The hydrolysis of SnF₂ in concentrated aqueous solution resulted in the formation of the tin(II) fluoride oxide, Sn₄OF₆. This is the first evidence for the formation of a basic tin(II) fluoride from an aqueous system. The crystal structure of Sn₄OF₆ has been determined using single-crystal X-ray diffraction and refined by full-matrix least-squares analysis to R= 0.0199. The compound crystallises in the orthorhombic space group P2₁2₁2₁ with a= 16.088(3), b= 10.681 (2), c= 4.940(1)Å and Z= 4. The structure consists of a three-dimensional polymeric network of bridging fluorine and oxygen atoms. Tin is present in four distinct sites one showing tetragonal-based pyramidal geometry while the others all show trigonal-pyramidal geometry with a fourth bridging fluorine atom at 2.4–2.5 Å. The non-bonding electrons are stereochemically active and appear to point into irregular channels which run parallel to the c axis.