New Cobalt(II) Field‐Induced Single‐Molecule Magnet and the First Example of a Cobalt(III) Complex with Tridentate Binding of a Deprotonated 4‐Amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐Triazole Ligand

Abstract

From Co(NO3)2·6H2O ‐ NaN3 ‐ abpt reaction system, a mononuclear complex [Co(abpt)2(N3)2] (abpt = 4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole) (1) and a dinuclear complex [Co2(abpt)(µ‐abpt‐H)2(N3)4]·1.12H2O (2) were obtained. The presence of neutral abpt, as well as azido ligands was proved by IR spectroscopy. X‐ray crystallography shows that 1 is a molecular CoII complex with two azido ligands coordinated in trans‐positions, while 2 is a dinuclear CoIII complex bridged by two abpt‐H ligands. π–π stacking interactions between pyridyl rings of abpt and N‐H···N and C‐H···N hydrogen bonds in 1 and 2 stabilize their structures by creating a 3D supramolecular network. The analysis of the magnetic properties of 1 revealed negative zero‐field splitting parameter D = –24.1 cm–1 supported also by CASSCF/NEVPT2 and CASSCF/CASPT2 theoretical calculations. The X‐band electron paramagnetic resonance also gives an evidence for a strong rhombic character of the anisotropy. The investigation of the ac susceptibility measurements identified 1 as a field‐induced single‐molecule magnet, in which direct, Raman and Orbach relaxation processes are present.

Cis and Trans Isomers of Fe(II) and Co(II) Complexes with Oxadiazole Derivatives ‐ Structural and Magnetic Properties

“…In case of Co(II) compounds 1 and 2 , the best agreement with the experimental data was found for negative and large D ‐values, D =−68.6 cm −1 for 1 and D =−39.9 cm −1 for 2 , with significant rhombicity, E / D >0.2. Negative D ‐parameter was found also in similar systems like [Co(abpt) 2 (N 3 ) 2 ] (abpt=4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole) [6b] and [Co(bppCOOMe) 2 ](ClO 4 ) 2 (bppCOOMe=methyl 2,6‐di(pyrazol‐1‐yl)pyridine‐4‐carboxylate), [19] and it is due to significant deviation from O h ligand‐field symmetry. Next, Fe(II) compounds 3 – 4 were analyzed resulting in D =11.0 cm −1 for 3 and D =3.92 cm −1 for 4 with practically zero rhombicity parameter E / D in both cases.…”

Influence of the phonon-bottleneck effect and low-energy vibrational modes on the slow spin-phonon relaxation in Kramers-ions-based Cu(ii) and Co(ii) complexes with 4-amino-3,5-bis-(pyridin-2-yl)-1,2,4-triazole and dicyanamide

“…Recently, we designed and constructed a variety of SIM coordination compounds with abpt and various types of linear and non-linear pseudohalide anions, except dicyanamide (dca). 5 a , b ,15 Dca shows different binding modes, which allows it to form coordination complexes with interesting structural and magnetic properties. This versatility of dca ligand also prompted chemists to use it for crystal engineering.…”

Ultrafast Jahn‐Teller Photoswitching in Cobalt Single‐Ion Magnets

“…In general, SMMs with S > 1 present a barrier to magnetization reversal, [10][11][12] while SMMs with S < 1 undergo light-induced magnetization. [13][14][15] For practical applications, the amplitude of the magnetization, its relaxation time and its blocking temperature should be maximized. [16][17][18] The possibilities of augmenting the magnetization by simply increasing the number of spins N are intrinsically limited, due to the fact that the spins cannot be easily controlled in SMMs of high nuclearity [19] and that D only scales as S (rather than S 2 ).…”