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Anhydrous double nitrates of the lanthanides with potassium have been obtained in crystalline form. Crystallographic and spectroscopic studies are reported. K3Pr2(N03)9 is cubic, with a = 13.52 (1) A and space group 06-/>4332. The experimental density is 2.53 (3) g cm"3 and the computed value is 2.57 (1) g cm"3 for four formula weights. The structure was solved with 529 independent reflections recorded with an automatic diffractometer utilizing the -2 scan method. A least-squares refinement based on all reflections and with isotropic temperature factors for all atoms gave R = 0.058. Each Pr atom is surrounded by twelve oxygen atoms belonging to six nitrate groups which form a distorted icosahedron. The nitrates form two nonequivalent sets, each with its distinct bonding characteristics to the Pr and K atoms. Infrared and Raman studies confirm a strong interaction between the oxygen atoms and the lanthanide ion and indicate typical bidentate bonding. The optical spectrum of K3Nd2(N03)9 was investigated at ambient and at high pressure. The enhancement of hypersensitive transitions was noted and discussed in comparison to other crystals in which the Nd3+ exists in low site symmetries.

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