A series of metal–organic frameworks based on polydentate Schiff-base ligands derived from benzil dihydrazone: synthesis, crystal structures and luminescent properties

Abstract

A series of metal–organic frameworks {[AgL¹]ClO₄}_n (1), {[AgL¹₂]BF₄}_n (2), {[AgL¹(NO₃)](CH₃CH₂OH)}_n (3), {[ZnL¹₂(NCS)₂]CH₃CN}_n (4), [AgL²(NO₃)]_n (5), {[FeL²₂Cl₂]·CH₃CN}_n (6), {[MnL²₂(NCS)₂]·(CH₃CH₂OH)}_n (7) and [ZnL²₂(NCS)₂]_n (8) have been synthesized and structurally characterized by IR spectroscopy, UV spectroscopy, thermogravimetric (TG) analyses, luminescent spectroscopy and complete single-crystal structure analyses, where L¹ is (N′,N′-bis[1-(pyridin-4-yl)methylidene]benzil dihydrazone) and L² is (N′,N′-bis[1-(pyridin-3-yl)methylidene]benzil dihydrazone), respectively. The structure of 1 exhibits a two-dimensional layer network featuring trimetal 36-membered non-planar macrocycles. Polymer 2 is a one-dimensional chain structure with tetranuclear metallacyclic rings. For polymer 3, each ligand acts as a bidentate ligand to bind two Ag(I) centers and each silver center is coordinated to two N-donors from two ligands forming a one-dimensional chain. Polymer 4 displays a two-dimensional layer network containing tetranuclear 68-membered metallocyclic rings. Polymers [AgL²(NO₃)]_n (5), {[FeL²₂Cl₂]·CH₃CN}_n (6), {[MnL²₂(NCS)₂]·(CH₃CH₂OH)}_n (7) and [ZnL²₂(NCS)₂]_n (8) show all one-dimensional chain structures containing bimetallic 8-membered rings and tetrametallic 42-membered rings for 5, bimetallic 34-membered quadrangular rings for 6 and 7, and bimetallic 30-membered quadrangular rings for 8, respectively. The luminescent properties of L¹, L² and 1–8 in the solid state were investigated.