We have obtained an X-ray diffraction data set at 10.5(5) K and a neutron diffraction data set at 12(2) K for the title compound. The atomic positional and displacement parameters derived from the two data sets agree satisfactorily, as the very low temperatures markedly reduce systematic errors. In the partial X-ray-neutron analysis of the X-ray data it was necessary to use a multipole model that introduces additional flexibility in the radial functions for valence orbitals of atoms. The electron density around the iron site is compared with that produced by a ligand-field model which has been used to interpret and collate a number of measurements of physical properties of the compound. Good agreement is obtained for the shape and orientation of the 3d density, but there are some quantitative differences. There are large 4p densities, due to covalent transfer from the ligating water molecules. We confirm on the one hand the ability of the X-ray experiment to give detailed chemically relevant information and on the other hand that, with care, ligand-field theory may be used in the quantitative prediction of transition metal ion physical properties.