Synthesis,Crystal Structure And Properties Of Metallacrowns Containing Pyrazine

Metal crown ether has broad application prospects in the fields of magnetic,biomedicine,catalytic and optical.In this paper,2-hydroxamic acid（pyzha）and 5-methyl-2-hydroxamic acid（mpyzha）were synthesized.Coodinated with Cu（II）and Ln（III）salts and using self-assembly method,we synthesized nine sixcoreheteronuclear metallacrowns which captured different rare earth metal ions,eight four-core expansion metallacrown complexes and one metal coordination polymer.These complexes were characterized by IR spectrum,UV absorption spectrum,fluorescence spectrum and TGA-DTA experiment.The crystal structures are determined by single crystal X-ray diffraction methods.The complexes are as follows:（1）[PrCu₅（pyzha）₅（H₂O）₅（OCH₃）（NO₃）₂]（2）[TbCu₅（pyzha）₅（H₂O）₇（NO₃）]·NO₃·ClO₄]（3）[YCu₅（pyzha）₅（H₂O）₆（OCH₃）（NO₃）（ClO₄）₂]·H₂O（4）[TmCu₅（pyzha）₅（H₂O）₈]·2（NO₃）·ClO₄·H₂O（5）[GdCu₅（pyzha）₅（H₂O）₈（ClO₄）₂]·NO₃（6）{[ErCu₅（pyzha）₅（OCH₃）₃（NO₃）1（ClO₄）₂]·H₂O}n（7）[ErCu₅（mpyzha）₅（H₂O）₆（ClO₄）（NO₃）]·2H₂O（8）[TbCu₅（mpyzha）₅（H₂O）₄（ClO₄）（NO₃）]（9）[GdCu₅（mpyzha）₅（H₂O）₅（μ-NO₃）（NO₃）]2X-ray diffraction experiments show that : complex 1,2,3,4,5,6,are monoclinic with space group P21/c respectively.Complex 7,8,9 are triclinic with space group P-1.Complex 1,2,3,4,5,7,8 are similar,all based on the structural unit of [-M-N-O-],capturing.Pr,Tb,Y,Tm,Gd and Er ions.Core ring atom tends to be at the same plane.Five metal atoms form the ring and the ring is similar to a regular pentagon,one metal iron coordinates with two ling and makes two five-membered chelate rings,and ten chelate rings form a star structure.Complex 6 is a metallacrown coordination polymer with two MC coordinated with a Cu-N（pyrazine）,to form a one dimensional coordination polymer.Complex 9 is a kind of dipolymer metallacrown with two NO₃-acting as bridge in the medium.IR spectral analysis showed that when combined with metal irons,the characteristic functional groups of coordination agent and its derivatives data will change.Uv–vis spectrum found that the ligand has no absorption between the 360-400 nm,but after the metal coordination,the complexes investigated in the present study have an absorption in this area,there absorption attributable to ligand charge transfer to the metal,which is LMCT.Ligand fluorescence spectra showed that the optimal excitation wavelengths is in the near ultraviolet region,the best emission is in the visible region.After the metal coordination,there is no fluorescence among all the complexes,maybe because of the quenching of Cu ion and the coordinated H₂ O.TGA-DTA analysis showed that when the lingand is coordinated with the metal,the decomposition temperature of the compound increases,the decomposition process becomes complicated,which means their thermal stability enhanced greatly...