1,2,3,6-Tetrahydrophthalic anhydride: Crystal structure and its application as a functional additive

Introduction

Tetrahydrophthalic (THP) anhydrides offer very attractive properties as intermediates or starting materials in chemical synthesis because they provide easy access to other cyclohexene-1,2-dicarboxylic anhydrides and their analogues. In the course of the structure determinations of a series of tetrahydrophthalic anhydride isomers, the authors found that the 1,2,3,6-tetrahydrophthalic anhydrides (Fig. 1) and 3,4,5,6-tetrahydrophthalic anhydrides adopt unexpectedly complex structures that are very different from those of geometrically similar molecules. Both isomers crystallize with two independent molecules per asymmetric unit (Z'=2), with Z=8 molecules per unit cell in the space group P21/a for cis-1,2,3,6-tetrahydrophthalic anhydride and Z=16 molecules in the unit cell of Pbca symmetry for 3,4,5,6-THP anhydride. Their crystal structures exhibit an interesting columnar packing pattern, sustained by an extensive network of non-bonded intermolecular C=O⋯C=O interactions of the dipole-dipole type. Discussion of these intermolecular interactions in terms of typical geometrical criteria allows us to argue that there is an obvious relationship between these specific intermolecular interactions and the packing modes of these crystal isomers.[1]

Crystal structure of 1,2,3,6-tetrahydrophthalic anhydrides

The 1,2,3,6-tetrahydrophthalic anhydrides isomer (Form I) showed polymorphism: Bolte et al[2]. crystallized it from solution in ether at 173 K and found an orthorhombic structure with Z=8 in space group Pca2₁. This new form II (space group: Pca2₁;Z'=2) was shown to have approximately the same packing motif with two nearly identical molecules as the monoclinic polymorph. A facile transformation to the orthorhombic is likely, as six of the eight molecules in the unit cell occupy almost exactly the same positions, whereas the remaining two are mutually related by a non-crystallographic mirror plane. It is important to note that this structure was determined in connection with a study of the possible chemical decomposition of the compound in different solvents and in contact with the atmosphere. The authors reported that no decomposition could be observed during the time of examination.

For 1,2,3,6-tetrahydrophthalic anhydride, calculation predicts clearly that this compound could potentially have several polymorphs. Calculations predicted several hypothetical structures with Z'=1 ,which are thermodynamically slightly more stable than the observed structures. For this molecule,the observed structure with Z'=2 cannot be explained simply on the basis of the energetic criterion. This study highlights the need for more theoretical and experimental collaboration to understand the factors that determine a molecule's crystal structure and polymorphic behavior.[1]

1,2,3,6-Tetrahydrophthalic anhydride used as a functional additive and its Mechanism

1,2,3,6-Tetrahydrophthalic anhydride (CTA) has been used as a functional additive in a carbonate baseline electrolyte (BE) for constructing the CEI film to enhance the cyclic stability of LNMO-based LIBs.

In this work, the researchers compared the effect of 1,2,3,6- tetrahydrophthalic anhydride (CTA) with unsaturated aromatic and acid anhydride groups and propionic anhydride (PA) only with an acid anhydride group as a film-forming additive on the stability of the cathode interphase and the performance of LNMO-based LIBs in high voltage. Notably, the cis-1,2,3,6- tetrahydrophthalic anhydride-derived CEI alleviates the parasitic reactions of electrolytes and safeguards the LNMO cathode structure, thereby enhancing the compatibility of LNMO in the carbonate electrolytes at an operating voltage from 3.5 to 4.9 V to improve the performance of LNMO-based LIBs. Furthermore, the working mechanism of cis-1,2,3,6-etrahydrophthalic anhydride on the stability of cathode interphase was demonstrated and revealed in detail.[3]

Working Mechanism of 1,2,3,6- tetrahydrophthalic anhydride

According to the above results, 1,2,3,6- tetrahydrophthalic anhydride as a functional additive can effectively boost the stability of the LNMO-electrolyte interphase in high voltage, thereby improving the cycling performance. CTA is oxidated to form the uniform CEI film encapsulating LNMO. The CEI film can facilitate the lithium-ions diffusion kinetics, obstruct the dissolution of transition metal cations, and resist the erosion of HF. Furthermore, the CEI film with a higher electronic impedence blocks the electronic transmission between the electrolyte solvent and the cathode to ensure the transmission of all electronics between the cathode and anode only via a conductive network and external circuitry at the initial stage of charge−discharge. Concurrently, the stability of the CEI film was strengthened due to increased antioxidative ability under the influence of field-effect from unsaturated aromatics. Specifically, 1,2,3,6-tetrahydrophthalic anhydride can rapidly combine with trace water to break the pathway to the decomposition of LiPF₆.[3]

References

[1]Fredj AB, Day GM. Modelling of crystal structure of cis-1,2,3,6 and 3,4,5,6-tetrahydrophthalic anhydrides using lattice energy calculations. J Mol Model. 2015;21(8):211. doi:10.1007/s00894-015-2756-4

[2]Bolte M, Bauch C. Cis-1,2,3,6-Tetrahydropthalic anhydrideat 173 K. Acta Crystallogr. 1999;C55:226-228.

[3]Tan C, Cui L, Li Y, et al. Stabilized Cathode Interphase for Enhancing Electrochemical Performance of LiNi0.5Mn1.5O4-Based Lithium-Ion Battery via cis-1,2,3,6-Tetrahydrophthalic Anhydride. ACS Appl Mater Interfaces. 2021;13(15):18314-18323. doi:10.1021/acsami.1c01979