Two Metal-Carboxylate Frameworks Featuring Uncommon 2D + 3D and 3-Fold-Interpenetration: (3,5)-Connected Isomeric hms and gra Nets

Two new interpenetrated metal-carboxylate frameworks (MCFs) [(CH3)2NH2][Zn2(BDC)(BTB)][Zn3(BTB)2(H2O)2]·4DMA·2C2H5OH·7H2O (MCF-25, 1, H2BDC = 1,4-benzenedicarboxylic acid, H3BTB = benzene-1,3,5-tribenzoic acid), and [(CH3)2NH2][Zn2(BDC)(BTB)]·3DMF·2H2O (MCF-26, 2), synthesized by solvothermal reaction and room-temperature evaporation, respectively, are constructed by Zn2(O2CR)5 (in 1 and 2) and Zn3(O2CR)6 (in 1) units incorporating mixed BDC2− and BTB3− ligands. 1 is composed of two different frameworks with 2D 63 bilayers and a rare (3,5)-connected 3D hms net giving an interesting 2D + 3D framework, whereas 2 features a novel 3-fold interpenetrated (3,5)-connected gra net with chiral, hexagonal helical channels. Structural analysis shows that the two 3D nets of hms in 1 and gra in 2 are strict isomers with the same components but different steric arrangements, which are derived from different orientations of the two axial carboxylate bridges in two isomeric Zn2(O2CR)5 SBUs.