Assembly Of Three-dimensional Networks Based Upon Silver-ethynide Complexes Bearing Pyridyl And Carboxylate Groups

Supramolecular chemistry has currently become an important field of chemistrywhich focuses on going―beyond‖molecular chemistry. The spatial structure assembledthrough metal and conjugated complexes bearing terminal alkynes has become a newhotspot due to its superiority as nonlinear optics, luminescence materials and rigid rodmolecular wires.In recent years, silver-ethynide complexes bearing pyridyl or pyrimidyl groups havebeen systematically investigated as building units to construct novel organometallicnetworks. It has been shown that N atom in pyridyl ring usually coordinates to one silverion in silver-ethynide complex unit. And an increase of ethynyl group attached on pyridylring led to construction of higher-dimensional architecture, while silver-ethynidecomplexes bearing carboxylate group exhibit complicated binding modes to generateunpredictable topologies. Considering the above, it is reasonable that an introduction ofcarboxylate group to pyridylethynide ligand could be an avenue of assembly of highdimensional networks. It is also known that both ethynide and carboxylate groups are ableto interact with several silver ions, hence a question is whether a substitution of ethynylunit by a carboxylic group in diethynylpyridine ligand could lead to a significantlystructural change of assembled network from silver-ethynide complexes. Therefore, twonew ligands （5-Ethynyl-nicotinic acid （H₂L₁） and5-Ethynyl-pyridine-2-carboxylic acid（H₂L₂）） bearing pyridyl and carboxylate groups were designed to synthesize newsilver-ethynide complexes ([Ag₂（L1）·AgNO₃]n（1）,{[Ag₁₂（L2）₆·12AgNO₃]·5H2O}n（2）).Crystallographic studies revealed that in1, the L1ligands connects linear silver chains toform2D layer through silver-ethynide interaction and Ag-carboxylate coordination bonds,and subsequently the layers are further linked through Ag-N （pyridyl） coordination bondsto generate a3D network; however in2, L2ligand interacts with Ag8units through Ag-N,Ag-O coordination bonds, silver-ethynide interaction and Ï€-Ï€ stacking directly to assemblea3D network. Interestingly it is observed that in silver-pyridyldiethynide complexes, asubstitution of one ethynide unit attached to pyridyl ring by carboxylate group does notlead to a significantly structural change of assembled network. In solid state, both complexes are luminescent at room temperature, assigned as intraligand n-Ï€*and Ï€-Ï€*transitions.