Crystal structure of [bis(2,6-diisopropylphenyl) phosphato-κO]tris(methanol-κO)lithium methanol monosolvate

In the first reported crystal structure of the family of lithium phosphate diesters, the Li atom is in a slightly distorted tetrahedral coordination environment and exhibits one intramolecular O—H⋯O hydrogen bond between a coordinating methanol molecule and the terminal non-coordinating O atom of the phosphate group. The unit is connected with two non-coordinating methanol molecules through two intermolecular O—H⋯O hydrogen bonds and with a neighbouring unit through two other O—H⋯O interactions.


Chemical context
Alkali metal phosphate diesters are of interest not only because of their fundamental biological importance (see, for example : Gerus & Lis, 2013, and references therein), but also because they are direct synthetic precursors of organophosphate d-and f-metal complexes, which may find applications in various catalytic reactions. For example, rare-earth tris-(diaryl phosphate) complexes may be successfully used in polymerization reactions of 1,4-dienes (Nifant'ev et al., 2013(Nifant'ev et al., , 2014.

Supramolecular features
All vibrational absorption bands (e.g. C-H, C-C, CCH, O-H etc.) in the IR spectrum of the solid are fully consistent with the formula with only one exception. Regardless of the O-H absorption bands at 3636, 3576 cm À1 , the usual methanol C-O absorption bands at 1025-1030 cm À1 are missing. A possible explanation is that the methanol molecules are coordinating to lithium and form a hydrogen-bonding network. Consequently, the C-O stretching frequency may be shifted to lower wavenumbers and can be camouflaged by the phosphate absorption band at 912 cm À1 . This explanation would correspond to the structure data as determined by X-ray diffraction in the current study.
inversion centers. Therefore, the orientations of the cations and anions switch in such a way as to allow the ions of neighbouring molecules in the chains to be involved in additional intermolecular Coulombic interactions (Fig. 3). The packing of the title compound is shown in Fig. 4. No significant hydrogen-bonding interactions are found between neighbouring chains. However, some short intrachain contacts between methyl groups are present, probably due to crystalpacking effects.

Database survey
According to the Cambridge Structural Database (CSD version 5.35 with updates, Groom & Allen, 2014), the number of (RO) 2 PO 2 M(solv) x structures (M is an alkali metal, solv is a solvent molecule) is rather small. Structures containing additional transition metal atoms have been excluded from the search.
For related structures of potassium or sodium phosphate diesters, see: Kumara Swamy et al. A mixed potassium and calcium phosphate diester has been described by Ś lepokura (2008), VIVRUO. All ten found crystal structures are sodium or potassium salts. No lithium compound phosphate diesters has been structurally characterized up to date. Therefore, crystal structures of alkali metal dialkyl and diaryl phosphates remain virtually unexplored.

Synthesis and crystallization
Synthesis of bis(2,6-diisopropylphenyl) phosphoric acid. Phosphoryl trichloride (12.6 ml, 21.0 g, 137 mmol, d = 1.67 g/ ml) was added to a stirred solution of 2,6-diisopropylphenol (52.60 g, 295 mmol) in benzene (60 ml). Et 3 N (44.0 ml, 32.0 g, 317 mmol, d = 0.728 g/ml, distilled over NaOH prior to use) was carefully added in small parts to the reaction mixture, while it was stirred vigorously. The reaction mixture consisted of a pale-yellow solution and an off-white precipitate of triethylamine hydrochloride. The mixture was heated under reflux for 2 days with occasional stirring. Then, water was added, and after stirring for 1 h, the organic and water layers were separated. The organic phase was evaporated under reduced pressure to produce a yellow oil. A mixture of acetone (85 ml) and water (25 ml, 1.39 mol) was added to the residue. The reaction mixture was then heated under reflux for five hours without stirring. All solvent was evaporated under One-dimensional framework of {[Li(CH 3 OH) 3 ][OOP(O-2,6-i Pr 2 C 6 H 3 ) 2 ]}(CH 3 OH). All intermolecular and intramolecular O-HÁ Á ÁO hydrogen bonds are shown. All but hydroxy hydrogen atoms are omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level.