Reversible thermo-induced spin crossover in a mononuclearcis-dicyanamido-cobalt(ii) complex containing a macrocyclic tetradentate ligand

Abstract

<p>For the first time, a mononuclear cobalt(<sc>ii</sc>) complex with dicyanamide coligands exhibiting reversible spin crossover behavior at high temperature is reported.</p>

Reversible Spin-State Switching and Tuning of Nuclearity and Dimensionality via Nonlinear Pseudohalides in Cobalt(II) Complexes

“…These values fall in the range of that expected for cobalt(II) LS complexes. 53,58,63,64 Similar to our previous report on cobalt(II) SCO complexes with the tetradentate macrocyclic ligand L, 63,64 a significant change was noticed only in the equatorial Co−N bonds, while the axial Co−N bonds remain almost unchanged. This can be explained by tetrahedral distortion and Jahn−Teller effects present in the complex.…”

“…The Co−N bond distances are very similar to those obtained in octahedral HS cobalt(II) complexes. 53,63,64,72,73 The N am −Co−N am angle 1 and Table S2). The average Co−N bond distance in 2 at 296 K is 2.080 Å with typical bond distance values of 2.320, 1.946, and 1.974 Å for Co−N am , Co−N Py , and Co−N tcm , respectively (Figure 6, Table 1, and Table S2).…”

“…25,53,63,64,73,74 The χT value decreases smoothly with a decrease in temperature down to 150 K to a value of 0.75 cm 3 mol −1 K and then remains almost constant down to 20 K. This χT value at 20 K is consistent with the expected value for two cobalt(II) ions in a LS state (S = 2 × 1/2, g = 2.0; χT = 2 × 0.35 cm 3 mol −1 K)). 53,63,64 The changes in χT value indicate an incomplete and gradual HS (S = 3/2) to LS (S = 1/2) spin-state switching in 2. With a further decrease in temperature, the χT value decreases to 0.53 cm 3 mol −1 K at 2 K, which is probably due to weak antiferromagnetic intra-and intermolecular interactions between the LS cobalt(II) centers.…”

Monitoring the Substrate‐Induced Spin‐State Distribution in a Cobalt(II)‐Salen Complex by EPR and DFT

“…Nevertheless Co(II)‐salen type complexes (bearing an N 2 O 2 ligand backbone) remain interesting systems to investigate, particularly as the SCO response can be induced by weak axial coordination of organic bases such as pyridine [25–31] . In some cases, variations to the Salen ligand framework in these Co(II) complexes have also been observed to undergo thermally induced SCO in the solid‐state [32–34] . On the other hand, substrate mediated SCO is arguably less well studied for such Co(II) systems.…”

“…[25][26][27][28][29][30][31] In some cases, variations to the Salen ligand framework in these Co(II) complexes have also been observed to undergo thermally induced SCO in the solid-state. [32][33][34] On the other hand, substrate mediated SCO is arguably less well studied for such Co(II) systems. For example, computational studies have shown how 5-coordinate d 7 Co(II)-salen type complexes bearing coordinated pyridine or imidazole as an axial substituent can produce a narrowing of the LS doublet (S = 1/2) and HS quartet (S = 3/2) energy gap, without the need for further external stimuli to induce the transition.…”