Na4Co3(PO4)2P2O7, a New Sodium Cobalt Phosphate Containing a Three-Dimensional System of Large Intersecting Tunnels

Abstract Single crystals of the new Co(II) phosphate Na 4 Co 3 (PO 4 ) 2 P 2 O 7 have been isolated and their structure has been determined by X-ray diffraction techniques. This compound crystallizes in the orthorhombic noncentrosymmetric space group Pn 2 1 a with a = 18.046(5) A, b = 6.533(2) A, c = 10.536(2) A, and Z = 4. The structure consists of infinite layers with composition (Co 3 P 2 O 13 ) ∞ parallel to the bc plane. Interlayer linkages are made via P–O–P bridges of the pyrophosphate groups in such a way that large tunnels extending along the [010] and [001] directions occur between two neighboring sheets. Besides, there also exist channels along the [100] direction crossing the (Co 3 P 2 P 13 ) ∞ layers. A complex scheme of tunnel intersections gives rise to the formation of a three-dimensional channel network which hosts the sodium cations.