K5H{Cu4O[Bo20O32(OH)8]} · 33 H2O, M = 1925.46 g/mol. triclinic, P1̄, a = 1627.4(7), b = 1799.6(9), and c = 1365.2(5) pm; α = 96.37(5), β = 110.93(5), and γ = 111.36(5)°; Z = 2; Dm = 1.96 (flotation) and Dx = 1.91. Mg · m-3; R = 0.155 for 5022 observed reflections, and Na5H{Cu{[B20O32(OH)8]}. 32 H2O, M = 1825.62 g/mol, tetragonal. I4̄, a = 1866 and c = 1042 pm; Z = 2; Dm = 1.63 and Dx = 1.67 Mg · m-3 have been investigated. The structure of the anion icosaboro-μ4-oxo-tetracuprate(II)(6-) contains the largest known isolated borate ion with 20 boron atoms. Each borate ion is a prophyrine-like ring, and encloses four Cu ions in a nearly planar Cu4O cation, thus forming a chelate-like complex. While the anion structure is clear, the positions of the alkalimetal ions and the water molecules are not yet known, although an exact analysis and thermoanalytic determinations confirm the formula.
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Heller et al. (1985) studied this question.