Abstract
The reaction of iron(III) acetylacetonate with molten benzoic acid yields Fe(C6H5COO)2 (2) besides small amounts of Fe3(C6H5COO)4(acac)2 (1), whereas cobalt(III) acetylacetonate or cobalt(II) carbonate quantitatively yield Co(C6H5COO)3 (3). Complex 1 forms triclinic red crystals with the space group PI and the lattice constants a = 1016.0(3) pm, b = 1099.9(2) pm, c = 969.8(2) pm, α = 92.68(2)°, β = 105.67(2)°, γ = 117.57(2)°, Z = 1. 3 is obtained as monoclinic violet needles with the space group C2/c and the lattice constants a = 1739.2(4) pm, b = 1413.8(3) pm, c = 1045.3(3) pm, β = 96.26(2)°, Z = 8. 3 consists of polymeric chains with a zigzag arrangement of the cobalt atoms (Co -Co = 314.5 pm) and an octahedral coordination for Co 1 and (4+2)-coordination for Co2. The benzoato ligands act differently. One benzoate group functions as bridging ligand between adjacent metal atoms, the other acts as a four-dentate ligand by chelating one cobalt atom and bridging its neighbours. Complex 2 was not obtained in form of single crystals, but its properties as well as its IR and Mößbauer spectra suggest a similar structure as for 3. Complex 1 is also polymeric, the chain of iron atoms is nearly linear. The acetylacetonate ligand acts chelating and bridging as a four-dentate ligand, whereas the benzoate anion is only bridging neighbouring Fe atoms. The Fe atoms exhibit octahedral and trigonal bipyramidal coordination.
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