METALS IN THE UNINEGATIVE OXIDATION STATE ERVIN COLTON Georgia Institute of Technology, Atlanta, Georgia
THE existence of a metallic element in the uninegative oxidation state is not only interesting but also highly unusual since we are accustomed to thinking of metallic atoms as losing electrons rather than gaining electrons in chemical reactions. The following brief discussion summarizes two notable cases of the display of this unusual chemistry.
which reacts readily with thallium(1) nitrate to yield a white precipitate, presumably thallium(1) rhenide. This precipitate is not stable and is converted in solution to elementary thallium and perrhenate ion. Elementary analysis of purified potassium rhenide points t o the fact that it probably exists as a tetrahydrate. Following the preparation of potassium rhenide a t RHENIUM the University of Kansas, Grosse (8)a t Temple UniverThe classic example of a metal exhibiting a negative sity prepared lithium rhenide by a slightly different oxidation state is rhenium. In 1937 Lundell and procedure. He reduced potassium perrhenate with Knowles (1) at the Bureau of Standards demonstrated lithium metal in aqueous solution under a nitrogen that rhenium could be reduced to the uninegative state atmosphere. The lithium rhenide t,hus formed was by passing a cold solution of perrhenate, Reon-, through separated from the admixed lithium hydroxide by a Joues reductor in the absence of air. Subsequent in- repeatedly crystallizing the mixture from water in an vestigations confirmed this unusual oxidation state for oxygen-free atmosphere. rhenium. The TomiEeks (8) demonstrated that a Lithium rhenide is reported to exist as a white, saturated zinc amalgam in 10 per cent hydrochloric crystalline solid which appears yellow in thick layers. acid reduced Re(VI1) to Re(-I). Lingane (3) showed Its concentrated or dilute aqneous alkali solutions are that an eight-electron exchange is involved when stable for extended periods if stored under nitrogen. perrhenate is reduced to some lower state of rhenium Hot acidified potassium permangaoate solution is at the dropping mercury electrode. Maun and David- readily reduced quantitatively by a solution of lithium son (4) attempted to prepare solutions containing rhenide. A rhenide solution quickly reduces a hydroRe(-I) in concentrations greater than lo-' M but chloric acid solution of bismuth(II1) chloride to were u~isucressfulin reducing Re(VI1) when the initial elementary bismuth, thus affording a sensitive test for M. the Re- ion. concentration of perrhenate was greater than Rulfs and Elving (5) prepared what they considered to The structure that the rhenide ion might possess is be thallous rhenide, TlRe--a white, crystalline solid, indeed an interesting subject of speculation. Magnetic isomorphous with thallous chloride--by bringing to- measurements on KRe,4H20 (7) a t 20" gave values of gether a solution of rhenide with thallous nitrate. 254 X 1O-B and 223 X 10-Q.g.s., respectively, for two Kowever, recent work (6) points t o the fact that thallous different samples, after correction for the presence of rhenide, if formed, is highly unstable and reverts to potassium hydroxide. This amount of paramagnetism finely divided thallium metal and perrhenate ion in is slight and may be attributed t'o partial oxidation of solution. rhenide to some higher st,ate of t,he element. Pauling It is always more satisfying and convincing when (9) has suggested that the rhenide ion probably would be dealing with new and unusual oxidation states toisolate, +coordinated square planar because it is isoelectronic if possible, solid materials that lend themselves to with Pt(I1). We might anticipate, therefore, that subsequent physical and chemical investigations. Re- uninegative rhenium mould possess a dspZ type of cently, Bravo, Griswold, and Kleinberg (6, 7) isolated bonding. the first solid rhenide. These investigators reduced potassium perrhenate in ethylenediamine-water solution with potassium metal in an inert atmosphere and obtained a white solid containing potassium rhenide, KRe, admixed with potassium hydroxide. Under optimum conditions 90 per cent of the starting material was converted to rhenide. Extractions of the white product with isopropyl alcohol eventually yielded a COBALT There are numerous reports in the literature wherein grayish solid containing 55-60 per cent rhenium, all as cobalt seems t o attain the uninegative oxidation state, rhenide. Potassium rhenide is described as a colorless solid e. g., in the unusual anion [Co(CO)J-. This ion may 118
