Structural, optical, dielectric, second and third-order nonlinear properties of new semiorganic crystal: Sodium (bis) boro succinate

Highlights

• Crystal structure of SBBS solved with R factor value is 0.069

• Crystal structure of SBBS is solved first time.

• SBBS crystal belongs to monoclinic system with space group of P2₁/n.

• NLO property was studied by Kurtz-Perry and Z-scan technique.

• Semi-organic SBBS crystal was grown by slow evaporation method.

Abstract

A new semiorganic nonlinear optical crystal Sodium (bis) boro succinate (SBBS) [Na₂ (C₄H₄O₄) (H₃BO₃)(H₂O)₄]·H₃BO₃ was grown from aqueous solution by slow evaporation growth technique. Single crystal X-ray diffraction analysis revealed that the crystal belongs to monoclinic crystal system with space group of P2₁/n. The crystalline nature of SBBS crystal was analyzed by Powder X-ray diffraction. The morphology and growth axis of grown crystal were investigated. The functional groups present in the compound were confirmed by FTIR and FT-Raman spectroscopy techniques. The cut-off wavelength, optical transmission and band gap energy of the grown crystal were analysed by UV–Visible spectral studies. Electrical behaviour of SBBS crystal was analysed by dielectric studies. Laser induced damage threshold study was carried out for SBBS crystal using Nd:YAG laser. Second harmonic generation and relation between particle sizes with respect to generated output were investigated by Kurtz-Perry powder technique. Third order nonlinear properties of SBBS crystal were analyzed by Z-scan method and the corresponding nonlinear refractive index, absorption coefficient and optical susceptibility were calculated.

Introduction

Recently many researchers have been focused on nonlinear optic (NLO) materials to tune UV laser light by frequency doubling conversion of solid state laser. The search for new NLO materials over the past decade has led to the discovery of many organic NLO materials with high nonlinear susceptibilities. However, their poor optical quality, lack of robustness, and inability to grow in to large size has impeded the use of organic single crystals in device applications. Whereas inorganic NLO material capable to grow into bulk size with good physio-chemical properties and wide transparency down to UV region are much attracted. But their NLO properties are comparatively lesser than its organic counterpart. Bridging the excellent properties of both organic and inorganic paved the way for semiorganic NLO materials [[1], [2], [3]]. Semiorganic crystal has gained great attention in the area of supramolecular chemistry and crystal engineering due to its potential application as functional material. Metal-organic frameworks is a newly developed and focused area by most of researchers due to its hybrid materials which consisting of blending the both NLO properties of the organic materials with splendid physical properties of inorganic materials. The huge number of metal organic frame works has been carried out owing to their organic linkers merging of with unlimited combination of inorganic building blocks thus enabling us to make new design NLO active materials. Large non linearity, high resistance to laser damage threshold, low angular susceptibility, and good material hardness are covered by metal organic frame works. In these metal-organic co-ordination complexes the organic ligand shows high non linear optical properties [4]. The borate crystal series have attracted much attention because of its different structures, large NLO response, high transparency especially in the UV range, large damage threshold [5]. Borate crystals have been grown by high temperature solution growth method, employing either flux method or melt techniques. It has been observed from the literature survey PBMH [6], ABL [7], LBMB [8], and DKBM [9] that the borate crystals were also grown by low temperature solution growth method due to α chiral combination strongly with dihydroxyl groups and their interactions with different metal cations. In this direction an attempt was made to grow a new semiorganic material consisting of boric acid mediated metal-organic frame works: sodium (bis) boro succinate (SBBS) crystal by mixing of borate and succinic acid along with sodium carbonate. The inorganic borate offers larger electronegativity and good transparency in the UV region when combine with metal. The predominant anionic groups present in the organic acid introduce excellent NLO properties and different types of structures while reacting with suitable metal cations. Boric acid with polyhydroxy compounds, including tartaric acid, salicylic acid, citric acid, malic acid, and other acids containing a BO₄ fragment of numerous stable complexes were reported [10,11]. Succinic acid is a bidental ligand, by which it offers two reactive sites and it binds with sodium metal ions through one site and other one with borate. Centrosymmetric nature of the SBBS crystals exhibits second harmonic generation which is due to supramolecular hydrogen bonded with intermolecular interactions [12,13]. The second harmonic generation can occur only in non-centro symmetric crystals. This is attributed to non-zero second order susceptibility of the non-centro symmetric crystals. Hence inversion lacking symmetry crystals has become one of the requisites for second harmonic generation. For centre of symmetry crystals inversion symmetry changes the sign of second order polarisation and hence second order susceptibility vanishes. Recently many centro-symmetric crystals are reported producing second harmonic generation [[14], [15], [16], [17]]. Crystals possessing supramolecular structure involving with weak intermolecular interactions via hydrogen bond, pi-pi and cation-pi interactions favours charge distortion resulting to non-zero susceptibility even in centre of symmetry crystals. It is evident from the crystal structure of SBBS that weak interaction is existing via hydrogen bond. Bond distance between Na metal ions and Oxygen is weaker (Na2O8: 2.4361 Å, Na1O6: 2.3634 Å, Na2O7:2.5533 Å) when compared with normal bond distance 1.92 Å. The weak interaction assists the ground state to turn into excited state charge separated form and generate the charge distortions in the SBBS crystals. Supramolecular architecture connects the SHG and centre of symmetry in supramolecular crystals. An intermolecular interaction is responsible for creation of new type of materials having with specific physical and chemical properties and crystal packing [18]. The structure of SBBS crystal contains two boric acid and succinic acid molecules. The asymmetric unit Na⁺ cations (Na1 and Na2) are octahedrally co-ordinated to four water molecules and through O atom of succinic anion and boric acid. The octahedral sphere produces chains extending three dimensionally through edge-sharing. In this paper physio-chemical characterizations such as X-ray diffraction, FTIR and FT-Raman, UV analysis, dielectric studies, laser damage threshold measurement, frequency doubling conversion with particle size analysis and Z-scan studies have been reported.