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

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.