MOFs Based On Linear Cluster Secondary Building Units And Their Reactivity

With the increasing in-depth understanding of metal-organic frameworks（MOFs）,chemists have developed post-synthetic modification methods to obtain structures that are not directly accessible through the“one-pot”reaction.Single-crystal to single-crystal conversion（SCSC）involves atomic rearrangement in the solid state without breaking the long-range order.The porous scaffold-like structures of MOFs thus allow an unlimited SCSC possibility because small molecules can penetrate into the pores of the MOFs to facilitate guest inclusion/exchange,metal ion metathesis/incorporation,coordination solvate/linker exchange,and linker modification,without severe framework distortion that would shatter the crystal.In this thesis,we used the benzene-1,3,5-tribenzoic acid（H₃BTB）to react with Cd²⁺and Co²⁺under different conditions to obtain a series of two-/three-dimensional（2D/3D）MOFs,and explored their SCSC reactivity.We also also explored the gas adsorption properties of the product obtained.The key results are briefly described as follows:I)We select a 2D double-layer MOF[Cd₃（BTB）₂（DEF）₄]·xDEF（1;DEF=N,N’-diethylformamide）as the starting material to react with dipyridyl ligands of different lengths and angles,including 4,4’-dipyridyl sulfide（DPS）,4,4’-dipyridyl disulfide（DPDS）and 2-bis（4-pyridyl）ethane（BPEA）to obtain two 3D non-interpenetrated structures[Cd₃（BTB）₂（DPS）₂]·xSol（3）and[Cd₃（BTB）₂（DPDS）₂]·xSol（4）,and one interpenetrated structure[Cd₃（BTB）₂（BPEA）（H₂O）₂]·xSol（5）.Subsequently,solvent-assisted linker exchange（SALE）of a documented 3D interpenetrated structure[Cd₃（BTB）₂（BPEE）（H₂O）₂]·xSol（2c;BPEE=trans-1,2-bis（4-pyridyl）ethylene）is selected to reacted with 4,4’-bipyridine（BIPY）,4,4’-azopyridine（AZOPY）,BPEA,1,3-bis（4-pyridyl）propane（BPP）,1,4-di（pyrid-4-yl）benzene（DPB）and pyrazine（PZ）,fromwhichaseriesoftopologicallyidenticaldaughterMOFs,[Cd₃（BTB）₂（BPEE）（BIPY）₂]·xSol（6a）,[Cd₃（BTB）₂（BPEE）（AZOPY）₂]·xSol（6b）,[Cd₃（BTB）₂（BPEE）（BPEA）₂]·xSol（6c）,[Cd₃（BTB）₂（BPEE）（BPP）₂]·xSol（6d）,[Cd₃（BTB）₂（BPEE）（DPB）₂]·xSol（6e）,[Cd₃（BTB）₂（BPEE）（PZ）（H₂O）]·xSol（7a）,[Cd₃（BTB）₂（BPEE）（PZ）₂]·xSol（7b）were obtained,in addition to the non-interpenetrated MOFs 3 and 4 upon its reaction with DPS and DPDS.Ultimately,with the long time exposure of 2c to a large excess of BPEE ligand,a 3D self-interpenetrated structure[Cd₃（BTB）₂（BPEE-a）（BPEE-b）_0.25（BPEE-c）_0.25（H₂O）_1.75]·xSol（8;the a,b,and c suffice denote BPEE ligands responsible for interpenetration,self-interpenetration and terminal coordination）is obtained.II)Doping of Co²⁺in MOF 1 results in a 2D heterometallic double-layer compound[Cd_2.25Co_0.75（BTB）₂（DEF）₄]?xDEF（9）with statistical Cd and Co distribution within the linear M₃ SBU.The SCSC conversion of compound 9 with DPS,DPDS,BIPY in CHCl₃ give rise to two 3D non-interpenetrated structures[Cd_2.25Co_0.75（BTB）₂（DPS）₂]?xSol（10）and[Cd_2.25Co_0.75（BTB）₂（DPDS）₂]?xSol（11）,and a 3D interpenetrated structure[Cd_2.25Co_0.75（BTB）₂（BIPY）（H₂O）₂]?xSol（12）.III)AsthecontentofCo²⁺increased,a3DMOF[Co₁₁（BTB）₆（NO₃）₄（DEF）₂（H₂O）₁₄]?xSol（13）without Cd²⁺is obtained.MOF 13 is sustained by a rare combination of a linear trinuclear Co₃ and two types of dinuclear Co₂ SBUs in a 1:2:2 ratio with permanent porosity,which has a significant adsorption effect on CO₂.IV)The incorporation of a secondary metal Ca²⁺（in the form of CaSO₄）targeting the heterometallic MOF topologically identical to MOF 1 unexpectedly leads to the isolation of a Cd₅-based 3D MOF of[Cd₅（BTB）₄（DEF）₂]?xDEF（14）.Although the compound contains a large non-linear Cd₅ SBU,significant“breathing effects”can be observed in different solvents and under vacuum.We have succeeded in collecting the single crystal structures in the corresponding products,[Cd₅（BTB）₄（DEF）₂]?xCHCl₃（14-CHCl₃）,[Cd₅（BTB）₄（DEF）₂]?xMeCN（14-MeCN）,[Cd₅（BTB）₄（DEF）₂]?xDEF（14-5h）,[Cd₅（BTB）₄（DEF）₃]?xDEF（14-10h）,[Cd₅（BTB）₄（DEF）（H₂O）₂]?xDEF（14-24h）.After immersing MOF 14 in 4-pyridine carboxyaldehyde（PYCA）and 4-acetylpyridine（ACPY）foroneweek,unconventionaladditionproducts[Cd₅（BTB）₄（DEF）₂（PYCA）₂]?xSol（15）and[Cd₅（BTB）₄（DEF）₂（ACPY）₂]?xSol（16）are also obtained obtained.