382
'
NOTES
in Class 3. The various terminal hydrogen atoms in the known hydrides are attached to borons of different formal charge,6 and those attached to the more positive boron atoms will presumably ionize off more readily. The borons of type6 I1 or I in B1oH14 are more positively charged than t'he others, and hence possible ionization of one or more of the attached hydrogens may be suggested. There is some evidence that B10H14 has an ionizable hydrogen,6 and the series of salts NaB10Hl3, NazB1oHl2, etc., may be suggested. When this suggestion is combined with the Class I type, Na2B10H14, we expect another series beginning with Na3B10H13, etc. 5. Ions Derived from Addition of H+ to a Single B-B Bond on the Edge.-The B6Hll+ ion derived by addition of a proton to the strained single B-B bond in the known' 4220 B6H10 structure is expected to be stable. Although no other of the known hydrides based upon icosahedral fragments have this structural feature, several of the possible hydrides and ions do, and might become stabilized by the addition of one or two protons. 6. Other Ions Based upon Icosahedral Fragments.-Ions like the 3122 B5H10- ion and the 3100 ion may also exist, as may the 2113 B4H9- and 2440 BsHlo-' both of which have one or more single B-B bonds along the edge (cf. Class 5 ) . Probably the most promisings ion of this type is B 1 2 H d , which is an 0.10.3.0 resonance hybrid in our localized-bond description. 7. Ions Based upon Tetrahedra, Octahedra or Their Fragments.-Our bonding scheme applies to any geometrical framework in which one can say that only close contacts represent valence interactions, and hence include 0230 B4H4-2, (0400 B4H4), 2040 BqHS-', 3030 B4H7- also listed in Class 2, (4020 B4H8), 5010 B4H9+and 6000 B4HlO+' all based on a tetrahedral boron arrangement; 2240 B G H ~ -3230 ~ , B6He-, 0430 Be&-' (see ref. 5 ) , 1420 BsH7-, (2410 B6H8) and 3400 B6H9+ all based on an octahedral boron arrangement; and a similar series based on the B6Hg arrangement. Within each of these groups these ions are interrelated by the process describing Class 5 as the charge increases, or Class 3 as the charge decreases. Ions involving features not present in the known hydrides have been omitted. While the above classifications and lists probably do not exhaust all possibilities, it may be hoped that the omissions do not overlook any obviously promising stable ions. For example, we have not considered ions based on linked polyhedra or linked fragments of polyhedra. We have not tried to list completely the results of applying the processes of Classes 3, 4 and 5 to all ions listed above. Finally, these principles are applicable to types of polyhedra other than those discussed here. The available experimental evidence for ionic (5) W. H.Eberhardt, B. L. Crawford, Jr., and W. pv'. Lipscomb, J . Chem. Phys., 22, 989 (1954). (6) G. A. Guter and G. W. Schaeffer,J . Am. Chem. Soc., 78, 3546 (1956). (7) F. L. Hlrshfeld, K. Eriks, R. E. Dickerson, E. L. Lippert, Jr., and W. N. Lipscomb, J . Chem. Phyls., 28,56 (1958). (8) H. C. Longuet-Higgins and M. de V. RobertR, Froc. Roy. Sor. ( L o n d o n ) , A230, 110 (1955).
Vol. 62
boron hydride fragments suggests that much careful experimental work is desirable. Stockg mentions NazBzHs and Na2B4Hl0,from which the original hydrides BZH6 and B4H10 are a t least partly recoverable. He also describes'O NazB5H9and NazB4H8 as a decomposition product of Na2B4H10. Recent work3~l1has shown that the diborane reaction gives NaBH4 and NaB3H8. The remarkable BzH,- ion'' prepared by reaction of BH4- with may possibly be formed only when BH4- can react with the double hydrogen bridge which occurs in BzH6 but not in the higher hydrides. However, similar studies have not yet appeared for the higher hydrides. I n summarv, the more stable ions are Drobablv B12H12-', BioH;4-', BioHia-, Bi"i+, B3Hs' , B4H7') B6Hed2,B6H107 B3H6+. The fact that both positive and negative ions might exist leads t o the suggestion of purely ionic hydrides possibly prepared by reactions of salts of these ions with one another.
0
i
z
(9) A. Stock, "Hydrides of Boron and Silicon," Cornell University Press, Ithaca, N. Y., 1933. (10) A. Stock, W. Sutterlin and F. Kurzen, 2.onorg. Chem., 226,225, 243 (1935); 228, 178 (1936). (11) J. S. Kasper, L. V. McCarty and A. E. Newkirk. J. Am. Chem. SOC.,71,2583 (1949). (12) H. C. Brown, P. F. Stehle and P. A. Tierney, i b i d , 79, 2020 (1957).
