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The molecular self‐assembly and the magnetic properties of two cyclooctatetraenide (COT)‐based single‐ion magnets (SIM) adsorbed on Ag(100) in the sub‐monolayer (ML) range are reported. Our study combines scanning‐tunneling microscopy, X‐ray photoemission spectroscopy and polarized X‐ray absorption spectroscopy to show that Cp*ErCOT (Cp* = 1,2,3,4,5‐pentamethylcyclopentadienide anion) SIMs self‐assemble as alternating compact parallel rows including standing‐up and lying‐down conformations, following the main crystallographic directions of the substrate. Conversely, K[Er(COT)2], obtained from subliming the [K(18‐c‐6)][Er(COT)2]·2THF salt, forms uniaxially ordered domains with the (COT)2− rings perpendicular to the substrate plane. The polarization‐dependent X‐ray absorption spectra reproduced by the multiX simulations suggest that the strong in‐plane magnetic anisotropy of K[Er(COT)2]/Ag(100) and the weak out‐of‐plane anisotropy of Cp*ErCOT/Ag(100) can be attributed to the strikingly different surface ordering of these two complexes. Compared to the bulk phase, surface‐supported K[Er(COT)2] exhibits a similarly large hysteresis opening, while the Cp*ErCOT shows a rather small opening. This result reveals that despite structural similarities, the two organometallic SMMs have strongly different magnetic properties when adsorbed on the metal substrate, attributed to the different orientations and the resulting interactions of the ligand rings with the surface. [ABSTRACT FROM AUTHOR]

Ligands such as N‐2‐pyrimidylimidoyl‐2‐pyrimidylamidine (Pm2ImAm) possess both a bidentate and tridentate coordination site within a single ligand framework. Taking advantage of this, two tetranuclear complexes with manganese ([MnIIIMnII3(Pm2ImAm)3Cl6]) and iron ([FeIII4(Pm2ImAm)3Cl9]) have been isolated, characterized by single‐crystal X‐ray analysis, and their magnetic properties have been investigated through SQUID magnetometry and Mössbauer spectroscopy. As well, a mononuclear ([FeIII(Pm2ImAm)Cl3]) and binuclear ([MnII2(µ‐Cl)2(Pm2ImAm)2Cl2]) complex employing this ligand framework were also isolated, characterized by single‐crystal X‐ray analysis and their magnetic properties were investigated. For comparison purposes, the previously reported mononuclear complexes [MnIII(Py2ImAm)3] and [FeIII(Py2ImAm)3] were also probed here via SQUID magnetometry due to the similarities between these mononuclear systems and fragments of the tetranuclear complexes. Through this approach, clear interpretation of the magnetic properties in [MnIIIMnII3(Pm2ImAm)3Cl6] and [FeIII4(Pm2ImAm)3Cl9] was achieved. These results reveal that employing our N‐imidoylamidine ligands facilitates the rational design of polynuclear complexes with differing metal ion spin states. Rational design of tetranuclear complexes with manganese and iron was achieved by employing N‐imidoylamidine ligands. Evaluation via SQUID magnetometry and Mössbauer spectroscopy reveal a unique combination of low and high spin states for the metal centers within these cluster aggregates. [ABSTRACT FROM AUTHOR]

The terpyridine-inspired tridentate ligand, 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridine (BTP), was synthesized and utilized to isolate five [MII(BTP)2]2+ (M = Fe and Co) transition-metal complexes of various anions (BF4-, ClO4-, and NCS-). Notably, when metal-halide precursors are employed, 1:1 M/L products [Co2II(μ-X)2(BTP)2X2] (X = Cl or Br) are obtained, exhibiting μ-halide bridges. All complexes were structurally characterized through single-crystal X-ray diffraction and their electrochemical and magnetic properties were investigated. Electrochemical studies reveal that the free BTP ligand has a single irreversible reduction, however; upon coordination to a metal center, stabilization of the reduced BTP ligand occurs and up to four reductive processes associated with the molecule are observed within the solvent window. The metal-centered redox processes were either reversible or partially reversible, and fall within the range of 0.13 < E1/2 < 0.90 V vs. Fc/Fc+. Although there was minimal effect on the redox properties of the metal centers, there is strong dependence on the spin state. SQUID magnetometry elucidated a low spin state for the FeII complexes at room temperature, revealing a diamagnetic electronic structure. On the other hand, the cobalt monometallic complexes, [CoII(BTP)2]2+, showed gradual spin crossover properties between 1.8-370 K, displaying a minor dependence on the spin crossover behavior based on the respective anion. Additionally, ferromagnetic exchange interactions of J = +2.57 and +2.98 cm-1 were obtained using the -2J formalism for the dinuclear CoII complexes, [Co2 II(μ-X)2(BTP)2X2] for X = Cl and Br, respectively. [ABSTRACT FROM AUTHOR]

Review: 38 refs. [ABSTRACT FROM AUTHOR]

Review: [76 refs. [ABSTRACT FROM AUTHOR]