Crystal structure of new polar rare earth borates Na2.62Ln2.12(BO3)3 (Ln = Pr, Nd, Sm) containing isolated BO3 groups

Three new rare earth borates, Na 2.62 Ln 2.12 (BO 3 ) 3 ( Ln = Pr, Nd, Sm), were synthesized via a high-temperature solution reaction using a BaCO 3 –H 3 BO 3 –NaF flux and structurally characterized by single-crystal X-ray diffraction analysis. The compounds crystallize in the orthorhombic space group Amm 2 with lattice parameters a = 5.0985(10) Å, b = 11.180(2) Å, c = 7.1483(14) Å, and a unit cell volume of 407.48(14) Å 3 (Z = 2) for Na 2.62 Pr 2.12 (BO 3 ) 3 , a = 5.0983(10) Å, b = 11.181(2) Å, c = 7.1491(14) Å, and a unit cell volume of 407.51(14) Å 3 (Z = 2) for Na 2.62 Nd 2.12 (BO 3 ) 3 , and a = 5.08630(10) Å, b = 11.0993(2) Å, c = 7.04200(10) Å, and a unit cell volume of 397.552(12) Å 3 (Z = 2) for Na 2.62 Sm 2.12 (BO 3 ) 3 . The new sodium rare earth borates crystallize in a three-dimensional framework consisting of zig-zag chains of lanthanide LnO 9 polyhedra and mixed Na/LnO 8 polyhedra linked to sodium NaO 7 and NaO 6 distorted polyhedra and trigonal planar BO 3 groups. The new rare earth borates Na 2.62 Ln 2.12 (BO 3 ) 3 ( Ln = Nd, Pr, Sm) are isostructural with the reported structures of Na 3 Ln 2 (BO 3 ) 3 (Ln = La, Nd, Sm), Na 2.67 Tb 2.11 B 3 O 9 and Na 3-3δ Eu 2+δ (BO 3 ) 3 (δ=0.16), however, there are some structural differences that are discussed. The Fundamental Building Block (FBB) consists of two isolated BO 3 trigonal planar units that can be written as 2: [(2Δ)]. • Crystals of new rare earth borates Na 2.62 Ln 2.12 (BO 3 ) 3 ( Ln = Pr, Nd, Sm) were grown by high-temperature solution reactions. • The new non-centrosymmetric sodium rare earth borates crystallize in a 3D framework constructed from infinite zig-zag chains of rare earth (Pr, Nd, Sm) polyhedra and sodium atoms in the voids. • The anionic part of the structure contains two independent boron atoms that form isolated triangles.