560 DUFF: COMPLEX METALLIC AMMINES. PART VIII.

LXVIII. Complex Metallic Ammines. Part VIII . The Introduction of Di- and Tri-basic Organic Acid Radicles into the Pentamminecobaltic Complex.

By JAMES COOPER DUFF. CARBONATOPENTAMMINECOBALTIC salts differ from the normal type of acidopentammine salts in that only one limb of the carbonate radicle is directly linked to cobalt in the co-ordination sphere, and it is usual to regard the other limb as attached to the complex in the form of a " bound " ion, as in formula I.

X (11.1 0-7

Other salts of this type which have been definitely characterised are the chromato-, sulphato-, sulphito-, and oxalato-salts.

The introduction of dibasic organic acid radicles, other than oxalate, in a similar form does not appear to have been described hitherto, or has not previously been found to be possible. The methods used by Jorgensen (2. anorg. Chem., 1896,11,426) for the oxalatopentamminecobaltic salts have been tested with malonic acid and the other acids of the same series, but without the desired result. It has, however, been found possible to use two methods, namely (1) the reaction between the dibasic acid and carbonato- pentamminecobaltic nitrate and (2) a modification of the method used by Briggs (T., 1919, 115, 69) for the formation of chromato- pentamminecobaltic salts (formula 11) in which use is made of the reaction between potassium chromate and aquopentamminecobaltic salts.

The two methods adopted gave two new series of complex salts which are discussed separately below ; the results obtained by using the two tribasic acids, citric and orthophosphoric, in a similar way are also mentioned.

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DUFF: COMPLEX METALLIC AMMINES. PART vm. 561

The Reaction between the Sodium Salts of the Oxalic Acid Series and Aquopentamminecobaltic Nitrate.

Briggs (Zoc. cit.) used a very dilute solution of aquopentammine- cobaltic nitrate for the reaction with potassium chromate. In the present series it was found necessary to work with a concentrated solution, and also to have a moderately high concentration of sodium salt. The resulting salts fall into three classes :

(1) Acidopentammine nitrates of the carbonato-type (formula I) are given by only two sodium salts, those of maleic and sulpho- acetic acids. The two nitrates are therefore represented by formulae I11 and I V :

(111.) (IV.)

Sodium oxalate displaced all the nitrate and gave aquopent-

(2) This class is a series of nitrates of a new complex type repre- amminecobaltic oxalate.

sented by formula V.

Y represents the dibasic acid radicle of the following acids :- malonic, maleic, malic, phthalic, citraconic, itaconic, glutaric, and adipic acids.

Following Werner's method of nomenclature, these salts may be regarded as decamminedicobaltic nitrates. In this class it is convenient to include the two salts (formula VI) derived from sodium mesotartrate and sodium methionate. In the former, which contains 4H20, Y is C2H2(OH),(CO*0),, and in the methionate Y is CH,(SO,*O),.

(3) Aquopentammine salts only were obtained from the sodium salts of succinic, tartaric, and fumaric acids. They are represented by VII, in which Y is the dibasic acid radicle.

The carboxyl groups of these three acids are much more averted from each other than those of the acids in the former two classes. This arrangement, and the comparative solubilities of the possible products, undoubtedly affect the nature of the substance obtained in each case. In this connexion it will be noticed that the three

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562 DUFF: COMPLEX METALLIC AMMINES. PART VIII.

acids, malonic, sulphoacetic, and methionic, when used in the form of their sodium salts, all behave differently, thus illustrating the modifying influence of a sulphonic group when it has replaced a carboxyl group.

It will be seen that only two new salts of the type of formula I have been obtained by this method. The salts in class (2) require special notice. They are all mauve pink, microcrystalline salts which are only moderately soluble in water. They hydrolyse slowly to aquopentammine salts. Dilute nitric acid precipitates aquopentamminecobaltic nitrate from their aqueous solutions. These properties show that they bear little, if any, resemblance to the usual types of decammine salts described by Werner (Ber., 1908, 41, 3916) in the series of decammine-p-aminodicobaltic salts and other similar polynuclear compounds. The present series thus really belongs to the pentammine type of salts, and it is proposed to name them as acidodipentamminecobaltic salts.

The constitution indicated by formula V is based on the following evidence: (a) The results of analysis, the estimation of nitrate being of most importance. (b) The absence of water indicates that the salts are not aquopentammine salts. This is also sup- ported by the conductivity results. (c ) The existence of the isomeric form with nitrate in the complex (formula VIII) is improbable,

7 0 3

/y ~03°c0 (m3) 51 \

~%*Co(NH&51\N03 “O3*Co(NE[,),Iy (Ix. 1 (VIII.)

since there is no evidence that a nitrate radicle will enter the com- plex in a warm neutral solution of what is essentially an aquo- pentammine nitrate a t the beginning. Even if this were probable, the resulting compound would be of the type IX, which does not agree with any of the salts obtained, except perhaps those from sodium mesotartrate and sodium methionate (compare formula VI). (d) The organic acids represented in this series of compounds all have a structure which brings their carboxyl groups close together in space. ( e ) The compounds are not mixtures of isomerides, since in several of the preparations the first crystals that separated and those that were subsequently deposited gave the same results on analysis. There was one exception to this, the maleato-salts; the first separation corresponded to formula V, but the crystals which separated afterwards consisted entirely of the compound represented by formula 111.

