Bis(4-methoxybenzylammonium) tetrabromido- cadmate(II)

Work on non-linear optical (NLO) crystals is an attractive field of interest in current research into applications of laser technology, optical data storage, optical communication, optical switching, optical signal processing, and optical power-limiting processes (Umarani et al., 2017; Mageshwari et al., 2016). Recently, researchers have concentrated on the design of new metal–organic NLO crystals. These materials enhance the desirable NLO response of organic crystals with the high thermal and mechanical properties of inorganic crystals. This new class of materials with remarkable properties are ideal for device fabrication. Incorporating transition metal ions such as Cd, Zn, Hg with filled electron d shells into organic materials creates more energy sublevels and enhances the optical non-linearity through a charge-transfer mechanism (Yang et al., 2013). As a part of a continuation of our research work on 4-methoxybenzylamine-based crystals, we report here the synthesis and crystal structure of the metal–organic title structure, bis(4-methoxybenzylammonium) tetrabromidocadmate(II). As the crystal belongs to the centrosymmetric monoclinic space group P21/n, it can be used in thirdharmonic generation for a Nd:YAG laser at a wavelength of 1064 nm (Mageshwari et al., 2016). Received 28 May 2018 Accepted 30 May 2018


Structure description
Work on non-linear optical (NLO) crystals is an attractive field of interest in current research into applications of laser technology, optical data storage, optical communication, optical switching, optical signal processing, and optical power-limiting processes (Umarani et al., 2017;Mageshwari et al., 2016). Recently, researchers have concentrated on the design of new metal-organic NLO crystals. These materials enhance the desirable NLO response of organic crystals with the high thermal and mechanical properties of inorganic crystals. This new class of materials with remarkable properties are ideal for device fabrication. Incorporating transition metal ions such as Cd 2+ , Zn 2+ , Hg 2+ with filled electron d shells into organic materials creates more energy sublevels and enhances the optical non-linearity through a charge-transfer mechanism (Yang et al., 2013).
As a part of a continuation of our research work on 4-methoxybenzylamine-based crystals, we report here the synthesis and crystal structure of the metal-organic title structure, bis(4-methoxybenzylammonium) tetrabromidocadmate(II). As the crystal belongs to the centrosymmetric monoclinic space group P2 1 /n, it can be used in thirdharmonic generation for a Nd:YAG laser at a wavelength of 1064 nm (Mageshwari et al., 2016).

data reports
The asymmetric unit of the the title compound consists of one tetrabromidocadmate anion, [CdBr 4 ] 2À , and two 4-methoxybenzylammonium cations, (C 8 H 12 NO) + , as shown in Fig. 1. The cadmium cation coordination environment is distorted tetrahedral. The 4-methoxybenzylammonium cations are sandwiched between the tetrabromidocadmate layers (Fig. 2). The crystal packing is stabilized by a complex hydrogenbonding system, involving the N-H bonds of the positively charged ammonium groups and, to a minor extent, the methylene group as donors, with the bromide ligands of the anions as acceptors (Table 1). The benzene rings of the cations are also linked by weak C-HÁ Á Á interactions (Fig. 3, Table 1).

Synthesis and crystallization
20 mmol (2.74 g) of 4-methoxybenzylamine (Sigma Aldrich 98%), 20 mmol of aqueous hydrobromic acid (Merck 48%), and 10 mmol (2.72 g) of cadmium (II) bromide (Sigma Aldrich 98%) were mixed in 50 ml of water. The solution was stirred at room temperature for more than 3 h and was then set aside to allow slow evaporation. Transparent crystals suitable for single-crystal X-ray diffraction were collected after two weeks.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.   Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
A partial packing diagram showing the C-HÁ Á Á interactions (details in Table 1).

Figure 1
A view of the asymmetric unit of the title compound showing the atom numbering with displacement ellipsoids drawn at the 30% probability level. Dashed lines indicate hydrogen-bonding interactions.  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.