Visible to Near-Infrared Emission from Ln(III)(Bis-oxazoline)-[Mo(V)(CN)8] (Ln = Ce-Yb) Magnetic Coordination Polymers Showing Unusual Lanthanide-Dependent Sliding of Cyanido-Bridged Layers.

Abstract

Complexes of lanthanides(III) (Ce-Yb) with 2,2'-bis(2-oxazoline) (Box) combined with octacyanidomolybdate(V) gave a series of magneto-luminescent coordination polymers, {[Ln(III)(Box)n(DMF)m][Mo(V)(CN)8]}·x(solvent) (1-12). They are built of cyanido-bridged layers of a mixed 4- and 8-metal rings topology and show unique sliding of layers dependent on a 4f metal ion. For light lanthanides, dominant phase A, {[Ln(III)(Box)2(DMF)2][Mo(V)(CN)8]}·1.5MeCN (Ln = Ce, 1; Pr, 2; Nd, 3), consists of ideally aligned, not shifted layers, giving large channels (13.7 × 14.0 Å). Intermediate lanthanides reveal phase B, {[Ln(III)(Box)2(DMF)2] [Mo(V)(CN)8]}·H2O (Ln = Sm, 4; Eu, 5; Gd, 6; Tb, 7; Dy, 8), of smaller pores (8.4 × 10.6 Å) due to layer-H2O hydrogen bonding, which induces sliding of CN(-)-bridged layers. Heavy lanthanides show phase C, {[Ln(III)(Box)(DMF)3][Mo(V)(CN)8]}·MeCN (Ln = Ho, 9; Er, 10; Tm, 11; Yb, 12), with large channels (13.7 × 13.7 Å) of a similar size to light lanthanides. This effect comes from the changes in Ln(III) coordination sphere affecting solvent-layer interactions. Compounds 1-12 reveal diverse emission depending on the interaction between Ln(III) and Box luminophors. For 2-5, 9, and 12, the ligand-to-metal energy-transfer-induced visible f-centered emission ranging from green for Ho(III)-based 9, orange from Sm(III)-based 4, to red for Pr(III)- and Eu(III)-containing 2 and 5, respectively. Near-infrared emission was found for 2-4, 9, and 12. Red phosphorescence of Box was detected for Gd(III)-based 6, whereas the selective excitation of ligand or Ln(III) excited states resulting in the switchable red to green emission was found for Tb(III)-based 7. The materials revealed Ln(III)-Mo(V) magnetic coupling leading to ferromagnetism below 2.0 and 2.2 K for 4 and 7, respectively. The onset of magnetic ordering at low temperatures was found for 6 and 8. Compounds 1-12 form a unique family of cyanido-bridged materials of a bifunctional magneto-luminescence character combined with dynamic structural features.