Crystal structure of (μ-hydrogen disulfato)-μ-oxido-bis[(4,4′-di-tert-butyl-2,2′-bipyridine)oxidovanadium(IV/V)] acetonitrile monosolvate

The crystal structure of a dinuclear oxidovanadium(IV/V) complex [V2O2(μ-O)(μ-H(SO4)2)(4,4′- t Bubpy)2] acetonitrile monosolvate has been determined.


Chemical context
The sulfate anion (SO 4 2-) plays an important role as a ligand for transition-metal compounds, including polyoxometalates (Walsh et al., 2016), metal sulfates (Natarajan & Mandal, 2008), and polynuclear complexes with organic ligands (Papatriantafyllopoulou et al., 2009).Based on these compounds, a variety of catalysts (Wang et al., 2021), magnetic materials (Go ´mez-Garcı ´a et al., 2016), and metal-organic frameworks (Mi et al., 2022) have been developed in recent years.A hydrogensulfate anion (HSO 4 À ) is also found in transition-metal compounds, and HSO 4 À more often acts as a counter-anion than as a ligand (Dı ´az-Torres & Alvarez, 2011).Thus, transition-metal complexes having an HSO 4 À ligand are still limited in number.In sulfated metal oxide catalysts (e.g., V 2 O 5 -based catalysts), however, a surface-protonated sulfate group is often proposed as a Brønsted acid site and affects the catalytic activity (Xie et al., 2021).Hence, a transition-metal complex having a protonated sulfate anion as the ligand is expected to be an appropriate model compound to understand the active site of sulfated solid catalysts at the molecular level.Herein, we report the crystal structure of a dinuclear oxidovanadium(IV/V) complex with 4,4 0 -di-tert-butyl-2,2 0 -bipyridine (4,4 0 -t Bubpy) ligands, the two vanadium ions of which are linked by an oxo anion and a unique protonated sulfate anion [H(SO 4 ) 2 3À ].

Structural commentary
A single-crystal X-ray structure analysis revealed a novel dinuclear oxidovanadium(  (Triantafillou et al., 2004;Inoue et al., 2018).For the S-O distances in the H(SO 4 ) 2 3-ion, the distances between S1 and O atoms (O3 and O5) attached to V atom are in the range of 1.4654 (13) to 1.5098 (12) A ˚, whereas the S O terminal [S1-O4; 1.4391 (13) A ˚] bond is substantially shorter.Although, like the O4 atom, the O6 atom is not attached to the V atom, the S1-O6 distance [1.5066 (13) A ˚] is comparable in length to the S1-O3 distance.Therefore, the S1-O6 distance can be attributed to the S-OH bond (Leszczyn ´ski et al., 2012).The hydrogen atom of the H(SO 4 ) 2 3-ligand is located with 0.5 occupancy at two positions (H6 and H6 i ) (Schindler & Wickleder, 2017) related by the C 2 axis passing through the midpoint of O6� � �O6 i and the O2 atom.In addition, the O6� � �O6 i distance (2.48A ˚) reflects the strong intramolecular hydrogen-bond interaction in the H(SO 4 ) 2 3ligand (Cleland et al., 1998).
Bond-valence-sum calculations of complex V 2 (Table 1) suggest that the two V atoms (V1 and V1 i ) are in a mixedvalence state of V 4+ and V 5+ .In addition, the UV-vis spectrum of V 2 in CH 3 CN shows two weak absorption bands at 553 nm (" = 82 M À 1 cm À 1 ) and 669 nm (" = 29 M À 1 cm À 1 ), which are considered to be the d-d bands of V 4+ (Ballhausen & Gray, 1962;Waidmann et al., 2009).To the best of our knowledge, the dinuclear structure of V 2 bearing the bridging H(SO 4 ) 2 3ligand is unprecedented, although there are a few examples of vanadium complexes having the protonated sulfate anion (e.g., HSO 4 À ) as the ligand (Nilsson et al. 2009;Datta et al. 2015).
After stirring for 2.5 h at 313 K, the solution was concentrated under reduced pressure, and the green precipitate was filtered using Et 2 O and dried to afford a green powder.Then, the powder was suspended in water, and an aqueous solution of sodium lauryl sulfate was added.After the mixture had been stirred overnight at ambient temperature, the supernatant liquid was separated from a dark-green oily precipitate by decantation, and the precipitate was washed with water.The precipitate was dissolved in an EtOH-Et 2 O mixed solvent.
After the color of the solution turned from green to orange, it was evaporated, and the precipitate was filtered using Et 2 O and dried to afford a yellowish brown solid, which was

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms were positioned geometrically (C-H = 0.95-0.98A ˚) and refined as riding with U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl ).

Figure 3
Crystal packing view of V 2 •CH 3 CN along the a axis.

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.

Fractional atomic coordinates and isotropic
with crystallographic C 2 symmetry (Fig. 1).Complex V 2 exhibits a distorted octahedral geometry around the vanadium centre, where the two 4,4 0t Bubpy ligands are nearly orthogonal to each other [the dihedral angle between the coordination planes of N1-V1-N2 and N1 i -V1 i -N2 i is 86.48 (8) � ].The two vanadium ions are linked by bridging O 2-and H(SO 4 (14) A ˚] bonds are within the expected values reported in the literature

Figure
Figure 1

Table 3
Experimental details.