ABSTRACT
We describe the synthesis, structures, and magnetochemistry of new M4Cl4 cubane-type cobalt(II) and nickel(II) complexes with the formula [M(µ3-Cl)Cl(HL·S)]4 (1: M = Co; 2: M = Ni), where HL·S represents a pyridyl-alcohol-type ligand with a thioether functional group, introduced to allow subsequent binding to Au surfaces. Dc and ac magnetic susceptibility data of 1 and 2 were modeled with a full spin Hamiltonian implemented in the computational framework CONDON 2.0. Although both coordination clusters 1 and 2 are isostructural, with each of their transition metal ions in a pseudo-octahedral coordination environment of four Cl atoms and N,O-donor atoms of one chelating HL·S ligand, the substantially different ligand field effects of Co(II) and Ni(II) results in stark differences in their magnetism. In contrast to compound 1 which exhibits a dominant antiferromagnetic intramolecular coupling (J = -0.14 cm(-1)), 2 is characterised by a ferromagnetic coupling (J = +10.6 cm(-1)) and is considered to be a single-molecule magnet (SMM), a feature of special interest for future surface deposition studies. An analysis based on density functional theory (DFT) was performed to explore possible magnetostructural correlations in these compounds. Using a two-J model Hamiltonian, it revealed that compound 1 has four positive and two (small) negative J(Co···Co) isotropic interactions leading to a S(HS) = 6 ground state. Taking into account the magnetic anisotropy, one would recover a M(S) = 0 ground state since D > 0 from computations. In 2, all the J constants are positive and, in this framework, the zero-field splitting energy characterising the axial anisotropy was estimated to be negative (D = -0.44 cm(-1)). The computational results are consistent with compound 2 being an SMM.
ABSTRACT
The reactions of NiCl2·2H2O or [NiCl2(DME)] (DME = dimethoxyethane) with 2-methyl-1-(pyridin-2-yl)propan-2-ol (HL) and 2-(pyridin-2-yl)ethanol (HLEt), in a 1:1 ratio, afforded the tetranuclear, cubane-type clusters [Ni(µ3-Cl)Cl(HL)]4 (3) and [Ni(µ3-Cl)Cl(HLEt)]4 (4), respectively. These are tetramers of the hypothetical mononuclear formula-isomers [NiCl2(HL)] and [NiCl2(HLEt)], respectively, and represent rare examples of structurally characterized cubane-like transition metal dihalogenide complexes. The 2:1 reactions between HL or HLEt and [NiCl2(DME)] yielded, instead, the mononuclear [NiCl2(HL)2] (1) and the dinuclear complex [Ni(µ-Cl)(HLEt)2]2Cl2 (2), respectively. The reaction of 3 with NaOH afforded selectively the cubane-type cluster [Ni(µ3-OH)Cl(HL)]4 (5) which differs only in the nature of the capping anions (Cl vs. OH, respectively). The magnetic properties of the unusual tetranuclear cubanes 3 and 5 have been investigated and revealed in both cases single-molecule magnet (SMM) behaviour.
ABSTRACT
A novel heterodifunctional phosphinite imidazolium salt was synthesized and reacted with Ag(I) to afford an unusual tetrasilver cubane-type cluster with two P-NHC ligands bridging between the Ag(I) centres of opposite Ag(2)I(2) faces.