Volatile lanthanide chelates. II. Vapor pressures, heats of vaporization, and heats of sublimation

Abstract

Thermodynamic measurements were undertaken on a series of remarkably volatile and thermally stable lanthanide chelates of 2,2,6,6-tetramethyl-3,5-heptanedione. The complexes are unusual examples of unsolvated monomeric lanthanide chelates in which the coordination number is six. Large differences were found in the vapor pressures, heats of vaporization, and heats of sublimation of the tetramethylheptanedionato complexes. The findings corroborate the trend detected by gas chromatography; complexes of the lanthanides with higher atomic number are considerably more volatile than those of the lighter, larger members of the lanthanide series. For example, at 200°v apor pressures range from ca. 5 mm for the ytterbium(III) complex down to 0.2 mm for the lanthanum(III) complex. A plot of the heat of vaporization of the chelates vs. the atomic number of the metal in general reflects the effects of the lanthanide contraction, but there is an irregularity at gadolinium.Although it has been known for many years that X*. ß-diketonates of metals in the first transition series are volatile, efforts to find similar volatile complexes of the lanthanides were always unsuccessful until very recently.2-4 Previously known chelates of the lanthanides were invariably either nonvolatile or thermally unstable. Indeed virtually all other reported lanthanide compounds are either nonvolatile or have very low volatility at temperatures below 700°. In part Is we recently described the synthesis and gas chromatographic behavior of the lanthanide complexes of 2,2,6,6-(1) (a)

Standard molar enthalpies of formation of eight lanthanide(III) 2,2,6,6-tetramethyl-3, 5-heptanedione chelates in the crystalline and gaseous states: mean Ln–O bond dissociation enthalpies

“…The infrared spectra contained the characteristic vibrations (in cm −1 ) assigned to C = O and C = C bonds, respectively at: La, 1593, 1570; Pr, 1590, 1567; Nd, 1594, 1577; Sm, 1593, 1572; Gd, 1593, 1572; Dy, 1596, 1572; Ho, 1597, 1572; Er, 1597, 1571, in excellent accordance with literature data. (17) In all cases, the O-H stretching bands around 3400-3600 cm −1 and also the δ(H-O-H) bending vibrations of water were not observed, which confirmed the unhydrated form of complexes.…”

“…Chelates of this type, Ln(DPM) 3 , are easily prepared from solution and purified by sublimation techniques. (17) These compounds show a series of properties which make them appropriate for some important applications, such as starting compounds for introduction of metals into high-temperature superconducting films, (18) proton n.m.r. shift reagents for a large number of organic molecules, (19) etc.…”

Green Emission from Tb-Doped GaN Grown by MOVPE

“…The supply rate of TMGa and NH 3 were 0.83 and 6600 mmol/min, respectively, under which the growth rate of the undoped GaN layer was about 0.8 mm/h. The Tb source used in this study is tris-(dipivaloylmethanato)-terbium [Tb(C 5 H(CH 3 ) 6 O 2 ) 3 , abbreviated as Tb(DPM) 3 ], which is a solid compound with a vapor pressure of about 9 Â 10 ± ±2 Torr at 150 C [9]. This source was vaporized in a stainless-steel container kept at 150 C and delivered to the reactor by the H 2 carrier gas.…”

Optical Fiber Fabrication Using Novel Gas-Phase Deposition Technique

“…Their relatively high volatility means that sufficient vapor to achieve high dopant concentrations is possible at a moderately low temperature of around 150 -200 ºC [7]. In addition, since the incorporation of the RE and modifier ions, such as Al 2 O 3 and P 2 O 5 , takes place simultaneously with the glass formation, there is the possibility of less RE clustering and reduced photodarkening, for a given level of doping, as compared with traditional solution doping.…”