Synthesis and crystal structure of acid phosphites RbH2PO3, CsH2PO3, and TlH2PO3

The reaction of Rb, Cs, or TI carbonates with a solution of phosphorous aci d gave crystalline acid phosphites RbH2PO3 (1), CsH2PO3 (11), and TlH2P03 ( 111), The crystal structures of the compounds were studied by a single-crys tal X-ray diffraction analysis at 150 K:I, monoclinic system, a = 7.530(2) Angstrom, b = 8.634(2) Angstrom, c = 12.426(2) Angstrom, beta = 102.46(3)de grees, V = 788.8(3) Angstrom (3), Z = 8, space group P2(1)/c, R-1 = 0.0409; II, monoclinic system, a = 7.930(2) Angstrom, b = 8.929(2) Angstrom, c = 1 3.163(3) Angstrom, beta = 104.84(3)degrees, V = 900.9(4) Angstrom (3), Z = 8, space group P2(1)/c, R-1 = 0.0239; III, orthorhombic system, a = 6.603(1 ) Angstrom, b = 6.785(1) Angstrom, c = 8.836(2) Angstrom, V = 395.9(1) Angs trom (3), Z = 4, space group Pna2(1), R-1 = 0.0350. The PHO3 tretrahedra in structures I-III are joined via hydrogen bonds into infinite zigzag-like c hains [HPHO3](n)(n-), which form layers alternating with layers of metal ca tions. The layers of anionic chains are wavelike in I and II and planar in III. Apparently, III is not isostructural to I or II due to the fact that T l (I) has a stereochemically active pair of electrons,