D. COKYELL l . ) a v r ~1'. MELLOKAND CHARLES
1786
Tri othcr cxperiments it has been possible to establish the presence of extremely small amounts of phosphorus aiid sulfur as a result of the appearance of the 14-day electron emitting activity of Pa.. The P3?was formed according to the react ions 13.31 + H2 p 3 2 + 1-11 (9) Pd'
s 3 2
-
+ n --+ + y + +I"2 j-I€' I'{S
ti
i 10) ill)
For example, a neutron bombardment of a sheet of paper revealed the presence of the sulfur as the result of reaction (11). This research has been made possible through thc generous cooperation of the Research Corporation, the Chemical Poundation and the Josiah Macy, Jr., Foundation.
Vol. ti0
S-rY It is shown how i t is possible to detect and identify very small amounts of impurities by meatis of their characteristic half-lives, aftcr the substance contairling the impurities has been rendered radioactive by bombardment with charged particles of high energy or with neutrons. With the help of a chemical separation after the bombardment, impurities present to the order of one part in a million can sometimes be detected. For example, a gallium impurity of six parts per million was found it1 a sample of iron. Impurities to the extent of uiie part in oiie thousand to ten thousand can ofteu be detected without subjecting the sample to chemical analysis. BERKELhY, c A L W O R N I A
I ~ ~ C L I V O DMAY16, 1938
[CONTRIBUlION PKOM THE GA'ILS AND CRhLLIN LABORATORIES OF CHEMISTRY O F THh CALIFORNIA INSTITUTE OF
TECHNOLOGY, No. 6421
The Magnetic Properties and Structure of Mmganous and Cobal4ous Dipyridine Chlorides BY DAVIDP. MELLORAND CHARLES D. CORYELL
It has been reported by Cox, Shorter, Wardlaw, and Way1 on the basis of a determinatiou of unit cell dimensions that manganous dipyridine chloride and the a-form of cobaltous dipyridine chloride have square trans-coordination of pyridine and chlorine about the metal atoms. Complexes of atoms with square bonds have been the object of much interest since this type of structure was first proposed by Werner to explain the existence of certain isomeric platinum compounds. With the extension of our knowledge about the nature of chemical bonds there has been formulated3 a reliable magnetic criterion by which the existence of square covalent structures for manganous, ferric, ferrous, cobaltic, cobaltous, and riickelous atoms may be determined. I t is concluded in this paper that the results of magnetic measurcmeiits on the manganous and a-cobaltous dipyridine chlorides are not compatible with the square coordinated structure proposed by Cox and coworkers, but that they arc compatible with an octahedral ionic type of structure. Magnetic measurements were carried out on the manganese compound by the GQUYmethod. ( 1 ) E G Cox, A J Shorter. Rr Wardtaw, and W J R Wav .7 Chem Soc , 1356 (1937) 12) A. Werner, 2 airovg allgem C h ~ n i3, , 267 (1803) ( 3 ) I, Pauling, THISJ U U R N A L , 63, 1367 (1931)
The forces in mg. ( Aw corrected for blank) for a cylindrical tube with water in the upper compartment and air in the lower compartment were for two different field strengths -2.03 and -3.39. The forces with manganous dipyridine chloride, twice crystallized from ethanol and packed to a density of 0.995 g./ml., were +135 and f B 3 4 , respectively, at 22" against air. With use of an estimated value of - 160 X for the molecular diamagnetism of the compound and with the assumption of the vajidity of Curie's law, the calculated values of the magnetic moment are 5.9-1. and 0.00 Bohr magnetons, the average being 5.97. The expected value of the moment for the manganous atom forming four dspZ bonds, essentially covalent and directed toward the corners of a square, is 3.88 plus a small orbital contribution; the expected value for the atom with tetrahedral spdbonds or for the ion is 5.92 magnetons with no orbital contribution (normal state IL). The measurements are in good agreement with the second of these values. Barkworth and Sugden4 have shown that the a-form (violet modificakion) of cabalbus dipyridine chloride has a moment of 5.34 Bohr magnetons, and that the p-form (blue nmdiication) has (4) 15 1) P Barkworth and S Sugden, .Vaiuvc, 189, 374 (1937).
Aug., 1938
STRUCTURE OF MANGANOUS AND COBALTOUS DIPYRIDINE CHLOR~DES
1737
a moment of 4.60 magnetons. The expected mo- modification suggests that there is tetrahedral ment for the cobaltous atom forming asp2 bonds coordination around the metal ions in this solid. Compounds with a coplanar configuration conis 1.73 plus orbital contribution, and that for the atom forming sp3 bonds or for the ion is 3.88 plus taining ionic bonds are to be expected only if the orbital contribution. We accordingly conclude electronegative groups are part of a rigid plane that the bonds to the cobalt atom are essentially structure, as for example in ferriherne chloride ionic, with an unexpectedly large orbital contribu- (hemin) and ferroheme, in both of which the iron tion in the case of the a-form. atoms were shown' to be held as ions. It seems A tetrahedral configuration is not compatible very likely that the bonds to beryllium in berylwith the small dimensions of the c-axes (3.73 and lium phthalocyanin and the bonds to magnesium 3.65 respectively) of the manganous and co- in chlorophyll are predominantly ionic. The exbaltous compounds, as pointed out by Cox and istence of these compounds accordingly is not his co-workers. This configuration is not, how- proof that the metals form square covalent bonds; ever, the only alternative to a square configura- whereas square coordination with groups which tion. A reasonable structure for the complexes, are free to rearrange is an indication of the pre-. one not considered by these workers, can be for- dominant covalent character of the mulated with each metal ion sharing four CO- Square bonds have not as yet been found in any planar chloride ions in pairs and holding two manganous compound; it has been reported that pyridine molecules a t right angles to the plane of impure cobalt phthal~cyanin~ and a n impure cothe chloride ions. The proposed structure thus baltous phenanthroline cyanideL0show magnetic contains an ionic octahedral complex with two evidence for square bonds, but these observations shared edges. The metal-metal distances in the have not been verified with pure substances. metal-dichloride chains are calculated6 to be 3.7 Summary and 3.G A., respectively. The pyridine rings lie in planes the same distance apart. The calcuThe magnetic criterion for bond type indicates lated distances agree with the observed c values that manganese and cobalt atoms in the dipyrito within the accuracy of the ionic radii. dine dichloride compounds form ionic bonds rather Both the a- and p-forms of the cobalt mm- than covalent asp2 bonds. It is suggested that an pound give in organic Solvents6identical blue solu- octahedral ionic type of structure occurs in the tions, which have been shown's6 to contain mono- manganese and a-cobalt compound and a tetrameric solute molecules in bromoform, chloroform, hedral ionic type occurs in the @-cobaltcompound. and phenol. It is probable that the configura- PASADENA, CALIF. RECEIVED APRIL4, 1938 tion about the cobalt ion is tetrahedral in these (7) L. Pauling and C. D. Coryell, Proc. N a l . Acad. Sci., 22, 159 solutions. The fact that the colors of the solu(1936). tions are nearly the same as that of the solid @(8) For a discussion of ionic and covalent character in bonds, see
w.,
(5) With the use of the crystal radii of L. Pauling, THIS JOUILNAL, 49, 765 (1927), not corrected for the effect of structure. (6) D P. Mellor and B.S Morris, article in press, Proc Roy SOC, New S. Wales (1938).
L. Pauling, THISJOURNAL, 64, 988 (1932). (9) L. Klemm and W. Klemm, J. prakt. Chem., 149, 82 (1935). (10) L. Cambi and A. Cagnasso, Rend. ist. Zombardo sci., 67, 741 (1934).
