BRIGGS CHROMATOCOBALTIAMMINES. 67 VI. -ChromatocobaltiammirLes. By SAMUEL HENRY CLIFFORD BRIGGS. PREVIOUS investigations have shown that the chromate radicle possesses considerable residual affinity and has a strongly marked tendency to form complex salts (Briggs Zeitsch. anorg. Chem., 1907 56 246; 1909 63 325; Groeger ibid. 1908 58 412). It was therefore to be expected that the chromatocobaltiammines would be a well-defined and stable class of substances containing one or more non-ionisable chromate radicles. As soluble compounds containing a non-ionieable chromate radicle have not previously been described the study of the chromatocobaltiammines was under-taken in order to compare the properties of the chromate radicle in non-ionisable combination with those of- the ionisable radicle in the ordinary chromates.The chromatocobaltiammines are readily prepared by the action of potassium chromate on the corresponding aquo-compounds in solution. Thus when a solution of potassium chromate is added to a warm solution of an aquopentamminecobaltic salt a chromato-0 68 BRIGFGS CHROMATOCOBALTIMMINES. pntamminecobaltic salt (I) crystallises out on cooling. The nitrate, chloride and chromate of this series were obtained in a pure condition. The chromatotetramminecobaltic salts (11) are formed in a similar manner and the chromate dichromate and nitrate were prepared in a pure state. When a solution of a diaquotetramminecobaltic salt is treated with an excess of potassium chromate trichromato-octamminedicolbalt (111) crystallises out on keeping.Trichromato-octamminedicobalt7 is isomeric with chromatotetramminecobaltic chromate (IV) but the two compounds are very different. The former is almost completely insoluble in water and forms greenish-black crystals containing five molecules of water of crystallisation, whilst the latter is obtained as a greenish-brown precipitate with three molecules of water of crystallisation; it is moderately soluble in water and its solution gives the reactions of the chromate ion. Attempts to prepare chromatotriammine compounds by the action of potassium chromate on triaquotriammineoobaltic nitrate were not successful the product being chrornatohydroxotriamminecobalt (V), which however was not obtained in a completely pure condition. It therefore appears that when more than two molecules of ammonia in the hexamminecobaltic radicle ar’e replaced by the chromate radicle the products are unstable in the presence of water and undergo hydrolysis.This explains why endeavours to prepare putassi um cobaltic chromate K3Col( CrO& by oxidising cobaltous salts in the presence of potassium chromate failed cobaltic hydr-oxide and potassium dichromate being obtained. The formation of chromatohydroxotriamminecob~alt in the above manner also supports the view that the basic chromates are hydroxo-compounds in accord-ance with Werner’s theory of basic salts (“ Neuere Anschauungen auf dem Gebiete der anorganischen Chemie,” 3rd led. pp. 177-178). Some evidence was obtained which pointed to the existence of a chromatoaquotriammine series (VI) a compound being prepared which had the composition of chromahaquotriamminecobaltic dichromate : (11.) (111.) w.1 w.1 (VI.) In the chromatopentammine- and chromatotetrammine-cobaltic salts the chromate radicle in the complex is non-ionisable no pre BRIGGS CHROMATOCOBALTIAMMINES.69 cipitate being obtained when silver nitrate is added to cold freshly prepared solutions of the pure nitrates. If the mixture is allowed to remain for some time however silver chromate is slowly deposited showirlg t.hat the chromato-salts have a tendency to pass into the corresponding aquo-salts as seen from the equation : I f the eolution is heated the change takes place a t once and silver chromate is immediately precipitated. The chromate radicle in these1 compounds reacts with hydrogen ions in the same way as in the ordinary