Aug. 20, 1961
COMB.IUNICATIONS TO r m EDITOR
directly within the microwave cavity by reduction of millimolar solutions of the neutral parent molecule using acetonitrile as solvent. Detailed e.s.r. and polarographic data for compounds in the table as well as several related compounds currently being studied will be presented in detail elsewhere. Financial support of the U. S. Army Research Office (Durham) and the U. S. Air Force Directorate of Solid State Sciences is gratefully acknowledged.
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The lack of observable coupling between the electronic spin in the biradicals here reported as well as in others previously described is a matter of some theoretical interest. Lye are continuing experimental studies of radicals bound together by various metal ions, including tripositive ones, in order to gather further information concerning spin couplings in many electron systems. (4) H hl McConnell, J Chon Phys , 33, 115 ( l Y b O ) , 186s (i96n).
zbid , 3 3 ,
WASHIXGTON UNIVERSITY NOBORU HIROTA DEPARTMENT OF CHEMISTRY Lours, MISSOURI S I \~-EISSMAN CORNELL UNIVERSITY DAVIDH. GESKE SAINT JOHX L. RAGLE ITHACA, A-EW YORK RECEIVED JULY 1, l N l RECEIVED J U L Y 11, 1961
BIRADICALS IN THE KETYL SERIES‘
Sir:
THE STEREOCHEMISTRY O F AN
ETHYLENEDIAMINETETRAACETATO COMPLEX OF MANGANESE(I1)’
Sir:
We have reported previously that the paraIn further elucidation of the frequently unmagnetic molecules formed on reduction of hexaof ethylenediaminemethylacetone and pentamethylacetone by sodium orthodox stereochemi~try?,~ or lithium are characterized by hyperfine splittings tetraacetato (EDTX, Xr-&) chelates, we have in which each unpaired electron spin is coupled to utilized spectrometrically measured X-ray dif the nuclei in one ketone molecule and two equiva- fraction data from the acid salt, Mn [Mn(OH:)lent alkali metal nuclei.2 Dimeric molecules in HYI2.8H20, to give the remarkable structural which the two organic radicals are joined through features noted below. The monoclinic cell contwo equivalent alkali metal ions could account for taining 2Mn[Mn(OHz)HY]2.8Hz0has a = 9.21, the observations. Such molecules are biradicals b = 16.10,c = 11.88A , , p = 90.60’; the space with each electron spin belonging predominantly group is PBl/’n. Intensity counts were taken with to one-half of the dimer but sharing the two alkali MoKa radiation for all forms. { hkl) in the range, metal nuclei with the other electron spin. The 0 < (sin f?)/A < 0.96. Results given herein are sharing refers to a time average and does not imply based upon the data for (sin e)/A < 0.67, comprissimultaneous presence of the electron spins a t a ing 4440 forms of which 90y0 are recordable above background. Objective analysis by Patterson particular site. We have carried out new experiments with and Fourier methods, with subsequent partial reketyls of the alkaline earths which suggest the for- finement by difference syntheses, yield structural mation of biradicals in which the two radicals are configurations with rather accurate bond paramjoined by a single dipositive alkaline earth ion. eters. Thermal parameters range from 1.50 for oxyReduction of xanthone or benzophenone by mag- for manganese in the anion to above 3 nesium, calcium, or barium in ethereal solvents gen in some water molecules. The discrepancy leads in each case to a single paramagnetic species index for all 4440 forms is 0.10. Manganous ions in fourfold positions of P21,!n with hyperfine couplings t o the protons in one molecule of the original ketone. The proton coupling are centered in sexadentate seven-coordinate ayuo constants are slightly dependent on the positive ion, complexes, [Mn(OHs)HT]-. ‘The geometry of varying monotonically with size of the positive ion. the inner coordination group is not that reported” N o trace of the dissociated ions is observed. The for [Fe(OHz)lT]-, but is roughly that of the configuration’, (cJ. electron transfer reactions between the dimeric sterically superior NbFi ketyls, both aliphatic and aromatic, and their ref. 4 f p diagram). Bond lengths, $0 thc nearest parent ketones are too slow (k < l o 5 h - l sec.-I) 0.005 A., ar? Mn-0, 2.210-2.260 A , , ayerage of to be measured by e.s.r. spectroscopy, while the five, 2.235 A . ; Mn-N, 2.350, 2.395 A. Apart reaction of the monomeric aromatic ketyls of the from those angles and boiids which involve the cen~ atoms, the geometry of ring systetns is very alkali metals are very rapid (k >lo8 M-’ ~ e c . - ~ )tral Use of magnesium enriched to 9370 of &g yields like that expected from earlier studies5,6of CoYfurther evidence bearing on the constitution of the and Ni(OHz)H2Y. hfanganous ions in twofold ketyls. In the case of benzophenone magnesium (7) positions of P&/n display octahedral cobrdiriaketyl the expected splitting by one &Ig nucleus tion; each such ion is bonded to four water mole(I = s/2) is observed. The interval between adja- cules ’ and two not otherwise complexed oxygen cent components is 0.3 gauss. The other ketyls (1) P a r t of a program supported by the National Science Foundawith &fg exhibit a broadening of all lines, but no tion. We thank also t h e U. S. Army Research Office (Durham) and the Advanced Research Projects Agency for support of the work rewell-resolved ZsMg splitting, (1) This work has been supported in p a r t by the U. S . Air Force under Contract a n d i n p a r t by an Equipment Loan Contract with 0 . N. R. Grateful acknowledgment is also made t o t h e donors of t h e Petroleum Research F u n d administered by t h e American Chemical Society for partial support of this research. (2) N. Hirota a n d S. I. Weissman, J. Ani. Chem. Sac., 82, 4424 (1960). (3) F. Adam and S. Weissman, ibid., 80, I R l X (1958).
ported herein. ( 2 ) Cf.J. I,. Hoard, G. S. Smith and 11. I.ind in “Advances i n the Chemistry of Coordination Compounds,” C. Stanley Kirschner, T h e Macmillan ComDanv. - - New York. N. Y . .”Tulv. _ .1961. (3) J. L. Hoard, hf. Lind and J. V. Silverton, J . A m . Chrm. S O ~83, , 2770 (1961). (4) ‘J. L. Hoard. ibid , 61, 1252 (1939). ( 5 ) H . A. Weakliem and J. I. Hoard, ibid., 81. 5 4 9 il95!?) ( 6 ) Ccxflion S . S m i t h and J I.. Hoard. ibiJ , 81,5 5 t i (I95$))
