Halogeno metallates of transition elements with cations of nitrogen-containing heterocyclic bases, IX. Moessbauer and ESR spectroscopic investigation of aquachloro- and bromoferrates(III). On the compatibility of structural information obtained by spectroscopic and diffraction methods☆

Abstract The 57 Fe-Moessbauer spectrum of (dmpipzH 2 ) 2 [Fe III (H 2 O) 2 Cl 4 ][Fe III Cl 4 ]Cl 2 ( 1 ) consists of two doublets caused by a strongly distorted octahedral and a non-distorted tetrahedral component. Both (dmpipzH 2 )[Fe III Br 4 ] 2 ( 2 ) and (trienH 2 )[Fe III Br 4 ]Br ( 3 ) show only one doublet indicating a more strongly distorted iron(III) species for 2 and a less-distorted one in the case of 3 . For all compounds investigated, the ESR spectra reveal the existence of ground states with predominant antiferromagnetic coupling. The Neel temperatures amount to 1 , ∼4 K for 3 and 48 K for 2 . In the case of 2 , both the Moessbauer and the ESR spectra reveal the formation of exchange-coupled {FeBr 4 } units which has been attributed to a significant cation influence. The fine structure of residual paramagnetic [FeBr 4 ] − subunits remaining in the crystalline matrix could be directly determined. Temperature dependent AC and DC susceptibility measurements of 2 and 3 confirmed the results.