Single crystals of a new oxyphosphate of bismuth and lead, Pb 5 Bi 18 P 4 O 42 , were studied using short-wavelength synchrotron X-ray radiation. The compound is monoclinic, I2/m, a โซุโฌ 11.885(2) A s , b โซุโฌ 11.540(2) A s , c โซุโฌ 15.636(3) A s , โซุโฌ 90.23(3)3, Z โซุโฌ 2. The crystal is twinned by pseudo-merohedry. The structure re5nement converged to R โซุโฌ 0.0366. There are 5ve crystallographically independent Bi atoms. The oxygen coordination polyhedron around Bi(1) is a slightly distorted cube with Bi+O bonds varying from 2.381(11) to 2.662(10) A s . The other four Bi atoms are in a severely distorted oxygen environment with bond lengths varying from 2.102(5) to 3.16(2) A s . A greater variation of the oxygen coordination polyhedra exists around the three crystallographically independent Pb atoms changing from a somewhat elongated cube to a monocapped pentagonal bipyramid; bond distances vary from 2.13(2) to 3.38(2) A s . Of 20 crystallographically independent oxygen ions 11 are disordered. The structure consists of two Bi+O layers parallel to (101). They are interconnected perpendicular to [010] by layers consisting of Pb and PO 4 . The two crystallographically independent PO 4 moieties are disordered. This compound displays a -Bi 2 O 3 6uorite superstructure. The locations of the nonbonded lone-pair electrons were calculated and vary from 0 to 1.1 A s . These displacements from the cation nucleus are indicative of the extent of s+p hybridization, where zero displacement represents the spherical nonbonded 6s 2 orbital. The extent of hybridization is a function of the distortion of the oxygen coordination polyhedron around the cation.