Neodymium β-diketonate showing slow magnetic relaxation and acting as a ratiometric thermometer based on near-infrared emission

Self-assembly of β-diketonate (Htta = thenoyl(trifluoro)acetone) and 4,4'-azopyridine (Azo-py) with neodymium(iii) ions in the presence of methanol resulted in the formation of mononuclear complex [Nd (TTA) (MeOH) ]·0.5Azo-py (A) in which two asymmetric units are linked by Azo-py through hydrogen bonding methanol. A reveals near-infrared emission (NIR) centred at about 895 and 1056 nm, in the 10-370 K temperature range, originating from the two emissive transitions on Nd(iii) from F to I and I levels, respectively. Furthermore, the NIR luminescence intensity of A at room temperature augments two times upon thermal elimination of one coordinated methanol molecule. The thermally activated A exhibits single centre ratiometric thermometer behaviour in a wide temperature range from 10 to 300 K. Moreover, fluorescence properties of A were compared to another mononuclear complex [Nd (TTA) (4-OHpy)(H O)] (B). Assembly A also exhibits field-induced slow magnetic relaxation properties with an energy barrier of Δ / = 19.7(7) K and an attempt time of relaxation, = 3.7(8) × 10 s for fresh sample A, and Δ / = 27.3 K and = 8.5(0) × 10 for assembly A after thermal treatment at 370 K.