What are structures of SO3 in gas phase as well as solid phase ( at room temperature)?

In gas phase sulphur atom of SO₃ has sp² hybridized and trigonal structure. In which three sigma bond give rise to trigonal planer shape and three delocalized π-bond, out of three π-bond one is pπ-pπ bond and another two are pπ-dπ bond.

In solid phase SO₃ exist at room temperature and have two different structures.

Important fact that cyclic trimer of SO₃ (S₃O₉) is also isoelectronic with P₃O₉^-3 and contains 120 electrons.

Structure of Si₃O₉^-6

Structure of P₃O₉^-3

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