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) [(CH 3 ) 2 NH 2 ][Zn 2 (BDC)(BTB)][Zn 3 (BTB) 2 (H 2 O) 2 ]·4DMA·2C 2 H 5 OH·7H 2 O (MCF-25, 1, H 2 BDC = 1,4-benzenedicarboxylic acid, H 3 BTB = benzene-1,3,5-tribenzoic acid), and [(CH 3 ) 2 NH 2 ][Zn 2 (BDC)(BTB)]·3DMF·2H 2 O (MCF-26, 2 ), synthesized by solvothermal reaction and room-temperature evaporation, respectively, are constructed by Zn 2 (O 2 CR) 5 (in 1 and 2 ) and Zn 3 (O 2 CR) 6 (in 1 ) units incorporating mixed BDC 2− and BTB 3− ligands. 1 is composed of two different frameworks with 2D 6 3 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 Zn 2 (O 2 CR) 5 SBUs.