Synthesis, Structure And Property Research Of Complexes Based On Metals And Bipyrazolyl Ligands

In this paper, three unprecedented semi-rigid bipyrazolyl ligands and their six complexes with Cu(â… ),Cu(â…¡),Ag(â… )å'ŒCd(â…¡) were synthesized, and characterized with element analyses, IR spectra, HNMR, MS and X-ray diffraction.The three ligands are: 4,4'-(2,3,5,6-tetramethyl-1,4-dimethylenephenyl)- 3,5-diphenylbipyrazole (H2L1) 4,4'-(2,3,5,6-tetramethyl-1,4-dimethylenephenyl)- 3,5-dimethylbipyrazole (H2L2) 4,4'-(2,7-naphthalenediylbis(methylene))-bis(3,5-diphenylbipyrazole) (H2L3)The six complexes are: {[Ag(H2L1)] (BF4)}n (1) [Ag2(H2L2)2](BF4)2·2H2O (2) {[Ag(H2L2)](NO3)}n (3) [Cd(H2L2(I)2]n (4) [Cu2(H2L2)4(SO4)2]·11H2O (5) [Cu6(L3)3]·4H2O (6)The complexes are divided into three categeries according to the styles ofcoordination:1. Dinuclear complexes: [Ag2(H2L2)2](BF4)2·2H2O (2) and [Cu2(H2L-)4(SO4)2]·11H2O (5) are OD dinuclear complexes. In which, the former adopts a discrete rectangular structure, and the later exhibits a discrete cage structure. The Ag(I) atoms are linear two-coordinated and the Cu(II) atoms are five-coordinated.2. Hexanuclear complex:[Cu6(L3)3]-4H2O (6) adopts an OD hexanuclear cage-like structure.In the structure, the pyrazolyl rings are deprotonated clearly, and the top and bottom of the cage are two nine-membered rings composite of three Cu(â… ) atoms and six N atoms. The two nine-membered rings are connected with three naphthyl rings.3. ID complexes:{[Ag(H2L')](BF4)}n (1),{[Ag(H2L2)](NO3)}n (3) and [Cd(H2L2)(â… )2]n (4) are all 1-D complexes. Ligand H2L1 adopts a trans-conformation in complex 1, and the pi-pi interaction consolidates the conformation. In complex 3, ligand H2L2 is in cis-conformation, alternate with Ag(â… ) atoms to form a 1-D chain. A zigzag chain structure is found in complex 4, in which each Cd(â…¡) atom has two I- coordinated as accessories.Conclusions can be drawn from this study:1. The substituent groups on 3,5 positions play a great role in self-assembly for bipyrazolyl ligands to adopt different conformation. Comparing with the ligand H2L2, H2L1 has C-HÏ€interaction in the free molecular and pi-pi stacking interaction in the self-assembly, which result in the difficulty to perform cis-conformation in the self-assembly with metal ions. When we use methyl group instead of the phenyl group, this problem is tackled.2. The tough thing in the self-assembly with bipyrazolyl ligands and metal ions is deprotonation. The deprotonated ligands can offer more coordination sites, and will make big contribution in the complication of the structures. However, experience indicates that in this semi-rigid bipyrazolyl system, it is difficult to be successful in deprotonation and obtaining crystals with proper size at the same time. Hence, we tried to solve this problem in hydrothermal condition, and be successful.