Spin density and bonding in Mn(H 2 O) 2+ 6 in ammonium manganese Tutton salt

Abstract

The structure of (NH 4 ) 2 Mn(SO 4 ) 2 6H 2 O has been determined at 4.2 K by neutron diffraction. It confirms the main features of an earlier X-ray structure and gives details of the water molecules and the hydrogen bonding. The flipping ratios associated with the more intense Bragg reflections were measured by polarized neutron diffraction. By using the neutron structure factors, 495 unique magnetic structure factors were obtained and the spin distribution in the Mn(H 2 O) 2+ 6 ion was modelled. There appears to be no reduction in spin population in the Mn 2+ d-orbitals (t 3.1 2g e 2.0 g ), but a small negative diffuse population, 4s 0.2 -, is present, which together with a total ‘overlap’ population of –0.1 spins balances the 0.2 net positive spin found on the water molecules. Unexpectedly, the spin on the water molecules seems to be concentrated on the side of the oxygen atoms far from the manganese atom, and to reside more on the hydrogen atoms than the oxygen atoms. Evidence for the expected negative spin component in the Mn—O bonds arising from antibonding overlap is found.