[C(NH₂)₃]₂MoO₂F₄·H₂O: Unique Chinese-Knot Structure Revealing Superior Nonlinear-Optical Properties

Abstract

A novel organic–inorganic hybrid guanidine fluoromolybdate, [C­(NH2)3]2MoO2F4·H2O, was successfully synthesized via our proposed cation–anion synergetic interaction strategy. The title compound features a unique Chinese-knot structure constructed by hydrogen-bonding interactions, which induces an all-around improvement of the optical band gap, second-harmonic-generation effect, and phase-matchable ability compared with the reported fluoromolybdates, demonstrating that it is a promising UV nonlinear-optical material.

C(NH2)3(I3O8)(HI3O8)(H2I2O6)(HIO3)4·3H2O: An Unprecedented Asymmetric Guanidinium Polyiodate with a Strong Second-Harmonic-Generation Response and a Wide Band Gap

“…Similarly, Yu et al successfully synthesized Cs 2 VOF 4 (IO 2 F 2 ) with a considerable band gap (4.82 eV) by substituting the I–O bonds by I–F bonds . Moreover, it has been proven that the band gap of the obtained compounds can also be improved by introducing a π-conjugated guanidinium [C­(NH 2 ) 3 + , GU] group . When the C­(NH 2 ) 3 + cation replaces Ba 2+ , the band gap increases significantly from 3.06 eV of Ba­(MoO 2 ) 2 (IO 3 ) 4 O to 3.55 eV of [C­(NH 2 ) 3 ] 2 Mo 2 O 5 (IO 3 ) 4 ·2H 2 O. , …”

“…28 Moreover, it has been proven that the band gap of the obtained compounds can also be improved by introducing a πconjugated guanidinium [C(NH 2 ) 3 + , GU] group. 29 When the C(NH 2 ) 3 + cation replaces Ba 2+ , the band gap increases significantly from 3.06 eV of Ba(MoO 2 ) 30,31 This is due to the fact that the strong C−N covalent bonds in the C(NH 2 ) 3 + group induce a wide optical transmission range and the planar π-conjugated molecular orbitals contribute to the generation of large SHG coefficients. 32 In addition, −NH 2 can form hydrogen bonds readily, which contributes to the growth of crystals.…”

Growth and Optical Properties of Large-Sized NaVO2(IO3)2(H2O) Crystals for Second-Harmonic Generation Applications

“…Nonlinear optical (NLO) crystals are critical functional materials in advanced solid-state laser technology. They can expand the wavelength range of coherent light sources based on their optical frequency conversion functions, including second-harmonic generation (SHG), optical parametric amplification (OPA), etc. − Inspired by their practical applications, exploring new NLO materials has aroused scientists’ intense interest. − Due to the intrinsic structure features of the IO 3 /IO 4 building units with asymmetric pyramidal coordination geometries and the stereochemically active lone pair electrons, metal iodates represent an attractive class of inorganic compounds as potential NLO crystal material. − As early as the 1970s, the simple ternary iodate α-LiIO 3 was studied as a well-known NLO crystal. − Large crystals of LiIO 3 have been successfully grown using the low-temperature solution method and have even achieved practical application as a commercial NLO crystal. − Since the beginning of the 21st century, metal iodates have regained wide attention, and many new metal iodates with excellent NLO properties have been discovered over the past two decades. ,− Based on the design strategy of combining d 0 transition metal (TM) ions (Ti 4+ , V 5+ , Nb 5+ , Mo 6+ , etc.) with IO 3 anionic groups, a large number of novel quaternary iodates with strong SHG effects have been discovered, such as Li 2 Ti­(IO 3 ) 6 (500 × α-SiO 2 ), Zn 2 (VO 4 )­(IO 3 ) (6 × KDP; KDP is the abbreviation of KH 2 PO 4 ), BaNbO­(IO 3 ) 5 (14 × KDP), Ba 2 [MoO 3 (OH)­(IO 3 ) 2 ]­IO 3 (8 × KDP), etc.…”

α- and β-(C4H5N2O)(IO3)·HIO3: Two SHG Materials Based on Organic–Inorganic Hybrid Iodates

“…Recently, π-conjugated planar organic moieties have been successfully developed as potential NLO-active groups due to their large polarizability anisotropy, ultrafast response time, and infinite design probabilities. – When the organic moieties act as anions, for instance, the (H x C 3 N 3 Q 3 ) (3– x )– (Q = O, S; x = 0, 1, and 2) groups have been harnessed to build many SHG crystals such as Ca 3 (C 3 N 3 O 3 ) 2 (SHG: >2 × β-BaB 2 O 4 ), KLi­(HC 3 N 3 O 3 )·2H 2 O (5.3 × KDP), RE 5 (C 3 N 3 O 3 ) (OH) 12 (RE = Y, Yb, and Lu) (2.5–4.2 × KDP), and Cs 3 Cl­(HC 3 N 3 S 3 ) (11.4 × KDP). – Theoretical calculations revealed that the organic moieties dominate the SHG effects of these materials. – The organic groups can also function as cations, for example, the [C­(NH 2 ) 3 ] + group has been widely used as a SHG building group as in [C­(NH 2 ) 3 ] 6 (PO 4 ) 2 ·3H 2 O (3.8 × KDP), C­(NH 2 ) 3 SO 3 F (5 × KDP), and [C­(NH 2 ) 3 ] 2 [B 3 O 3 F 4 (OH)] (1.4 × KDP). ,– It is noticed that the pyridine and pyrimidine derivative groups featuring nitrogen-containing heteroaromatic rings could be protonated and used to build organic–inorganic hybrid SHG crystals such as [ o -C 5 H 4 NHOH] 2 [I 7 O 18 (OH)]·3H 2 O (8.5 × KDP), (C 5 H 6 ON) + (H 2 PO 4 ) − (3 × KDP), and (C 4 H 6 N 3 ) + (H 2 PO 3 ) − (2 × KDP). ,, …”