Crystal structure and Hirshfeld surface analysis of the 1:3 adduct of tetraaquatrinitratoneodymium(III) with 3-amino-1,2,4-triazine

The asymmetric unit of the adduct contains a neodymium(III) cation, three coordinated nitrate anions, four coordinated water molecules and three uncoordinated neutraltriazine molecules. The crystal structure consists of a three-dimensional supramolecular framework held together by a network of O—H⋯O and O—H⋯N hydrogen bonds between the coordinated water molecules, nitrate ions and triazine molecules. The uncoordinated neutral triazine moieties form N—H⋯N hydrogen bonds. Hirshfeld surface and fingerprint plots identify the major contributors to the intermolecular interactions.


Chemical context
Lanthanide complexes with organic ligands have many applications related to the design and synthesis of potential anticancer and antibacterial agents (Eliseeva & Bunzli, 2010;Liu et al., 2008;Kostova & Stefanova, 2009;Siddiqi et al., 2009;Taha et al., 2011;Hermann et al., 2008;Gassner et al., 2008;Xu et al., 2010). Some lanthanide complexes also have potential roles in the treatment of malignant cells (Kostova et al., 2004). In addition, coordination polymers of lanthanide ions have been investigated for use as sensors, catalysts and MRI contrast agents and in applications in the areas of magnetism, gas absorption, self-assembly and medicine (Li et al., 2015;Bunzli et al., 2015;Wang et al., 2016;Zhang & Lin, 2014).

Structural commentary
The asymmetric unit of the title compound (Fig. 1) contains a neodymium(III) cation, three coordinated nitrate anions, four coordinated water molecules and three uncoordinated neutral 3-amino-1,2,4-triazine molecules. The Nd III ion is ten coordinate and has a distorted bicapped square-antiprismatic geometry, being surrounded by six oxygen atoms from three nitrate ions and four oxygen atoms from coordinated water molecules. The lengths of the Ni-O bonds (Table 1)

Figure 2
A view of the O-HÁ Á ÁO hydrogen-bonding interactions (shown as dotted lines) between coordinated water molecules and nitrate ions, which generate a sheet-like structure.
C) are linked through weak C-HÁ Á ÁO [C3B-H3BAÁ Á ÁO6B ix and C3C-H3CAÁ Á ÁO4B vii ] hydrogen bonds formed with the coordinated nitrate atoms (B). All these intermolecular interactions appear to play a significant role in stabilizing the crystal structure and result in the formation of a threedimensional supramolecular framework (Fig. 4).

Hirshfeld surface analysis
Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and two-dimensional fingerprint plots, which are useful tools for describing the surface characteristics of the crystal structure, were generated using CrystalExplorer3.0 (Wolff et al., 2012). A view of N-HÁ Á ÁN hydrogen-bonded pairs (shown as dotted lines) between triazine moieties (A and C) extending into zigzag chains.

Figure 4
An overall view of the three-dimensional supramolecular framework of the title compound.

Figure 5
Three-dimensional Hirshfeld surfaces of the title compound plotted over d norm .

Figure 6
Two-dimensional fingerprint plots of the title compound showing the contributions of the different interactions. d e and d i represent the distances from a point on the Hirshfeld surface to the nearest atoms outside (external) and inside (internal) the surface, respectively.

Synthesis and crystallization
The title compound was prepared by adding a hot methanolic solution (20 ml) of 3-amino-1,2,4-triazine (0.043g) (Aldrich) to a hot methanolic solution (20 ml) of Nd(NO 3 ) 3 Á6H 2 O (0.219g) (Alfa Aesar). Dichloromethane (5 ml) was then added and the mixture refluxed for 7 h at 353 K. The resulting solution was then allowed to cool slowly to room temperature. After two weeks, brown-coloured crystals were obtained, m.p. = 378 K.

Tetraaquatrinitratoneodymium(III)-3-amino-1,2,4-triazine (1:3)
Crystal data Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The observed criterion of F 2 > 2sigma(F 2 ) is used only for calculating -R-factor-obs etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Nd1