Zirconium(IV) N-Methoxybenzamidate vs. N-Methoxybenzamide: Synthesis, Crystal Structure, and Phase Transitions

• Published in: Journal of structural chemistry 2024-08, Vol.65 (8), p.1531-1540
• Main Authors: Vikulova, E. S., Cheremnykh, K. P., Vinogradova, A. A., Sukhikh, A. S., Dorovskikh, S. I., Ilyin, I. Y., Pishchur, D. P., Morozova, N. B.
• Format: Article
• Language: English
• Subjects: Atomic; Atomic/Molecular Structure and Spectra; Carbonyls; Chemical bonds; Chemistry; Chemistry and Materials Science; Contact melting; Crystal structure; Inorganic Chemistry; Ligands; Melting points; Molecular; NMR; Nuclear magnetic resonance; Optical and Plasma Physics; Oxygen atoms; Phase transitions; Physical Chemistry; Single crystals; Solid phases; Solid State Physics; Unit cell; Zirconium
• ISSN: 0022-4766; 1573-8779
• DOI: 10.1134/S0022476624080067

First example of a Zr(IV) complex with an aromatic carboxyamidate ligand, Zr(mba) 4 (mba = N-methoxybenzamidate), is prepared. Its structures in the solution ( 1 H, 13 C{ 1 H} NMR) and in the crystal phase (single-crystal XRD) are determined and compared with those of the initial N-methoxybenzamide Hmba. During the complexation, mba – ligands exhibit a bidentate cyclic function through oxygen atoms. The coordination polyhedron of the metal atom is a distorted square antiprism, the lengths of Zr–O bonds with carbonyl and methoxy groups fall within 2.08-2.09 Å and 2.29-2.33 Å, respectively. Despite the presence of available phenyl rings, the Zr(mba) 4 and Hmba crystals contain no intermolecular π–π-interactions, but exhibit C–H⋯π and N–H⋯O contacts, respectively. According to the DSC data, Hmb a undergoes no phase transitions from 130 K up to the melting point (335.0±0.5 K, Δ H  = 15.1±0.1 kJ/mol, Δ S  = 45.2±0.2 J/(mol·K)), while Zr(mba) 4 exhibits a reversible solid-phase transition ( T onset  = 177.4±0.5 K, Δ H  = 0.68±0.20 kJ/mol, Δ S  = 3.8±0.1 J/(mol·K)). Studying the Zr(mba) 4 crystals at 150 K and 200 K shows that this transition is not accompanied by the crystal deformation and is apparently caused by the rotation of phenyl groups. Due to this conversation, the space group changes from P 2 1 / c to P 2 1 / n , and one of the unit cell parameters increases by 3 times.