Synthesis, structure and spectroscopy of rare earth hypophosphites: 3. Ytterbium hypophosphite

Yb(H2PO2)(3) crystallizes in space group C2/m. Planar rectangular arrays of Yb3+ ions are doubly bridged by hypophosphite ions in the b direction and singly bridged in the c direction, giving rise to a stacking of corrugated layers in the crystal structure. The YbO6 site symmetry is C-2h, but not fa r from D-4h. The vibrational spectra of the hypophosphite anion have been i nterpreted in detail using unit cell group analysis and are shown to be con sistent with the crystallographic data. The 10 K electronic absorption spec trum confirms the presence of two nonequivalent Yb3+ ions situated at centr osymmetric sites in the unit cell. For the first time, the two-centre trans itions in the vibronic sidebands have been assigned to the excitation of in dividual unit cell group modes, showing a one-to-one correspondence with th e vibrational spectra. The importance of moiety mode-hypophosphite mode cou plings, and of Yb3+ -hypophosphite interactions of the type quadrupole-dipo le, or higher, is indicated in the interpretation of the intensities of the cooperative vibronic transitions. (C) 2000 Elsevier Science Ltd All rights reserved.