Synthesis,structure And Properties Of Coordination Polymers Based On Viologen Carboxylate Ligands

Chromic materials refer to a class of functional materials whose colors change reversibly under external physical or chemical stimulation.They have received widespread attention because of their actual and potential application value in daily life and various high-tech fields.Due to their unique optical and electrical properties,viologen derivatives have attracted considerable attention from the chemical community at large because of their widespread use in electrochromic devices,visible-light-driven catalysis,supramolecular chemistry and so on.Introducing viologens into the coordination polymers can not only combine the advantages of organic and inorganic components,but also show good chromic properties through the synergy between them.Therefore,they have been paid more and more attention.At present,the research on the factors affecting the chromic behavior of viologens is mainly focused on the modification of guest,N-substituents and counteranions,while there are few reports on the effect of transition metal ions and auxiliary ligands on their chromic behaviors.In this paper,the asymmetric viologen derivative 1-（2-carboxyethyl）-4,4’-bipyridine bromide（HCBbpy Br）is selected as the main functional ligand,different benzenecarboxylic acids are introduced as the auxiliary ligands,and transition metal ions are used as the metal centers to construct novel viologen coordination polymers（CPs）.This article elaborates and analyzes the synthesis,crystal structures and chromic properties of thirteen coordination polymers,explains their chromic mechanism.The effects of transition metal ions and benzenecarboxylic acids as auxiliary ligands on the structure and chromic properties of the coordination polymers are also studied.The main research contents of this paper are as follows:1.1-（2-carboxyethyl）-4,4’-bipyridine bromide（HCBbpy Br）is selected to coordinate with different transition metal ions Ni²⁺,Co²⁺,Cu²⁺,Zn²⁺,and benzenecarboxylic acids1,2,4,5-benzenetetracarboxylic acid（1,2,4,5-H₄BTEC）and 1,4-dicarboxybenzene acid（p-H₂BDC）are introduced,eight similar one-dimensional（1D）double-chain like coordination polymers are obtained by solution volatilization:{[Ni_0.5（CBbpy）（H₂O）]Br·H₂O}_n（1）,{[Co_0.5（CBbpy）（H₂O）]Br·H₂O}_n（2）,{[Cu（CBbpy）₂（H₂O）]Br₂·H₂O}_n（3）,{[TM_0.5（CBbpy）（H₂O）][TM（H₂O）₆]_0.5（H₂BTEC）·H₂O}_n{TM:Zn（4）,Ni（5）,Co（6）},{[Ni（CBbpy）₂（H₂O）₂]（p-BDC）·6H₂O}_n（7）,{[Co（CBbpy）₂（H₂O）₂]（p-HBDC）₂·3H₂O}_n（8）.The study finds that compounds 3 and 4 have photochromic properties,compounds 5 and 7 have dual function of photochromic properties and dehydration-induced color changes,compound8 has thermochromic properties,while compounds 1,2 and 6 have no chromic behavior.The crystal structure of 1-3 is similar,the properties and coordination modes of the metal cations are different,resulting in different chromic properties;compounds 4-6 with the same structure also show that metal cations have different electronegativity and electron-withdrawing ability,which makes them exhibit different chromic behavior;at the same time,the similar structure of 7 and 8 also shows that metal ions have an obvious regulation effect on their chromic performance.In this section,the effect of transition metal ions on the chromic properties of viologen coordination polymers is studied.2.1-（2-carboxyethyl）-4,4’-bipyridine bromide（HCBbpy Br）is still selected as the main functional ligand,benzenecarboxylic acids iso-phthalic acid（m-H₂BDC）,1,4-dicarboxybenzene acid（p-H₂BDC）,1,3,5-benzenetricarboxylic acid（1,3,5-H₃BTC）are used as auxiliary ligands,and different transition metal ions are introduced to construct five novelcoordinationpolymersbysolutionvolatilization,{[Cd₂（CBbpy）（m-BDC）₂（H₂O）₄]·H₂O}_n（9）,{[Cd（CBbpy）（p-BDC）][Cd（CBbpy）（p-BDC）]·2H₂O}_n（10）,{[Cd（CBbpy）（HBTC）（H₂O）]·H₂O}_n（11）,{[Mn Na（CBbpy）（BTC）（H₂O）₃]·H₂O}_n（12）,{[Zn₃（CBbpy）₂（BTC）₂（H₂O）]·H₂O}_n（13）,of which,compounds 9,10,11,13 show photochromism,While no photochromic behavior of 12 is observed.Compounds 9-11 have the same CBbpy ligand and metal Cd²⁺center,the three complexes exhibit completely different two-dimensional structures due to the different auxiliary ligands of benzenecarboxylic acids.Compounds 11-13 have the same CBbpy ligand and the auxiliary ligand of 1,3,5-H₃BTC.Due to the different metal cations,the three complexes show different structural configurations and photochromic behaviors.In this section,we mainly study the effects of transition metal ions and auxiliary ligands on the structures and chromic properties of the coordination polymers.