Multicomponent Self-assembly Of Iron(?) Imidazole Coordination Supramolecules And Their Properties

Based on the assembly concept of supramolecular chemistry,considerable attention has been paid to the construction of supramolecular coordination compounds with highly complex and hierarchical structures.The application of the general principles of metal ions combined with multidentate ligands has allowed the rational design of a wide range of highly symmetric architectures on the basis of self-assembly concept.In this paper,a seris of mononuclear,tetranuclear and octonuclear iron???imidazole coordination supramolecules were well-designed and constructed through the multicomponent self-assembly approach.Moreover,their spin-crossover properties and host-guest behaviors were further investigated.The main research work is composed of four sections as follows:?1?Polymorphism of mononuclear iron???supramolecular complex:two homochiral polymorphs?1 and 2?of mononuclear iron???complex fac-?-[Fe?L₁?₃]?BF₄?₂[L₁=S-1-phenyl-N-?1-buty-imidazole-2-ylmethylene?ethylamine]were obtained.X-ray single crystal diffraction results showed that polymorph 1 crystallized in the cubic space group P2₁3,while polymorph 2 crystallized in the trigonal space group R₃.The different crystal packing,which results from the differences in C-H…?interactions pattern,were responsible for the existence of the two polymorphs.Moreover,polymorph 1 underwent a gradual spin-crossover behavior,whereas polymorph 2 remained high-spin state but showed a typically ferroelectric feature.?2?Supramolecular isomerism of mononuclear iron???supramolecular complex:two iron???supermolecularisomers,namelyfac-?-[Fe?L₂?₃]?ClO₄?₂?3?(L₂=R-1-phenyl-N-??1-hexyl-5-methyl-1H-imidazol-2-ylmethylene?ethanamine?and fac-?-[Fe?L₃?₃]?ClO₄?₂?4??L₃=R-1-phenyl-N-?1-hexyl-4-methyl-1H-imidazol-2-ylmethylene?ethanamine?,were obtained.The structures of these two isomers were extremely similar with only methyl position differences of the ligands.Magnetic investigations,X-ray crystal structures and density functional theory?DFT?calculation verified that 3 underwent a partial spin transition due to the strong ligand field imparted by the electron-donating methyl groups at 5-position on imidazole moieties.In contrast,4 was stabilized at high-spin state because of the strong steric hindrance when the three methyl“legs''were changed from 5-position to 4-position on imidazole moieties.In addition,a new complex 5 without methyl groups attached to imidazole rings was introduced and characterized to further corroborate the steric influence on spin state.Complex 5 exhibited a gradual spin-crossover behaviour with T_1/2=258 K.?3?Tetrahedral Fe₄^?L₆ coordination cages:Two di?imidazole aldehyde?derivative building blocks were synthesized from hydroquinone and 1,4-dihydroxynaphthalene,respectively.And the di?imidazole aldehyde?components,R-1-?naphthalen-2-yl?ethanamine,and iron???ions were choose as building blocks to further allow the construction of metal-organic cages[Fe₄?L₄?₆]?CF₃SO₃?₈?6?and[Fe₄?L₅?₆]?CF₃SO₃?₈?7?through the multicomponent self-assembly approach.Single crystal X-ray diffraction analysis confirmed the edge-capped capsules,which were assembled from six imidazole Schiff-base ligands and four iron???ions.Interestingly,these tetrahedral metal-organic cages had rare cubic-like cavities with benzene?or naphthalene?moieties situated at each face,and iron???ions occupyed half vertices of the artificial cube.Host-guest chemistry study in solution revealed that cages 6-7 possesse enclosed cavities suitable for encapsulation fullerene C₆₀ forming 1:1host-guest complexes,while no encapsulation of C₇₀ guest in the hosts were observed.Both the size and shape of the cavities and aromatic panels to provide favourable aromatic stacking interactions were crucial for achieving selectively encapsulate fullerene guests.In addition,the solid state spin-crossover properties of the iron???centers were influenced by guest binding of fullerene C₆₀.?4?Octonuclear Fe₈^?L₁₂ coordination cages:Two di?imidazole aldehyde?derivative building blocks were synthesized from resorcinol and 3,5-dihydroxytoluene,respectively.And the di?imidazole aldehyde?components,R-1-?4-methoxyphenyl?ethanamine,and iron???ions were choose as building blocks to further allow the construction of metal-organic cages[Fe₈?L₆?₁₂]?CF₃SO₃?₁₆?8?and[Fe₈?L₇?₁₂]?CF₃SO₃?₁₆?9?through the multicomponent self-assembly approach.Single crystal X-ray diffraction analysis confirmed the edge-capped capsules,which were assembled from twelve imidazole Schiff-base ligands and eight iron???ions.Amazingly,the cubic metal coordination cages,which served as secondary building units,were further assembly into a higher-order porous supramolecular frameworks through crystal packing.The porous materials 8 and 9 could adsorb iodine?I₂?,while the adsorption capacity of tetrathiafulvalene?TTF?was very slow.Interestingly,when 8 and 9 adsorbed a certain amount of I₂ before the adsorption of TTF,the adsorption rate of TTF were improved dramatically.The collaborative adsorptions could be attribute to the charge-transfer phenomena between I₂ and TTF.In addition,magnetic investigations of 8 and 9 showed gradual spin-crossover behaviours,respectively.