Systhesis, Crystal Structure And Properties Of Metallacrowns Containing Pyrazine

Metallacrowns has broad application prospects in the fields of optical, magneticand catalytic. In this paper,5-methyl-2-hydroxamic acid (mpyzha),salicylaldehyde-5-methyl pyrazine hydrazones (hbzpyzh) andpyrazine-2,3-dihydroxamic acid (pyzdha) was synthesized. Coodinated with Cu(II)and Ln (III)salts using self-assembly method, we synthesized foursix-coreheteronuclear metal crown ethers which has capture different rare earth metalions, one four-core expansion metal crown ether complexe and one metalcoordination polymer. These complexes were characterized by IR spectrum, Uv-visabsorption spectrum, fluorescence spectrum and TGA-DSC experiment. The crystalstructures are determined by single crystal X-ray diffraction methods.The complexes are as follows:Diethyl pyrazine-2,5-dicarboxylate (diEpyza)[LaCu5(mpyzha)5(H2O)8](ClO4)34H2O(1)[NdCu5(mpyzha)5(H2O)5(SO3)(NO3)2](ClO4)5H2O(2)[NdCu5(mpyzha)5(H2O)8(NO3)2](NO3)7H2O(3)[SmCu5(mpyzha)5(H2O)6(ClO4)(NO3)](NO3)7H2O(4)[Cu2(hbzpyzh)2(COO)(H2O)(DMF)] ClO43H2O(5)[Cu2(pyzdha)2(H2O)2](ClO4)22H2O(6)X-ray diffraction experiments show that: diEpyza and complex2are bothmonoclinicwith space group P21/c. Complexes1,3,4,5are triclinic, space group are P.Complex6is orthorhombic, space group is P212121.diEpyza is locatedaround aninversion center, the molecule is essentially planar. Cmplexes1-4are similar, allbased on the structural unit of [-M-N-O-], captures La, Nd and Sm ions. Core ringatom tends to be at the same plane. Five metal atoms form the ring are similar to aregular pentagon, one metal iron coordination with two lingand makes twofive-membered chelate rings, ten chelate rings form a star structure. The moleculesare bowl-shaped, cmplexe4have a greater difference with the other three complexes,two metal crown ethermolecules associating with each other to form the associatingmolecules. Complex5is a quad-core ring structure: four copper iron coordinate withtwo hbzpyzh, a cavity is formed between the two ligand structure while two formicacid combines them. Complex6is a coordination polymer, a metal coordinate with two ligands forms a linear structure. Apipe structure is formed by hydrogen bondingbetween two polymer chainsIR spectral analysis showed that when combine with metal irons,thecharacteristic functional groups ofcoordination agent and its derivatives data happenspecific change.Uv–vis spectrum found that the ligand has no absorption in the360-410nm, butafter the metal coordination, the complexes investigated in the present study have aabsorption in this area, there absorption attributable to ligand charge transfer to themetal, which is LMCT.Ligand fluorescence spectra showed that: the optimal excitation wavelengths inthe near ultraviolet region, the best emission is in the visible region.After the metalcoordination, optimal excitation wavelength compounds1,4and best emissionwavelength blue shift has occurred, and the optimal excitation wavelength isabsorbed by nearby LMCT. The remaining complexes have appeared redshift.TGA-DSC analysis showed that when the lingand is coordinate with the metal,the decomposition temperature of the compound increases, the decomposition processbecomes complicated, means their thermal stability greatly enhanced.Quantum chemistry calculated frontier molecular orbital energy value show thatLUMO and HOMO orbital of complexesenergy gap decreases, consistent with theexperimental results.