chromates.When an acid is added t o a solution of a chromatopentammine or chromato-tetrammine salt the complex is decomposed as seen from the change in colour of the solution. I n the chromatopentammine salts the chromate radicle fills one co-ordination position according to Werner's theory whereas in the chromatotetrammine salts it fills two positions. The entrance of the chromate radicle into the complex is accom-panied by marked intensification of colour and all the chromato-cobaltiammines are deeply coloured substances. E X P E I X I M E N T A L . P e n t a m rn in e S e r i e s. Chroma t opeittammineco bal tic Nitrate (Co;:?) NO,.-Carbon-atopentamminecobaltic nitrate was converted into aquopentammine-cobaltic nitrate and potassium chromate was then added to the solution the details of the preparation being as follows.Carbonatopentamminecobaltic nitrate (2.5 grams) was dissolved in 100 C.C. of water a little dilute nitric acid was added and the solution was gently warmed to expel carbon dioxide. The liquid was then just neut,ralised by potassium hydroxide diluted to 300 c.c. and heated to 60-70°. One and a-half grams of potassium chromate in 100 C.C. of water also heated t o 60-70° were added and the clear solution was allowed t o crystallise. The chromatopentamminecobaltic nitrate sepa'rated in brownish-red, acicular cryst.als (2.2 grams) which were collected washed with a little water and dried in the air. Found Co = 18.51 ; Cr03= 31.74 ; NH,= 26-36.(COT::) NO requires c*o = 13.35 ; CrOB = 31.05 ; NH3 = 26.44 per cent. The salt was moderately soluble in cold water and the freshl 70 BRIQQS CHROMATOCOBALTIAMMINES. prepared solution was not precipitated by silver lead or barium salts but precipitation took place a t once on heating. The chromate radicle is therefore situated in the complex as shown by the above formula and the salt is isomeric with Jorgensen’s nitratopent-amminecobaltic chromate (CoS”g?)CrO ( J . F. CJlem. 1881 [ii], 23 245). Chromat opentammhLeco baltic Cht?oride (C‘of;$) Cl.-Chloro-pentamminecobaltic chloride was converted into aquopentammine-cobaltic chloaide by Werner’s method (Bey. 1907 40 4104) and this was treated with potassium chromate. Twenty-five grams of c’hloropentamminecobaltic chloride were heated with 625 C.C.of water and 62.5 C.C. of concentrated aqueous ammonia until the chloride was completely dissolved. After cooling, the liquid was just neutralised with hydrochloric acid and heated to 60°. Sixteen grams of potassium chromate in 500 C.C. of water, also heated t o 60° were then added and the mixture was allowed to cooll. After crystallisation was complete the salt was collected, washed with a little water and dried in the air. Twenty-three grams of brownish-red crystals ( A ) were thus obtained. The mother liquor was heated t o 50° and 4 grams of potassium chromate dis-solved in a little water were added. On cooling 1.2 grams of a second salt ( B ) were1 obtained in yellowish-brown prisms almost insoluble in cold water but readily soluble on warming t o give a yellow solution.The salt A was anhydrous but B contained water of crystallisation ; otherwise the salts were similar in composition as seen from the analyses : A . Found Co = 19.86 ; CrO,= 33.97 34.27 ; C1= 12.02 ; NH3= 27.30 27.15 27-08. (CO$$~)CI requires Co = 19.96 ; Cr3 = 33-83 ; C1= 12.00 ; NH = 28.81 per cent. B. Found Co=16.91; C1=9*80; Cr03=29*94; NH3=26*6; H20 = 13.95. 