Unexpected 4-Fold [2+2] Interpenetration and Polycatenation Behaviors in Porous Luminescent Zinc Metal-Organic Frameworks Constructed from Flexible 3,5-Bis(4-pyridylmethoxy)benzoate Ligand

Six zinc metal organic frameworks, namely, [Zn(bpmb)(HCOO)](n)center dot[Zn(bpmb)(OH)](n)center dot 4nH(2)O (1), [Zn-(bpmb)(HCOO)](n) (2), [Zn-2(bpmb)(2)(fum)](n)center dot 9nH(2)O (3), [Zn-3(bpmb)(2)(D-cam)(2)](n) (4), [Zn-2(bpmb)(1,3,5-btc)](n)center dot nDMA (5), and [Zn(bpmb)(1,2,4,5-H(2)btec)](n)center dot 4nH(2)O (6) (Hbpmb = 3,5-bis(4-pyridylmethoxy)benzoic acid; H(2)fum = fumaric acid; D-H(2)cam = D-camphoric acid; 1,3,5-H(3)btc = 1,3,5-benzenetricarboxylic acid; 1,2,4,5-H(4)btec = 1,2,4,5-benzenetetracarboxylic acid; DMA = N,N-dimethylacetamide), were synthesized under solvotherrnal conditions. Their structures were characterized by EA, IR, PXRD, TG, and single-crystal XRD. Complex 1 is constructed of two independent neutral 3D MOFs with large 1D nanosized square channels, which are further entangled by each other to give an unexpected 4-fold [2 + 2] interpenetrating architecture. Complex 2 is a 3D MOP constructed from tetradentate bpmb and bidentate formate ligands, which is an isomer of the [Zn(bpmb)(HCOO)](n) piece in 1. Complex 3 displays a 2D double-layered network that possesses 1D nanosized pores. Each 2D double layer is further interlocked with two neighboring ones to form an interesting 3D polycatenation array. Complex 4 possesses a 2D network constructed from a trinuclear [Zn-3(COO)(6)N-4] cluster and Zn-cam double-helical chain. Complex 5 is a 3D porous MOF constructed from tridentate bpmb and hexadentate 1,3,5-btc ligands. Complex 6 exhibits a 2-fold interpenetrating 2D wavelike (4,4) network constructed from bidentate bpmb and 1,2,4,5-H2btec ligands. The bpmb ligand adopts four types of coordination modes in 1-6. The secondary carboxylate ligands have obvious effects on their coordination architectures. Tetrahedral-, octahedral-, and trigonal-bipyramidal geometries around Zn(II) ions are observed. A general solvothermal method is proposed for preparing carboxylate complexes in DMF-H2O solution without any basic additive. In the preparation of 3, maleic acid is converted to a fumarate ligand. The thermal stabilities of six complexes and N-2 adsorption behaviors of 1 and 3 are investigated. All the Zn(II) complexes emit blue luminescence originating from ligand-centered emission.