Abstract
Herein we report two pentanuclear Mn
-substituted sandwich-type polyoxotungstate complexes, [{Mn(bpy)}
Na(H
O)
(MnCl)
{Mn(H
O)}(AsW
O
)
]
and [{Mn(bpy)}
Na(H
O)
(MnCl){Mn(H
O)}
(SbW
O
)
]
(bpy = 2,2'-bipyridine), whose structures have been obtained by single-crystal X-ray diffraction (SCXRD), complemented by results obtained from elemental analysis, electrospray ionization mass spectrometry, Fourier transform infrared spectroscopy, and thermogravimetric analysis. They consist of two [B-α-XW
O
]
subunits sandwiching a cyclic assembly of the hexagonal [{Mn(bpy)}
Na(H
O)
(MnCl)
{Mn(H
O)}]
and [{Mn(bpy)}
Na(H
O)
(MnCl){Mn(H
O)}
]
moieties, respectively, and represent the first pentanuclear Mn
-substituted sandwich-type polyoxometalates (POMs). Both compounds have been synthesized by reacting MnCl
·4H
O with trilacunary Na
[XW
O
]·27H
O (X = As
and Sb
) POM precursors in the presence of bpy in a 1 M aqueous sodium chloride solution under mild reaction conditions. SCXRD showed that the alternate arrangement of three five-coordinated Mn
ions and two six-coordinated Mn
ions with an internal Na cation formed a coplanar six-membered ring that was sandwiched between two [B-α-XW
O
]
(X = As
and Sb
) subunits. The results of temperature-dependent direct-current (dc) magnetic susceptibility data indicated ferromagnetic interactions between Mn ions in the cluster. Moreover, alternating-current magnetic susceptibility measurements with a dc-biased magnetic field showed the existence of a ferromagnetic order for both samples. Electrochemistry studies revealed the presence of redox processes assigned to the Mn centers. They are associated with the deposition of material on the working electrode surface, possibly Mn
O
, as demonstrated by electrochemical quartz crystal microbalance experiments.