Homochiral lanthanoid(iii) mesoxalate metal–organic frameworks: synthesis, crystal growth, chirality, magnetic and luminescent properties

Abstract

The achiral chelating and bridging mesoxalato ligand (H 2 mesox 2À ), the conjugate base of mesoxalic or dihydroxymalonic acid (H 4 mesox), is a new enantiopurity enforcer in extended structures by yielding the L/D-metal configured homochiral MOFs 2D-[Ln 2 (m-H 2 mesox) 3 (H 2 O) 6 ], [with Ln(III) ¼ La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Er (10) and Yb (11)]; through self-resolution during crystallization. Single crystals of the compounds have been grown in agarose gel. All the compounds obtained are isostructural as deduced by means of single crystal and powder X-ray diffraction analysis and exhibit the Ln(III) ions covalently connected by the mesoxalato ligands into a corrugated grey arsenic-type (6,3)-net (or layer) with chair-shaped six-membered rings. Luminescence measurements reveal that the Eu(III) compound ( 6) exhibits several strong characteristic emission bands for isolated europium(III) ions in the visible region when excited between 350 and 420 nm; similarly the terbium(III) compound ( 8) displays the characteristic emission bands for isolated terbium(III) ions. Magnetic susceptibility measurements show deviations from the Curie law mainly owing to the split of the ground term due to the ligand field and spin-orbit coupling in the case of Sm(III) (4) and Eu(III) (6) compounds.Scheme 1 Left: di-negative doubly deprotonated mesoxalato ligand. Middle: tri-negative triply deprotonated mesoxalato ligand. Right: bischelating bridging mode of the di-negative mesoxalato ligand, dotted line represents the hydrogen bonds from the C-OH groups of the neighboring mesoxalato ligand and the H-atoms of aqua ligands.

Charge-Assisted Hydrogen-Bonded Networks of NH4+ and [Co(NH3)6]3+ with the New Linker Anion of 4-Phosphono-Biphenyl-4′-Carboxylic Acid

“…Finally, we note that in both structures, 1 and 2, the H-bonds to the phosphonato groups are so-called charge-assisted hydrogen bonds. The hydrogen bond donor and/or acceptor carry positive and negative ionic charges, respectively, hence are usually stronger and shorter than neutral H-bonds [12,46,47,[50][51][52][53][54]. In 1 these are bonds NH 4 (+)¨¨¨p´q O-P and NH 4 (+)¨¨¨( H)O-P, -P-OH¨¨¨p´qO-P (Figure 1c).…”

Synthesis and structure of coordination polymers of praseodymium(III) and erbium(III) with hydrogen maleate and benzene-1,3-disulfonate as linkers

“…Water molecules serve as donors and negatively charged sulfonate and carboxylate groups serve as acceptors among these charge-assisted H-bonds. Such charge-assisted H-bonds are found to be stronger than H-bonds formed between neutral atoms and are known to play crucial role in supramolecular assemblies [46][47][48][49][50][51][52]. A strong intramolecular hydrogen bond is formed due to the hydrogen atom in hydrogen maleate anion (HMA) and because of this hydrogen bond the anion exists in a bent conformation making it topologically very similar to the disulfonate ligand.…”

Chiral Lanthanide Metal-Organic Frameworks

“…If all the metal centers in the crystal keep the same L-or D-configuration the crystal will be chiral, the reaction yielding equivalent quantities of both crystal enantiomorphs (opposite handedness) of MOFs. Therefore, the helix, an attractive and evocative expression of chirality, exists as a secondary structure in a chiral framework and frequently interacts with each other by a specific interaction [78,79] (Fig. 22).…”

“…Gil-Hernandez et al [78,97] prepared the L/D-metal configured homochiral MOFs 2D-[Ln 2 (μ-dhm) 3 (H 2 O) 6 ] (Ln ¼ La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb) by using achiral chelating and bridging dhm 2À ligand through self-resolution during crystallization. All the compounds are all isostructural and crystallize in the space group R32.…”