Li₄Ca₂B₈O₁₆: A Borate with a Unique Fundamental Building Block and a Short Cutoff Edge

Abstract

A complex alkali and alkaline-earth metal borate Li 4 Ca 2 B 8 O 16 has been synthesized successfully via the high-temperature solution method. Li 4 Ca 2 B 8 O 16 crystallizes into the space group P1̅ (No. 2) of the triclinic crystal system. The crystal structure exhibits a threedimensional framework consisting of the [B 8 O 16 ] ∞ chains connected by the [LiO n ] (n = 3, 4, 6) and [CaO 7 ] polyhedra. The fundamental building block [B 8 O 18 ] differs from those of other anhydrous octa-borates, which can be identified as a unique one. Furthermore, Li 4 Ca 2 B 8 O 16 shows three different Li−O units, which is unique among all non-disordered anhydrous borates. It shows a short UV cutoff edge less than 190 nm.To better study the relationships between the crystal structure and properties, the DFT calculations were used for the evaluations of the optical band gap and birefringence.

Sn3B8O15: A Ternary Tin(II) Borate with Flexible [B8O18]12– Fundamental Building Block Formed by [B7O16]11– and [BO3]3– Groups

“…The [B 8 O 18 ] 12– FBBs were reported recently as a unique one in Li 4 Ca 2 B 8 O 16 by our group, while Sn 3 B 8 O 15 features a different connection configuration, such as torsion angles between hexatomic B-O rings and extended structures. First, the torsion angles of adjacent hexatomic B-O rings (or adjacent BO 3 ) in the [B 8 O 18 ] 12– FBBs are 86.490, 65.494, and 88.868°, respectively, in Li 4 Ca 2 B 8 O 16 (Figure d), while they are 88.390, 62.636, and 87.294°, respectively, in Sn 3 B 8 O 15 (Figure a).…”

“…Moreover, the bands between 484 and 737 cm –1 show the bending vibrations of BO 3 and BO 4 groups . The IR spectrum confirms that BO 3 and BO 4 groups coexist in the structure, and the peak assignments are in good accordance with other borates according to former reports. ,, The calculated infrared spectrum further verifies the validity of the structure (Figure S2b).…”

“…Type one: the hexatomic B-O rings connect with the adjacent ring by sharing one O atom to form a “Hand in Hand” polyborate group, which can be described as “1+1+1” type (Figure a), such as [B 9 O 17 ] 7– in α-CsB 9 O 14 and [B 9 O 19 ] 11– in Na 2 Cs 2 Sr­(B 9 O 15 ) 2 . Type two: the hexatomic B-O rings connect with the adjacent ring via sharing a boron atom to compose “shoulder to shoulder” B-O groups, which eventually form “3+0 (I)” connection type (Figure b), such as [B 7 O 15 ] 9– in ABaB 7 O 12 (A = Cs, Rb), [B 7 O 14 ] 7– in Li 4 Cs 3 B 7 O 14 and Q 18 Mg 6 (B 5 O 10 ) 3 (B 7 O 14 ) 2 F (Q = Rb, Cs), [B 7 O 16 ] 11– in Rb 3 BaTeB 7 O 15 , and [B 8 O 18 ] 12– in Li 4 Ca 2 B 8 O 16 . Type three: two hexatomic B-O rings connect via one B atom to form a pentaborate group ([B 5 O 10 ] 5– , [B 5 O 11 ] 7– , [B 5 O 12 ] 9– , etc.…”

Na2SrB16O26: a new borate with independent interpenetrating B–O networks and deep-ultraviolet cutoff edge

“…5a, the curve of birefringence versus wavelengths demonstrates that the birefringence of Na 2 SrB 16 O 26 is about 0.07 at 1064 nm. This value is comparable to those of other alkali and alkaline-earth metal borates, such as LiRbB 8 O 13 (0.08@1064 nm), 67 Li 4 Ca 2 B 8 O 16 (0.015@1064 nm) 71 and CsBaB 9 O 15 (0.073@1064 nm), 72 etc . To further explore the origin of the optical anisotropy, the REDA method was adopted to evaluate the contribution of the constituent structural units.…”

The First Mixed Calcium Zinc Borate with a Flexible [B8O17] Fundamental Building Block and Short UV Cutoff Edge

“…In a nutshell, the B−O and Zn−O groups dominate the bandgap and the optical properties. In addition, the first‐principles calculation results suggest that the birefringence of CaZnBO is about 0.045 at 1064 nm, which is comparable to those of other octa‐borates, such as Li 4 Ca 2 B 8 O 16 (0.015@1064 nm), [26] Ba 4 B 8 TeO 19 (0.055@1064 nm), [22] etc.…”