C(NH₂)₃Cd(C₂O₄)Cl(H₂O)·H₂O and BaCd(C₂O₄)_1.5Cl(H₂O)₂: Two Oxalate Chlorides Obtained by Chemical Scissors Strategy Exhibiting Low-Dimensional Structural Networks and Balanced Overall Optical Properties

Abstract

Low-dimensional crystalline materials have attracted much attention due to their special physical and chemical properties. Herein, two new oxalate chlorides, C(NH 2 ) 3 Cd(C 2 O 4 )Cl(H 2 O)•H 2 O and BaCd(C 2 O 4 ) 1.5 Cl(H 2 O) 2 , were synthesized.They showed large measured band gaps, which were 3.76 and 4.53 eV, respectively, and the latter was the largest band gap in the A-M-C 2 O 4 -X (A = Monovalent cationic or alkaline earth metals, X = F, Cl, Br, I) family. They exhibit a large calculated birefringence of 0.075 and 0.096 at 1064 nm, respectively. This study promotes the exploration of synthesizing low-dimensional crystalline materials with balanced overall optical performances by a chemical scissors strategy.L ow-dimensional compounds are widely used in materials science. Duo to its physical and chemical properties, it has received attention from the fields of magnetics, ferroelectricity, photoelectricity, catalysts, and nanodevices. 1−7 2D ferroelectrics could show special properties that are rarely found in 3D, for instance, the locking between in-plane and out-ofplane ferroelectric polarization in two-dimensional In 2 Se 3 . 8 Graphene, as a well-known material, has a two-dimensional structure of single atom thickness and exhibits ultrathin, ultralight, ultrahard, ultrasoft, transparent, excellent electrical conductivity, thermal conductivity, heat resistance, photoelectric properties, and surface adsorption properties. 9 Lowdimensional compounds also have good applications in laser science. 10−15 KBe 2 BO 3 F 2 (KBBF) with a layered structure is the only deep ultraviolet nonlinear optical crystal that is commercially available. 16−18 In addition, layer structures have also been found to favor enhanced birefringence. 19−21 It is worthwhile to explore new low-dimensional materials and their synthesis strategies.Starting from compounds with a three-dimensional structure, it is a common strategy to change them into compounds with a lower dimensional structure by introducing atoms or groups as "scissors". The introduction of halogens (F − , Cl − , Br − , I − ), as common terminal atoms, into threedimensional structure compounds is to the benefit of obtaining low-dimensional structure compounds. 22−26 Especially for F − and Cl − , their small ionic radii and large polarizability facilitate more contact with cations and produce scissor-like effects. For instance, from BPO 4 to KB(PO 4 )F, the insertion of F reduces the dimension of the structure, forming a {[BPO 4 F] − } ∞ layer made up of [BO 3 F] 4− and [PO 4 ] 3− , with the charge balance of a cation. 27,28 Then, the OH − and coordinated H 2 O, as terminal groups, have similar effects as halogens. 29 Compared to the Te 2 O 5 with a 3D framework, the Te−O bonds of the

Gradual Increase in Birefringence of Antimony Oxalates through Precise Tuning of the Sb3+/[C2O4]2– Ratio

“…As shown in Figure b, the four compounds exhibit birefringences of 0.02@546 nm, 0.07@546 nm, 0.10@546 nm, and 0.21@546 nm, respectively. Remarkably, Na 3 Sb­(C 2 O 4 ) 2 F 2 ·2H 2 O exhibits a large birefringence compared with those of many other oxalates, such as Cs 2 C 2 O 4 (0.022@1064 nm), Rb 2 C 2 O 4 (0.03@1064 nm), C­(NH 2 ) 3 Cd­(C 2 O 4 )­Cl­(H 2 O)·H 2 O (0.075@1064 nm), RbSb 2 (C 2 O 4 )­F 5 (0.09@546 nm), BaCd­(C 2 O 4 ) 1.5 Cl­(H 2 O) 2 (0.096@1064 nm), K 2 Sb 2 (C 2 O 4 )­F 6 (0.097@546 nm), Rb 2 Sb­(C 2 O 4 ) 2.5 (H 2 O) 3 (0.110@546 nm), NH 4 Sb 2 (C 2 O 4 )­F 5 (0.111@546 nm), K 2 Sn­(C 2 O 4 ) 2 ·H 2 O (0.113@546 nm), (CN 4 H 7 )­SbC 2 O 4 F 2 (H 2 O) 0.5 (0.126@546 nm), RbSb­(C 2 O 4 )­F 2 (H 2 O) (0.162@546 nm), KSb 2 (C 2 O 4 )­F 5 (0.170@546 nm), and Na 2 Sb 2 (C 2 O 4 )­F 6 (0.188@546 nm), which means that Na 3 Sb­(C 2 O 4 ) 2 F 2 ·2H 2 O is an excellent example of a birefringent material. As is widely acknowledged, macroscopic birefringence emerges from the overlay of microscopic anisotropic polarization rates within the fundamental building units.…”