New Modular Organic Platform For Understanding The Effect Of Structural Changes On Slow Magnetic Relaxation In Mononuclear Octahedral Copper(II) Complexes

Abstract

Current advances in molecular magnetism are aimed at the construction of molecular nanomagnets and spin qubits for their utilization as high-density data storage materials and quantum computers. Mononuclear coordination compounds with low spin values of S=½ are excellent candidates for this endeavour, but their construction via rational design is limited. This particularly applies to the single copper(II) spin center, having been only recently demonstrated to exhibit slow relaxation of magnetisation in the appropriate octahedral environment. We have thus prepared a novel, modular organic scaffold that would allow one to gain in-depth insight into how purposeful structural differences affect the slow magnetic relaxation in monometallic, transition metal complexes. As a proof-of-principle, we demonstrate how one can construct two, structurally very similar complexes with isolated Cu(II) ions in an octahedral ligand environment, the magnetic properties of which differ significantly. The differences in structural symmetry effects and in magnetic relaxation are corroborated with a series of experimental and theoretical techniques, showing how symmetry distortions and crystal packing affect the relaxation behaviour in these isolated Cu(II) systems. Our highly modular organic platform can be efficiently utilized for the construction of various transition-metal ion systems in the future, effectively providing a model system for investigation of magnetic relaxation via targeted structural distortions.

Field-assisted slow relaxation of magnetization in Cu(ii) complexes with pentaheterocyclic triphenodioxazine ligands: the quasi-one-dimensional versus the binuclear case

“…The obtained components of the g-tensor are in good agreement with those previously reported for isomorphic quasi-one-dimensional complex 24 and correspond to the easy-axis type magnetic anisotropy as for all known Cu(II) complexes exhibiting fieldinduced slow magnetic relaxation. 13,[22][23][24][25][26][27][28][29] The w M T for 2 shows (Fig. 5b) a very weak practically linear w M T(T) dependence in the temperature range 50-300K, which Fig.…”

“…Note in this context that for most 3d metal complexes with S = 1/2 exhibiting slow magnetic relaxation, the temperature dependence of the relaxation time is described by the combination of the direct and Raman mechanisms, [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] which is quite understandable. First, for such systems the zero-field splitting is inoperative and thus no spin-inversion barrier can exist, which excludes the contribution of the Orbach relaxation mechanism.…”

“…It should be noted that the value H DC = 400 Oe of the optimal DC magnetic field is significantly lower than the optimal fields in other slowly relaxing 3d complexes with S = 1/2, 11-21 including Cu(II)-based complexes. 13,[22][23][24][25][26][27][28][29] Unlike the quasi-one-dimensional complexes, the binuclear complex 2 demonstrates the slow magnetic relaxation only at T 4 6 K, and at a sufficiently high value of the applied DC magnetic field of 2500 Oe (Fig. 6b).…”

“…Thus, slow magnetic relaxation in mononuclear complexes with S = 1/2 has been reported for such 3d ions as V IV , 11-13 Mn IV , 14 Fe III , 15 Ni I , 16,17 Ni III , 18 and Co II , [19][20][21] which are characterized by strong spin-orbit coupling associated with the unquenched orbital angular momentum in the ground states. At the same time, the majority of 3d metal complexes with S = 1/2 demonstrating slow magnetic relaxation are characterized by low stability in the presence of atmospheric oxygen and moisture, which is related to the unusual coordination and/or oxidation state of the central ions.Interestingly, the slow magnetic relaxation is also observed for Cu(II)-complexes, 13,[22][23][24][25][26][27][28][29] in which the ground state does not carry any unquenched orbital momentum and thus the spin-orbit…”

“…Interestingly, the slow magnetic relaxation is also observed for Cu(II)-complexes, 13,[22][23][24][25][26][27][28][29] in which the ground state does not carry any unquenched orbital momentum and thus the spin-orbit…”