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

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.