It is not clear why these various acid radicles should enter and constitute part of the co-ordination complex. Briggs (Zoc. cit.)

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DUFF: COMPLEX METALLIC AMMINES. PART VIII. 563

considered the formation of chromatopentammine salts to be due to the considerable residual affinity of the chromate radicle, which enables i t to displace the water in the aquopentammine complex. He did not start with pure aquopentammine salts, but prepared these in solution from the corresponding acidopenfarnrnine salts. The author has found that an aqueous solution of a pure aquo- pentammine salt, whilst it is suitable for making the chromato- salts, is not capable of giving pure salts of types 111 and V ; the product always contains some aquo-salt, as shown by its high conductivity in solution. On the other hand, by starting with the carbonatopentammine nitrate and preparing the aquopent- ammine nitrate in solution from this, there is no difficulty in obtaining salts which are free from aquo-salts. Possibly the presence of sodium nitrate in the solution causes a state of equilib- rium between nitratopentammine nitrate and aquopentammine nitrate. The organic radicle may then replace the nitrate in the complex and thus cause the formation of more of the nitrato-salt until the reaction with the organic sodium salt is complete. It may be mentioned, in support of such a possibility, that although the dipentammine salts are only slightly soluble they separate very slowly from solution, a good yield being obtained in some cases only after several weeks. Further evidence on this point is given in the note a t the end of the paper.

The Reaction between Acids of the Oxalic Acid Series and Carbonato- pentamminecobaltic Nitrate.

The results obtained in this into three classes :

1. The salts represented by by maleic and sulphoacetic unexpectedly into this class, cobaltic nitrate (X) .

0 -- -l/

co

type of reaction can also be divided

formuh I11 and I V are again given acids. Phthalic acid also comes as it yields phthalatopentammine-

(X. 1 (XI. 1 Mesotartaric acid also gives a salt which is apparently similar

in type but less stable in solution, the mesotartrate radicle leaving the complex as a result of hydrolysis; this explanation of the instability has been confirmed by conductivity measurements (compare the evidence previously obtained with a mesotartrato- salt, T., 1922, 121, 452).

The salts of this class resemble carbonatopentamminecobaltic

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564 DUFF: COMPLEX METALLIa AMWNES. PART Vm.

nitrate in not giving a precipitate with a solution of potassium chromate, except in the case of the mesotartrato-salt, which is slowly converted into chromatopentamminecobaltic nitrate. Oxalic acid behaves abnormally in this series, again displacing all nitrate to give the aquopentammine oxalate. The oxalato-nitrate has not been described previously; only the acid nitrate has been men- tioned (Jorgensen, 2. anorg. Chem., 1896,11, 426).

2. Dipentamminecobaltic salts represented by formula V I are again given by malonic, malic, itaconic, citraconic, and glutaric acids. The salts are distinguished from those of class 1 by giving yellow, crystalline precipitates with potassium chromate. These precipitates react as a nitrate and a chromate in accordance with formula VI.

3. Aquopentammine salts (XI) are given by succinic, fumaric, tartaric, adipic, and methionic acids. Conductivity measurements indicate, however, that succinic, tartaric, and adipic acids tend to give the dipentammine type of salt described above in class 2.

The salts of this third class are characterised by their reaction in solution with potassium chromate, which converts them into chromatopentamminecobaltic nitrate.

The results obtained in the two general methoda of preparation already described show that the dibasic acids employed differ too much in their behaviour to enable a definite rule to be stated.

The Introduction of Tribasic Acid Radicles into the Pentammine-

It has been found possible to introduce citrate and orthophosphate radicles into the pentammine complex by using the free acids and also their sodium salts.

When sodium phosphate and sodium citrate react with the specially prepared solution of aquopentammine nitrate they give salts which seem to be best represented by formulae XI1 and XIII,

cobaltic Complex.

/-O \ [ (NH3),Co ]-O-P=0,2H20 1-0'

!L -2 J-02C*CH2

(XII.) (XIII.)

and may be named respectively orthophosphatopentamminecobalt and citratopentamminecobalt. Although both contain water of crystallisation which is not removed a t loo", they are not the aquopentammine salts. Conductivity measurements place them in the same class as carbonato- and similar pentamminecobaltic salts, It is shown in the note a t the end of this paper that pure

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DUFF: COMPLEX METALLIO AMMINES. PART vm. 565

aquopentammine nitrate gives a different compound from the above in the case of the citrate which has much higher conductivity values, and even higher values when aquopentammine chloride is used as the starting material. These facts emphasise the labile nature of the nitrate radicle in the special solution used for the preparations, a point which has a bearing on the nature of the compounds formed from dibasic acids.