2 C O ~ ~ ~ Cr0,,5H20 requires Co = 17.31 ; C1= 10.41 ; CrO = 29.36 ; ( cl,> NH = 25.0 ; H,O = 13-22 per cent. The solution of the salt ,4 on addition of silver nitrate gave a copious precipitate. Tliis was filtered off and on treatment with dilute nitric acid was found to consist of silver chloride coloured by the presence of a trace of silver chromate.The reddish-yellow filtrate on heating deposited a precipitate of silver chromate Th BRIGCIS CHROMATOCOBALTIAMMINES. salt A was therefore chrornatopentamminecolbaltic The solution of the salt I3 on addition of silver nitrate 71 chloride, gave a red precipitate which was filtereld off the filtrate being only faintly coloured. The precipitate consisted of silver chromate. It dis-solved in dilute nitric acid leaving only a trace of silver chloride. The salt B was therefore a hydrated chloropentarnminecobaltic Vari'ous preparations of the salt A (chromatopentamminecobaltic chloride) were made but? in all cases the ammonia content was low. The salt conld not ble purified by crystallisation from hot water as it was then fonnd to contain a little of the corresponding chromate, which is very sparingly soluble in water.The reason for tlie low percentage of ammonia could not be ascertained, and this is all the more remarkable as the salt on treatment with silver chromate gave t'he corresponding chromate in a high degree of purity. Chromatopeiztamminecobaltic Chromate ( C O ; ~ ? ) T r O, 3H20. -Two grams of silver nitrate were precipitated in-the cold with 1 gram of potassium chro,mate and the precipitate was washed two or three times by decantation. The supernatant liquid was separated as far as possible by decantation and the precipitate was then poured into a solution of 3 grams of chromatopentamminecobaltic chloride in 150 C.C. o,f water a t 60° the mixture being well shaken.After a few minutes the silver chloride assumed a dense form and crystallisation began. The silver chloride was then rapidly col-lected and the filtrate which no longer gave the reactions of the chloride ion was allowed to! crystallise. Chromatoperttammine-cobaZtic chromate separated in glistening scaly crystals similar in colour to silver chromate. The crystals consiiste'd of a trihydrate which lo& 22 molecules of water after expoisure o'ver sulphuric acid in a vacuum f o r two or three weeks (Ioss=7*16. 2$H,O require a loss of 7-17 per cent.). The resulting The yield was 1.5 grams. hydrate 4 (Co cr04 ) Cr04,H,0 became anhydrous above looa. The 5N% 2 complete analysis of the trihydrate gave : Found Co = 17.48 ; CrO,= 43-64 ; NH = 24.83 ; H,O = 7.64.( CoiG$8)2(ki ),,3 H2( J requires Co = 17.09 ; CrO = 43 6 ; NH = 24.6s ; H20 = 7.83 per cent 72 BEUQGS CHROMATOCOBALTIAMMINES. Tetrammine Series. Carbonatotetramminecobaltic nitrate was prepared by Jorgensen’s method (Zeitsch. anorg. Chem. 1892 2 ZSZ) and this was con-verted into diaquotetramminecobaltic nitrate by acidification of its solution. On treating the solution of diaquotetramminecobaltic nitrate with potassium chromate either chromatotetrammine-cobaltic nitrate chromatotetramminecobaltic chromate or tri-chromato-octamminedicobalt could be obtained in the pure state, according to the conditions employed. Chromatotetramminecobaltic Nitrate 2(Co~~~)N03,H20.-A solution of 4 grams of carbonatotetramrninecobalti; nitrate in a little water was treated with dilute nitric acid warmed gently to expel carbon dioxide just neutralised with potassium hydroxide, and the volume made tip to 40 C.C.Twenty grams of ammonium nitrate were dissolved in the liquid and a solution of 1.2 grams of potassium chromate in 10 C.C. of water was added drop by drop in the cold with vigorous stirring. The stirring was continued for a minute or two until crystallisation was complete and the dark reddish-brown deposit was then immediately collected washed with a little water and dried in the air. The yield was 0.9 gram. The product was a hemihydrate which lost its water of crystallisation after exposure for two days over sulphuric acid in a vacuum. Found Co = 18.86 ; CrO = 31.68 ; NH,= 21.34 ; H,O = 3.67. ~ ( C O F ~ ~ ~ ) N O ~ ‘ I requiresco- 18.77 ; Cr0,=31*83; KH3= 21.69 H,O = 2.87 per cent.The salt was moderately soluble in water giving a deep brown solution. Silver barium or lead salts did not precipitate the freshly prepared cold solution but precipitation to,ok place a t once on heating. The cold solution was also completely precipitated if allowed to remain for several days after the addition of the reagent, showing that the chromate radicle is gradually eliminated with the formation of a diaquotetrammine salt for example, Chromat otetramminecobnl t ic Chroma t e ( C O ; ~ ~ ) Cr04,3H20.