catena-Poly[barium(II)-μ2-(dimethyl sulfoxide)-κ2 O:O-bis(μ2-2,4,6-trinitrophenolato-κ4 O 2,O 1:O 1,O 6)]

The BaII atom in the polymeric title compound, [Ba(C2H6OS)(C6H2N3O7)2], lies on a mirror plane and is coordinated by ten oxygen atoms, two of which stem from symmetry-related DMSO ligands and eight from four symmetry-related picrate anions.

The asymmetric unit of the title barium coordination polymer, [Ba(C 6 H 2 N 3 O 7 ) 2 -(C 2 H 6 OS)] n , consists of a barium cation (site symmetry m) and a dimethyl sulfoxide (DMSO) ligand (point group symmetry m) and a 2,4,6-trinitrophenolate anion located in general positions. The S atom and the methyl group of DMSO are disordered over two sets of sites. The DMSO ligand bridges a pair of Ba II atoms resulting in a chain extending parallel to the a axis. The unique 2,4,6-trinitrophenolate anion also bridges a pair of Ba II ions via the phenolic oxygen atom, with each Ba II being additionally bonded to an oxygen atom of an adjacent nitro group. The 2 -monoatomic bridging binding mode of both types of ligands results in the formation of an infinite chain of face-sharing {BaO 10 } polyhedra flanked by the remaining parts of the 2,4,6-trinitrophenolato and DMSO ligands. In the one-dimensional coordination polymer, parallel chains are interlinked with the aid of C-HÁ Á ÁO hydrogen bonds.

Structure description
As part of an ongoing research program, we were investigating the synthetic and structural aspects of bivalent metal salts of picric acid (also known as 2,4,6-trinitrophenol) containing zwitterionic glycine ligands . During the course of these studies, the glycine-free title compound, [Ba(C 6 H 2 N 3 O 7 ) 2 (C 2 H 6 OS)] (1), was obtained serendipitously.
The asymmetric unit of (1) consists of a barium(II) cation and the S and O atom of a dimethyl sulfoxide (DMSO) ligand located on a mirror plane. The 2,4,6-trinitrophenolate anion is located in a general position (Fig. 1). Atom S11 of the DMSO ligand and the attached methyl group (C11) are disordered over two sets of sites. Bond lengths and angles of the picrate anion and the DMSO ligand are in agreement with reported data (Srinivasan et al., , 2020. The central Ba II atom exhibits ten-coordination and is bonded to eight oxygen atoms of four symmetry-related picrate anions and two oxygen atoms of two DMSO ligands resulting in a distorted {BaO 10 } polyhedron (Fig. 2). The deviation of the {BaO 10 } coordination polyhedron from a regular shape can be evidenced by the Ba-O bond lengths which range from 2.725 (2) to 2.970 (3) Å and the O-Ba-O bond angles which vary between 57.15 (12) and 151.94 (9) . Both DMSO and picrate ligands exhibit an 2 -monoatomic bridging binding mode resulting in chains extending parallel to the a axis with an identical BaÁ Á ÁBa separation of 4.1933 (2) Å (Fig. 3). The oxygen O11 atom of DMSO binds with a Ba II atom at a Ba1-O11 distance of 2.906 (4) Å and further coordinates with a symmetryrelated Ba iv [symmetry code: (iv) x + 1, y, z] atom at a shorter distance of 2.783 (4) Å .
In the crystal structure of (1), the phenolate atom O1 makes a short Ba-O1 bond of 2.730 (2) Å and is further linked to a symmetry-related Ba ii [symmetry code: (ii) x À 1, y, z] atom The distorted {BaO 10 } coordination polyhedron in the crystal structure of [Ba(C 6 H 2 N 3 O 7 ) 2 (C 2 H 6 OS)]. Symmetry codes are as in Fig. 1.

Figure 3
(Top) Ba II cations bridged by O11 of DMSO, which results in the formation of chains extending along the a-axis direction. For clarity, the disordered S atom and the methyl group of the DMSO ligands as well as the picrate ligands are not displayed; (bottom) the chain showing the 2 -monoatomic bridging binding of the picrate and DMSO ligands. For clarity, only the bridging O11 atom of the DMSO ligands are shown. Each Ba II atom in the chain is bonded to ten O atoms (see Fig. 2).

