Capture and Characterization of a Iron(II) Precursor Complex [FeCl3(Hpipz)(pipz)] for Coordination Polymer Synthesis from a Piperazine Melt

By reacting iron(III) chloride with a melt of piperazine, the complex [FeCl3(Hpipz)(pipz)] is formed containing equatorial chloride anions and axial piperazine ligands constituting a trigonal bipyramidal coordination polyhedron. The obtained product is an example for the capture of a precursor complex under melt conditions for the formation of coordination polymers and is thus of limited crystallinity. Characterization was achieved by solution and refinement of the crystal structure by a combination of powder X-ray diffraction, geometrical optimization methods, 57Fe-Mo beta bauer, and IR spectroscopy, magnetic investigations, and elemental analysis. In addition, corroboration by X-ray single crystal data was used to prove the results from powder diffraction as suitable single crystals were finally achieved by modification of the synthesis with the auxiliary solvent pyridine.