Crystal Structures, Thermal and Luminescent Properties of Gadolinium(III) Trans-1,4-cyclohexanedicarboxylate Metal-Organic Frameworks

Abstract

Four new gadolinium(III) metal-organic frameworks containing 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen) chelate ligands and trans-1,4-cyclohexanedicarboxylate (chdc2−) were synthesized. Their crystal structures were determined by single-crystal X-ray diffraction analysis. All four coordination frameworks are based on the binuclear carboxylate building units. In the compounds [Gd2(bpy)2(chdc)3]·H2O (1) and [Gd2(phen)2(chdc)3]·0.5DMF (2), the six-connected {Ln2(L)2(OOCR)6} blocks form a 3D network with the primitive cubic (pcu) topology. In the compounds [Gd2(NO3)2(phen)2(chdc)2]·2DMF (3) and [Gd2Cl2(phen)2(chdc)2]·0.3DMF·2.2dioxane (4), the four-connected {Ln2(L)2(X)2OOCR)4} units (where X = NO3− for 3 or Cl− for 4) form a 2D square-grid (sql) network. The solid-state luminescent properties were investigated for the synthesized frameworks. Bpy-containing compound 1 shows no luminescence, possibly due to the paramagnetic quenching by Gd3+ cation. In contrast, the phenathroline-containing MOFs 2–4 possess yellow emission under visible excitation (λex = 460 nm) with the tuning of the characteristic wavelength by the coordination environment of the metal center.

Anion-Induced Structural Diversity and Optical Chromism in a Series of Cyano-Bridged Heterometallic 3d-4f Coordination Polymers

“…Exceptions to this trend exist, where even close-sized Ln ions, such as erbium and ytterbium, template remarkably different architectures, underlining the difficult predictability of the resulting compound [ 14 ]. On the other hand, the role of the (non-linker) counteranion in determining the structural arrangement of polynuclear molecular compounds is relatively less explored, especially in regard to Ln ions [ 15 , 16 , 17 ]. In this work, we present a rare study, where the structure and morphology of the coordination network are dictated by the counteranion while no discrimination is established based on the size difference of heavy and light Ln ions.…”

Properties of Aliphatic Ligand-Based Metal–Organic Frameworks

“…In this regard, low photoactivity of the aliphatic backbone could be applied in a manner reversed to that described above: to dilute photoactive centers bound into the polymeric coordination framework for improvement in its stability to photodegradation or for finetuning the emission color and other characteristics of the emissive blocks interconnected by transparent aliphatic struts [112,113]. The hydrophobicity of the saturated ligand core should also be mentioned as a factor which possibly increases the stability of luminophore to hydrolysis, obviously a very important property in terms of practical relevance.…”