Schultenite, PbHAsO₄, and PbHOP₄: Syntheses and crystal structures with a discussion on their symmetry

Summary Schultenite PbHAsO₄ a=4.859(1) Å,b=6.756(1) Å,c=5,843(1) Å, =95.40(1)°] and PbHPO₄ a=4,6838(3) Å,b=6,6451(2) Å,c=5.7817(3) Å =97.138(4)°] are isotypic and crystallize monoclinic. For both compounds a transition from space groupPc toP2/c has been described atT _c312 K. The structure type of schultenite is characterized, by a short hydrogen bond between two XO₄ tetrahedra which are combined by a center of symmetry in space groupP2/c. The O–H...O bond length is for both these compounds 2.46 Å. Based on X-ray single crystal structure refinements it has been shown, that the transition fromPc toP2/c is obviously caused only by an ordering of the H atom; all the other atoms are also at room temperature centrosymmetrically arranged within limits of error.