Lanthanide Luminescence Thermometry and Slow Magnetic Relaxation in 3-D Polycyanidometallate-Based Materials.

Two three-dimensional (3-D) polycyanidometallate-based luminescent thermometers with the general formula {Ln 4 Co 4 (CN) 24 (4-benpyo) 17 (H 2 O)·7H 2 O} n Ln = (Dy(III)( 1 ), Eu(III)( 2 )), based on the red-emissive diamagnetic linker [Co(CN) 6 ] 3- and the bulky pyridine derivative that possesses the N-oxide moiety, 4-benzyloxy-pyridine N-oxide (benpyo), were prepared for the first time. The structure of compound 1 has been determined by single-crystal X-ray crystallography while the purity and structure of 2 have been confirmed by CHN, Fourier transform infrared spectroscopy (FT-IR), and powder X-ray diffraction (PXRD) analysis. Magnetic AC susceptibility measurements at zero field show no single-molecule magnet (SMM) behavior indicating fast relaxation operating in 1 . Upon application of an optimal field of 2 kOe, the SMM character of compound 1 is revealed while the τ( Τ ) can be reproduced solely considering the Raman process τ -1 = CT n with C = 7.0901(3) s -1 K - n and n = 3.58(1), indicating that a high density of low-lying states and optical as well as acoustic phonons play a major role in the relaxation mechanism. Micron-sized superconducting quantum interference device (μ-SQUID) loops show a very narrow opening in agreement with the AC susceptibility studies and complete active space self-consistent field (CASSCF) calculations. The interaction operating between the Dy(III) ions was quantified from CASSCF calculations. Good agreement is found by fitting the experimental DC χ M Τ ( Τ ) and M ( H ), employing the Lines model, with J Lines = -0.087 cm -1 (-0.125 K). The excitation spectra of compound 2 are used for temperature sensing in the 25-325 nm range with a maximum relative thermal sensitivity, S r = 0.6% K -1 at 325 K, whereas compound 1 operates as a luminescent thermometer based on its emission features in the temperature range of 16-350 K with S r ≈ 2.3% K -1 at 240 K.