When orthophosphoric acid reacts with carbonatopentammine- cobaltic nitrate, the product is orthophosphatopentamminecobaltic dihydrogen phosphate (XIV).

1 I 0- \ o>P*O*C~(NH,), H,P04,2H,0 (XIV.)

where A = C,H50,. Citric acid reacts readily with the carbonatonitrate to give a

very sparingly soluble salt which has been identified as citratotri- pentamminecobaltic dihydrogen citrate (XV). The formation of this unusual polynuclear complex seems quite possible, since there will be no interference with its production if $he middle carboxyl group in citric acid is averted from the other two.

E x P E R I M E N T A L.

Salts Derived from Apuo~entammi?zewbaltic Nitrate. The following method applies to all the salts which come under

this heading. Five grams of carbonatopentamminecobaltic nitrate, 20 C.C. of

water, and 20 C.C. of 2 N-nitric acid were maintained a t 45" until effervescence ceased. The solution was neutralised with 2N- sodium hydroxide and a t once treated with the sodium salt (1 mol.) under investigation, dissolved in water (20 c.c.) a t 45". Having been maintained a t 45" for twenty minutes, the solution was filtered, and, after the addition of 8 C.C. of ethyl alcohol, left a t room tem- perature for a week or more, when the crystals which had separated were collected. The majority of the salts form microscopic, rose- pink crystals and are sparingly soluble in cold water. Cobalt; was estimated as the anhydrous sulphate, ammonia by distillation with sodium hydroxide solution, and nitrate by reduction to ammonia and subsequent distillation with alkali.

Aquopentamminewbaltic oxalate, [H,0~Co(NH3),],(C,0,),,4H,0, was obtained in minute, brick-red crystals in very good yield. It

The details are given here to save repetition.

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566 DUFF: COMPLEX METALLIC AMMINES. PART VIII.

was found to be identical with that prepared by Jorgensen (2. anorg. Chem., 1898, 17, 461) from chloropentamminecobsltic chloride (Found : Co = 18.01 ; NH, = 25.43 ; C20, = 40.38. Calc., Co = 17-86; NH, = 25.75; C,O, = 40.00 per cent.).

co-- 0, Oxakztopentumminecobaltic nitrate, [ b0 0 Co ( NH,) ,]NO,, 2H2 0, was prepared from the above oxalate as follows: 3.3 grams of aquopentamminecobaltic oxalate, dissolved in 200 C.C. of water at 90°, having been treated with barium nitrate (1.3 grams ; 1 mol.) in 20 C.C. of water, the solution was immediately cooled, filtered, and evaporated at 70" to about 25 C.C. The nitrate separated in minute, brick-red crystals. Yield = 1.8 grams. The salt is moderately soluble in cold water and gives no precipitate with calcium chloride until ammonia solution is added or the solution heated (Found : Co = 17.89 ; NH, = 25.28 ; NO, = 19.01 ; C20, = 26.78. NH, = 25.75 ; NO, = 18.79; C204 -- 26.66 per cent.).

Malon~todipentamminecobaEtic nitrate [V, with Y = CH,(CO*O),] was obtained in minute, rose-red, elongated plates. Yield = 2 grams after three weeks (Found : Co = 18.18; NH, = 25.78; NO, = 38.08; H20 = 3-05. C,H,20,,N,,Co,,H20 requires Co = 17.98; NH, = 25.91 ; NO, = 37.80 ; H,O = 2.74 per cent.). The aqueous solution gives a precipitate with barium chloride only after boiling. Potassium chromate gives a brownish-yellow precipitate of a chromate.

Sulphoacetatopentamminecobaltic nitrate (IV) was obtained in a yield of 2.2 grams (Found : Co = 16-55; NH, = 23.29; NO, = 16.99. C,H170sN,SCo,H,0 requires Go = 1629; NH, = 23-48; NO, = 17-12 per cent.).

The salt is only moderately soluble in water and the aqueous solution gives no precipitate with potassium chromate. Methionatodipentumminewbaltic nitrate methionute (VI) was ob-

tained in a yield of 3.6 grams (Found : Co = 15.50; NH, = 22.34; NO, = 16.45. C2H,4018N12S4C02 requires Co = 15-52; NN, = 22.37; NO3 = 16.32 per cent.). The aqueous solution gives with potassium chromate a brownish-yellow, crystalline precipitate which is both a nitrate and a chromate.

Mesotartratodipentamminecobaltic nitrate mesotartrate (VI) was obtained in a yield of 3.3 grams (Found : Go = 15.03; NH, = 21.55; NO3 = 15.55. C,H,,0,sN1,Co2,4H,0 requires Co = 15.12 ; NH, = 21.78; NO, = 15.89 per cent.). The salt does not lose water at 100". A warm aqueous solution gives with potassium chromate a brownish-yellow precipitate which is both a nitrate and a chromate.

