Syntheses and crystal structures of rare earth basic nitrates hydrates Part III. [Ln6(μ6―O)(μ3―OH)8(H2O)12(η2―NO3)6](NO3)2·XH2O, Ln = Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; x = 3, 4, 5, 6