Crystal structure of diethylammonium dioxido{Z)-N-[(pyridin-2-yl)carbonylazanidyl]pyridine-2-carboximidato}vanadate(1−) monohydrate

A new ionic dioxidovanadium(V) compound with an O,N,O donor ligand is reported. In the crystal, extensive hydrogen bonding is observed.


Chemical context
Vanadium, a biologically important trace element with the +V oxidation state, has received considerable attention among the three (viz., +III, +IV and +V) physiologically important oxidation states.In this oxidation state, vanadium exists in three different motifs, viz., VO 3+ , V 2 O 3 4+ and VO 2 + .The formation and stability of these three motifs depends upon the nature of the solvent, the pH of the reaction medium and basicity of the donor atoms of the ligand(s), with a preference for N, O-donor ligands because of the hard acidic nature of V V .It is evident from the literature (Mondal et al., 2010(Mondal et al., , 2008) ) that the vanadium complexes containing VO 2 + motifs are formed in basic media.Vanadium compounds show the catalytic cycle of haloperoxidase activity has been suggested to proceed through hydrogen-bonding interactions (Colpas et al., 1996;Messerschimdt & Wever, 1996;Weyand et al., 1999;Isupov et al., 2000).In the presence of appropriate hydrogen-bond donors, hydrogen bonding is a general feature of vanadium(IV) and vanadium(V) complexes (Mondal et al., 2010;Plass, 1997Plass, , 1998;;Plass & Yozgatli, 2003;Pohlmann & Plass, 2001;Pohlmann et al., 2005;Vergopoulos et al., 1993;Sutradhar et al., 2006).In general, these examples lead to the formation of hydrogen-bonded molecular assemblies ranging from simple dimers to three-dimensional networks.
In this work, an ionic compound of dioxidovanadium(V) containing a symmetric N-(pyridine-2-ylcarbamoyl)picolinamide (Shao et al., 1999) ligand (H 2 L) bound to vanadium through NNO in an asymmetric fashion, was synthesized in the presence of diethylamine in good yield and characterized by X-ray crystallography.The title compound may be used for antidiabetic drug development (Jia et al., 2017).

Structural commentary
The solid-state molecular structure was confirmed by singlecrystal X-ray characterization.The title compound crystallizes in the triclinic crystal system, space group P1.The asymmetric unit (Fig. 1a) comprises a diethylammonium cation, a complex dioxidovanadium(V) and a water molecule, which is interlinked between the two ionic parts of the compound through hydrogen bonding (Fig. 1b).The anionic part of the compound consists of one crystallographically independent V 5+ ion, two oxido ligands and one NNO donor ligand with coordination sphere of the VO 3 N 2 type (Fig. 1a).The V 5+ ion is coordinated by two oxygen (O1 and O2) atoms (oxido ligands), one nitrogen (N1) atom of the pyridine ring, one deprotonated amide nitrogen (N2) atom and a deprotonated amide-oxygen (O3) through enolization (Fig. 2) of the ligand.The fivecoordinate V 5+ ion has a distorted square-pyramidal geometry with one of the two oxido oxygen atoms (O1) at the apex.The extent of distortion from a perfect square-pyramidal geometry can be quantified by the structural index parameter (� = 0.35), as determined from the equation � = (� -�)/60 (where � and � are the two largest L-M-L angles), which is 0 for an idealized square pyramid and 1 for a trigonal bipyramid (Nair et al., 2018;Ghosh et al., 2022).The square plane consists of one nitrogen atom from the pyridine ring (N1), one deprotonated amide nitrogen (N2), one enolate oxygen (O3) and one oxido oxygen (O2) atom of the ligands.The vanadium atom is located 0.555 (4) A ˚above the equatorial plane and displaced towards the axial O1 atom.Selected bonds involving the V atom are given in Table 1.The V-O1 bond is longer than V-O2, probably due to the involvement of O1 in a hydrogen bond with the water hydrogen atom H5C (Table 2).Among the three V-O bonds, the longest is the V-O3 bond length due to the absence of a V-O �-bond (Mondal et al., 2010;Jia et al., 2017).In the absence of diethylamine, the formation of neutral dioxido complex has been reported in which the uncoordinated pyridine atom N4 is protonated (Jia et al., 2017), but in this case the protonation of the diethylamine moiety (pK a = 10.98) is probably due to its higher basicity than pyridine (pK a = 5.23).

Supramolecular features
The oxygen (O5) atom of water acts as a hydrogen-bond donor with an acceptor oxido group (O1) of the dioxidovanadium(V) complex in the same asymmetric unit (O5-H5C� � �O1) and a symmetry-related amide oxygen (O4) atom in a neighbouring asymmetric unit (O5-H5D� � �O4) (Table 2).The O5 atom also acts as a hydrogen-bond acceptor for the amine H5A atom (N5-H5A� � �O5).Another amine hydrogen (H5B) is hydrogen bonded with the N3 atom research communications Figure 1 (a) The molecular structure with the atom-numbering scheme and ellipsoids drawn at the 50% probability level and (b) the intramolecular hydrogen bond.

Figure 2
The keto-enol tautomeric forms of the ligand.
(N5-H5B� � �N3) of an adjacent complex.Two C-H� � �O and one C-H� � �N interactions are also observed.These hydrogen bonds within the same and different asymmetric units enhance the crystal packing of the compounds (Figs.1b and 3).The mono-periodic constructs are packed perpendicular to the bc plane, giving rise to an overall three-dimensional packing arrangement (Fig. 4).

Synthesis and crystallization
To a solution of picolinohydrazide (0.137 g, 1 mmol) in methanol (25 ml) was added ethyl picolinate (0.151 g, 1 mmol).The solution was heated under reflux for 3 h.The reaction mixture was cooled to room temperature and a methanolic solution (20 ml) of [V IV O(acac) 2 ] (0.265 g, 1 mmol) was added with stirring.After stirring for 2 h, a methanolic solution (10 ml) of diethylamine (1 ml) was added with continuous stirring.The solution immediately turned yellow and the reaction mixture was then refluxed for 1 h.The reaction mixture was then kept for slow evaporation at room temperature.A yellow X-ray quality crystalline compound was obtained, which was filtered, washed with methanol and dried over silica gel (fused).Yield: 0.34 g (82%).Crystals of the research communications Acta Cryst.(2024).E80, 277-280 The three-dimensional packing arrangement of the components of the title compound.
complex were obtained after 4-days on slow evaporation at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. N-bound H atoms were refined with U iso (H) = 1.2U eq (N).C-bound H atoms and water H atoms were placed at calculated positions (C-H = 0.93-0.97A ˚, O-H = 0.85 A ˚) and refined as riding with U iso (H) = 1.2U eq (C) or 1.5U eq (C-methyl,O).Initially, residual electron density ws noted near to C15.The part command was used to locate the two positions of C15 (i.e., C15A, in PART 1; and C15B, in PART 2).The site occupancie are 0.7 and 0.3, respectively.Subsequently, an isotropic refinement was done and finally, an anisotropic refinement is performed.

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.

Table 3
Experimental details.