Ba₂M(C₃N₃O₃)₂ (M = Sr, Pb): Band Engineering from p−π Interaction via Homovalent Substitution in Metal Cyanurates Containing Planar π-Conjugated Groups

Abstract

The two new metal cyanurates Ba2M­(C3N3O3)2 (M = Sr, Pb) were successfully grown by a solid-state cyclotrimerization reaction. The electronic energy bands of Ba2M­(C3N3O3)2 are totally divergent in spite of their same structures and similar interlayer distances. Theoretical calculations show the narrowing band gap of Ba2Pb­(C3N3O3)2 stems from the strong interaction between Pb 6p orbitals and anti-π orbitals in (C3N3O3)3– groups.

How To Maximize Birefringence and Nonlinearity of π-Conjugated Cyanurates

“…The majority of the non-hydro-cyanurates known to date show γ = 0° with only two exceptions, LiSrC 3 N 3 O 3 ( 22 , Table ) and SrC 3 N 3 O 3 OH ( 23 , Table ). − ,,, In addition, the cocrystal trihydro-cyanurate, LiCl·H 3 C 3 N 3 O 3 , is synthesized, but no single-crystal data is available. Regarding these two types of compounds, because of the lack of Δ n data, their Δ n –γ correlation cannot be discussed herein.…”

“…Nicely, the maximum Δ n value of 0.4 in the cyanurate system known to date is realized by II , in which all the HCY rings are lying on the (001) crystal plane achieving the maximum coplanarity of the π-conjugated electrons. Such a Δ n value is larger than those of the non-hydro-cyanurates (ranging from 0.31 to 0.372), − , because the H atom per HC 3 N 3 O 3 ring promotes the uniform planar arrangement of the HCY rings through O–H···N hydrogen bonding interactions. Equations and allow us to predict the Δ n of any of the cyanurates once the crystal structure is established.…”

“…However, its implication as an NLO material had been overlooked until 2017; Lin theoretically demonstrated for the first time that the (C 3 N 3 O 3 ) 3– group is NLO active, although Meyer reported that the (C 3 N 3 O 3 ) 3– ring (CY) is a planar π-conjugated group and is isoelectric to the (B 3 O 6 ) 3– group in 2013. Since then, 25 (C 3 N 3 O 3 ) 3– -based compounds have sprung up and some show stronger SHG intensities than the commercially available benchmark material β-BaB 2 O 4 (BBO), e.g., Sr 3 (C 3 N 3 O 3 ) 2 . − More strikingly, cyanurates exhibit very large birefringence. For instance, Ba 2 Ca­(C 3 N 3 O 3 ) 2 shows a Δ n = 0.34 that is much greater than those of the well-known birefringent materials, such as a -BBO (Δ n = 0.122 at 532 nm) and CaCO 3 (Δ n = 0.16 at 800 nm) .…”

LiGaF2(IO3)2: A mixed-metal gallium iodate-fluoride with large birefringence and wide band gap

“…Generally, two types of oxide-based units with large macroscopic anisotropic mainly contribute to the birefringence: planar π-conjugated anions and second-order Jahn-Teller (SOJT) distorted cations. The former type is widely studied like metal cyanurates, borates and borate derivatives [14][15][16][17][18][19][20][21][22]. Cyanurates contain a considerable polarization unit with large birefringence and short absorption edge [17][18][19][20][21][22].…”

AZn4(OH)4(C3N3O3)2 (A = Mg, Zn): Two Zn-Based Cyanurate Crystals with Various Cation Coordination and Large Birefringence

“…As shown in Figure 3, the calculated birefringence values of these two compounds are 0.318 and 0.316, respectively, at the wavelength of 400 nm, which indicates that they have large birefringence in the UV region. Moreover, their birefringence values are much larger than that of α-BBO (0.12 at 532 nm) and are comparable to those of most cyanurates and hydroisocyanurates, such as Ba 3 (C 3 N 3 O 3 ) 2 (0.32 at 800 nm), 34 Ba 2 Pb(C 3 N 3 O 3 ) 2 (0.31 at 800 nm), 35 Ba 2 Ca(C 3 N 3 O 3 ) 2 (0.345 at 800 nm), 2 0 Pb 2 Cd-(HC 3 N 3 O 3 ) 2 (OH) 2 (0.291 at 800 nm), 32 and Cs 3 Na-(H 2 C 3 N 3 O 3 ) 4 •3H 2 O (0.29 at 514 nm). 38 To gain insight into the structure−property relationships of Zn 5 (OH) 4 (C 3 N 3 O 3 ) 2 and MgZn 4 (OH) 4 (C 3 N 3 O 3 ) 2 , first-principles calculations were performed.…”