Two
series of lanthanide metal–organic frameworks (Ln-MOFs)
from two structurally related flexible carboxylate-based ligands were
solvothermally synthesized. H3L2 with additional −CH2− group provides more flexibility and different
coordination modes and conformations compared with H3L1.
As a result, 2-Ln MOFs are modulated from two-dimensional
kgd
of 1-Ln to three-dimensional
rtl
topological frameworks and further achieve
enhanced chemical stability. The Eu- and Tb-MOFs exhibit strong fluorescent
emission at the solid state because of the antenna effect of the ligands.
Interestingly, the emissions can be tuned by simply doping Eu3+ and Tb3+ of different concentrations within the Eu
x
Tb
1–x
MOFs. Notably, 2-Ln MOFs realize nearly white light emission by means of
a trichromatic approach (red of Eu(III), green of Tb(III), and blue
of the H3L2 ligand). Furthermore, 2-Ln MOFs
also exhibit water stability and demonstrate high selective and sensitive
sensing activities toward Fe(III) and Cr(VI) in aqueous solutions.
The results further highlight the importance of the ligand flexibility
on tuning MOF structures with improved structural stability and ion-sensing
properties.
Three new luminescent transition coordination polymers, namely, {[Cd(L)(4,4-bpy)]·DMF·H2O}n (1), {[Cd2(L)2(bpe)2]·3DMF·2.5H2O}n (2), and {[Cd(L)(bibp)]·2DMF}n (3), (H2L = 4,4'-[benzene-1,3-diylbis(methanediylsulfanediyl)]dibenzoic acid, 4,4-bpy = 4,4-bipyridine, bpe = 1,2-bis(4-pyridyl)ethylene, and bibp = 4,4'-bis(benzoimidazo-1-ly)biphenyl), were solvothermally synthesized using Cd2+ ions and S-containing dicarboxylate acid in the presence of different N coligands. These complexes were fully characterized via elemental analysis, infrared spectroscopy (IR), single crystal X-ray diffraction analysis, and thermal gravimetric analysis (TGA). Complexes 1-3 consist of 2-D structures through the connectivity of similar 1-D Cd-L chains by different N coligands. With an increase in the size of the N coligands, these complexes show structural changes from 2D → 3D with 3-fold interpenetration of complexes 1 and 2 to the 2-D packing modes of complex 3. The luminescence properties of these three complexes were studied in detail. The results reveal that each complex exhibits selectivity and sensitivity towards Fe3+ and Cr2O72- ions, and complex 2 demonstrates the lowest detection limit towards both ions.
Two 1-D Co(ii) compounds with different coordination geometries of the same coordination sphere exhibited field-induced slow relaxation magnetization with different D values.
Reaction of the flexible phenolic carboxylate ligand 2‐(3,5‐dicarboxylbenzyloxy)benzoic acid (H3L) with nickel salts in the presence of 1,2‐bis(pyridin‐4‐yl)ethylene (bpe) leads to the generation of a mixture of the two complexes under solvolthermal conditions, namely poly[[aqua[μ‐1,2‐bis(pyridin‐4‐yl)ethylene‐κ2N:N′]{μ‐5‐[(2‐carboxyphenoxy)methyl]benzene‐1,3‐dicarboxylato‐κ3O1,O1′:O3}nickel(II)] dimethylformamide hemisolvate monohydrate], {[Ni(C16H10O7)(C12H10N2)(H2O)]·0.5C3H7NO·H2O}n or {[Ni(HL)(bpe)(H2O)]·0.5DMF·H2O}n, 1, and poly[[diaquatris[μ‐1,2‐bis(pyridin‐4‐yl)ethylene‐κ2N:N′]bis{μ‐5‐[(2‐carboxyphenoxy)methyl]benzene‐1,3‐dicarboxylato‐κ2O1:O5}nickel(II)] dimethylformamide disolvate hexahydrate], {[Ni2(C16H10O7)2(C12H10N2)3(H2O)2]·2C3H7NO·6H2O}n or {[Ni2(HL)2(bpe)3(H2O)2]·2DMF·6H2O}n, 2. In complex 1, the NiII centres are connected by the carboxylate and bpe ligands to form two‐dimensional (2D) 4‐connected (4,4) layers, which are extended into a 2D+2D→3D (3D is three‐dimensional) supramolecular framework. In complex 2, bpe ligands connect to NiII centres to form 2D layers with Ni6(bpe)6 metallmacrocycles. Interestingly, 2D+2D→3D inclined polycatenation was observed between these layers. The final 5‐connected 3D self‐penetrating structure was generated through further connection of Ni–carboxylate chains with these inclined motifs. Both complexes were fully characterized by single‐crystal analysis, powder X‐ray diffraction analysis, FT–IR spectra, elemental analyses, thermal analysis and UV–Vis spectra. Notably, an interesting metal/ligand‐induced crystal‐to‐crystal transformation was observed between the two complexes.
A novel three-dimensional coordination polymer, namely, poly [[diaquabis(-4,4 0 -bipyridine)bis{ 3 -5-[(2-carboxyphenoxy)methyl]isophthalato}tricadmium(III)] dimethylformamide monosolvate 2.5-hydrate], {[Cd 3 (C 16 H 9 O 7 ) 2 (C 10 H 8 N 2 ) 2 -(H 2 O) 2 ]Á2C 3 H 7 NOÁ5H 2 O} n , was obtained by the reaction of ether-linked 5-[(2-carboxyphenoxy)methyl]isophthalic acid (H 3 L) with Cd II salts in the presence of 4,4 0 -bipyridine (bpy) under solvothermal conditions. In this complex, the Cd II centres are connected by the carboxylate ligands to form two-dimensional wave-like layers, which are pillared by bpy ligands and extended into a rare three-dimensional (3,6)-connected sqc27 framework. The complex demonstrated good water stability and strong luminescence emissions. It not only possesses excellent luminescence sensing activities toward Fe 3+ and Cr 2 O 7 2À in aqueous solution, but can also distinguish between Cr 2 O 7 2À and CrO 4 2À by luminescence. Furthermore, it could be simply and quickly regenerated at least five times. A study of the sensing mechanism indicated that luminescence quenching may be related to the energy competition between the complex and sensing analytes. Figure 1(a) The asymmetric unit of complex 1. Displacement ellipsoids are drawn at the 50% probability level [symmetry codes: (i) Àx + 1, Ày + 2, Àz + 1; (ii) x, Ày + 2, z + 1 2 ; (iii) x, y + 1, z; (iv) Àx + 2, y, Àz + 1 2 ]. (b)/(c) Top and side views of the 3D plane of complex 1 along the bc plane composed of Cd II centres and L 3À ligands. (d) Perspective view of the 3D framework of complex 1, showing (e) the pores within the structure.
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