-Four grams of carbonatotetrarnminecobaltic nitrate in 80 C.C. of water were converted into diaquotetrami~~inecobaltic nitrate aa described above in the preparation od chromatotetramminecobaltic nitrate.To the cold neutral solution of diaquotetramminecobalti BRIBBS CHROMATOCOBALTIAMMINES. 73 nitrate thus obtained (100 c.c.) 3 grams of potassium chromate, dissolved in 50 C.C. of wat'er were added with vigorous stirring. A brown crystalline precipitate was formed which waa collected immediately washed with water and dried with alcohol and ether. The! yield was 2.8 grams. The salt contained three molecules of water as water of crystal-lisation only being readily evolved when the. substance was exposed in a vacuum over sulphuric acid. The salt was sparingly soluble in water and its solution was immediately precipitated by silver nitrate showing that some of the chromate content was ionis-able. It follows from these facts and the analyses that the com-pound must have the formula assigned to it.Found Col= 18.14 ; CrO,= 45'31 ; NH = 20.61 ; H,O = 8-26. ( C O ~ % ~ ) F ~ ) ~ H ~ O ; Co=17*97; Cri),=45.71; NH,=20*77; H,O = 8.26 per cent. Yrichr om at 0- o c tamminedico bal t , -Two grams of carbonatotetramminecobaltic nitrate in 30 C.C. of water were converted into diaquotetramminecobaltic nitrate in the manner already described and the cold neutral solution (50 c.c.) was added with stirring to a cold solution of 5 grams of potassium chromate in 50 C.C. of water. The clear liquid deposited a greenish-black crystalline substance on keeping. This was collected washed with a litble water and dried in the air. Found Co=17*14; Cr03=43.32; NH3=19'44; H20=13'05. C O ~ N H ~ ( C ~ O ) ~ ~ H ~ O requires Co= 17-04 ; Cr03= 43.33 ; NH = 19-68 ; H,O = 13-01 per cent.The five molecules of water were readily evolved on exposing the compound in a vacuum over sulphuric acid and all were therefore water of crystallisation only. I n view of the facts ascertained with regard to chromatotetramminecobaltic chromate and described above it follows that this isomeric compound must be a non-ionis-able octamminedicobalt derivative. Its almost complete insolu-bility in water affords further confirmation of this view. Again, since in the diaquotetramminecobaltic salts the water molecules are in the " cis" position (Werner " Neuere Auschauungen auf dem Gebiete der anorganischen Chemie," 3rd ed. p. 347) this tri-chromato-octamminedicobalt must also have the chromate radicles in the " cis " position and is therefore a 1 1' 2-2~-trichromatc-octammz'redicobalt pentahydrate.Attempts to prepare the corre-sponding '' tra?is " compound by various methods were unsuccessful. J3 74 BRIGGS CHROMATOCOBALTIAMMINES. CrO Chroma t o t e tram mineco b a1 t ic Dic hro ma t e ( C'04 H43),Cr20,,2H20. -Four grams of carbonatotetramminecokaltic nitrate were con-verted into diaquotetramminecobaltic nitrate as described ab,ove, and the neutral solution (80 c.c.) wts added slowly with stirring to a cold solution of 8 grams of potassium dichromate in 80 C.C. of water. The precipitate was immediately collected washed with a little water and dried in the air. The yi,eld was 1.9 grams. Three separate preparations were analysed and the ammonia content was low in every case for some reason that could not be ascertained.Found Co=15*94; CrO,=53*41 54-01; NH,=17*48 16.6 16.4; (C!O~;~~),C~&,~H~O requires Co= 15.97 ; CrO = 54.19 ; XH3= H20 = 4.98 4.76 5.04. 