Inexpensive Low-Frequency IR Windows Using Tupperware Seals and Polyethylene Coffee Can Lids Vinita C. Dew Northeast Missouri State University, Kirksviile, MO 63501 observed as neither NaCl nor KBr is IR-transparent below approximately 500 em-'. CsI windows can be used but are expensive, hydroscopic, easily fogged, fairly soft, and easily scratched. Polyethylene is also transparent in this region, and commercial windows are available. However, very inexpensive windows that give acceptable spectra can be obtained using disks cut from polyethylene coffee can lids. Samples prepared as Nujol mulls are sandwiched between 1 these disks and mounted in a demountable holder (Fies. . and 2). For low-temperature studies using single-temperature evacuable cryostats (Fig. 3), both the sample disk and the outside windows must he polyethylene. The coffee can lids are not rigid enough to withstand the applied vacuum. An inexpensive polyethylene window substitute that is large enough to be used in this type of cryostat and rigid enough to hold a vacuum can be found in a Tupperware tumbler seal. These seals are transparent in the 600-200-cm-' range (Fig. 4) and the lip around the edge of the seal is quite rigid. Best of all, Tupperware tumbler seals are readily available and cost less than $0.40 each.
During infrared analysis of coordination compounds the 600-200-cm-' spectral region provides considerable information since most metal-ligand stretches occur in this region. For instance, the terminal M-X stretching bands appear in the 750-100-cm-' region (M-F, 400-200 cm-'; M-C1, 300-200 cm-'; M-Br, 300-200 cm-'; M-I, 200-100 cm-I). Stretching frequencies for bridging halogens also fall in this region at slightly lower frequencies than the terminal halogens. Metal alkoxides, M(0R). where R is an ally1 group, generally exhibit M-0 stretches below 650 cm-'? Aside from compound characterization these vibrations are very useful in distinguishing stereochemical isomers. The number of infrared active M-X stretching bands can be predicted from group theory and compared with the observed number of bands. Unfortunately, the traditional, inexpensive, and convenient, solid-sample preparations as KBr pellets or Nujol mulls between salt plates will not allow this region to he
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poIyethi(iene c o f f e e can lmd
Nakamoto. Kazuo. InfraredSoectra ofInormnicandCoordination Compounds; 2nd ed.; ~iley-lntekscience:~ e ~wo r k 1970; . p 214.
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- 70%
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Figure 1. IR spectrum of polyethylene coffee can lid in 600-200-cm-' region.
Figure 2. IR spectrum of [Ru(NH3),S02CI] CI, in 600-200-em-' region. The Samole WBS oreoared as a Nuioi mull sandwiched between coffee can lid . . disks.
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Figure 3. Single-temperature cryostat for low-temperature IR specha
Figure 4. IR spectrum of Tupperware seals in, 600-200-cm-' region.
Volume 64 Number 11 November 1987
975