MEASUREMENT OF T H E ABSORPTION SPECTRA OF NEPTUNIUM IONS I N HEAVY WATER SOLUTION FROM 0.35 TO 1.85 p BY W. C.WAGGENER Contribution from the Chemistry Division, Oak Ridge Nalional Laboral o r y , Oak Ridge, Tennessee Received Noiiember 87, 1967
Numerous inorganic ions undoubtedly have characteristic aqueous absorption bands which occur above 1.2 1 where the strong absorption of ordinary water precludes their measurement. The wectral region'i between 1.2 and 1.8 p is easily accissible to Geasurement by changing to heavy water aqueous media since DzO is much more transparent than HzOto radiation in the near infrared.' The following preliminary study of the spectra of neptunium ions in heavy water solution suggests a fruitful extensicn for epectroscopy of aqueous solutions in general into the range from 1.2 to a t least 1.8 p . By following the prcgressive catalytic reduction of a solution of NpOz(C104)~in 1 M DClO4-DzO over the range from 0.35 to 1.85 ~rten new absorption maxima have been characterized (see Table I). Five of these maxima, including the strong peak for Np(V1) ion a t 1.223 p , were first measured in light water solutions. '
Experimental The neptunium solution used was prepared by evaporating a 30 mg. sample2of Np2a7 to dryness twice with HC104. An excess of HClOd, then added, was converted to DClOd by repeated dilution and evaporation with D20 (99.8b). Finally, constant boiling acid was evaporated to requisite weight for dilution to unit molarity in DClOI. (1) W C. Waggener, Anal. Chem., in press. (2) Courtesy of P. M. Lantz and G. W. Parker, CherniRtry Division, Oak Ridge National Tshoratory.
h
1
NOTES
March, 1958
383
RESOLUTION (i) ESTIM,ITED FROM SLIT WIDTHS.
3.9
2.4
2.0
I
2.2
2.8
2.3
I
I
I
j.8
;///I
1.9
2.4
2.4
3.3
I
I
I
I
3.0
,
4.2
4.5
6.9
1
I
I
. ........... . ,
__
I
BACKGROUND ABSORBANCE
i
ii
WAVELENGTH (microns 1,
Fig. 1.-Absorption
spectra of 0.0276 Jf neptunium perchlorate in 1 M DC1O4-D20 from 0.35 to 1.85 p.
The concentration of Np237in the deuterated sample was 0.0276 M by radiometric assay. One molar DCIO4 for the reference cell was prepared from HC104 in the manner described for the neptunium sample. The sample was held in a conventional 1 cm. fused quartz cell which was fitted with a long neck and a Teflon stopper. Reduction of the sample was done outside the spectrophotometer by inserting a fine platinized P t capillary helix through which a slow stream of Dz(g) was paseed. The Cary Model 14M Spectrophotometer was used with cell compartments thermostated at 25’. Undispersed radiation was passed through the cells, and d i t operation was automatic, providin a constant power signal from the reference beam to the Pb% detector. Background absorbance was determined from 0.35 to 1.85 p with 1 M DClO4 in both cells. The oxidized sample was then scanned and reduced alternately until the neptunium was 98% converted into the 111 state.
Results and Discussion The spectral curves in Fig. 1 represent the maximum concentration recorded, respectively, for Np(VI), (V), (IV) and (111) ions in tlhe deuterated medium during reduction. The valence composition given in Fig. 1 for each curve was determined froin the data with the aid of published results for neptunium ions in 1 M ~c10~.3 Beer’s law behavior and a negligible effect of change of solvent were assumed. The molar absorptivities coniputed for 19 bands between (3) R. Sjoblom and J . 0. Hindman, J . A m . Chem. Soc., 75, 1741 ( 1951).
0.428 and 1.023 p are in reasonable agreement with the data of Sjobloin and Hindman if their entire curve for Np(V) is dropped 4 absorptivity units: €obs/€SH = 0.95 0.05. No evidence has been found for this background absorption, either in HClOl or DC104; it is also not shown by the spectrum of Np(V) in HC1 as measured by Hindman and co-workers.4
*
TABLE I
ESTIMATED MOLARABSORPTIVITIES AND VALENCEASSIGNMENTS OF NEWNEPTUNIUM MAXIMABELOW1.85 p X
(p)
1.800 1.697 1.620 1.480 1.360
Valence
6
4
5 49 4 5 43
4
5 6 3
X
(p)
1.223 I . 180 1.145 1.117 1.096
Valence
t
6 3 4
45 3 11 6 23
5 5
None of the absorption maxima were tested for constancy of e. However, the intensities of the sharpest bands, e.g., 0.9600 and 0.9800 p of Np(1V) and (V), respectively, did not appear to be sensitive to appreciable changes in slit width. Acknowledgment.-The author acknowledges the assistance of his wife, Rose Marie, in preparing the graph. (4) J. C. Hindman, I,. B. hfagnusson and T. J. LaChapelle, “National Nuclear Energy Series,” I V , 14B No. 15.2, McGraw-Hill Rook C o . , Inc., New York. N. Y.,1949.