C2HI5O7N6Co,2HZO requires Co = 17.87 ;

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DUFF: COMPLEX METALLIC AMMINES. PART VllI. 567

Aquopentamminecobaltic tartrate dinitrate [VII, with Y = C2H2( OH),(CO*O),] was obtained in brownish-red aggregates of small, rhombic crystals. Yield = 3.5 grams (Found ; Co = 16.14; NH, = 23.65; NO, = 33.98. C4H,,02,,N1,Co2requiresCo = 16.38; NH, = 23.61 ; NO, = 34.44 per cent.). A warm aqueous solution reacts with potassium chromate to give brown crystals of chromato- pentamminecobaltic nitrate.

Aquopentamminecobaltic succinute dinitrate (VII) was obtained in small, brownish-red, rhombic crystals. Yield = approx. 3.5 grams (Found : Co = 17.16; NH, = 24.92; NO, = 36.40. C,H,,O,,~,,Co, requires co = 17.14 ; NH, = 24.71 ; NO3 = 36.05 per cent.). The salt is only sparingly soluble in cold water but more readily on heating. A warm solution gives, with potassium chromate, cliromatopentamminecobaltic nitrate as in the case of the tartrate above.

Aquopentamminecobaltic fumarate dinitrate (VII, with 2H20, where Y = CO,*CH:CH*CO,), was obtained in a yield of 3.2 grams (Found : Co = 16.65 ; NH, = 22.99 ; NO, = 33.55 ; H,O = 2.51. C4H,,0,,N14~2,2H20 requires co = 16.33 ; NH, = 23.41 ; NO, ==

34.35 ; H20 = 4-98 per cent.). The salt is moderately soluble in water and immediately gives a precipitate of silver fumarate with silver nitrate. Potassium Chromate, added to the aqueous solution, gives crystals of chromatopentammine nitrate. The salt loses only half its water of crystallisation a t 100".

Maleatodipentumminecobaltic nitrate (V, with Y = C0,*CH:CH*C02) was obtained in a yield of 1 gram (Found : Co = 18.05; NH, = 26.10 ; NO, = 38-07. C4H,,016N,,Co2 requires co = 18.14 ; NH, = 26.15; NO, = 38.15 per cent.). The salt is only moderately soluble in warm water, and must be heated for some time with barium chloride to give a precipitate of barium maleate. Potassium chromate gives a brownish-yellow precipitate of a chromate. Maleatopentamminewbaltic nitrate (111) was obtained when the

filtrate from the previous salt, having been reheated at 60" for thirty minutes, was left for three weeks to crystallise. Yield 1.8 grams (Found : Co = 1820; NH, = 26-44; NO, = 19.20. C,H1707N6Co requires co = 18.44; NH, = 26.53; NO, = 19.37 per cent.). It is moderately soluble in water and unlike the previous salt gives no precipitate with potassium chromate.

Malatodipeittamminecobaltic nitrate [V, with Y = CO,*CH( OH)*CH,*CO,]

was obtained in a yield of 2 grams (Found : Co = 17.43; NH, = 25.14 ; NO, = 35.77. C4H,,0,,Nl,Co2 requires Co = 17.65 ; NH, = 25.44; NO, = 35.62 per cent.). Addition of potassium chromate to it warm aqueous solution causes the separation of a brown chromate.

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568 DUFF: COMPLEX METALLIC AMMMES. PART VIII.

Phthalatodipentumminecobaltic nitrate [V, with Y = C6H4(CO*O),] was obtained in a yield of 2.4 grams (Found : Co = 16.93; NH, = 26.45; NO3 = 35.81. C8H34016Nl,Co, requires CO = 16.85; NH, = 24.29 ; NO, = 35.43 per cent.). The salt is moderately soluble in warm water. It gives no reaction for phthalate until after hydrolysis with aqueous ammonia. Potassium chromate, added to the aqueous solution, gives a brownish-yellow precipitate of a chromate. Citraconatodipentamminecobaltic nitrate (V, with Y =

CO,*CMe:CH*CO,) was obtained in a yield of 1.5 grams (Found : Co = 17.83; NH, = 25.29; NO, = 37.98. C5H,01,Nl,Co, requires Co = 17.76; NH, = 25.60; The aqueous solution, treated with potassium chromate, gives a brownish-yellow pre- cipitate of a chromate.

NO, = 37.35 per cent.).

Itawnatodipentamminecobaltic nitrate [V, with Y = CO,*C(:CH,)-CH,*CO,]

was obtained in a yield of 1.3 grams (Found : Co = 17.68; NH, = 25.34 ; NO, = 37-43. c5H,016Nl,~o, requires Co = 17.76 ; NH, = 25.60; NO, = 37.35 per cent.). With potassium chromate, its aqueous solution gives an almost insoluble brownish-yellow chromate.

Gluturatodipentumminecobaltic nitrate (V,with Y = CO,*[CH,],*CO,) was obtained in a yield of 1.6 grams (Found : Co = 17-86; NH, = 25-44 ; NO, = 37.13. C,H,,016N14Co, requires Co = 17.71 ; NH,= 25-53; NO, = 37.24 per cent.). It reacts with aqueous potassium chromate to give a brownish-yellow chromate.

