Synthesis, Magnetic Properties, and STM Spectroscopy of Cobalt(II) Cubanes [Co^II₄(Cl)₄(HL)₄]

Abstract

Reaction of cobalt(II) chloride hexahydrate with N-substituted diethanolamines H(2)L(2-4) (3) in the presence of LiH in anhydrous THF leads under anaerobic conditions to the formation of three isostructural tetranuclear cobalt(II) complexes [Co(II) (4)(Cl)(4)(HL(2-4))(4)] (4) with a [Co(4)(mu(3)-O)(4)](4+) cubane core. According to X-ray structural analyses, the complexes 4 a,c crystallize in the tetragonal space group I4(1)/a, whereas for complex 4 b the tetragonal space group P$\bar 4$ was found. In the solid state the orientation of the cubane cores and the formation of a 3D framework were controlled by the ligand substituents of the cobalt(II) cubanes 4. This also allowed detailed magnetic investigations on single crystals. The analysis of the SQUID magnetic susceptibility data for 4 a gave intramolecular ferromagnetic couplings of the cobalt(II) ions (J(1) approximately 20.4 K, J(2) approximately 7.6 K), resulting in an S=6 ground-state multiplet. The anisotropy was found to be of the easy-axis type (D=-1.55 K) with a resulting anisotropy barrier of Delta approximately 55.8 K. Two-dimensional electron-gas (2DEG) Hall magnetization measurements revealed that complex 4 a is a single-molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep-rate dependencies below a blocking temperature of about 4.4 K. The hysteresis loops collapse at zero field owing to fast quantum tunneling of the magnetization (QTM). The structural and electronic properties of cobalt(II) cubane 4 a, deposited on a highly oriented pyrolytic graphite (HOPG) surface, were investigated by means of STM and current imaging tunneling spectroscopy (CITS) at RT and standard atmospheric pressure. In CITS measurements the rather large contrast found at the expected locations of the metal centers of the molecules indicated the presence of a strongly localized LUMO.

Conductive Self-Assembled Monolayers of Paramagnetic {CoIICo4III} and {Co4IICo2III} Coordination Clusters on Gold Surfaces

“…The coordination modes of the ligands in the synthesized metal complexes are illustrated in the Supporting Information. Note that the N - n -H 2 bda ligand is not often present in homonuclear cobalt complexes (see e.g., Scheurer et al, 2010).…”

Mesomerization of S4‐Symmetric Tetrahedral Chelate Complex [In4(L3)4]: First‐Time Monitored by Temperature‐Dependent 1H NMR Spectroscopy

“…Energies are ZPE-corrected on the same level, and the Gaussian 03 suite of programs was used throughout. [8] Supporting Information (see footnote on the first page of this article): Line-shape analysis of the tBu signals of 3, Eyring plot of the data obtained from the VT 1 …”

“…NMR spectroscopy was shown to be an effective tool for the investigation of these self-assembled coordination compounds and for the study of their dynamic behavior in solution. [3,4] In this context, we reported on variable-temperature (VT) 1 H NMR spectroscopy studies revealing tetrahedral, racemic, homochiral (∆,∆,∆,∆)-[(NH 4 ) 4 ʝ{Mg 4 -(L 1 ) 6 }] i (Λ,Λ,Λ,Λ)-[(NH 4 ) 4 ʝ{Mg 4 (L 1 ) 6 }] (NH 4 -1) to enantiomerize.…”

Biomimics of phenazine oxidase activity of a cobalt (III)‐dipyridylamine complex: Spectroscopic, structural, and computational studies†

“…[ 22–24 ] Typically, suitable polydentate chelators help to regulate the reactivity of the cobalt center indirectly or through ligand–metal cooperativity leading to the development of emerging catalysts, smart molecular magnets, interesting building block in functional materials, promising therapeutics, photon harnessing functional materials, and so on. [ 25–33 ]…”