Synthesis, Structure, and Spectroscopy of Rare Earth Hypophosphites. 1. Anhydrous and Monohydrated Lanthanide...

The lanthanide hypophosphite complexes Ln(H(2)PO(2))(3) (Ln = La, Pr, Nd) and Ln(H(2)PO(2))(3).H(2)O (Ln = La, Pr) crystallize in the space group P&onemacr; (No. 2), Z = 2. The lattice constants for La(H(2)PO(2))(3) are a = 6.7912(6) Å, b = 7.0801(8) Å, c = 8.863(1) Å, alpha = 82.64(1) degrees, beta = 74.43(1)( o), gamma = 71.91(1) degrees; for La(H(2)PO(2))(3).H(2)O, a = 7.2291(4) Å, b = 7.983(1) Å, c = 8.934(1) Å, alpha =110.57(1) degrees, beta = 98.26(1) degrees, gamma = 104.35(1) degrees. In both structures hypophosphite ions bridge adjacent 8-coordinate lanthanide ions to give infinite chains. Infrared and Raman spectra (300-20 K) are shown to be consistent with the crystallographic data, with 52 of the 54 fundamental hypophosphite modes of vibration assigned. The electronic spectra of the anhydrous compounds consist mainly of bands due to pure electronic electric dipole transitions. Two-center vibronic transitions observed in the (3)H(4) --> (1)D(2) spectrum of Pr(H(2)PO(2))(3) are not well-simulated by a model with dipole-dipole interaction terms between the two centers. The energy level scheme of Pr(3+) in Pr(H(2)PO(2))(3) was fitted to a model Hamiltonian for a C(2)(v)() site symmetry Pr(3+) ion, including configuration interaction of 4f(2) with 4f6p. Theoretical crystal field parameters were in reasonable agreement with those derived from the energy level fitting. The results highlight the C(2)(v)() (k even) and C(1) (k odd) distortions from the ideal D(4)(d)() antiprismal structure, which slightly modify the 4f(2) energy level scheme, and largely determine the spectral intensities in Pr(H(2)PO(2))(3), respectively. The derived energy level scheme of Nd(H(2)PO(2))(3) is similar to that for 8-coordinated Nd(3+) in NdCl(3).6H(2)O.