A Chain of Vertex-Sharing {Co₂^IIICo₂^II}_n Squares with Single-Ion Magnet Behavior

A new mixed-valence one-dimensional coordination polymer of formula {[Co-II(MeOH)(2)][(mu-NC)(2)Co-III(dmphen)(CN)(2)](2)} (n)center dot 2nH(2)O (1) was obtained by reacting the Ph4P[Co-II(dmphen)(CN)(3)] metalloligand (dmphen = 2,9-dimethyl-1,10-phenanthroline and Ph4P+ = tetraphenylphosphonium ion) with cobalt(II) acetate tetrahydrate. The structural analysis shows the formation of a neutral 4,2-ribbon-like chain of vertex-sharing cyanido-bridged {(Co2Co2II)-Co-III} squares in which the metalloligand underwent an oxidation process and a reorganization to form {Co-III(dmphen)(CN)(4)}(-) linkers that coordinate to the [Co-II(MeOH)(2)](2+) units through single cyanido ligands. Both cobalt(II) and Co(III) cations are six-coordinated in distorted octahedral environments. The shortest intrachain distance between the paramagnetic cobalt(II) ions is 7.36 angstrom, a value which is shorter than the shortest interchain one (10.36 angstrom). Variable-temperature (1.9-300 K) static (dc) magnetic measurements for 1 indicate the occurrence of magnetically isolated high-spin cobalt(II) ions with a D value of +67.0 cm(-1). Dynamic alternating current (ac) magnetic measurements between 2.0-13 K reveal that 1 exhibits slow magnetic relaxation under non-zero applied dc fields, being thus a new example of field-induced SIM with easy-plane magnetic anisotropy. Theoretical calculations by CASSCF/NEVPT2 on 1 support the results from magnetometry. The relaxation of the magnetization occurs in the ground state under external dc fields through a two-phonon Raman process and one intra-Kramers mechanism.