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Integrating 31 P DOSY NMR Spectroscopy and Molecular Mechanics as a Powerful Tool for Unraveling the Chemical Structures of Polyoxomolybdate‐Based Amphiphilic Nanohybrids in Aqueous Solution
Author(s) -
Shestakova Pavletta,
Absillis Gregory,
MartinMartinez Francisco J.,
De Proft Frank,
Willem Rudolph,
ParacVogt Tatja.
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304969
Subject(s) - chemistry , aqueous solution , diffusion , spectroscopy , nuclear magnetic resonance spectroscopy , heteronuclear molecule , analytical chemistry (journal) , molecular diffusion , chromatography , thermodynamics , organic chemistry , physics , quantum mechanics , metric (unit) , operations management , economics
Novel organic–inorganic hybrids of various sizes were generated by reaction of 1,8‐octanediphosphonic acid (ODP) and (NH 4 ) 6 Mo 7 O 24 in aqueous solution. The formation of rodlike hybrids with variable numbers of covalently bound ODP and polyoxomolybdate (POM) units can be tuned as a function of increasing (NH 4 ) 6 Mo 7 O 24 concentration at fixed ODP concentration. The chemical structure of the ODP/POM hybrids was characterized by 1 H, 31 P, and 95 Mo NMR spectroscopy. Heteronuclear 31 P DOSY (diffusion‐ ordered NMR spectroscopy) and molecular mechanics (MM) calculations were applied to determine the size and shape of the nanosized hybrids generated at various ODP/POM ratios. For this purpose, the structures of ODP/POM hybrids with variable numbers of ODP and POM units were optimized by MM and then approximated as cylinder‐shaped objects by using a recently described mathematical algorithm. The thus‐obtained cylinder length and diameter were further used to calculate the expected diffusion coefficients of the ODP/POM hybrids. Comparison of the calculated and experimentally determined diffusion coefficients led to the most probable ODP/POM hybrid length for each sample composition. The 31 P DOSY results show that the length of the hybrids increases with increasing POM concentration and reaches a maximum corresponding to an average of 8 ODP/7 POM units per chain at a sample composition of 20 m M ODP and 14 m M POM. With excess POM, above the latter concentration, the formation of shorter‐chain hybrids terminated by Mo 7 clusters at one or both ends was evidenced on further increasing the POM concentration. The results demonstrate that the combination of 31 P DOSY and MM, although virtually unexplored in POM chemistry, is a powerful innovative strategy for the detailed characterization of nanosized organic–inorganic POM‐based hybrids in solution.