A {CoII9CoIII3} dodecanuclear cluster based on o-vanillin oxime: Synthesis, structures and properties

Linear, Planar, Orbicular, and Macrocyclic Multinuclear Zinc (Meth)acrylate Complexes

Zinc carboxylate complexes are widely utilized as artificial models of metalloenzymes and as secondary building units of PCPs/MOFs. However, the relationship between the structure of the monodentate carboxylato ligand and the molecular arrangement of multinuclear zinc carboxylate complexes is not fully understood because of the coordination flexibility of the Zn ion and carboxylato ligands. Herein, we report the structural analysis of a series of complexes derived from zinc (meth)acrylate which has a linear infinite chain structure. The molecular structure of μ4-oxido-bridged tetranuclear complexes [Zn4(μ4-O)(OCOR)6] revealed a distorted Zn4O core. Crystallization of zinc acrylate under aqueous conditions afforded a μ3-hydroxido-containing pentanuclear complex [Zn5(μ3-OH)2(OCOR)8] as the repeating unit of an infinite sheet-like structure in the solid state. It was also obtained by the hydrolysis of the μ4-oxido-bridged tetranuclear complex. In sharp contrast, the methacrylate analog retained the methacrylato ligands under aqueous crystallization conditions to form a macrocyclic dodecanuclear complex with methacrylato as the sole ligand.

From tetranuclear to pentanuclear [Co-Ln] (Ln = Gd, Tb, Dy, Ho) complexes across the lanthanide series: effect of varying sequence of ligand addition

Two new families of cobalt(ii/iii)-lanthanide(iii) coordination aggregates have been reported: tetranuclear [LnCoL₂(N-BuDEA)₂(O₂CCMe₃)₄(H₂O)₂]·(MeOH)_n·(H₂O)_m (Ln = Gd, 1; Tb, 2; Dy, 3; n = 2, m = 10 for 1 and 2; n = 6, m = 2 for 3) and pentanuclear LnCo^IICoL₂(N-BuDEA)₂(O₂CCMe₃)₆(MeOH)₂ (Ln = Dy, 4; Ho, 5) formed from the reaction of two aggregation assisting ligands H₂L (o-vanillin oxime) and N-BuDEAH₂ (N-butyldiethanolamine). A change in preference from a lower to higher nuclearity structure was observed on going across the lanthanide series brought about by the variation in the size of the Ln^III ions. An interesting observation was made for the varying sequence of addition of the ligands into the reaction medium paving the way to access both structural types for Ln = Dy. HRMS (+ve) of solutions gave further insight into the formation of the aggregates via different pathways. The tetranuclear complexes adopt a modified butterfly structure with a more complex bridging network while trapping of an extra Co^II ion in the pentanuclear complexes destroys this arrangement putting the Co-Co-Co axis above the Ln-Ln axis. Direct current (dc) magnetic susceptibility measurements reveal weak antiferromagnetic coupling in 1. Complexes 2 and 5 display no slow magnetic relaxation, whereas complexes 3 and 4 display out-of-phase signals at low temperature in ac susceptibility measurements. All compounds were analyzed with DFT and CASSCF calculations and informations about the single-ion anisotropies and mutual 4f-4f/4f-3d magnetic interactions were derived.

Structural characterization and magnetic property studies of a mixed-valence {CoIIICo} complex with a μ4-oxo tetrahedral {Co} motif

We have synthesized and structurally characterized a new mixed valence pentanuclear Co complex, bearing a rare μ4-O-tetrahedral CoII4 unit, by employing a pyridine-like Schiff base ligand. We have performed DC magnetic susceptibility and magnetization measurements over polycrystalline samples and chemical quantum computations in order to understand the exchange interaction pattern within Co(ii) sites and ground state magnetic anisotropy. This new complex shows an overall antiferromagnetic exchange interaction whose strength strongly depends on the local symmetry of Co(ii) sites. Also, local ion magnetic anisotropy reveals a strongly axial behaviour with the lowest Kramers doublet (KD) at each Co(ii) ion sufficiently isolated from excited states at low temperatures. Two Co(ii) sites show tetrahedral symmetry and the spin only formalism including axial zero-field splitting (ZFS) term properly described them; on the other hand, the other two Co(ii) sites have distorted octahedral and square base pyramidal coordination spheres, and a strong orbital contribution leads to a failure of the spin only formalism. A model of four Seff = 1/2 exchange interacting sites is necessary in order to account for low temperature magnetization behaviour. In view of the strongly anisotropic KD states, the exchange interactions are forced to be modelled as anisotropic ones. Overall, experimental data and quantum chemical computations are in good agreement, supporting the proposed model for magnetic behaviour.