9Be and 31P NMR analyses on the influence of imino groups on Be2+ complex stabilities of a series of cyclo‐μ‐imido triphosphate anions. (17th December 2013)

• Record Type: Journal Article
• Authors: Maki, Hideshi; Tsujito, Masahiko; Nariai, Hiroyuki; Mizuhata, Minoru
• Is Part Of: Magnetic resonance in chemistry. Volume 52:Number 3(2014:Mar.)
• Page Start: 69
• Page End: 81
• Publication Date: 2013-12-17
• Subjects: Nuclear magnetic resonance spectroscopy -- Periodicals; Chemistry, Organic -- Periodicals; Magnetic resonance -- Periodicals; 538.36
• DOI: 10.1002/mrc.4037
• Languages: English
• ISSNs: 0749-1581

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>The complexation behaviors of Be<sup>2+</sup> with <italic>cyclo‐μ</italic>‐imido triphosphate anions, cP<sub>3</sub>O<sub>9−<italic>n</italic></sub>(NH)<italic><sub>n</sub></italic><sup>3−</sup> (<italic>n</italic> = 1, 2), have been investigated by both <sup>9</sup>Be and <sup>31</sup>P NMR techniques at −2.3 °C in order to clarify the coordination structures of the complexes. The spectra showed that cP<sub>3</sub>O<sub>9−<italic>n</italic></sub>(NH)<italic><sub>n</sub></italic> (<italic>n</italic> = 1, 2) ligands form ML, ML<sub>2</sub>, and M<sub>2</sub>L complexes with Be<sup>2+</sup> ions, and the formation of complexes coordinating with nitrogen atoms of the cyclic framework in the ligand molecule has been excluded. These complexation trends are very similar to those of Be<sup>2+</sup>‐cP<sub>3</sub>O<sub>6</sub>(NH)<sub>3</sub><sup>3−</sup> system, which has been reported by us. The peak deconvolution of <sup>9</sup>Be NMR spectra made these beryllium complexes amenable to stability constant determinations. The stability constants of the complexes increase with an increase in the protonation constants of the ligands as the number of imino groups, which constitute the ligand molecules, is ascended. This increase is primarily attributable to the lower electronegativity of nitrogen atoms than oxygen atoms, which are directly bonded to central phosphorus atoms; moreover, tautomerism equilibrium in the entire of the imidopolyphosphate molecule is also responsible to the higher basicity. <sup>31</sup>P NMR spectra measured concurrently have verified the formation of the complexes estimated by the <sup>9</sup>Be NMR measurement. Intrinsic <sup>31</sup>P NMR chemical shift values of the phosphorus atoms belonging to ligand molecules complexed with Be<sup>2+</sup> cations have been determined. Not only the protonation constants but also the stability constants of all Be<sup>2+</sup> complexes increase approximately linearly with an increase in the number of imino groups. Copyright © 2013 John Wiley & Sons, Ltd.</p> </abstract>