClO4- and ZnCl4-, respectively. This has provided an opportunity to showcase anion-directed supramolecular networks for these compounds. Compounds 1, 2 and 4 with perchlorate anions show similar and comparable intermolecular interactions in their 3D networks. On the other hand, the supramolecular self-assembly of 3 is dominated by a variety of intermolecular interactions such as C-HCl, N-HCl, O-HCl and C-HO due to the presence of a tetrachlorozincate(ii) ion. Moreover, the role of weak intermolecular interactions in the crystal packing has been analysed and quantified using Hirshfeld surface analysis. Furthermore, compound 4 exhibiting an open Lewis acid site has been found to be a very efficient and recyclable heterogeneous catalyst for the solvent-free cyanosilylation of various aldehydes with trimethylsilyl cyanide (TMSCN) producing the corresponding trimethylsilyl ether in high yields.