ABSTRACT
The trinuclear high-spin iron(III) complex [Fe3Cl3(saltagBr)(py)6]ClO4 {H5saltagBr = 1,2,3-tris[(5-bromo-salicylidene)amino]guanidine} was synthesized and characterized by several experimental and theoretical methods. The iron(III) complex exhibits molecular 3-fold symmetry imposed by the rigid ligand backbone and crystallizes in trigonal space group P3Ì with the complex cation lying on a crystallographic C3 axis. The high-spin states (S = 5/2) of the individual iron(III) ions were determined by Mößbauer spectroscopy and confirmed by CASSCF/CASPT2 ab initio calculations. Magnetic measurements show an antiferromagnetic exchange between the iron(III) ions leading to a geometrically spin-frustrated ground state. This was complemented by high-field magnetization experiments up to 60 T, which confirm the isotropic nature of the magnetic exchange and negligible single-ion anisotropy for the iron(III) ions. Muon-spin relaxation experiments were performed and further prove the isotropic nature of the coupled spin ground state and the presence of isolated paramagnetic molecular systems with negligible intermolecular interactions down to 20 mK. Broken-symmetry density functional theory calculations are consistent with the antiferromagnetic exchange between the iron(III) ions within the presented trinuclear high-spin iron(III) complex. Ab initio calculations further support the absence of appreciable magnetic anisotropy (D = 0.086, and E = 0.010 cm-1) and the absence of significant contributions from antisymmetric exchange, as the two Kramers doublets are virtually degenerate (ΔE = 0.005 cm-1). Therefore, this trinuclear high-spin iron(III) complex should be an ideal candidate for further investigations of spin-electric effects arising exclusively from the spin chirality of a geometrically frustrated S = 1/2 spin ground state of the molecular system.
ABSTRACT
Controllable quantum systems are under active investigation for quantum computing, secure information processing, and nonvolatile memory. The optical manipulation of spin quantum states provides an important strategy for quantum control with both temporal and spatial resolution. Challenges in increasing the lifetime of photoinduced magnetic states at T > 200 K have hindered progress toward utilizing photomagnetic materials in quantum device architectures. Here we demonstrate reversible light-induced magnetization switching in an organic thin film at device operating temperatures of 300-330 K. By utilizing photochromic ligands that undergo structural changes in the solid state, the changes in ligand field associated with photoisomerization modulate the ligand field and in turn the oxidation and spin state of a bound metal center. Green light irradiation (λexc = 550 nm) of a spirooxazine cobalt-dioxolene complex induces photoisomerization of the ligand that in turn triggers a reversible intramolecular charge-transfer coupled spin-transition process at the cobalt center. The generation of photomagnetic states through conversion between a low-spin Co(III)-semiquinone doublet and a high-spin Co(II)-bis-semiquinone sextet state has been demonstrated in both solution and the solid state and is described as a photoisomerization-induced spin-charge excited state (PISCES) process. The high transition temperature (325 K) and long-lived photoinduced state (τ = 10 s at 300 K) are dictated by the photochromic ligand. Theory provides effective modeling of the phenomenon and long-term strategies to further modulate the lifetimes of photomagnetic states for quantum information technologies at the single molecule level.
ABSTRACT
The new tritopic triaminoguanidine-based ligand 1,2,3-tris[(pyridine-2-ylmethylidene)amino]guanidine (H2pytag) was synthesized. The reaction of a mixture of cobalt(II) chloride and cobalt(II) perchlorate with the ligand H2pytag in pyridine solution leads to the formation of the trinuclear cobalt(II) complex [Co3(pytag)(py)6Cl3]ClO4. Three octahedrally coordinated high-spin cobalt(II) ions are linked through the bridging triaminoguanidine backbone of the ligand leading to an almost equilateral triangular arrangement. The magnetic properties of the complex were investigated by magnetic measurements, variable-temperature, variable-field magnetic circular dichroism (MCD) spectroscopy, and density functional theory as well as ab initio calculations. A rather strong antiferromagnetic exchange interaction between the cobalt(II) centers of ca. -12 cm-1 is determined together with a strong local anisotropy. The single-ion anisotropy of all three cobalt(II) centers is found to be easy-plane, which coincides with the tritopic ligand plane. MCD measurements and theoretical investigations demonstrate the presence of rhombic distortion of the local Co surrounding.
ABSTRACT
We present the synthesis and crystal structure of the trinuclear copper complex [Cu3(saltag)(bpy)3]ClO4·3DMF [H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine; bpy = 2,2'-bipyridine]. The complex crystallizes in the trigonal space group R3Ì , with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (JCuCu = -324 cm(-1)). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate S = (1)/2 ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions.
