Construction of acylhydrazidate-extended metal–organic frameworks

Abstract

Under hydrothermal conditions, the reactions of Ba²⁺/Zn²⁺, aromatic polycarboxylic acids and N₂H₄ with or without oxalic acid were carried out, affording four new acylhydrazidate-extended metal–organic frameworks (MOFs) [Ba(pmdh)] (pmdh = pyromellitdihydrazidate) 1, [Ba(sdpth)(H₂O)₂]·0.5H₂O (sdpth = 4,4′-sulfoyldiphthalhydrazidate) 2, [Ba₂(cpth)₂(H₂O)₂] (cpth = 4-carboxylphthalhydrazidate) 3 and [Zn₂(pdh)₂(ox)]·H₂O (ox = oxalate, pdh = pyridine-2,3-dicarboxylhydrazidate) 4. The acylhydrazidate molecules pmdh, sdpth, cpth and pdh in compounds 1–4 derived from the hydrothermal in situ acylation of N₂H₄ with aromatic polycarboxylic acids. X-ray single-crystal diffraction analysis revealed that (i) in compound 1, the pmdh I molecules link the Ba²⁺ ions into a two-dimensional (2D) layer with a (4,4) topology, and then the pmdh II molecules extend these layers into a three-dimensional (3D) network; (ii) in compound 2, the sdpth molecules link the Ba²⁺ ions to form a one-dimensional (1D) square tube. Interestingly, the tubes are further linked into a 3D supramolecular network via the N–H⋯O interactions, creating synchronously big channels; (iii) in compound 3, the cpth I molecules link the Ba1 ions into a 3D network with a (10,3) topology. Ba2 and cpth II are distributed on the channels; (iv) in compound 4, Zn²⁺ and pdh aggregate to form two types of Zn₄(pdh)₄ clusters. The ox molecules act as the secondary linkers, extending the Zn₄(pdh)₄ secondary building units (SBUs) into a 3D network with a 6⁶ topology. The photoluminescence analysis indicates that compounds 3 and 4 emit green light with maxima at 495 nm for 3 (λ_ex = 397 nm), and 522 nm for 4 (λ_ex = 395 nm), respectively. At 77 K, the activated 2 and 4 can adsorb N₂ in amounts of 58.31 cm³ g⁻¹ for 2 and 38.38 cm³ g⁻¹ for 4, respectively.