Pillaring of CdCl2-Like Layers in Lanthanide Metal-Organic Frameworks: Synthesis, Structure, and Photophysical Properties

• Published in: Chemistry : a European journal Vol. 14; no. 19; pp. 5839 - 5850
• Main Authors: Mahata, Partha, Ramya, K. V., Natarajan, Srinivasan
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 27.06.2008; WILEY‐VCH Verlag
• Subjects: carboxylate ligands; hydrothermal synthesis; lanthanides; luminescence; metal-organic frameworks
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200800240

A hydrothermal reaction of lanthanide salts, pyridine‐2,3‐dicarboxylic acid, benzene‐1,4‐dicarboxylic acid, and water gave rise to a new series of three‐dimensional mixed carboxylates (homocyclic and heterocyclic) of lanthanides with the general formula [M2(H2O)4][{C5H3N(COO)2}2{C6H4(COO)2}], M=La (I), Pr (II), and Nd (III). The structure consists of M2O14N2 dimeric units connected by pyridine‐2,3‐dicarboxylate moieties to form two‐dimensional layers that are pillared by terephthalate units. The structures also possess two coordinated water molecules, which are arranged to form one‐dimensional helical chains and can be reversibly adsorbed. The connectivity within the layers closely resembles that of the CdCl2 layered structure with 36 topology. To the best of our knowledge, this is the first observation of CdCl2 topology in lanthanide metal–organic framework compounds. Partial substitution of La3+ in I by Eu3+ and Tb3+ (2 and 4 %) gives rise to characteristic red/pink or green emission, which suggests a ligand‐sensitized metal‐centered emission. The Nd compound III shows interesting UV and blue emission through an up‐conversion process. A colorful life: Lanthanide pyridine‐2,3‐dicarboxylate layers resembling CdCl2 layers (see picture) are pillared by 1,4‐benzenedicarboxylate units to form a 3D mixed carboxylate compound. Doping of Eu3+ and Tb3+ in place of La3+ gives rise to ligand‐sensitized metal‐centered emission (Eu=pink, Tb=green) with lifetimes of 29.4 and 14.3 μs, respectively. The Nd‐containing compound shows a two‐photon up‐conversion behavior when excited at 580 nm.