title: Solid-State27Al NMR Spectroscopy of the γ-Al13Keggin Containing Al Coordinated by a Terminal Hydroxyl Ligand.
abstract: We report solid-state27Al NMR spectroscopic results for the sulfate salt of the γ-Al13Keggin cluster, γ-[AlO4Al12(OH)25(OH2)11][SO4]3·[H2O]14, that provide a spectroscopic signature for partial hydrolysis of this Keggin-type cluster. In27Al multiple-quantum magic-angle spinning NMR spectra, all 13 Al positions of the cluster are at least partially resolved and assigned with the aid of density functional theory (DFT) calculations of the27Al electric field gradients. The isotropic chemical shift of the single tetrahedral site, 75.7 ppm, is nearly identical to that reported for solutions from which the cluster crystallizes. Reflecting broadly similar coordination environments, the octahedral Al show mostly small variations in isotropic chemical shift (+7 to +11 ppm) and quadrupolar coupling constant (CQ; 6-7.5 MHz), except for one resonance that exhibits a much smaller CQand another site with a larger value. DFT calculations show that deprotonation of a terminal water ligand, to form an η-OH group, causes a large reduction in the27Al CQ, allowing assignment of a distinct, narrow peak for octahedral Al to this hydroxyl-terminated site. This result suggests a relationship between octahedral27Al NMR line width and hydrolysis for solids prepared from Keggin-type clusters.
authors.affiliation: Department of Geosciences, Stony Brook University , Stony Brook, New York 11794-2100, United States.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Phillips
authors.affiliation: School of Chemistry, Monash University , Clayton, Australia.
authors.forename: C André
authors.initials: CA
authors.lastname: Ohlin
authors.affiliation: Department of Geosciences, Stony Brook University , Stony Brook, New York 11794-2100, United States.
authors.forename: John
authors.initials: J
authors.lastname: Vaughn
authors.affiliation: Department of Geosciences, Stony Brook University , Stony Brook, New York 11794-2100, United States.
authors.forename: William
authors.initials: W
authors.lastname: Woerner
authors.affiliation: Colgate-Palmolive Company , 909 River Road, Piscataway, New Jersey 08855, United States.
authors.forename: Scott
authors.initials: S
authors.lastname: Smart
authors.affiliation: Colgate-Palmolive Company , 909 River Road, Piscataway, New Jersey 08855, United States.
authors.forename: Ravi
authors.initials: R
authors.lastname: Subramanyam
authors.affiliation: Colgate-Palmolive Company , 909 River Road, Piscataway, New Jersey 08855, United States.
authors.forename: Long
authors.initials: L
authors.lastname: Pan