| The d-f heteronuclear complexes with novel and unique structures have potential applications in luminescent materials,sensors,and crystal functional materials,in which the luminescence of Ln（III）sensitized by transition metal complexes has become a research hotspot recently.V-type bis-Schiff base ligands not only have multiple coordination sites,multiple coordination modes and strong chelating coordination ability,but also have inner donor N2O3to coordinate with transition metal ions,and the outer site O2O2 to coordinate with Ln（III）,making it one of the best ligands for construction of d-f heteronuclear complexes.Therefore,studies on the synthesis and properties of d-f heteronuclear complexes based on V-type bis-Schiff base were carried out,and the effects of ZnII/CdII and auxiliary ligands on the structure and properties of heteronuclear complexes were deeply explored,further revealing the structure-activity relationship between transition metal complex units and sensitization of Ln（III）luminescence,and laying a theoretical foundation for its application.In this paper,V-type bis-Schiff base:bis（5-bromo-2-hydroxy-3-methoxy）-3-oxopentane-1,5-diamine（H2L1）and bis（2-hydroxy-3-methoxy）-3-oxopentane-1,5-diamine（H2L2）are selected as the main ligands,nicotinic acid（HNIC）,isonicotinic acid（HIN）and 4-4’-bipyridine（4-4’-bipy）are auxiliary ligands,and six kinds of Zn-Ln heteronuclear clusters and four kinds of Cd-Ln heteronuclear polymers are obtained through interfacial diffusion as follows:（1）Zn-Ln heteronuclear clusters:[Zn Ln L1（OAc）（NO3）2（CH3OH）]·x（CH2Cl2）·y（CH3OH）{Ln=Sm（1）;Eu（2）;Tb（3）;Dy（4）;Gd（5）};[Zn2Dy L22（OAc）（NIC）]NO3（6）.Among them,1-5 are heterodinuclear clusters,the auxiliary ligand niacin is introduced on this basis to obtain6,forming a heterotrinuclear cluster structure.All Zn（II）of 1-6 are five-coordinate adopting a distorted triangle-bipyrimidal configuration,and Ln（III）are ten-coordinated in a distorted bicapped square antiprism configuration.（2）Cd-Ln heteronuclear polymers:[Cd Ln L2（4-4’-bipy）（NO3）3]n·（x CH2Cl2）n·（y CH3CH2OH）n{Ln=Sm（7）;Eu（8）};[Cd Gd L1（IN）（NO3）（OAc）（CH3OH）]·（3CH2Cl2）n（9）;[Cd2Nd2L22（IN）2（NO3）2（CH3OH）2（OAc）]n（）NO3n（10）.7-9 are one-dimensional coordination polymers,and 10 are two-dimensional coordination polymers.Cd（II）in 7-10 are seven-coordinated pentagonal bipyramidal configurations,while the coordination modes of Ln（III）in7-10 make some differences,forming distorted bicapped square antiprism configuration with ten-coordinate in 7-8,nine-coordinate distorted capped square antiprism configuration in 9.As in 10,among the adjacent[Nd Cd L2]units,one is eight-coordinate distorted square antiprism configuration,and the other is ten-coordinate distorted bicapped square antiprism configuration.In summary,the radius of Cd（II）is larger than that of Zn（II）,resulting in different coordination abilities of the two and then the different types of auxiliary ligands are introduced,the synergy of the two aspects together leads to the structural differences of Zn/Cd-Ln complexes.The solid-state fluorescence properties suggest that 1-10 all appear the emission of ligand in the range of 400-460 nm with a significant blue shift about 69-106 nm.Furthermore,Zn-Sm（1）,Cd-Sm（7）,Zn-Tb（3）appear the corresponding Ln（III）characteristic emission,in which the fluorescence of the Zn-Sm（1）,Cd-Sm（7）is red,and the fluorescence of Zn-Tb（3）is green.By comparing the solid-state fluorescence of single Ln（III）complex and d-f heteronuclear complexes,it is concluded that ligands cannot sensitize the emission of Ln（III）directly,but can achieve the sensitization through the complex units forming by transition metal ions.And the similar conclusions in liquid fluorescence properties can be obtained.It is worth noting that only Cd-Sm（7）still appear the characteristic emission of Sm（III）,indicating that the solvent may have a great effect on the sensitization effect.The solid and liquid fluorescence properties depict that[Zn L1]unit can sensitize Sm（III）and Tb（III）,in which the efficiency of sensitizing Sm（III）is higher than that of Tb（III）,and[Cd L2]unit can sensitize Sm（III）.In addition,the sensitization efficiency of[Cd L]unit is higher than that of[Zn L]unit.The IC50 for scavenging hydroxyl radicals of H2L1,H2L2,and 1-10 were 14.7μM,13.1μM,3.72-13.7μM,respectively,and the IC50 for scavenging superoxide radicals were 40.7μM,24.5μM,and 7.43-40.5μM,respectively,showing the activity of complex is stronger than that of the ligand.Since the activity of the complex is mainly derived from the Schiff base ligand,indicating that the formation of the d-f heteronuclear complex can enhance the activity.The recognition performance and mechanism of 1-10 towards explosives were investigated in DMF solution.Zn-Ln clusters show high selectivity towards 2,4-dinitrophenol（DNP）and picric acid（TNP）（quenching efficiency is up to more than 90%）,and its theoretical detection limits for DNP and TNP are 1.76×10-7-2.03×10-7 M,1.93×10-7-2.16×10-7M,respectively.When the concentration of DNP and TNP is between 0-250μM,clusters 1-6 can achieve quantitative detection of the two,indicating that Zn-Ln clusters can detect DNP and TNP with high sensitivity and can be used as potential fluorescent sensors to analysis explosives.In summary,two series of Zn-Ln and Cd-Ln complexes were synthesized,and it is found that the Zn（II）and Cd（II）complex units can sensitize luminescence of Ln（III）,finally realizing the regulation in the structure and properties of the d-f heteronuclear complex based on V-type bis-Schiff base ligand. |
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