Pyridinium Salts of Dehydrated Lanthanide Polychlorides.

The reaction of lanthanide (Ln) chloride hydrates ([) with pyridine (py) yielded a set of dehydrated pyridinium (py-H) Ln-polychloride salts. These species were crystallographically characterized as [[py-H-py][py-H][LnCl]] (; Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) or [[py-H][LnCl(py)]] ((; Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu). The metal centers adopt an octahedral (-6) geometry, binding six Cl ligands. The -3 charge is off-set by two py-H moieties and a di-pyridinium (py-H-py) ion. For the species, an -6 anion is formed by the Ln cation binding a single py and five Cl ligands. The remaining -2 charge is offset by two py-H cations that H-bond to the anion. Significant H-bonding occurs between the various cation/anion moieties inducing the molecular stability. The change in structure from the to is believed to be due to the Ln-contraction producing a smaller unit cell, which prevents formation of the py-H-py cation, leading to the loss of the H-bonding-induced stability. Based on this, it was determined that the structures only exist when the lattice energy is small. While dehydrated polychloride salts can be produced by simply mixing in pyridine, the final structures adopted result from a delicate balance of cation size, Coulombic charge, and stabilizing H-bonding.