18.4 ; H20 = 4.88 per cent. The threle molecules of water were readily given off in a vacuum over sulphuric acid and all were therefore water of crystallisation only. From the proportion ,of cobalt t o chromium (2Co :4Cr) it is evident that the salt is chromatotetramminecobaltic dicliromate, ( C O G ~ ~ ) C ~ ~ O and not dichromatotetramminecobaltic chromate, ( C O Y ~ $ ) ~ C ~ O in which the propo,rtioas am 2Co 5Cr. Conse-quently the dichr0mat.e radicl'e is ionisabmle and the chromate radicle non-ionisable. The salt was moderately soluble in water, and the solution was immediately precipitated by silver and barium salts.Triammine Series. Chromatohydroxotriammiaecobalt.-Two grams of trinitratotri-amminecobalt prepared by Jorgensen's method (Zeitsch. anorg. Chem. 1895 5 185) were dissolved in 40 C.C. of cold water and the solution was added to a cold solution of 6 grams of potassium chromate in 40 C.C. of water. The brown precipitiate (1) was col-lected wasled with cold water and dried in the air when it weighed 1.7 grams. The filtrate on spontaneous evapofation deposited crystals of potassium dichromate as well. as of potassium chromate. Two other preparations were made (2 and 3) in which 1 gram of potassium chromate in 10 C.C. of water was mixed with 6.25 C.C. of potassium hydroxide solution (1 C.C.= 0.0448 gram KOH) and the mixture was poured into a solution of 1.5 grams of trinitratotri-amminecobalt in 10 C.C. of cold water. The analyses gave BRIUUS CHBOMATOCOBALTIAMMINES. 75 Foun'd (1) H,0=11*5; CrO,=36.3; Co=22'9; NH3=15*1. (2) H20=11*4; CrO,=34*5; Co=22*5; NH3=16.8. (3) NH,= 16.7. ( C b b ~ ) 2 € € 0 requires H,O=12.9 ; CrO,=35*8; Co=21*1 ; Although impure the compound was clearly a hydrated chromato-hydroxotriamminecobalt. Chromatoapuotrianaminecobdt~c Dichromute.-Two grams of tri-nitratotriamminecobalt in 10 C.C. of cold water were added t o a solution of 3 grams of sodium dichromate in 10 C.C. of water and the mixture was treated with a solution of 0.75 gram of anhydrous sodium chromate in 10 C.C. of water in the cold.A copious brown precipitate was formed which was allowed to settle and then col-lected washed with a little water and dried with alcohol and ether. The product which weighed 1.4 grams was only sparingly soluble in cold water. I n a vacuum over sulphuric acid it lost 3 mole-cules of water after three days and a further quarter molecule after eighteen days the weight then remaining constant. The analysis agreed cloeely with the formula given below. Found 3H20=7*22; 3$H20=8.16; Co=16.06; CrO,=54*09; NH,= 18.3 per cent. NH3= 13.63. ( 2 ~ 4 ) ~ r 2 0 7 2 H 2 0 requires 3HaO = 7.30 ; 34H,O = 7.91 ; Co = 15.93 ; CrO = 54.04 ; NH = 13.81 per cent. iVote m the Preprution of Carbonat~pentarn?ninecobultic Nitrate. The following method of preparation was found'to be more oon-venient and more economical than that described by Werner and Goslings (Ber.1903 36 2380). Twenty grams of cobalt carbonate were dissolved in the smallest possible quantity ,of dilute nitric acid and the clear solution (100 c.c.) was poured into a mixture of 250 C.C. of concentrated aqueous ammonia and 100 grams of powdered ammonium carbon-ate. Air was drawn through for two or three hours and the solu-tion was then allowed t o remain f o r twenty-four hours. The mix-ture was heated for twenty minutes in a porcelain dish on the water-bath with frequent addition of a small piece of amm,onium carbonate. The brown colour of the liquid changed t o deep red, and the mixture was allowed t6 remain until crystallisation was complete. After filtration and washing with a little water the salt D* 76 JONES CILYCERYL METHYL ETHER DINITRATE was digested with cold water to remove any ammonium carbonate still present. The air-dried product weighed 21 grams. (Found, Co= 20.54 ; NH = 29.63. (Co5z:3) NO,,H,O requires Co = 20.76 ; NH3=29.95 per oent.) The water was not given off a t looo or in a vacuum over sulphuric acid a t the ordinary temperature. [Received October 23rd 1918.