Trapping of a Pseudotetrahedral CoIIO4 Core in Mixed-Valence Mixed-Geometry [Co5] Coordination Aggregates: Synthetic Marvel, Structures, and Magnetism

A systematic one-step one-pot multicomponent reaction of Co(ClO4)(2)center dot 6H(2)O, H3L (2,6-bis((2-(2-hydroxyethylamino)ethylimino)methyl)-4-methylphenol), and readily available carboxylate salts (RCO2Na; R = CH3, C2H5) resulted in the two structurally novel coordination aggregates [(CoCo4L2)-Co-II-L-III(mu(1,3)-O2CCH3)(2)(mu-OH)(2)](ClO4)(4)(center dot) 4H(2)O(1) and [Co(II)co(4)(III)L(2)(mu(1,3)-O2CC2H5)(2)(mu-OH)(mu-OMe)](ClO4)(4)center dot 5H(2)O (2). At room temperature, reactions of H3L in MeOH with cobalt(II) perchlorate salts led to coassembly of initially formed ligand-bound {Co-2(II)} fragments following aerial oxidation of metal centers and bridging by in situ generated hydroxido/alkoxido groups and added carboxylate anions. Available alkoxido arms of the initially formed {L(mu(1,3)-O2CCH3)(mu-OH/OMe)Co-2}(+) fragments were utilized to trap a central Co-II ion during the formation of [Co-5] aggregates. In the solid state, both complexes have been characterized by X-ray crystallography, variable-temperature magnetic measurements, and theoretical studies. Both 1 and 2 show field-induced slow magnetic relaxation that arises from the single pseudo-T-d Co-II ion present. The structural distortion leads to an easy-axis magnetic anisotropy (D = -31.31 cm(-1) for 1 and -21.88 cm(-)1 for 2) and a small but non-negligible transverse component (E/D = 0.11 for 1 and 0.08 for 2). The theoretical studies also reveal how the O-Co-O bond angles and the interplanar angles control D and E values in 1 and 2. The presence of two diamagnetic {Co-2(mu-L)} hosts controls the distortion of the central {CoO4} unit, highlighting a strategy to control single-ion magnetic anisotropy by trapping single ions within a diamagnetic coordination environment.