Structural diversity and properties of five 3D metal-organic frameworks based on a pyridine-substituted triazolyl benzoate ligand

Three new 3D metal-organic frameworks, namely {[Zn(L)₂]} _n (2), {[Cu(L)3H₂O]3H₂O}n (4), and {[Ag(L)]3H₂O}n (5) where HL≤4-[3-methyl-5-(pyridin-4-yl)-1,2,4- triazol-4-yl]benzoate, have been synthesized by reaction of the HL ligand and ZnII, CuII, and AgI salts under similar experimental conditions. By introducing the secondary ligand terephthalic acid (H₂bdc), another two new compounds {[Zn_1.5L2(bdc)_0.5]3H₂O}n (1) and {[Cu(L)(bdc)_0.5H₂O]}_n (3) with different 3D structures were obtained. Compound 1 possesses a three-fold interpenetrating framework, with {3².4².5⁴.6²} 2{3².4².5⁶.6⁵} topology. To the best of our knowledge, 2 is an unusual example of four-fold framework guest-free metal organic framework material. Compound 3 reveals a seven-connected ose topology; magnetic susceptibility measurements indicate that it has dominating antiferromagnetic couplings between metal centres. Photoluminescence measurements of 1, 2, and 5 in the solid state at room temperature show that all coordination networks exhibit a red shift in the emission spectra, which can be assigned to an intraligand π-π*transition.