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(III)(TTA)(3)(MeOH)(2)]·0.5Azo-py (A) in which two asymmetric units are linked by Azo-py through hydrogen bonding via 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 (4)F(3/2) to (4)I(9/2) and (4)I(11/2) 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(III)(TTA)(3)(4-OHpy)(H(2)O)] (B). Assembly A also exhibits field-induced slow magnetic relaxation properties with an energy barrier of ΔE/k(B) = 19.7(7) K and an attempt time of relaxation, τ(0) = 3.7(8) × 10(−7) s for fresh sample A, and ΔE/k(B) = 27.3 K and τ(0) = 8.5(0) × 10(−8) for assembly A after thermal treatment at 370 K.