Figure 1
The coordination environment of the Ba II atom in the crystal structure of [Ba(C 6 H 2 N 3 O 7 ) 2 (C 2 H 6 OS)]. Displacement ellipsoids are drawn at the 50% probability level for non-hydrogen atoms. [Symmetry codes: (i) x, accompanied by the shortest Ba-O bond of 2.725 (2) Å . Each of the Ba II atoms bridged by O1 is further coordinated by an oxygen atom of the nitro group with longer bond lengths [Ba1-O7 ii = 2.865 (2) Å ; Ba1-O2 = 2.970 (3) Å ]. Thus, the unique 2,4,6-trinitrophenolate anion bridges a pair of Ba II ions via the phenolic oxygen atom, and each Ba II atom is bonded to an oxygen atom of an adjacent nitro group resulting in a 2monoatomic bridging bis-bidentate binding mode for this ligand. In the chain, each Ba II atom is bonded to eight oxygen atoms of four symmetry-related picrate anions, and a pair of adjacent Ba II atoms are bridged by two symmetry-related phenolate oxygen atoms (Fig. 3).
A polyhedral chain of face-sharing {BaO 9 } units flanked by organic ligands was reported recently in the one-dimensional polymeric compound [Ba(H 2 O) 2 (NMF) 2 (4-nba) 2 ] (NMF = N-methylformamide; 4-nba = 4-nitrobenzoate) due to a 2 -binding aqua ligand and a pair of symmetry-related 2 -monoatomic bridging 4-nba ligands (Bhargao & Srinivasan, 2019). Likewise, the monoatomic bridging binding modes of the unique DMSO and the phenolate oxygen atoms of the picrate ligands in the structure of (1) result in the formation of an infinite chain of face-sharing {BaO 10 } polyhedra flanked by 2,4,6-trinitrophenolate and dimethyl sulfoxide ligands (Fig. 4). In the reported water-rich compound [Ba(H 2 O) 5 (C 6 H 2 N 3 O 7 ) 2 ]ÁH 2 O, however, the central Ba II atom exhibits ten-coordination and is bonded to five monodentate aqua ligands and a bidentate picrate anion (Harrowfield et al., 1995). A second unique picrate anion is a 2 -bridging tridentate ligand and binds to a Ba II atom via a phenolate oxygen atom. The cation is also linked to an oxygen atom of an ortho nitro group and is bridged to a second Ba II via an oxygen of the nitro group trans to the phenolate oxygen (Fig. 4). In this one-dimensional coordination polymer, discrete {BaO 10 } polyhedra are bridged by a picrate anion due to the absence of any monoatomic bridge.
The aromatic hydrogen atoms H3 and H5 are attached to the C3 and C5 donor atoms while the nitro oxygen atoms O4 and O6 function as hydrogen acceptors, resulting in interchain C-HÁ Á ÁO hydrogen bonding interactions. In this way, each chain is linked on either side to two other chains (Table 1, Fig. 5) into a three-dimensional network.

Synthesis and crystallization
To a slurry of barium carbonate (0.395 g, 2 mmol) in water, picric acid (0.916 g, 4 mmol) in water (40 ml) was added and the reaction mixture was heated on a water bath. Brisk effervescence was observed resulting in dissolution of the insoluble carbonate. The reaction mixture was then filtered into a beaker containing glycine (4 mmol, 0.3002 g) in water. The filtrate was left aside for crystallization. A yellow precipitate was filtered off and subsequently dissolved in DMSO (10 ml); this solution was left undisturbed. The crystalline product, which separated after two days, was isolated by filtration, washed with dichloromethane and dried in air; yield 0.95 g. Compound (1) can also be obtained without addition of glycine in the reaction by dissolving barium carbonate in aqueous picric acid to obtain the dipicrate of barium in situ. Concentration of the reaction mixture to a small volume followed by addition of DMSO afforded (1) as above.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Figure 5
Interchain C-HÁ Á ÁO hydrogen bonds, shown as broken pink lines for the C3-H3Á Á ÁO4 v interaction on the right and for the C5-H5Á Á ÁO6 vi interaction on the left, link adjacent polymeric chains. [Symmetry codes: (v) 1 À x, 1 À y, Àz; (vi) 3 À x, 1 À y, 1 À z.] data reports  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 1.73 e Å −3 Δρ min = −1.10 e Å −3 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.