Adipatodipentamminecobaltic nitrate (V, with Y = CO,*[CH,],*CO,) is similar to the glutarato-salt (Found : Co = 17.18 ; NH, = 25.03 ; NO, = 36.97. C6H,8016Nl,~o, requires C O = 17.34; NH, = 25.00; NO, = 36-47 per cent.). Orthophosphutopentamminecobalt (XII) was obtained in brick-red,

flattened needles by using a solution of 6.73 grams of hydrated disodium hydrogen phosphate to which 18.75 C.C. of N-sodium hydroxide had been added to make a solution of trisodium phosphate. Yield 3 grams (Found : Co = 21.26 ; NH, = 31-03 ; PO, = 34-16. H,,0,N5PCo,2H,0 requires Co = 21.44; NH, = 30.91 ; PO, = 34.54 per cent.). It is only sparingly soluble in warm water. The solution gives a precipitate with silver nitrate but not with ferric chloride. Jorgensen ( J . pr . Chem., 1885, [ii], 31, 83) described an aquopentamminecobaltic orthophosphate to which he gave the formula

This salt loses 2H,O at 100" and the method of preparation also distinguishes it from the above salt.

The salt does not lose water at 100".

[H,O*Co (NH3) 5](OH) (PO,H) ,H,O*

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DUFF: COMPLEX METALLIC AMMINES. PART VIII. 569

Citratopentumminecohlt (XIII) was obtained in minute, pink crystals. Yield 2.8 grams from 6.1 grams of potassium citrate, used with the cobaltamrnine reagent [Found : Co = 15-89; NH, = 22-55 ; C6H,07 = 51.51. C6H,,0,N,Co,2H20 requires co = 15.97 ; NH, = 23.03; C6H50, = 51.22 per cent.). The salt is only sparingly soluble in warm water. No water of crystallisation is lost at 100". .Citrate was estimated by boiling with excess of standard sodium hydroxide, filtering, and titrating the residual sodium hydroxide with standard sulphuric acid.

Salts Derived from Carbonatopentumminecobaltic Nitrate.

The following general method was used for all the acids inves- tigated in this series. Five grams of carbonatopentammine- cobaltic nitrate, mixed with 10 C.C. of water, were treated with a solution of the acid (1 mol.) in 30 C.C. (or more if necessary) of water at 60". The filtered solution was evaporated to about 25 C.C. at 60°, and, on standing over-night, the desired salt usually separated. The salts, the majority of which again form microscopic, rose-pink crystals, are arranged below in three classes.

1. Salts related to carbonatopentamminecobaltic nitrate. Maleatopentumminecobaltic nitrate (111) and sulphoacetutopentammine- cobaltic nitrate (IV) were both again obtained (see pp. 566, 567) (Found : for the former, Co = 18-32; NH, = 26.58; NO, = 19.14; for the latter, Co = 16.40; NH, = 23-43; NO, = 17-29 per cent.). Phthalatopentumminecobaltic nitrate (X) was obtained in a yield

of 3.2 grams (Found : Co = 14.89; NH, = 21-03; NO, = 15.65; H,O = 8.70. C8Hl,07N6Co,2H,0 requires Co = 14.53; NH, = 20.93; NO, = 15-27; H20 = 8-82 per cent.). It is moderately sduble in cold water and gives no precipitate with potassium chromate. Mesotartratopentamminecobaltic nitrate,

[C2H2(OH)2(C0°0)2Co(NH,)51N0,,3H,0, was obtained in a yield of 3.2 grams (Found : Co = 14.65; NH, = 20-96; NO, = 15.48. C,Hl,0$N,Co,3H20 requires Co = 14.45; NH, = 20.83 ; NO, = 15.19 per cent.). It is moderately soluble in cold water and hydrolyses somewhat readily, being converted by potassium chromate into chromatopentamminecobaltic nitrate.

Oxalic acid gives the same result as sodium oxalate in the previous series, aquopentamrninecobaltic oxalate again being formed (Found : Co = 17.95; NH, = 25.61 ; C,O, - 40.36 per cent.). The oxalato- nitrate is described in the previous series.

2. Dipentamminecobaltic salts having the general formula VI. VOL. CXXTIT. x

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570 DUFF : COMPLEX METALLIC AMMINES. PART VIII.

Malonatopentumminewbaltic mabnate nitrate was obtained in minute, purple-red crystals (Found : Co = 17.79; NH, = 25.94; NO, = 18.86; H,O = 5.72. C6H,,01,N,,Co2,2H20 requires co = 18.09; NH, = 26.07; NO, = 19.01 ; H20 = 5.52 per cent.).

Malatodipentamminecobultic malute nitrate was obtained in a yield of 2.6 grams (Found : Co = 17.36; NH, = 25-10; NO, = 18.22. C,H,,01,N12C02 requires Co = 17.44; NK, = 25.15; NO, = 18.34 per cent.). Citraconcctodipentarnminecobaltic citracomte nitrate was obtained

in a yield of 1.2 grams (Found : Co = 16.76; NH, = 24.64; NO, = 17.97. Cl,H,,014~12C02,2H,0 requires co = 16.75 ; NH, = 24.15; NO, = 17.61 per cent.).

