New metal-organic frameworks with large cavities: selective sorption and desorption of solvent molecules

Five novel transition metal complexes [Cd(II) (3)(tpba-2)(2)(SCN)(6)].6 THF.3 H(2)O (1), [Cu(II) (3)(tpba-2)(2)(SCN)(6)].6 THF.3 H(2)O (2), [Ni(II) (3)(tpba-2)(2)(SCN)(6)].6 THF.3 H(2)O (3), [Cd(II) (2)(tpba-2)(SCN)(3)]ClO(4) (4), [Cu(I) (3)(SCN)(6)(H(3)tpba-2)] (5) [TPBA-2 = N',N'',N'''-tris(pyrid-2-ylmethyl)-1,3,5-benzenetricarboxamide, THF=tetrahydrofuran] were obtained by reactions of the corresponding transition metal salts with TPBA-2 ligand in the presence of NH(4)SCN using layering or solvothermal method, respectively. The results of X-ray crystallographic analysis showed that complexes 1, 2 and 3 are isostructural and have the same 2D honeycomb network structure with Kagomé lattice, in which all the M(II) (M = Cd, Cu, Ni) atoms are six-coordinated, and the TPBA-2 ligands adopt cis,cis,cis conformation while the thiocyanate anions act as terminal ligands. Capsule-like motifs are found in 1, 2 and 3, in which six THF molecules are hosted, and the results of XPRD and solid-state (13)C NMR spectral measurements showed that the compound 1 can selectively desorb and adsorb THF molecules occurring along with the re-establishment of its crystallinity. In contrast to 1, 2 and 3, complex 4 has different 2D network structure, resulting from TPBA-2 ligands with cis,trans,trans conformation, thiocyanate anions serving as end-to-end bridging ligands, and the incomplete replacement of perchlorate anions, which further link the 2D layers into 3D framework by the hydrogen bonds. In complex 5, the Cu(II) atoms are reduced to Cu(I) during the process of solvothermal reaction, and the Cu(I) atoms are connected by thiocyanate anions to form a 3D porous framework, in which the protonated TPBA-2 ligands are hosted in the cavities as templates.