Isomorphous Lanthanide Metal–Organic Frameworks Based on Biphenyldicarboxylate: Synthesis, Structure, and Photoluminescent Properties

Abstract

We report the structures of six anionic, isomorphous metal–organic frameworks [Ln­(bpdc)2 –]­[NH2(CH3)2 +], where Ln = La, Ce, Nd, Eu, Gd, Er, and bpdc2– = biphenyl-4,4′-dicarboxylate = –O2C­(C6H4)2CO2 –. The Ln­(III) metal centers exhibit eight-coordinate binding to six different bpdc2– ligands (four of which are μ-2 bridging and two are bidentate) and the framework is charge-balanced by a dimethylammonium cation. The materials all possess the same 3D structure and crystallize in the orthorhombic space group Pbcn. All exhibit thermal stability up to ca. 300 °C and decompose to Ln2O3 after 800 °C. The Eu-based structure exhibits strong fluorescence in the 612–620 nm range. These materials significantly expand the known chemistry and luminescence of the less studied f-block metal–organic frameworks.

Combined Experimental/Theoretical Study on the Luminescent Properties of Homoleptic/Heteroleptic Erbium(III) Anilate-Based 2D Coordination Polymers

“…Additionally, 41 quartet and 112 doublet spin states were also considered that correspond to the combinations of singlet spin states of the anilate ligands (π−π*) 1 and quartet and doublet spin states of the metal center. In [Er(ClCNAn) 2 (F 4 BDC)] 3− , calculations were performed with a RAS[15,1,1,2,7,2]SCF active space on top of a CAS (11,7)SCF wave function used to model the static correlation arising from the 4f 11 Er III ion. Only two bonding and two antibonding orbitals centered on the anilate ligands were added in the RAS1 and RAS3 space, respectively (Figure S4).…”

“…Some of the widely explored organic linkers behaving as valuable antennas are ligands with functional groups, such as pyridyl, carboxylate derivatives, β-diketonates, etc. [6][7][8][9][10][11] A major drawback in the case of NIR-emitting complexes is the non-radiative deactivation due to C-H, N-H, O-H vibrations from ligands/solvents in the close vicinity to Ln III ions which significantly quenches the luminescence. To overcome this issue, fluorinated ligands are often used, which reduce fluorescence quenching effects of the overtones of C-H vibrations by considering low-frequency C-F vibrations.…”

“…Lanthanide Coordination Polymers (Ln-CPs) and Metal–Organic Frameworks (Ln-MOFs), built by the self-assembly of Ln III metal ions and conjugated organic linkers, have been extensively studied in recent years because of their intriguing structural topologies, optical properties and several applications in various fields such as sensing, data storage, molecular spintronics and electronics, telecommunications, bioimaging, etc . − By proper tailoring of the coordination environment around the Ln III metal ions, through (i) the various coordination modes of organic linkers and (ii) a selection of linkers with high absorptivity, thus acting as suitable antennas for sensitizing Ln ions, interesting supramolecular frameworks with peculiar luminescent properties , have been obtained. Some of the widely explored organic linkers behaving as valuable antennas are ligands with functional groups such as pyridyl, carboxylate derivatives, β-diketonates, etc . − A major drawback in the case of near-IR (NIR)-emitting complexes is nonradiative deactivation due to C–H, N–H, and O–H vibrations from ligands/solvents in close vicinity to Ln III ions, which significantly quenches the luminescence. To overcome this issue, fluorinated ligands are often used, which reduce the fluorescence quenching effects of the overtones of C–H vibrations by considering low-frequency C–F vibrations. , In this context, 2,3,5,6-tetrafluoroterephthalic acid (F 4 BDC) is a valuable ligand for the construction of multidimensional Ln-CPs and also for its versatile and multidentate coordination modes to Ln ions through carboxyl O atoms. , On the other hand, CPs based on 3,5-disubstituted-2,6-dihydroxy-1,4-benzoquinone, commonly called anilates, have been widely studied over the past decade. − Anilates are excellent building blocks for the construction of layered mono/multifunctional materials showing magnetic, − conducting, − and luminescent properties. − Among them, the first example of a heterosubstituted anilate, the chlorocyananilate ligand (3-chloro-6-cyano-2,5-dihydroxybenzoquinone, ClCNAn 2– ), is an interesting antenna linker for the construction of Ln-CPs because of the absence of IR quenchers in its molecular structure .…”

Dual Emission in a Ligand and Metal Co-Doped Lanthanide-Organic Framework: Color Tuning and Temperature Dependent Luminescence

“…In this contribution, we report the preparation and study of a homologous series of ligand and metal co-doped lanthanide-organic frameworks where a parent framework [La(bpdc)Cl(DMF)] (1) [13] is doped with the strongly fluorescent diamino derivative of the bpdc 2− bridging ligand dabpdc 2− and with the luminescent lanthanide ion Eu 3+ . The lanthanide MOF (LnMOF) ([La(bpdc)Cl(DMF)] (1) was chosen as a doping platform because: (i) its highly reproducible synthesis and chemical robustness, as dry crystals of 1 can be left in air for several months without showing any sign of deterioration; (ii) the bpdc 2− bridging ligand has been demonstrated to be a good sensitizer for the luminescence of the Eu 3+ ion [14][15][16]; (iii) the possibility to obtain strong Ln 3+ -based emission due to the absence of water from the coordination sphere of the Ln 3+ ion which would provide an efficient non-radiative deactivation pathway for f-f excited states through vibrational coupling with O-H oscillators [17]. Thus, following the above mentioned doping procedure, we prepared an isostructural series of materials with the formula [La 1−x Eu x (bpdc) 1−y (dabpdc) y Cl(DMF)] (x = 0-0.025; y = 0 or 0.1) which show emission from both chromophores.…”

Polymeric coordination complex of lithium(I) with aqua and cyanurate ligands

“…Such compounds find potential applications in catalysis, gas storage, ion exchange, magnetic materials, sensors, optics and batteries (Qu et al, 2016). The various possible metal and linker combinations are endless and have led to the synthesis of thousands of new materials with different metal geometries and functionalities (Chatenever et al, 2019). Among the metals investigated, lithiumbased complexes have unique advantages, exploiting properties of the lithium cation such as small ionic radius, high polarizing power, aqueous solubility and low economic cost (Ge et al, 2018;Wan et al, 2012).…”