Enhancing the Blocking Temperature in Single‐Molecule Magnets by Incorporating 3d–5d Exchange Interactions

Abstract

We report the first single-molecule magnet (SMM) to incorporate the [Os(CN)(6)](3-) moiety. The compound (1) has a trimeric, cyanide-bridged Mn(III)-Os(III)-Mn(III) skeleton in which Mn(III) designates a [Mn(5-Brsalen)(MeOH)](+) unit (5-Brsalen=N,N'-ethylenebis(5-bromosalicylideneiminato)). X-ray crystallographic experiments reveal that 1 is isostructural with the Mn(III)-Fe(III)-Mn(III) analogue (2). Both compounds exhibit a frequency-dependent out-of-phase χ''(T) alternating current (ac) susceptibility signal that is suggestive of SMM behaviour. From the Arrhenius expression, the effective barrier for 1 is found to be Δ(eff)/k(B)=19 K (τ(0)=5.0×10(-7) s; k(B)=Boltzmann constant), whereas only the onset (1.5 kHz, 1.8 K) of χ''(T) is observed for 2, thus indicating a higher blocking temperature for 1. The strong spin-orbit coupling present in Os(III) isolates the E'(1g(1/2))(O(h)*) Kramers doublet that exhibits orbital contributions to the single-ion anisotropy. Magnetic susceptibility and inelastic neutron-scattering measurements reveal that substitution of [Fe(CN)(6)](3-) by the [Os(CN)(6)](3-) anion results in larger ferromagnetic, anisotropic exchange interactions going from quasi-Ising exchange interactions in 2 to pure Ising exchange for 1 with J(parallel)(MnOs)=-30.6 cm(-1). The combination of diffuse magnetic orbitals and the Ising-type exchange interaction effectively contributes to a higher blocking temperature. This result is in accordance with theoretical predictions and paves the way for the design of a new generation of SMMs with enhanced SMM properties.

Modelling spin Hamiltonian parameters of molecular nanomagnets

“…110 By generating various configurations using DFT calculations, various components of the three-axis anisotropic exchange was computed for complexes 97-99 (see Table 4 and Figure 16b for spin density plots). 111,112 This estimates are consistent with a experimental studies 110 (magnetic studies, INS and Tera-hertz EPR) carried out to extract these SH parameters in these complexes.…”

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…An X-band EPR experiment using a polycrystalline material made of the complex (Ph 4 P)[Os III (CN) 6 ]•6H 2 O determined anisotropic g-factors of g ┴ = 1.79 and g ǁ = 1.21 [195]. Moreover, their potential use as building blocks for heterometallic magnetic complexes with strong anisotropic magnetic exchange interactions has also been demonstrated [114,138,190,191,193]. According to the hole formalism, the d orbital/spectroscopic term splitting pattern is the same for d 1 and d 6 ions [197], and thus the magnetic anisotropy of high-spin d 6 ions (Fe II or Co III ) is expected to be as interesting as that of d 1 ions (vide supra).…”

“…Examples of low-spin d 5 complexes that exhibit considerable magnetic anisotropy mainly comprise Re II [112,[177][178][179][180][181][182], Ru III [138,[183][184][185][186][187][188][189], and Os III [114,138,[190][191][192][193][194][195]. The magnitude of  for free Re II ranges between 300 and 2000 cm -1 .…”

Evolvement of molecular nanomagnets in China

“…Owing to the synthetic difficulty of the 4d and 5d compounds, the SMMs based on the heavy metal centres are still very limited compared with the vast amount of 3d analogues [32][33][34][35][36][37][38][39][40]. In this respect, the building block approach, especially using the cyanometalates, was proved to be of crucial importance.…”