Synthesis, structure and magnetism of a S-shaped multi-iron substituted arsenotungstate containing a trivacant Keggin [B-α-AsVW9O34]9− and a hexavacant Keggin [α-AsVW6O26]11− fragments

A S-shaped multi-iron substituted arsenotungstate [enH2]2[(α-H2AsVW6O26)Fe3(H2O)(B-α-H4AsVW9O34)]2[Fe]2·8H2O (1) (en=ethylenediamine) has been prepared by reaction of K14[As2IIIW19O67(H2O)]·nH2O with Fe2(SO4)3·xH2O under hydrothermal conditions and structurally characterized by elemental analyses, IR spectra, UV spectra, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. The skeleton of 1 consists of two asymmetric sandwich-type subunits [(α-H2AsVW6O26)Fe3(H2O)(B-α-H4AsVW9O34)]5− linked by a di-FeIII cluster. Moreover, magnetic susceptibility measurements demonstrate that 1 indicates the antiferromagnetic coupling interactions within FeIII centers with the best-fitting set of parameters of J1=−7.07 cm−1, J2=−0.45 cm−1 and g=2.05, which are generated by the addition of the expressions of the molar susceptibilities of two tri-FeIII clusters and one di-FeIII cluster derived from for spin pairs coupled through the isotropic exchange interactions.