J . Phys. Chem. 1984, 88, 3847-3851
3847
Magnetic Susceptibilities and Electron Paramagnetic Resonance Spectra of a Ceside and an Electride Dheeb Issa, Ahmed Ellaboudy, Ramamurthi Janakiraman, and James L. Dye* Department of Chemistry, Michigan State University, East Lansing, Michigan 48824 (Received: August 24, 1983)
The magnetic susceptibilities and EPR spectra of compounds formed from cesium metal and 18-crown-6 (1SC6) were investigated. Preliminary studies of residues formed by evaporation of methylamine or ammonia solutions which contained various mole ratios of cesium to lSC6 showed that spin pairing is common and that at least two EPR active species can be formed. Isolation and identification of a crystalline ceside, Cs+(18C6),.Cs-, and a crystalline electride, Cs+(18C6)2*e-,permitted quantitative studies of their magnetic properties. The ceside salt, as precipitated from 2-aminopropane-diethyl ether mixtures in the presence of dissolved lithium contained 1-2% trapped electrons and obeyed the Curie-Weiss law, xMe= LfC/( T - S)] + E, in which xMeis the electronic contribution to the magnetic susceptibility,fis the fraction of Cs- replaced by e-, C is the Curie constant, S is the Weiss constant, and B is the diamagnetic contribution of Cs- to the susceptibility. Three samples yielded the average values, f = 0.019,S = -1.4 K, and B = -52 X The EPR spectrum showed two peaks, the broader of which had g values and line widths which varied with temperature and crystal orientation. The electride Cs+(18C6)2-enearly followed the Curie-Weiss law with B = 0, f = 0.74, and S = -1.4 K, but the deviations from this expression were systematic. The EPR spectrum consisted of a single asymmetric line of width 0.5 G, independent of temperature from 3 to 250 K at g = 2.0023, also independent of temperature. The ratio of the low-field to high-field amplitudes, A/B, increased with increasing temperature which indicated the presence of substantial microwave conductivity.
Introduction The remarkable enhancement of alkali metal solubility in amines and ethers by cation complexation with cryptands and crown ethers'" has permitted the synthesis of two new classes of ionic solids called alkalides and electrides. Alkalides are salts which contain the complexed cation ML' (or MLzf) and an alkali metal anion N-. Electrides are similar, but the anions consist of trapped electrons. Until very recently, only alkalides could be prepared by crystallization from s ~ l u t i o n . ~Both - ~ ~ alkalides and electrides could be formed as films or powders by solvent evapo r a t i ~ n ~ Jor ~ -by ' ~direct vapor deposition." By using dissolved lithium to stabilize metal solutions in 2-aminopropane-diethyl ether mixturesI8 or by using mixtures of dimethyl ether and trimethylamine as crystallization solvent^,^^*^^ new crystalline al-
(1) The abbreviation Cmno will be used in this article for the macrobicyclic polyether cryptand [m.n.o.];18C6, 15C5 represent the cyclic polyethers 18crown-6 and 15-crown-5, respectively. (2) Dye, J. L.; DeBacker, M. G.; Nicely, V. A. J . Am. Chem. SOC.1970, 92, 5226. (3) Lok, M. T.; Tehan, F. J.; Dye, J. L. J . Phys. Chem. 1972, 76, 2975. (4) Dye, J. L.; Lok, M. T.; Tehan, F. J.; Coolen, R. B.; Papadakis, N.; Ceraso, J. M.; DeBacker, M. G. Ber. Bunsenges. Phys. Chem. 1971, 75,659. ( 5 ) Dye, J. L. In "Electrons in Fluids"; Jortner, J., Kestner, N. R., Ed.,; Springer-Verlag: Berlin, 1973; p 77. (6) Dye, J. L.; Andrews, C. W.; Mathews, S. E. J . Phys. Chem. 1975, 79, 3065. (7) Dye, J. L.; Ceraso, J. M.; Lok, M. T.; Barnett, B. L.; Tehan, F. J. J . Am. Chem. SOC.1974, 96, 608. (8) Tehan, F. J.; Barnett, B. L.; Dye, J. L. J . Am. Chem. SOC.1974, 96, 7203. (9) Dye, J. L. Angew. Chem., Int. Ed. Engl. 1979, 18, 587. (10) Dye, J. L. J . Chem. Educ. 1977,54, 332. (11) Van Eck, B.; Le, L. D.; Issa, D.; Dye, J. L. Inorg. Chem. 1982, 22, 1966. (12) Dye, J. L. J . Phys. Chem. 1980,84, 1084. (13) Dye, J. L.; Yemen, M. R.; DaGue, M. G.; Lehn, J.-M. J . Chem. Phys. 1918, 68, 1665. (14) DaGue, M. G.; Landers, J. S.; Lewis, H. L.; Dye, J. L. Chem. Phys. Lett. 1979, 66, 169. (15) Dye, J. L.; DaGue, M. G.; Yemen, M. R.; Landers, J. S.; Lewis, H. L. J . Phvs. Chem. 1980, 84, 1096. (16) Landers, J. S.; Dye, J. L.; Stacy, A.; Sienko, M. J. J . Phys. Chem. 1981, 85, 1096. (17) Le, L. D.; Issa, D.; Van Eck, B.; Dye, J. L. J . Phys. Chem. 1982,86, 7.
(18) Issa, D.; Dye, J. L. J . Am. Chem. SOC.1982, 104, 3781.
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kalides21,z2and a crystalline electrideZ2have recently been synthesized. While the optical transmission spectra of filmsl3-I7have provided the principal means of identification of electrides, two electrides were studied more extensively by EPR and magnetic susceptibility methods. The residues left by evaporation of methylamine or ammonia from solutions of potassium and cryptand [2.2.2]23and lithium with cryptand [2.1.1]16924 were used in these studies with different mole ratios, R, of metal to complexant. For the K-C222 system with R = 1 the optical ~ p e c t r u r n , ' ~microwave ~'~ cond u ~ t i v i t yand , ~ ~asymmetry ratio, AIB, in the EPR spectrumz3 all indicated substantial electron delocalization and a tendency toward metallic character. The behavior of the Li-C21 1 system depended strongly on R (which essentially determines the electron density). For R