Itacomtodipentamminecobaltic itaconute nitrate was obtained in a yield of 1.1 grams (Found : Co = 17.53 ; NH, = 25.57 ; NO, = 18.65. ~ l o H , 8 0 1 4 ~ , 2 ~ 0 2 requires Co = 17.66; NH, = 25.45; NO, = 18.56 per cent.).

Glutaratodipentumminecobaltic gluturate nitrate was obtained in a yield of 1.9 grams (Found : Co = 17.70 ; NH, = 25.24 ; NO, = 18.41. CloH4,014N12C02 requires Co = 1755; NH, = 25.29; NO, = 18.45 per cent.).

All the salts in this section are sparingly soluble in cold water and are characterised by giving, with potassium chromate, a yellow precipitate which is both a nitrate and a chromate.

Aquopentumminecobaltic nitrate suc- cinate [XI, with Y = (CO,),(CH,),] was obtained in a yield of 3.3 grams (Found : Co = 16.92; NH, = 24.91 ; NO, = 18.04. C4H,10,N,& requires Co = 17.34; NH, = 25.00; NO, = 18-24 per cent.).

3. Aquopentammine salts.

Aquopentumminecobaltic nitrate tartrate [XI, with P =

(CO,),(CH*OH),I separated as a brownish-red crust of minute crystals. Yield 3.5 grams (Found : Co = 15.59 ; NH, = 22.73 ; NO, = 16.91. C4H2,010N,Co requires Co = 15935; NH, = 22.85; NO, = 16.66 per cent.).

Aquopentumminecobaltic nitrate fumarate, [H2O0Co(NH,)5IY(NOs),2H2O,

where Y = C02*CH:CH-C02, was obtained in a yield of 2.7 grams (Found : Co = 16.01 ; NH3 = 22.75; NO, = 16.82; H20 = 9-44. C,H,,08N,Co,2H20 requires co = 15.77 ; NH, = 22.73 ; NO, = 16.57; H20 = 9.62 per cent.).

Aquopentumminecobaltic nitrate adipate (XI, where Y = CO,*CCH,I,*CO,)

was obtained in a yield of 1.4 grams (Found : Co = 16.06; NH, = 23.21 ; NO, = 16-70. C6H2508N,& requires c o = 16.02 ; NH, = 23.10; NO, = 16.85 per cent.).

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DUFF: COMPLEX METALLIC AMMINES. PART VIII. 571

A popentumminecobaltic nitrate methionate [XI, where Y = (SO,),CH,] was obtained in brownish-red, prismatic needles (Found : Co = 14.37 ; NH, = 20.69 ; NO, = 14-98. CHl,0,,N,S2Co,H20 requires Co = 14.65; NH, = 20.43; NO, = 14.90 per cent.). All the above salts are sparingly soluble in cold water and are

converted by potassium chromate into chromatopentammine- cobaltic nitrate. Orthophosphatopentamminecobaltic dih ydrogen orthophosphte (XIV)

was obtained in small, reddish-brown, flat needles on the addition of 5 grams of the carboiiato-nitrate to a solution of 3 grams of orthophosphoric acid in 25 C.C. of water at 40". Yield 2.8 grams (Found : Co = 15.91 ; NH, = 22.42 ; PO, = 50.98 ; H20 = 9-72. [HPO,~CO(NH~)~]H~PO,,~H,O requires Co -- 15.81 ; NH, = 22.79 ; PO, = 50.94 ; H20 = 9.65 per cent.), The salt is very sparingly soluble in cold water and readily soluble in dilute alkali or mineral acid solutions. The water of crystallisation is lost over sulphuric acid at the ordinary temperature. The salt melts at the temperature of the steam-oven. Citratotripentamminecobaltic dihydrogen citrate (XV) was obtained

in minute pink crystals in almost quantitative yield when 5 grams of the carbonato-nitrate were added to a solution of 4 grams of citric acid in 40 C.C. of water a t 50". The solution was kept a t 50" until effervescence ceased, and the salt separated quickly on cooling (Found : Co = 9.52; NH, = 14.34; C,H,O, = 75-44, C42H,0,,Nl,Co, requires Co = 9.99 ; C,H,O, = 74.80 per cent.). This salt is only sparingly soluble in warm water. It has an acid reaction and dissolves in sodium bicarbonate solution, but cannot be reprecipitated by acid. The constitution was further checked by titrating the salt with standard alkali solution [O-3471 gram required 23-2 C.C. of N/lO-barium hydroxide (theory 23.53 c.c.). 0.4751 Gram required 16.5 C.C. of N/S-sodium hydroxide (theory 16.1 c.c.), using phenolphthalein as indicator].

NH, = 14.41 ;

dfolecuhr Conductivities.

