New refinement of lead bis(dihydrogenphosphate) Pb(H2PO4)2 and crystal chemistry of M(H2PO4)2 (M = Ca, Sr, Ba, Pb, Sn)

Single crystals of Pb(H2PO4)2 were grown under hydrothermal conditions. X-ray crystallography showed that the title compound crystallizes in the triclinic system with space group P1 and lattice parameters a = 7.812, b = 8.311, c = 5.859 Å, α = 108.23°, β = 96.85°, γ = 108.62°, Z = 2, and ρcal = 4.011 g·cm−3. The structure was solved from 3705 independent reflections with R = 0.043 (wR = 0.11). It can be regarded as made of independent [PO4] tetrahedra. Two apices of each [PO4] tetrahedron are connected to two H atoms to form [H2PO4]− anions arranged in a way to delimit large and distorted cavities occupied by lead cations. The resulting arrangement could be seen as made of infinite strips, developing along [001] and connected through hydrogen bonds.