270 Research Article Received: 9 September 2009 Revised: 15 December 2009 Accepted: 8 January 2010 Published online in Wiley Interscience: 22 February 2010 (www.interscience.com) DOI 10.1002/mrc.2572 Structural characterization of silver dialkylphosphite salts using solid-state 109 Ag and 31 P NMR spectroscopy, IR spectroscopy and DFT calculations Fu Chen and Roderick E. Wasylishen ∗ High-resolution solid-state 109 Ag and 31 P NMR spectroscopy was used to investigate a series of silver dialkylphosphite salts, Ag(O)P(OR) 2 (R = CH 3 ,C 2 H 5 ,C 4 H 9 and C 8 H 17 ), and determine whether they adopt keto, enol or dimer structures in the solid state. The silver chemical shift, CS, tensors and |J( 109 Ag, 31 P)| values for these salts were determined using 109 Ag ( = 4.652%) NMR spectroscopy. The magnitudes of J( 109 Ag, 31 P) range from 1250 ± 10 to 1318 ± 10 Hz and are the largest reported so far. These values indicate that phosphorus is directly bonded to silver for all these salts and thus exclude the enol structure. All 31 P NMR spectra exhibit splittings due to indirect spin – spin coupling to 107 Ag (I = 1/2, NA = 51.8%) and 109 Ag (I = 1/2, NA = 48.2%). The 1 J( 109 Ag, 31 P) values measured by both 109 Ag and 31 P NMR spectroscopy agree within experimental error. Analysis of 31 P NMR spectra of stationary samples for these salts allowed the determination of the phosphorus CS tensors. The absence of characteristic P O stretching absorption bands near 1250 cm −1 in the IR spectra for these salts exclude the simple keto tautomer. Thus, the combination of solid-state NMR and IR results indicate that these silver dialkylphosphite salts probably have a dimer structure. Values of silver and phosphorus CS tensors as well as 1 J( 109 Ag, 31 P) values for a dimer model calculated using the density functional theory (DFT) method are in agreement with the experimental observations. Copyright c  2010 John Wiley & Sons, Ltd. Keywords: NMR; 109 Ag; 31 P; silver dialkylphosphite salts; CS; indirect spin – spin coupling; DFT; IR Introduction Observation of 1 J( 31 P, 1 H) values in the range of 500–700 Hz and infrared frequencies characteristic of P–H stretching, 2350–2440 cm −1 , clearly established that dialkylphosphites, (RO) 2 P(O)H, exist predominately as the keto tautomers. [1–4] For metal dialkylphosphites, several structures have been proposed (Scheme 1); [5] however, definitive information appears to be un- available for many metals. Surveying the literature, one finds that considerable confusion concerning the structure of metal dialkylphosphites resulted from early X-ray studies [6,7] that indicated the silver salts have the enol structure while the sodium salts have the keto structure. Early infrared studies of sodium dialkylphosphite salts supported the X-ray data showing a characteristic P O stretching frequency near 1250 cm −1 . [8] A 1958 infrared study of sodium and silver dialkylphosphite salts by Daasch [5] was the first to conclude that IR provides no evidence for the enol form in dialkylphosphites as pure compounds or in solutions of proton-accepting solvents. Four years later, Butcher et al. [9] provided molecular weight data, presumably based on colligative properties, that mercury dialkylphosphite salts exist as dimers in benzene solution. Furthermore, infrared and 31 P NMR data supported the notion that the phosphorus of the mercury salts is pentavalent (consistent with the keto tautomer or dimer structure) as opposed to trivalent (enol tautomer). Silver salts were also investigated by Butcher et al., [9] but they were too insoluble to be studied by 31 P NMR spectroscopy. Nevertheless, the infrared data was consistent with a dimer structure for the silver salts. More recently, a solid-state 31 P NMR study of mercury(II) dialkylphosphites indicated 1 J( 199 Hg, 31 P) values greater than 11 kHz, [10] clearly confirming the presence of a mercury–phosphorus bond. Also, a low-temperature 31 P NMR study of silver(I) diethylphosphite in strongly coordinating solvents (e.g. pyridine) confirmed the presence of a Ag – P bond on the basis of a large J( 109 Ag, 31 P) value, 1097 Hz. [11] Here, we present definitive information about the structure of several silver dialkylphosphite salts, AgP(O)(OR) 2 , (R = CH 3 , C 2 H 5 ,C 4 H 9 and C 8 H 17 ), in the solid state based on 31 P and 109 Ag cross-polarization with magic angle spinning (CP/MAS) NMR spec- troscopy and Fourier transform infrared spectroscopy. Quantum chemistry density functional theory (DFT) computations have also been performed to complement our solid-state NMR data. Definitions and Background Theory Solid-state 31 P and 107,109 Ag NMR spectroscopy are excellent complementary methods for providing structural information con- cerning silver dialkylphosphite salts (vide infra). While applications of solid-state 31 P NMR are well known in the NMR literature, [12] ∗ Correspondence to: Roderick E. Wasylishen, Department of Chemistry Gun- ning/Lemieux Chemistry Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2G2. E-mail: roderick.wasylishen@ualberta.ca Department of Chemistry, Gunning/Lemieux Chemistry Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2G2 Magn. Reson. Chem. 2010, 48, 270–275 Copyright c  2010 John Wiley & Sons, Ltd.