Ligand Effect on the Single-Molecule Magnetism of Tetranuclear Co(II) Cubane

Abstract

A clear dependence on the ligand has been observed for the magnetic properties of a closely related series of Co(II) cubane structures, viz. [Co(mbm or bm)(ROH)Br] (1-MeOH, 1-EtOH, 2-MeOH, and 2-EtOH, where 1 = [Co(mbm)Br], 2 = [Co(bm)Br], bm = (1H-benzo[d]imidazol-2-yl)methanolate. and mbm = 1-Me-bm.) The [Co(OR)] cubane core consists of an octahedral Co center chelated by the alkoxide oxygen and imidazole nitrogen atoms from monoanionic bm or mbm and coordinated by methanol/alcohol and bromine. Interestingly, electrospray ionization mass spectrometry (ESI-MS) indicates that 1-MeOH and 2-MeOH are unstable in methanol and transformed to the butterfly [CoL] but that 1-EtOH and 2-EtOH are stable in ethanol. Their magnetic susceptibilities suggest ferromagnetic coupling between the nearest cobalt centers to give a theoretical S = 4 × 3/2 ground state with considerable magneto-crystalline behavior. The packing and intermolecular interactions appear to influence the geometry of the cubes and thus the anisotropy of cobalt, which leads to different blocking temperatures (T). Consequently, the compounds with mbm, 1-MeOH and 1-EtOH, exhibit T > 2 K as shown by the relaxation of magnetization in zero applied dc field where the barriers U/k are respectively 27 and 21 K and relaxation times are τ = 1.3 × 10 and 9.7 × 10 s. However, the compounds with bm, 2-MeOH and 2-EtOH, remain paramagnetic above 2 K and do not show nonlinear response of the ac susceptibilities. These findings reaffirm the subtle dependence of single-molecule magnetism on coordination geometry and intermolecular interaction.

Tracking the Transformation Process of a Pair of Zn(II) Coordination Clusters: Crystallography and Mass Spectrometry

“…It is worth noting that a very weak species corresponding to [Zn 6 (LÀH) 4 À7H] + fragment appeared at m/z 1556.92, the appearance of high nuclear fragment demonstrates the possibility of further assembly of Zn 4 into high nuclear clusters. [17] The mass spectrum of the reaction solution at 100 8C and 120 8C is basically the same as 80 8C, with little changes on peak relative intensity. No peaks containing dehydrated form ligand fragments was detected in Figure 2.…”

Acid–base resistant ligand-modified molybdenum–sulfur clusters with enhanced photocatalytic activity towards hydrogen evolution

“…The m/z values and isotopic distributions of all the major peaks in the ESI-MS spectra of MoS-MBTZ are shown in weak interaction rather than decomposing, evidence of its strong structural robustness. 34,47,48 Aer one month of immersion in a strong acid or base, the ESI-MS spectra were basically unchanged and no other fragment peaks were identied (Fig. 2c).…”

“…The peaks at m / z 2056.89 and 2101.82, are assigned to {[Mo IV 3 S 7 (MBTZ) 3 ] 2 (OH)(H 2 O)} + and {[Mo IV 3 S 7 (MBTZ) 3 ] 2 Br} + , respectively, indicating that [Mo IV 3 S 7 (MBTZ) 3 ] + could further form a dimer by weak interaction rather than decomposing, evidence of its strong structural robustness. 34,47,48 After one month of immersion in a strong acid or base, the ESI-MS spectra were basically unchanged and no other fragment peaks were identified (Fig. 2c).…”

One-Pot Self-Assembly of Dinuclear, Tetranuclear, and H-Bonding-Directed Polynuclear Cobalt(II), Cobalt(III), and Mixed-Valence Co(II)/Co(III) Complexes of Schiff Base Ligands with Incomplete Double Cubane Core

“…The bond distances and bond angles relevant to the coordination core of cobalt ions are given in Table S4. planar, μ3-cubic, and μ-pyramidal arrangements at these bridging centers similar to Co and mixedvalenec (Co II /Co III ) complexes [53,[77][78][79][80][81][82][83][84][85]. In 4, a symmetric network of reasonably strong, intermolecular H-bonding interactions (2.765-2.930 Å ) between oxygen atoms (O(9), O(10), O(11)) of the uncoordinated NO3 -ions and the uncoordinated protonated ethanoate oxygen (O(5)) atom in the side arm of the ligand (H2L1 2− ) (O(11)-O(5) = 2.805 Å ), in one tetranuclear unit and the coordinated amino group (NH2) (O(9)-N(2) = 2.930 Å ) and the uncoordinated hydroxy (O8)) of THMAM (O(10)-O(8) = 2.765 Å ) of the neighboring tetranuclear unit, direct the formation of a beautiful 2D-sheet structure (Figure 7).…”