Molybdenum-95 T1 measurements of molybdenum hexacarbonyl encapsulated in NaY zeolite

Abstract

On the basis of 95Mo T\ measurements made on samples of Mo(CO)6 encapsulated in dried Na-Y zeolite over the temperature range 223-323 K, it is confirmed that Mo(CO)6 experiences significant rotational freedom in the 13-A zeolite supercages. In addition, it is found that the activation energy for rotation is about 40 ± 4 kJ mol"1, and the ambient temperature rotational correlation time, rc, is approximately 3 orders of magnitude longer than is rc in solution.There has been considerable interest in recent years in the species formed on the sorption of metal carbonyl complexes on oxide surfaces such as silica, alumina, and zeolites.1 Techniques utilized to date to investigate these interesting systems include infrared, Raman, ESR, and NMR spectroscopy, temperature programmed decomposition (TPD), analysis of gaseous products, EXAFS and X-ray structure determinations, adsorption studies, and elemental analyses. A wealth of information exists concerning the nature both of the initially formed, physisorbed molecular carbonyl species and of a variety of chemisorbed subcarbonyl and fully decarbonylated species formed on the thermal decarbonylation of the physisorbed compounds.1Of considerable importance in this context are the species formed on encapsulation of molybdenum hexacarbonyl, Mo(CO)6, in the supercages of faujasitic zeolites, both because of the very interesting butadiene hydrogenation catalysts which result22 and because of the possibility of synthesizing new and interesting materials on encapsulating this and similar compounds in zeolite cavities.215 In addition, recent work has shown that the 13-Ádiameter supercage lattices of Y-type zeolites can activate Mo-(CO)6 to very novel CO substitution reactions.20It is well established, on the basis of a number of IR, TPD, and 23Na NMR investigations,4 that sorption of Mo(CO)6 into, for instance, the supercages of Na-Y zeolite at ambient temperatures results in retention of the structural integrity of the Mo(CO)6.The latter binds loosely to the sodium ions in the zeolite supercages of Na-Y via either electrostatic interactions or a Lewis acid-Lewis base type of interaction, species of the types {(OC)5MoCO~Na+} and {(OC)4Mo(CO)2-(Na+)2} having been postulated.20•40•6^Heating above ~350 K results in thermal decomposition and stepwise decarbonylation,42"0 but a detailed(1) (a) Bailey, D.

Sorption Sites, Energetics, and Reactions of Molybdenum Hexacarbonyl and Benzene Cosorbed in Faujasitic Zeolites

“…In choosing the archetypical reaction between Mo(CO) 6 and benzene, the following criteria should be satisfied: (i) the reaction has been well studied in homogeneous solutions; (ii) the intrazeolite benzene is structurally and spectroscopically well documented in FAU, Na 56 FAU, and Na 85 FAU, − respectively. In addition, the mobility of benzene in FAU and Na 56 FAU has been recently studied by molecular dynamics calculations; − (iii) pertinent knowledge to the characterization of the intrazeolite Mo(CO) 6 and Mo(CO) 3 species as well as dynamic motions has been acquired to date. − …”

“…In addition, the mobility of benzene in FAU and Na 56 FAU has been recently studied by molecular dynamics calculations; 20-24 (iii) pertinent knowledge to the characterization of the intrazeolite Mo(CO) 6 and Mo-(CO) 3 species as well as dynamic motions has been acquired to date. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Techniques utilized to date to investigate the metal carbonyl species encapsulated in zeolites include chemical techniques, IR, Raman, ESR, NMR, XPS, EXAFS spectroscopy. However, many of these techniques are particularly devoted to highly loaded samples.…”

13C and 23Na Solid-State NMR Study on Zeolite Y Loaded with Mo(CO)6

“…In NaY there is a high mobility of the hexacarbonyl complex which is described as liquid-like at room temperature on the basis of 95 Mo NMR T 1 relaxation data . Here, the static 13 C NMR line at room temperature is narrowed by a completely averaged chemical shift anisotropy of the carbonyl ligands in NaY.…”

Hexacarbonyls and Carbonyl Complexes of Carbon σ-Bonded Ligands of Chromium, Molybdenum and Tungsten

“…40 ' 145 ' 149 ' 150 ' 153 " 5 ' 164^8 In other studies, [W(C0) 6 ] has been shown to physisorb onto porous Vycor glass to give a pentacarbonyl species whose electronic and EPR spectra suggest a squarepyramidal C 4 v structure with either silanol or chemisorbed water occupying the sixth site. Activation parameters with CO suggest that the W(CO) 5 -PVG interaction energy is <29.3 kJ mol" 1 .…”