Crystal structure, characterisation and vibrational study of a mixed compound Cs0.4Rb0.6H2Po4

Abstract The crystal structure of Cs1-x Rb x H2PO4, x = 0.6 (CRDP) which crystallises in space group P21/m and is isostructural with the monoclinic phase of CsH2PO4 (CDP), has been refined at room temperature using single-crystal X-ray diffractometer data. The cell parameters are a = 4.8183(9)å, b = 6.2671(6) å, c = 7.7620(10)å, β= 108.260(10)°, V = 222.58(5)å3, Z = 2, Dx = 3.009g cm−3. F(000)=187, T = 298(2)K (room-temperature phase), R = 0.0355 and wR = 0.0949 for 654 observed reflections. CRDP contains two crystallography inequivalent hydrogen bonds in the unit cell. The shorter bond (Ko – o = 2.453(7) A) links the phosphate groups into chains running along the b-axis and the longer bond (Ko – o = 2.488(6) A) which is always ordered, crosslinks the chains to form (001) layers. The phase transitions in the mixed Cs0.4Rb0.6H2PO4 (CRDP) were characterised by differential scanning calorimetry which shows two anomalies at about 293 and 525 K. The Raman and infrared spectra at room temperature were investigated in the frequency ranges 10–3500 and 200–4000 cm−1 respectively. An assignment of all the bands is given. The bands are in agreement with the monoclinic room-temperature phase implying high dynamical disorder of the acidic proton O-H s–O hydrogen bond.

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