Layered Metal–Organic Frameworks Based on Octahedral Lanthanides and a Phosphonate Linker: Control of Crystal Size

The
hydrothermal reaction between lanthanide salts and residues
of (benzene-1,3,5-triyltris­(methylene))­triphosphonic acid (H6bmt) promotes the formation of a new series of isotypical layered
lanthanide–organic frameworks (LnOFs), [Ln2(H3bmt)2]·H2O [where Ln3+ = Eu3+ (1), Gd3+ (2), Tb3+ (3), Dy3+ (4), Ho3+ (5), Er3+ (6), Tm3+ (7), and Yb3+ (8)]. The crystal structure was unveiled from powder X-ray diffraction
data (both laboratory and synchrotron) in tandem with other characterization
techniques (namely thermogravimetry, thermodiffractometry, vibrational
spectroscopy, and elemental analysis). It is shown that the lanthanide
contraction leads, on average, to a reduction of the average crystallite
size, up to the nanometer scale in the case of compound 8. The unique structural features of the ∞2[Ln2(H3bmt)2] layers are discussed
in detail, in particular, the six-coordination environment of the
lanthanide cations and its topological relationship with the formation
of the first 5,5L4 binodal network based on chelating phosphonate
groups.