Crystal chemical data on RbLn(SeO 4 ) 2 , where Ln=La, Ce, Pr or Nd

The double selenates, RbLn(SeO 4 ) 2 (where Ln = La, Ce, Pr or Nd) are synthesized and studied crystallographically. These are monoclinic with space group P 2 1 / n containing four formulae per unit cell. The lattice parameters are: for RbLa(SeO 4 ) 2 , a = 8.036(8), b = 5.382(5), c = 18.11(2) Å, β = 92.00(12)°, V = 783 Å 3 , D obs = 4.34, D calc = 4.33 Mg m −3 ; for RbCe(SeO 4 ) 2 , a = 8.012(10), b = 5.376(7), c = 18.04(3) Å, β = 91.93(17)°, V = 777 Å 3 , D obs = 4.37, D calc = 4.37 Mg m −3 ; for RbPr(SeO 4 ) 2 , a = 7.969(11), b = 5.352(7), c = 17.91(3) Å, β = 91.67(13)°, V = 764 Å 3 , D obs = 4.43, D calc = 4.46 Mg m −3 ; for RbNd(SeO 4 ) 2 , a = 7.943(14), b = 5.333(10), c = 17.91(4) Å, β = 91.72(18)°, V = 758 Å 3 , D obs = 4.44, D calc = 4.52 Mg m −3 . The JCPDS Powder Diffraction File No. for RbCe(SeO 4 ) 2 is 33–1496.