Four organo-templated structures with DFT-zeotype topology: Variation in symmetry of similar microporous structures

Abstract

Four novel microporous compounds H2(C2H8N2)(ZnAsO4)2 (1), H2(C2H8N2)(Co0.1Zn0.9AsO4)2 (2), H1.8(C2H8N2)(Fe0.1Zn0.9AsO4)2 (3) and H2(C2H8N2)(ZnPO4)2 (4) containing ethylenediammonium cation, H2(C2H8N2)2+ (H2en2+), and ethylenediamine molecule, C2H8N2 (en), have been hydrothermally synthesized. While 1–3 exhibit twinned DFT-zeotype structure and crystallize in P42/n, 4 is characterized by the appearance of new orthorhombic space group Pcca, previously not observed among the known DFT-zeotype compounds. The symmetry relationships analyses revealed the extended Bärnighausen tree. The main feature of the cobalt blue and reddish brown compounds 2 and 3 is their novel chemical composition which was confirmed by SEM/EDX analysis. In the structure of 1, H-atoms positions, previously not reported, were calculated and refined to reasonable positions using riding model.The DFT anionic frameworks of 1–4 are characterized by 4M, 6M and 8M tetrahedral rings, which produce three mutually perpendicular 8M ring channels. At the intersections of these channels H2en2+ cations are accommodated and hydrogen-bonded to the adjacent oxygen atoms of the framework. Only in 3, H2en2+ is partly substituted by electroneutral en to maintain charge compensation. The single-crystal Raman spectra and Fourier transform infrared (FTIR) absorption spectra were interpreted on the basis of characteristic vibrations of AsO4 and PO4 groups, as well as of NH3, NH2 and CH2 groups from the H2en2+ cation or en molecule.The results of lattice distortion and similarity analyses showed that the DFT-zeotype structures, which incorporate larger tetrahedral cations, have a higher degree of lattice distortion and are less similar to the ideal structural models derived from the aristotype.