Since few chemical reactions are possible with the complex salts described in this paper owing to their sparingly soluble nature, the determination of their molecular conductivities has been found useful in checking the formuh suggested for them. The electrical conductivities were measured with the identical apparatus described in Part VII of this series (T., 1922, 121, 453). All measurements were made at 25" and so far as possible all solutions were made at 25" and were freshly prepared for each stage of dilution. Owing to the moderate solubility of the salts and the need for obtaining a

x 2

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572 DUFF : COMPLEX METALLIC AMMINES. PART VIII.

solution quickly to avoid much hydrolysis, measurements have only been made for v = 512 and 1024 litres.

The results have been divided into five classes corresponding to the five classes of compounds already described. To simplify the table, the following five general formuh are referred to :-XVI, V,

[YCo(NH,),]NO, (XVI.) VI, VII, XI.

A peculiar catalytic action has been discovered during the measure- ment of the electrical conductivities. It is most marked in the case of the salts represented by formula XVI. These salts show little or no hydrolysis of the complex in dilute solution even above 25", until the solution is in contact with the platinum electrodes. Then hydrolysis a t once begins, in some cases quickly, and aquo- salts are produced. The oxalato- and chromato-nitrates give reactions for oxalate and chromate after remaining in the electro- lytic cell for one hour, whilst a solution outside the cell will show no such reaction even on the next day. The catalytic hydrolysis is apparently due to the platinum black on the electrodes and only occurs in the solution immediately surrounding these. It is not necessary to have any current passing for the effect to be produced. It may be that this unusual effect is connected with the presence of a " bound " ion in the structure of these salts (see forrnuh I, 11, 111, IV), but further investigation is necessary on this point.

Whilst the catalytic hydrolysis is most marked in the foregoing class, it is also in evidence in the others except those containing the aquo-salts. It is evident that the electrodes can hasten hydrolysis of the complex in these series of salts. It is also notice- able in a less degree in a normal type of salt like nitratopentammine- cobaltic nitrate.

Some aquo-salts show evidence of hydrolysis, particularly a suocinate and a tartrate. This may be regarded as indicating that there is a tendency in these cases for the organic acid radicle to enter the complex.

The chromato- and carbonato-nitrates have been included in the first class, as no record of their conductivity could be found in the journals. Sulphatopentamminecobaltic nitrate is also included, since Werner and Miolati (2. physihl . Chem., 1896, 21, 235) record that, for v = 512 and 1024, p = 94.64 and 101.6, respec- tively, without any observation that hydrolysis occurred. This has been found to be unusually small in this case.

In order that the results may be more readily compared, w represents the volume of solution containing one gram-atom of cobalt.

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D U F F : COMPLEX METALLIC AMMINES . PART VIII . 573

P A . * Y in formula c-*--

XVI . ~ = 5 1 2 . I

Carbonato- ...... Sulphato- ......... Chromato- ......... Oxalato .......... Maleato- ......... Sulphoacetato- ... Phthalato- ......... Mesotartrato- ...

Y in formula V . Malonato- ......... Malea t o .......... Malato- ............ Phthalato- ......... Citraconato- ...... Itaconato- ......... Glutarato- ......... Adipato- .........

136.4 86.5

125.6 136.4 145.4 128.1 97.2

212.9

233.3 234.6 255.7 270.0 245.5 243.4 256-4 254.9

Y in formula VI . Malonato- ......... 240-6 Malato- ............ 246.5 Citraconato- ...... 270.1 Itaconato- ......... 228.0 Glutarato- ......... 235-1 Methionato- ...... 273-3 Mesotartrato- ... 210.8

Y in formula XI . Succinate ......... 250.0 Tartrate ............ 269.5 Fumarate ......... 239.7 Adipate ............ 306-6 Methionate ...... 274.6

Y in formula VII . Succinate ......... 350.5 Tartrate ............ 247.9 Fumarate ......... 229.2

v = 1024 . Phosphato .

pentammine- cobalt ............ 143.9

Citratopentam- minecobalt ...

2, = 1024 . 143.4 101.4 120.3 148-5 148.7 120.6 99.6

241.4

249.2 266-2 267.8 271.6 252.0 251.2 256.5 257-1

260.7 266.2 267.9 229.8 241.3 282.7 243.0

271.6 300.4 250.3 318.4 297.5

367.0 268-9 248.7

2048 .

133.7

137.1

m.* PC.*

v=512 . 136.4 98.2

125.6 136.4 145.4 131.4 99.1

216.5

243.4 239-3 255.7 272.4 254.3 260.7 268.7 267.8

242-9 258.6 272-4 229-8 247.9 276.0 215.2

251.2 269.5 239.7 308.6 274.6

350.5 247.9 229.2

1024 .

147.4

2, = 1024 . 143.4 101.9 120-3 148.5 148.7 122.6 100.8 241.4

263.7 273.3 267.8 278-3 272.5 282.3 273.6 283.5

266.9 281.8 270.1 231.4 257.7 287-8 245.9

274.1 303.4 250.3 324.2 297.5

367.0 268.9 248.7

2048 .

