Molecular Magnetic Materials Based on {Co III (Tp*)(CN) 3 } - Cyanidometallate: Combined Magnetic, Structural and 59 Co NMR Study.

The cyanidocobaltate of formula fac-PPh 4 [Co III ( Me2 Tp)(CN) 3 ] ⋅ CH 3 CN (1) has been used as a metalloligand to prepare polynuclear magnetic complexes ( Me2 Tp=hydrotris(3,5-dimethylpyrazol-1-yl)borate). The association of 1 with in situ prepared [Fe II (bik) 2 (MeCN) 2 ](OTf) 2 (bik=bis(1-methylimidazol-2-yl)ketone) leads to a molecular square of formula {[Co III {( Me2 Tp)}(CN) 3 ] 2 [Fe II (bik) 2 ] 2 }(OTf) 2  ⋅ 4MeCN ⋅ 2H 2 O (2), whereas the self-assembly of 1 with preformed cluster [Co II 2 (OH 2 )(piv) 4 (Hpiv) 4 ] in MeCN leads to the two-dimensional network of formula {[Co II 2 (piv) 3 ] 2 [Co III ( Me2 Tp)(CN) 3 ] 2  ⋅ 2CH 3 CN} ∞ (3). These compounds were structurally characterized via single crystal X-ray analysis and their spectroscopic (FTIR, UV-Vis and 59 Co NMR) properties and magnetic behaviours were also investigated. Bulk magnetic susceptibility measurements reveal that 1 is diamagnetic and 3 is paramagnetic throughout the explored temperature range, whereas 2 exhibits sharp spin transition centered at ca. 292 K. Compound 2 also exhibits photomagnetic effects at low temperature, selective light irradiations allowing to promote reversibly and repeatedly low-spin⇔high-spin conversion. Besides, the diamagnetic nature of the Co(III) building block allows us studying these compounds by means of 59 Co NMR spectroscopy. Herein, a 59 Co chemical shift has been used as a magnetic probe to corroborate experimental magnetic data obtained from bulk magnetic susceptibility measurements. An influence of the magnetic state of the neighbouring atoms is observed on the 59 Co NMR signals. Moreover, for the very first time, 59 Co NMR technique has been successfully introduced to investigate molecular materials with distinct magnetic properties.