Unusual slow magnetic relaxation in a mononuclear copper(II) complex.

A hexacoordinate Cu(II) complex with the {CuO4O'N} donor set shows an intermolecular π-π stacking owing to which a 1D-chain structure is formed. The DC magnetic data at low temperature are consistent with the Curie law. The AC susceptibility shows a field supported slow magnetic relaxation that survives up to 7 K. The relaxation time at T = 2.0 K and BDC = 0.2 T is τ = 0.23 ms and it increases at BDC = 0.6 T to τ = 2.9 ms.

Effect of the Distant Substituent to Slow Magnetic Relaxation of Pentacoordinate Fe(III) Complexes.

Pentacoordinate Fe(III) complexes [Fe(LMeO)2X] and [Fe(LEtO)2X], X = Cl and Br, show the slow magnetic relaxation that is enhanced by the applied static magnetic field. A substitution of the distant ethoxy group to the methoxy group residing at the phenyl ring of a Schiff base N,O-donor ligand (LMeO vs LEtO) considerably influences the relaxation characteristics. In the chlorido complex [Fe(LMeO)2Cl], the following three slow relaxation channels are recognized as possessing different relaxation times: τLF = 0.47 s, τIF = 13 ms, and τHF = 26 µs at the static field BDC = 0.2 T and T = 1.9 K. In the bromido complex [Fe(LMeO)2Br], only the following two relaxation channels are seen: τLF = 0.30 ms and τHF = 139 µs at BDC = 0.15 T and T = 1.9 K. Due to D > 0, the Orbach relaxation mechanism does not apply, and the temperature dependence of the high-frequency relaxation time can be described by two Raman-like terms.

Exceptionally slow magnetic relaxation in a mononuclear hexacoordinate Ni(ii) complex.

A hexacoordinate mononuclear [Ni(pydm)2](dnbz)2 complex shows field-induced slow magnetic relaxation with two or three relaxation channels that are strongly supported by an external magnetic field. At BDC = 0.8 T and T = 1.9 K, the low-frequency (LF) relaxation time is as slow as τ(LF) = 1.3 s with the mole fraction of x(LF) = 0.47.

Breaking the Magic Border of One Second for Slow Magnetic Relaxation of Cobalt-Based Single Ion Magnets.

Instead of assembling complex clusters and/or expensive lanthanide-based systems as single ion magnets, we are focusing on mononuclear cobalt(II) systems among which the complex under study, [Co( pydca)( dmpy)]2·H2O (1), shows a field supported slow magnetic relaxation on the order of seconds at low temperature ( pydca = pyridine-2,6-dicarboxylato, dmpy = 2,6-dimethanolpyridine). The low-frequency relaxation time is as slow as τ(LF) = 1.35(6) s at T = 1.9 K and BDC = 0.4 T. The properties of 1 are compared to the previously reported nickel and copper analogues which were the first examples of single ion magnets in the family of Ni(II) and Cu(II) complexes.

Field influence on the slow magnetic relaxation of nickel-based single ion magnets.

A mononuclear Ni(ii) complex, [Ni(pydca)(dmpy)]·H2O, pyridine-2,6-dicarboxylato-2,6-dimethanolpyridine nickel(ii) monohydrate, exhibits a slow magnetic relaxation under an applied magnetic field with two and/or three relaxation channels. While at BDC = 0.2 T, the low-frequency relaxation mode is weakly developed, its intensity grows rapidly with the field so that at BDC = 0.6 T, this is the dominating relaxation path giving rise to a relaxation time of τLF = 322 ms at T = 2.0 K. At BDC = 1.2 T the relaxation time is as slow as τLF = 876 ms.

A mononuclear Co(ii) complex formed from pyridinedimethanol with manifold slow relaxation channels.

A mononuclear hexacoordinate complex [Co(pydm)2](dnbz)2 formed from 2,6-pyridinedimethanol in the coordination sphere of Co(ii) and dinitrobenzoato anions exhibits magnetic anisotropy of an easy axis type and a field induced slow magnetic relaxation with manifold relaxation channels. The low-frequency relaxation time is as slow as τLF = 0.13 s at BDC = 0.4 T and T = 1.9 K.

Field Supported Slow Magnetic Relaxation in a Mononuclear Cu(II) Complex.

A mononuclear hexacoordinate Cu(II) complex shows a field induced slow magnetic relaxation that is not facilitated by an energy barrier to spin reversal due to the zero-field splitting. Two relaxation channels were found: the magnetic field strongly supports the low-frequency relaxation path with a relaxation time as long as τ = 0.8 s at T = 1.9 K and B = 1.5 T. The mechanism of the relaxation at low temperature involves the dominant Raman process for this S = 1/2 spin system along with a temperature-independent term belonging to a quantum tunneling.

Bis-phenoxido and bis-acetato bridged heteronuclear {Co(III)Dy(III)} single molecule magnets with two slow relaxation branches.

Two bis-µ-phenoxido-bis-µ-acetato heterobimetallic {Co(III)Dy(III)} complexes and , formulated as [Co(III)Dy(III)L(µ-OAc)2(NO3)2] derived from the comparable hexadentate Schiff bases N,N'-ethylenebis(3-ethoxysalicylaldimine) and N,N'-ethylenebis(3-methoxysalicylaldimine) were synthesized and X-ray structure analysis confirms their nearly identical structures. These are the first examples of bis(µ-phenoxido)-bis(µ-carboxylato) {Co(III)Dy(III)} systems. The AC susceptibility measurements show that both complexes exhibit a field-induced slow magnetic relaxation with two relaxation branches. While the high-frequency process spans the usual range of the relaxation time for analogous single molecule magnets (τ0 ∼ 10(-7) s), the low-frequency branch is as slow as τ ∼ 0.1 s at T = 1.9 K and B = 0.2 T.

A mononuclear Ni(ii) complex: a field induced single-molecule magnet showing two slow relaxation processes.

The mononuclear complex [Ni(pydc)(pydm)]·H2O, pyridine-2,6-dicarboxylato-2,6-bis(hydroxymethyl)pyridine nickel(ii) monohydrate, features a highly axially compressed pseudo-octahedral chromophore with significant rhombic contribution that is responsible for the sizable magnetic anisotropy of the Ni(ii) ion, D/hc≈-14 cm(-1). This complex displays superparamagnetic behaviour in an applied external field that culminates at BDC = 0.2 T. Two relaxation processes are evidenced; the faster can be analyzed in terms of the Orbach, direct, and Raman processes yielding U/kB = 21.2 (±1.3) K and τ0 = 3.83 (±1.21) × 10(-7) s. This is the first example of a field-induced single-molecule magnet in the class of hexacoordinate Ni(ii) complexes.