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The crystal structure of the heterocyclic mole-from N-methylimidazole by conversion into the appropriate cule 1,3-dimethyl-2( 3H)-imidazolethione and its lH n.m.r. dialkylimidazolium iodide and treatment with sulphur in spectrum have been interpreted as showing partial methanolic K,CO,. An X-ray structure determination was double-bond character in the N-C-N system, but no undertaken to decide which of the three structures (a), (b), aromaticity.or (c) (Figure 1) best described the molecule.AN investigation of the molecular structure of 1,3-dimethyl- S S-. s-2(3H)-imidazolethione, (I), was undertaken when it was Me, ) , Me Me, ; &Me N N' s s L=L/ LJ found that the compound had an unusually high melting Crystals suitable for X-ray investigation were grown from point (181-1 82") compared with its 1-methyl-3-ethyl water : orthorhombic, a 8.475 A, b 6.826 A, G 11.306 A, homologue, (11) (51"). Both compounds were synthesized Systematic absences show the

Counter intensity data for zinc molybdenum(IV) oxide, Zn2Mo3Os, have been collected and a refinement of the structure has been carried out. The new data are consistent with space group P63mc; cell dimensions are a= 5"759, c= 9.903/~. The refined structure confirms the presence of triangular groups of bonded molybdenum ions. The oxygen coordination scheme -octahedral (with edge sharing) around molybdenum ions, octahedral for half the zinc ions and tetrahedral for the other half-is also confirmed.

7417found in Table I for several solvents and for different synthetic material prepared independently by two different workers. Free ligand 1,lO-phenanthroline impurity emission is ruled out by the data in Figure 1; adding AgCFsSO3 in small amounts does not alter the emission properties; the complexes are "pure" by elemental analysis and 'H NMR and by IR immediately prior to and after emission spectroscopy measurements. None of the solvents or reagents used in synthesis, workup, or purification exhibits emission like that (lifetime, energy) found for the four cations for L = 1,lO-phenanthroline. All sources of "impurity" emission are thus ruled out; the essential results detailed in Table I and Figure 1 are also independent of concentration in the range 10-4-10-5 M.

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