A colorimetric temperature sensor exploring a wide range of emission colours and a ratiometric temperature sensor utilizing sharp emission lines of Tb ^III and Dy ^III are achievable with cyanido-bridged TbCo and Tb _0.5 Dy _0.5 Co heterometallic assemblies.

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 ⁴F_3/2 to ⁴I_9/2 and ⁴I_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)(H₂O)] (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, τ₀ = 3.7(8) × 10⁻⁷ s for fresh sample A, and ΔE/k_B = 27.3 K and τ₀ = 8.5(0) × 10⁻⁸ for assembly A after thermal treatment at 370 K.

The ab initio calculations were correlated with magnetic and emission characteristics to understand the modulation of properties of NIR-emissive [Yb^III(2,2′-bipyridine-1,1′-dioxide)₄]³⁺ single-molecule magnets by cyanido/thiocyanidometallate counterions, [Ag^I(CN)₂]⁻ (1), [Au^I(SCN)₂]⁻ (2), [Cd^II(CN)₄]^2–/[Cd^II₂(CN)₇]^3– (3), and [M^III(CN)₆]^3– [M^III = Co (4), Ir (5), Fe (6), Cr (7)]. Theoretical studies indicate easy-axis-type ground doublets for all Yb^III centers. They differ in the magnetic axiality; however, transversal g-tensor components are always large enough to explain the lack of zero-dc-field relaxation. The excited doublets lie more than 120 cm^–1 above the ground one for all Yb^III centers. It was confirmed by high-resolution emission spectra reproduced from the ab initio calculations that give reliable insight into energies and oscillator strengths of optical transitions. These findings indicate the dominance of Raman relaxation with the power n varying from 2.93(4) to 6.9(2) in the 4–3–5–1–2 series. This trend partially follows the magnetic axiality, being deeper correlated with the phonon modes schemes of (thio)cyanido matrices.

Molecular crystals acting as temperature sensors, designed for multiple measurement techniques, can be a promising pathway for self‐calibrating thermometers. The molecular assemblies [Dy_x^IIIY_1–x^III(phen)₂(μ‐OH)₂(H₂O)₂]·[Au^I(SCN)₂]₂·phen·0.5MeCN·0.5H₂O (x = 0, 0.1, 0.02; phen = 1,10‐phenanthroline) which contain weakly bonded lanthanide(III) and Au(I) metal complexes are reported. They have Raman scattering in the low‐frequency (LF) region with sharp peaks, one of the prerequisites to design Raman thermometers. The Raman thermometric behaviors are characterized by three vibrational bands, and their thermal sensitivity is compared with their emission thermometric ability. The LF phonon linked with the Au···Au vibration helps increase the thermometric sensitivity of emission and Raman thermometers. Additionally, magnetically diluted complexes containing both Dy³⁺ and Y³⁺ ions are prepared to demonstrate the effect of temperature sensing capability through Raman and emission spectroscopy among isostructural mixed‐metal materials. Compounds are immersed inside various benchtop solvents to unravel the robustness and functioning of Raman thermometers. Furthermore, they reveal single‐molecule magnet properties, which disclose the effect of LF phonons on the spin relaxation process. Therefore, the reported molecular materials are Raman and luminescent thermometers, and they contain a molecular magnetic center with thiocyanidoaurate ions playing a critical role due to their emissive and Raman activities.

Two new complexes [Fe(3-bpp) ₂ ](XO ₄ ) ₂ ·solv (X = Cl, 1 and Re, 2 ) have been prepared. Both systems show desolvation-assisted spin crossover (DASCO) and light-induced excited spin-state trapping (LIESST) phenomena.