Mercury(II) Diphosphate, Hg₂P₂O₇

Mercury(II) diphosphate, Hg₂P₂O₇, belongs to the M₂X₂O₇ family of compounds with dichromate-type crystal structures and is isotypic with Cd₂P₂O₇. It consists of alternating layers built from P₂O₇ groups and highly distorted HgO₆ polyhedra with bond distances in the ranges 2.120 (6) ≤ d(Hg1O₆) ≤ 2.793 (7) Å and 2.208 (6) ≤ d(Hg2O₆) < 2.509 (6) Å. The diphosphate anion has a bridging angle (P—O—P) of 133.4 (4)°. The average P—O bond length is 1.604 Å for bridging and 1.524 Å for terminal bonds. [Hg1₂O₁₀] and [Hg2₂O₁₀] form chains running along [110] through edge-sharing dimers. These chains link to form layers parallel to (10) via common vertices.

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