Crystal structure and Hirshfeld surface analysis of diaquabis(N,N-diethylnicotinamide-κN 1)bis(2,4,6-trimethylbenzoato-κO)manganese(II)

The MnII complex is centrosymmetric and the molecules are linked by O—H⋯O and C—H⋯O hydrogen bonds into the three-dimensional supramolecular network.


Chemical context
Nicotinamide (NA) is one form of niacin. A deficiency of this vitamin leads to loss of copper from the body, known as pellagra disease. Victims of pellagra show unusually high serum and urinary copper levels (Krishnamachari, 1974). The nicotinic acid derivative N,N-Diethylnicotinamide (DENA) is an important respiratory stimulant (Bigoli et al., 1972). The crystal structure of the complex [Co(CH 3 CO 2 ) 2 (DE-NA) 2 (H 2 O) 2 ] (Mikelashvili, 1982) is isostructural with the analogous Ni, Mn, Zn and Cd complexes (Sergienko et al., 1980). The structures of some complexes obtained from the reactions of transition metal(II) ions with nicotinamide (NA), N,N-Diethylnicotinamide (DENA) and some benzoic acid derivatives as ligands, e.g.  Bigoli et al., 1972] have been determined previously. In complex (VII), DENA is a bidentate ligand, while in complexes (V), (VI), (VIII) and (IX), ISSN 2056-9890 DENA is a monodentate ligand. In complex (V), the four 4-(diethylamino)benzoate (DEAB) ions act as bidentate ligands bridging the two Zn atoms.
The structure-function-coordination relationships of the arylcarboxylate ion in Mn II complexes of benzoic acid derivatives may change depending on the nature and position of the substituted groups on the benzene ring, the nature of the additional ligand molecule or solvent, and the pH and temperature of synthesis (Shnulin et al., 1981;Nadzhafov et al., 1981;Antsyshkina et al., 1980;Adiwidjaja et al., 1978). When pyridine and its derivatives are used instead of water molecules, the structure is completely different (Catterick et al., 1974). In this context, the Mn II -containing title compound, (I), with 2,4,6-trimethylbenzoate (TMB) and DENA ligands, namely diaquabis(N,N-diethylnicotinamide -N 1 )bis(2,4,6-trimethylbenzoato-O 1 ) manganese(II), [Mn(DENA) 2 (TMB) 2 -(H 2 O) 2 ], was synthesized and its crystal structure is reported on herein.

Structural commentary
The asymmetric unit of the crystal structure of the mononuclear title complex, contains one Mn II cation located on an inversion centre, one 2,4,6-trimethylbenzoate (TMB) anion and one N,N-diethylnicotinamide (DENA) molecule together with the one water molecule, with all ligands coordinating to the Mn II cation in a monodentate manner (Fig. 1).

Figure 1
The molecular structure of the title complex with the atom-numbering scheme for the asymmetric unit. Unlabelled atoms are related to labelled ones by the symmetry operation (Àx, Ày, Àz). Displacement ellipsoids are drawn at the 50% probability level. Intramolecular O-HÁ Á ÁO hydrogen bonds, enclosing S(6) ring motifs, are shown as dashed lines.

Hirshfeld surface analysis
Visulization and exploration of intermolecular close contacts in the crystal structure of the title complex is invaluable. Thus, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) was carried out by using Crystal-Explorer17.5 (Turner et al., 2017) to investigate the locations of atom-atom short contacts with potential to form hydrogen bonds and the quantitative ratios of these interactions and those of the -stacking interactions. In the HS plotted over d norm (Fig. 3), the white surface indicates contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the van der Waals radii, respectively (Venkatesan et al., 2016). The bright-red spots appearing near DENA-O3, carboxylate-O2, and hydrogen atoms H41, H42, H9C and H11 indicate their roles as the respective donors and acceptors in the dominant O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds; they also appear as blue and red regions corresponding to positive and negative potentials on the HS mapped over electrostatic potential (Spackman et al., 2008;Jayatilaka et al., 2005) as shown in Fig. 4. The blue regions indicate the positive electrostatic potential (hydrogenbond donors), while the red regions indicate the negative electrostatic potential (hydrogen-bond acceptors). The shapeindex of the HS is a tool to visualize thestacking interactions by the presence of adjacent red and blue triangles; if there are no adjacent red and/or blue triangles, then there are nointeractions. View of the three-dimensional Hirshfeld surface of the title complex plotted over d norm in the range À0.6741 to 1.6440 a.u.
The overall two-dimensional fingerprint plot, Fig. 6a, and those delineated into HÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH, CÁ Á ÁC, HÁ Á ÁN/NÁ Á ÁH and NÁ Á ÁC/CÁ Á ÁN contacts (McKinnon et al., 2007) are illustrated in Fig. 6b-g, respectively, together with their relative contributions to the Hirshfeld surface. The most important interaction is HÁ Á ÁH, contributing 70.0% to the overall crystal packing, which is reflected in Fig. 6b as widely scattered points of high density due to the large hydrogen content of the molecule. The single spike in the centre at d e = d i = 0.96 Å in Fig. 6b is due to a short interatomic HÁ Á ÁH contact (Table 2). In the fingerprint plot delineated into HÁ Á ÁO/OÁ Á ÁH contacts Fig. 6c View of the three-dimensional Hirshfeld surface of the title complex plotted over electrostatic potential energy in the range À0.1032 to 0.1415 a.u. using the STO-3G basis set at the Hartree-Fock level of theory. The O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen-bond donors and acceptors are viewed as blue and red regions around the atoms corresponding to positive and negative potentials, respectively.

Figure 5
Hirshfeld surface of the title complex plotted over shape-index.

Synthesis and crystallization
The title compound was prepared by the reaction of MnSO 4 ÁH 2 O (0.85 g, 5 mmol) in H 2 O (100 ml) and N,N-diethylnicotinamide (1.78 g, 10 mmol) in H 2 O (10 ml) with sodium 2,4,6-trimethylbenzoate (1.86 g, 10 mmol) in H 2 O (150 ml). The mixture was filtered and set aside to crystallize at ambient temperature for three weeks, giving colourless single crystals.

Refinement
The experimental details including the crystal data, data collection and refinement are summarized in Table 3. Water H atoms H41 and H42 were located in a difference-Fourier map and freely refined. C-bound H atoms were positioned geometrically, with C-H = 0.93, 0.96 and 0.97 Å for aromatic, methyl and methylene H atoms, respectively, and constrained to ride on their parent atoms, with U iso (H) = k Â U eq (C), where k = 1.5 for methyl H atoms and k = 1.2 for other H atoms. The disordered ethyl group (C17, C18) was refined over two sets of sites with distance restraints and SIMU and DELU restraints (Sheldrick, 2008). The refined occupancy ratio of the two orientations is 0.282 (10)   Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009).

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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness 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 threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) 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.