The Construction And Properties Of Complexes Based On Nitrogen Heterocyclic Carboxylic Ligand

Due to unique structure and wide application,compounds have received more and more attention in recent years.Because the carboxylate ions in nitrogen heterocyclic carboxylic acid ligands have strong coordination and chelation with metal ions.The combination of two orphaned electrons of per oxygen atom and multiple coordination modes with metal ions is used to synthesize organic framework complexes.In the paper,a total of sixteen complexes were synthesized based on 5-（3-carboxy-phenyl）-pyridine-2-carboxylic acid（H₂cppca）,4-（4-carboxyphenyl）picolinic acid（H₂cppc）,pyridine-3,5-dicarboxylic acid（3.5-H₂pydc）and characterized by single crystal X-ray diffraction,elemental analysis,infrared spectroscopy,thermogravimetry and powder X-ray diffraction.And their magnetic and fluorescent properties were also researched.The details are as follows:1.Fiveisomorphiclanthanidemetal-organicframeworks{[Ln₂（cppca）₂（ox）（H₂O）₂]·2H₂O}_n[Ln=Eu（1）,Gd（2）,Nd（3）,Pr（4）,Tb（5）],were synthesizedsuccessfullywhichwereconstructedfrom5-（3-carboxy-phenyl）-pyridine-2-carboxylic acid（H₂cppca）,oxalate（H₂ox）and lanthanide metal salt.Compounds 1-5 are three-dimension network structures with 1D channel of6.31×10.13?²,showing an（4,5）-connected topology net with Schlafli symbol{4⁴.6²}{4⁴.6⁴.8²}.Fluorescent experiment indicated that compounds 1 and 5 showed sensitive luminescence quenching response to aniline,and the corresponding quenching constants（Ksv）are 2.81×10⁴M^-11 for 1 and 3.14×10⁴ M^-11 for 5,respectively.The detection limits of them to aniline are 3.06μM for 1 and 2.29μM for 5.Moreover,complexes 1 and 5 are very stable and their reusability is relatively high and the fluorescence can be easily recovered after washing.2.Ten kinds of compounds were synthesized successfully under solvothermal conditions which were constructed from 4-（4-carboxyphenyl）pyridinecarboxylic acid（H₂cppc）and transition metal ions Co（II）,Ni（II）,Mn（II）,Zn（II）,Pb（II）,Cd（II）,Cu（II）and lanthanide metal ions La（III）and Eu（III）.And their structures were investigated in turn.Then compounds6-13 were characterized and analyzed in detail by single-crystal X ray diffraction,elemental analysis,IR spectroscopy,thermal analysis and powder X-ray diffraction.At the same time,the magnetic properties of the complexes 6,7,9,and 13 and fluorescence properties of 8,10,11,and 12 were also investigated.The single crystal X-ray diffraction analysis showed that compounds 6-8 belong to isomorphic complexes,and the structures of the complexes 9 and10 are also the same,belonging to the same crystal system and space group,respectively.The rest of compounds are two-dimensional structures except for complex 13 which is one-dimensional chain structure.Compound 12 was synthesized by H₂cppc,oxalic acid and La（II）ion with a two-dimensional two-layer structure.The metal center of complex 15 is Eu（III）and Co（II）,which are bonded and form a 12-membered ring via a carboxyl group O,which are interconnected to form a two-dimensional network structure.The magnetic properties of the complexes 6,7,9,and 13 showed that the complexes 6 and 9 exhibited antiferromagnetic interactions,but compounds 7 and 13 displayed the ferromagnetic interactions.The fluorescence properties of these complexes showed that the fluorescence emission peaks of the complexes 8,10,11,and 12 were similar to the ligand,indicating that the fluorescence of them may be derived from the fluorescence of the ligand（H₂cppc）,which were attributed to the n→π*andπ→π*charge transitions in ligands（LLCT）and interactions between H₂cppc and the central metal（LMCT）.3.A novel compound[PbCuCl（3.5-pydc）]_n（16）（3.5-H₂pydc=pyridine-3,5-dicarboxylic acid）was obtained through the hydrothermal method.In compound 16,two Pb（II）are bridged into a Pb₂O₂ dimer by two carboxyl oxygen atoms from 3,5-pydc^2-anions,and each Pb₂O₂dimer interconnected with each other into a 2D puckered Pb-O-Pb layer.Two Cu ions are bridged into a Cu₂Cl₂ dimer by two chlorine ions,and the-Pb-O-Pb-layer and Cu₂Cl₂ dimers are joined into a novel 2D puckered-Pb-O-Pb-Cu-Cl-layer,which are further pillared to form a 3D network by 3,5-pydc^2-anions.Compound 16 exhibits weak blue light emission under the UV light with the maximum emission peak at 383 nm upon excitation at 260 nm.