VOLUME 33, NO. 3, MARCH, 1956
be looked upon as heing derived from the parent compound cobalt carbonyl hydride, HCo(CO)&,which was first prepared by Hieber and Schulten (10). In cobalt carhonyl hydride the effective atomic number of cobalt is 36. The cobalt atom in the ion [Co(CO)& also possesses an E.A.N. of 30. A number of derivatives of HCO(CO)~have been prepared, the cations heing atoms electropositive elements ( l i ) , e . g., Na[Co(CO)J, K [ c ~ ( c o ) ~ ] , Ca[Co(CO)4],, and [CO(NH&][CO(CO)~]~ These comuounds behave as t v ~ i c asalts. l and it would be difficult to assign an oxidatibn state other than minus o.le to cobalt in these substances. The cations of the B subgroup metals, however, yield compounds which exhibit and covalent characteristics, e . g., C~[CO(CO)~], Rg[Co(CO)rls. Recently, detailed investigations on the further hehavior and characteristics of the tetracarbonylcohaltate (-I) ion have appeared. Hieber and Fischer (13) have studied the reaction of carbon monoxide and cobalt(I1) salts in the presence of dithionite ion and have isolated a complex nickel salt of [CO(CO)~]-as an orange, flocculent precipitate.
structure ($0,$1). Hence, in the anion [CO(CO)~]we might expect the CO groups to be held with sp3bonding.
of
TECHNETIUM
Although technetium has recently been prepared artificially and still is rather costly, enough work has been done to indicate that chemically it is more like rhenium than like manganese. The gradual change in color of the anion M04- (Mn = purple, Tc = yellow or pink, Re = colorless), for example, would suggest that the properties of technetium should lie somewhere between those of manganese and those of rhenium. Mn(O), Mn(I), and now Re(-I) are well chararterioed species; hence i t seems very likely that Tc(-I) should exist also. ACKNOWLEDGMENT
The helpful discussion and suggestions of Dr. Mark
M. Jones are greatly appreciated. LITERATURE CITED
Dicohalt octacarbonyl is capable of reacting with methyl isonitrile to form the cobalt(1) derivative of ICo(CO)r]-, i. e . , [CO(CNCH&][CO(CO)~] (15). The equivalent condurtance of 94.15 ohm-' in acetone at a dilution of 679.7 l./mole points to the presence of two ions in the cohalt(1)-cobalt(-I) complex. The phenylisonitrile derivative has also been prepared (15). Sodium tetraearbonylcohaltate(-I) reacts with so- (5) dium cyanide in liquid ammonia, with evolution of (6) carbon monoxide, to form the complex anion [ C O ( C O ) ~ (7) CiV-- (14). Only 33 per cent of the carhonyl groups in [CO(CO)~]-are replaced, however, and a mixture of (8) Na[Co(CO)J and Na2[Co(C0)&N] results. With (9) sodium thiocyanate a similar complex carbonyl- (10) thiocyanate is obtained, [CO(CO)~SCN]--(1.4). Nitric oxide reacts with dicohalt octacarbonyl to (11) form the partially substituted cohalt carbonyl CO(CO)~NO (15). Cobalt nitrosyl carbouyl exists as a red (12) liquid, is diamagnetic (16), and has been shown t o be best described as a tetrahedral molecule (17). Re- (13) cently, isonitrile derivatives of cobalt nitrosyl carhonyl (14) have been prepared (18). Compounds of the type (15) Co(NO) (CNR)r, where R = p-CH,C6H4,p-C1C6H4,and p-CH30C6Hc are all diamagnetic. Since the nitrosyl (16) group generally has been considered to co0rdinat.e as (17) the unipo~itivegroup NO+ (IQ), cobalt must assume (18) the uninegative oxidation state in these substituted carhonyls. (19) The structure of the uninegative cohalt atom probably is tetrahedral as has been shown for cobalt nitrosyl (20) carbonyl (17). Co(-I), furthermore, is isolectron& ('21) with Ni(O), which is best described as a tetrahedral
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