Structural diversity of lanthanoid salicylate hydrates

From metathesis reactions between lanthanoid salts and sodium salicylate (Na(salH)) in water, four classes of lanthanoid salicylate hydrates have been identified. Single crystal X-ray studies established a new monomeric class [Ln(salH)3(H2O)3]·3H2O (6Ln). This new rhombohedral R3c, Z = 6 form '6Ln' has the nine coordinate metal atom on a crystallographic 3-axis, for Ln = Sm–Gd, Ho, Er, Yb, Lu, Y. We also have augmented or defined the previously known different forms, consolidating or extending their putative 'domains of existence'. The monohydrate, Ln = '1Ce', monoclinic, P21/n, has been re-examined at lowtemperature suggesting further elasticity in its formulation beyond the recently proposed '[Ln(H2sal) (Hsal)(sal)H2O)](∞|∞)' for the Ln = Gd complex, '1Gd', one of the protonic hydrogen atoms being associated with a very short phenoxyl–O···carboxylate–O distance (2.427(3) A). With refinement and the insights from a previous Ln = Eu study, suggest the protonic disposition to be around the O···O median. The 'domain of existence' for this form embraces Ln = La (dependent on a powder diffraction study) – Gd. The tetrahydrate is manifested in two forms: triclinic, centrosymmetric binuclear Ln2(salH)6(H2O)4]·4H2O, P·1, Z = 1, '4Ln' recorded here in a 153 K determination, for Ln = Ho, consolidating the assignment of its domain of existence to be Ho–Er, Y, and 'polymeric mononuclear' [Ln(salH)3(H2O)2](∞|∞)·2H2O, '4Ln,' recorded here for Ln = Tb–Er, Yb, Lu, Y. The 6Gd hexahydrate shows paramagnetic f7 magnetic behaviour. The reaction conditions leading to the isolation of a particular structural type of lanthanoid salicylate could not be reliably identified, indicating that a fine balance exists in the preferential crystallization of the lanthanoid salicylate hydrate phases. The discovery of the monomeric class has applications for the species acting as a corrosion inhibitor in dilute aqueous solution.