부산대학교 도서관

Ionothermal synthesis is a novel synthetic method with the advantages of characteristic physicochemical properties of ionic liquids (ILs), thus to provide different reaction conditions to obtain new-type metal-organic frameworks.In our experimental design strategy, fully filled d10-shell metals of Zn2+ and Cd2+ and half filled Mn2+ and d8 of Ni2+ were chosen to react with 1,3,5-benzenetricarboxylic acid (H3BTC) in four sorts of 1-alkyl-3-methylimidazolium halide ([RMI]X) ILs with alkyl chain lengths ranging from 2 to 5 carbons (R = Ethyl (E), n-Propyl (P), n-Butyl (B), n-Amyl (A)) and X = Cl, Br, and I, which aims at the exploration to the effects of ILs (including cation and anion parts) on their structural features.The first series reactions of Zn(NO3)2 and H3BTC in [RMI]Br media under the same reaction conditions except for mole ratios yielded seven 3D MOFs, [Zn3(BTC)2(H2O)2]∙2H2O (1 and 2), [Zn4(BTC)2(?g4?VO)(H2O)2] (3), [EMI][Zn(BTC)] (4), [PMI][Zn(BTC)] (5), [BMI]2[Zn4(BTC)3(OH)(H2O)3] (6) and [AMI][Zn2(BTC)(OH)Br] (7). The diverse structural features, including various coordination numbers of Zn2+, the coordination modes of the BTC from ??3 to ??6 and the role of the IL cation in the final structures, demonstrated remarkable advantages of the ionothermal reaction systems in obtaining novel MOF compounds.The second series ionothermal reactions between Cd(NO3)2 and H3BTC in two groups of [EMI]X and [PMI]X ILs produced three 3D MOFs ([EMI][Cd2(BTC)Cl2] (8), [EMI][Cd(BTC)] (9) and [PMI][Cd(BTC)] (10), in which ILs play an essential structure-directional and charge-compensating role. Our results showed that there was finer subtlety for the nature of halide ions, coupled with the influence of the cation part in ionic liquid. The third exploration on Ni2+-H3BTC system with various combinations of ILs, three groups of ILs ([EMI]X, [PMI]X and [BMI]X), produced five 3D MOFs with two kinds of frameworks: type A [RMI]2[Ni3(BTC)2(OAc)2] (R = Ethyl (E) (11), n-Propyl (P) (12), n-Butyl (B) (13); type B [RMI]2[Ni3(HBTC)4(H2O)2] (R = P (14) and B (15)). The results indicated that the relative thermodynamic stability between the structure types depended on the cation size because of the size matching between the guest and host cage, exhibiting the effects of IL cations on the MOF structures. The halide ions of ILs also exert important effects on the structure formation through their nucleophilicty and/or basicity, which governs the form of the ligand and, hence, the resultant MOF structures.The fourth series based on the Mn-H3BTC system in two groups of [EMI]X and [PMI]X achieved three compounds with a single type of framework [RMI][Mn(BTC)] (EMI for 16; PMI for 17 and 18). The experimental results suggested [RMI][M(BTC)] was a preferred product when the metal was half filled d5-shell and the cation of ILs was [EMI]/[PMI], indicating the crucial combination influence of metal-direction and the IL cation on the MOF structures.Two compounds [BMI][Zn2(BTC)(OH)(I)] (19) and [AMI][Ni3(BTC)2(OAc)(MI)3] (20) were obtained with the auxiliary ligands coming from the reaction environment, implying that the addition of an auxiliary ligand may benefit to the synthesis of MOFs with desired properties in ionothermal reactions.In summary, our exploratory work discovers the nature of ILs actions to the MOFs: the cations often act as template, charge-compensating groups to incorporate the frameworks; the IL anions also exert important effects on the structure formation through their nucleophilicity and/or basicity. The other factors, such as metal centers and the auxiliary ligands may be a combination control factor in the configurations of MOFs.