Structural Diversity Modulated by the Ratios of a Ternary Solvent Mixture: Syntheses, Structures, and Luminescent Properties of Five Zinc(II) Metal–Organic Frameworks

A series of metal–organic
frameworks (MOFs) were systematically
synthesized through a solvent-ratio-controlled assembly: {[Et2NH2]2[Zn5(L)2(H2O)4]·2C2H5OH·2H2O}n (1), {[Et2NH2]4[Zn7(HL)2(H2L)2]·4C2H5OH·6H2O}n (2), {[Et2NH2]4[Zn6(L)2(H2L)­(H2O)2]·2C2H5OH·2H2O}n (3), {[Et2NH2]4[Zn4(L)2(H2O)2]·4H2O}n (4), and {[Et2NH2]2[Zn2(L)]·C2H5OH}n (5) (H6L = [1,1′;4′,1″]­terphenyl-3,5,2′,5′,3″,5″-hexacarboxylic
acid, DEF = N,N-diethylformamide).
Along with the altering of ratios of the ternary mixed-solvent DEF/H2O/C2H5OH used in the synthetic processes,
the coordination modes of the ligand change, which further leads to
the different structures of resultant complexes. Owing to diverse
metal centers and clusters and distinct ligand coordination modes,
these five complexes exhibit totally different and novel topologies:
complex 1 displays a (5,8)-connected 3D net, in which
the 8-connected nodes are based on trinuclear metal clusters; complexes 2–4 all exhibit 3D 4-nodal nets based
on two kinds of metal centers and two kinds of ligand coodination
modes; complex 5 shows a 6-connected uninodal 3D net.
These five complexes have been characterized by single-crystal X-ray
diffraction, thermogravimetric (TG) analyses, elemental analyses (EA),
and powder X-ray diffraction (PXRD). Luminescent properties of complexes 1–5 at room temperature and 77 K show
that all the five complexes exhibit temperature-dependent emission
properties. The calculation of density of states (DOS) was carried
out to get a better insight into the nature of the luminescence. The
obvious change of spectral colors of 3 at different temperatures
suggests that it may be well applied in temperature-sensing devices.