Tuning Different Kinds of Entangled Networks by Varying N-Donor Ligands: From Self-Penetrating to Multi-interpenetrating

Abstract

Via hydrothermal synthesis, the self-assembly of Zn(II) ions and H2fum with four flexible N-donor ligands, bpp, bib, bix, and bmix, generated five interesting entanglement systems (H2fum = fumaric acid, bpp = 1,3-bi(4-pyridyl)propane, bib = 1,4-bis(N-imidazolyl)butane, bix = 1,4-bis(imidazol-1-ylmethyl)-benzene, bmix = 1,4-bis(2-methylimidazol-1-ylmethyl)-benzene): {[Zn(fum)(bpp)]·H2O}n (1), {[Zn(fum)0.5(bib)1.5(H2O)]·NO3·3H2O}n (2), {Zn(fum)(bib)}n (3), {[Zn2(fum)2(bix)2]·3H2O}n (4), and {[Zn(fum)(bmix)0.5]·0.5H2O}n (5). Their structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses, IR spectra, X-ray powder diffraction (XRPD), and thermogravimetric (TG) analyses. Compound 1 exhibits a rare 3D self-penetrating network with an unprecedented (85·10) topology. Compound 2 features a normal mode of 4-fold diamondoid interpenetrating net. However, in compound 3, five diamond networks interweave to form an interpenetrated diamond framework in an “abnormal” [3 + 2] mode. Compound 4 crystallizes in the orthorhombic crystal system and chiral space group P212121, which can be defined as an unusual 4-fold [2 + 2] interpenetrated unc-c net. Compound 5 displays a 2-fold interpenetrated 3D network with the classical pcu topology. A comparison of all compounds demonstrates that the structural characteristics of flexible N-donor ligands play a great role in the assembly of such different frameworks. Moreover, the luminescent properties of compounds 1–5 in the solid state have also been investigated.