Syntheses, topological analyses, and NLO-active properties of new Cd(ii)/M(ii) (M = Ca, Sr) metal–organic frameworks based on R-isophthalic acids (R = H, OH, and t-Bu)

Abstract

Solvothermal syntheses of Cd(NO₃)₂·4H₂O and R-isophthalic acids (R = H, OH and t-Bu) in the presence of Ca(II) or Sr(II) lead to four new three-dimensional Cd(II)/Ca(II) or Cd(II)/Sr(II) heterometallic frameworks: [CdCa(m-BDC)₂(DMF)₂] (1), [CdSr₂(m-BDC)₂(NO₃)₂(DMF)₄] (2), [CdCa(OH-m-BDC)₂(H₂O)₂]·2Me₂NH (3), and (Me₂NH₂)₂[Cd₂Ca(Bu^t-m-BDC)₄] (4) (m-H₂BDC = isophthalate, OH-m-H₂BDC = 5-hydroxyisophthalate and Bu^t-m-H₂BDC = 5-butylisophthalate). All of these compounds except for 4 crystallize in acentric (or chiral) space groups and the bulk materials for 1 and 3 display strong powder SHG efficiencies, approximately 1.54 and 2.31 times than that of a potassium dihydrogen phosphate (KDP) powder. Topological analyses show that 1 and 2 have structures with sxb and dia topologies, respectively, while both 3 and 4 exhibit pcu topological nets when the metal carboxylate clusters are viewed as nodes. The fluorescence properties and thermal stabilities for these compounds are also investigated.