Benzoatokomplexe des Eisens und Cobalts Synthese und Eigenschaften von Fe3(C6H5COO)4(acac)2, Fe(C6H5COO)2 und CO(C6H5COO)2 , Kristallstruktur von Fe3(C6H5COO)4(acac)2 und Co(C6H5COO)2 / Benzoato Complexes of Iron and Cobalt Synthesis and Properties of Fe3(C6H5COO)4(acac)2, Fe(C6H5COO)2 and Co(C6H5COO)2, Crystal Structure of Fe3(C6H5COO)4(acac)2 and Co(C6H5COO)2

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.