Mixed Ligand Complexes of Cobalt(II) – Synthesis, Structure, and Properties of Co₄(thd)₄(OEt)₄

Abstract

Synthesis, crystal structure, thermal stability, and magnetic properties of mixed‐ligand complexes of cobalt(II) with ß‐diketonato (thd = C11H19O2−) and alkoxides (OR mainly OMe = methoxide = CH3O− or OEt = ethoxide = C2H5O−) are reported. Direct reaction between Co(thd)2 (1) and EtOH gives a new complex with the structural formula [Co4(thd)4(OEt)4] (2) whereas MeOH correspondingly reacts to [Co4(thd)4(OMe)4(MeOH)4] (3). The yield of these products decreases with increasing size of the R group owing to increased solubility of 1 in the alcohol. The structure of 2 is determined from single‐crystal X‐ray diffraction data. At 100 K 2 takes a monoclinic structure (space group C2/c): a = 15.108(2), b = 19.428(2), c = 21.240(3) Å, and β = 108.882(2)°. At 295 K 2 has transformed to a closely related orthorhombic structure (space group Fddd): a = 15.233(3), b = 19.712(3), c = 40.916(7) Å. Protracted hydrolysis accompanied by oxygenation of complexes 2 and 3 in laboratory air (viz. simultaneous exposure to moisture and oxygen) leads to a new complex 4 with empirical formula corresponding to [Co(thd)(OH)(O2)]. Magnetic susceptibility data show that Co takes the valence state II in all complexes 1–4. For 4 this implies that dioxygen has to form an adduct‐like association to the rest of the complex. Unfortunately complex 4 has hitherto only been obtained in the amorphous state, but all here produced evidences point at 4 as a distinct entity and that products of 4 obtained from 2 and 3 are chemically identical (but differ somewhat with regard to short‐ and longer‐range order in the atomic arrangement). The interatomic distances in the crystal structure of complexes 1–3 are briefly discussed in terms of the bond‐valence concept.

Diastereodifferentiation of Novel Naphthalene Dyads by Fluorescence Quenching and Excimer Formation

“… Idealised versions of cubane‐like atomic arrangements in mixed‐ligand cobalt complexes. (a) Cobalt analogue2 of Mn 4 (thd) 4 (EtO) 4 (EtOH) 4 12. (b) Co 4 (thd) 4 (EtO) 4 2.…”

“…(a) Cobalt analogue2 of Mn 4 (thd) 4 (EtO) 4 (EtOH) 4 12. (b) Co 4 (thd) 4 (EtO) 4 2. (c) Co 3 (thd) 3 (EtO) 4 ( tert ‐BuCOO).…”

“…Co(thd) 2 was prepared as described in literature 2. The mixtures of complexes 1 and 2 were obtained by heating Co(thd) 2 (0.0096 mol) in absolute ethanol (200 mL) to reflux for 2 d in air or pure oxygen atmosphere.…”

“…An 8‐term spherical harmonic correction for preferred orientation was applied to data collected on flat plates. The structural models for orthorhombic and monoclinic Co(thd) 3 were taken from Ahmed et al2 and atomic positions were not refined.…”

“…Our original aim was to survey the oxidation of Co II to Co III in complexes with the thd ligand [(thd) – = anion of H(thd) = C 11 H 20 O 2 = 2,2,6,6‐tetramethylheptane‐3,5‐dione] under different conditions. Some accounts of the behaviour of Co(thd) 2 under different conditions (solid or dissolved state, solvent for dissolution, inert or oxidising atmosphere, temperature, and length of the exposure) are already reported 1,2…”