137.1

138.7

v=512 . 189.3 101.7 228.0 173.2 156.4 141.3 104.7 247-4

319.5 296-9 324.1 356.1 267.5 274.9 298.5 331.1

259.5 299.2 275.3 233.8 283.5 287.1 250.1

260.7 304.1 239.7 324.1 274.6

350.5 247.9 229.2

1024 .

180.1

w = 1024 . 254.9 106.8 309-4 204.7 159-7 151.2 112.7 328.7

348-9 312.8 343.7 348.9 278.0 300-8 3254 348.9

300.4 331.1 273.3 231.4 316.1 295.6 307.6

292.7 331-8 250.3 325.2 297-5

367.0 268.9 248.7

2048 .

214-1

2 15.4

* PA represents the values for freshly-made solutions. pLg the values for the same solutions. kept for one hour in the flask. and pc the values for the same solutions after contact with ths electrodes for one hour without being disturbed in any way .

To the phosphato- and citrato-salts mentioned above have been given formuh (XI1 and XIII) which indicate that they should be non-electrolytes in solution. for the formation of ions is impossible unless hydrolysis occurs . If they are aquo.salts. the values of p should exceed 300 . It appears rwonable to suggest that

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574 DUFF: COMPLEX METALLIC AMMINES. PART VIII.

hydrolysis has occurred during solution, because the salts are very insoluble and heating to 50" was necessary to obtain the solution for v = 1024 in the case of the phosphato-salt and for v = 2048 in the case of the citrato-salt. The fact that the value of p for v = 2048 is less than that for v = 1024 supports this conclusion in the case of the phosphato-salt. After the solution has been pre- pared, and the temperature maintained at 25", hydrolysis proceeds but slowly until the platinum electrodes disturb the equilibrium ; thereafter the rate of hydrolysis is accelerated as in the cases men- tioned above. It was mentioned in the section on preparations that the phosphato-salt in solution gives a precipitate with silver nitrate; this result can be similarly explained as due to hydrolysis having occurred, whereby the phosphate radicle is removed from the complex.

The view that the behaviour of the foregoing substances in solution is due to hydrolysis is supported by the fact that the phosphato- and citrato-salts do not lose their water of crystallisation a t 100". It would seem that this water is firmly bound in the molecule in some way which enables the salt to change into an aquo-salt. It has been found that the crystals of both salts change on keeping, apparently into aquopentammine salts. The following figures were obtained four months after the values already given had been measured. For v = 2048, the phosphato-salt and the citrato-salt now gave p = 214.1 and 218, respectively, these values remaining constant. These results support the suggested formulae (XI1 and XIII) for the salts, when freshly prepared, and account for the conductivity values obtained.

The change which occurs on keeping the crystals of these salts is paralleled by the observation of Jorgensen ( J . pr. Chem., 1885, [ii], 31, 50) that crystals of aquopentamminecobaltic nitrate change at the ordinary temperature into nitratopentamminecobaltic nitrate after several months.

Addendum. Additional experimental evidence is given below to show that

the solution of aquopentamminecobaltic nitrate, prepared as described (p. 565), is different in chemical behaviour from an aqueous solution of pure aquopentamminecobaltic nitrate. If is suggested that the aquo-nitrate in solution can change into the nitratopentammine nitrate and that the presence of sodium nitrate facilitates this conversion. Measurement of the conductivities of solutions of pure aquo-nitrate support this view.

For v = 256, 512, and 1024, Werner and Miolati (2. p h p i k d . Chern.: 1896, 21, 237) give the values of p as 344.6, 362.3, and 379.4. If fresh solutions be made a t each stage, the value of p

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DUFF: COMPLEX METALLIC AMMINES. PART VIII. 575

will be found to decrease owing to the action of the electrodes. The present author thus obtained the following values :

For ZI = 256 p = 351.1 340.6 (after 1 hr.) 340.1 (after 2 hrs.) = 512 p = 374.9 360.0 > ? 359.0 Y,

= 1024 p = 396.9 380.0 3 9 378.0 9 9

The most probable explanation is that there has been conversion into nitratopentammine nitrate to a small degree. The change was found to occur slowly when the solution was not put into the Kohlrausch cell.

When trisodium phosphate was allowed to react with a solution of pure aquopentammine nitrate, minute, brick-red crystals were readily obtained which were identical with the phosphatopent- amminecobalt already described. A similar salt was obtained from aquopentamminecobaltic chloride. Whilst the salt from the aquo-nitrate gave results for molecular conductivity identical with those already recorded for phosphatopentamminecobalt, the phos- phate obtained from the aquo-chloride gave much higher figures, namely, for v = 2048, p = 206-9, and this became 211.2 after one hour in the cell, showing that this salt was at least in part aquo- pentamminecobaltic phosphate. This suggests that the aquo- nitrate changes more readily into the acido-salt than does the aquo-chloride.

Potassium citrate also was allowed to react with the aquo- pentammine nitrate and the chloride. Crystals were readily obtained which in each case were identical with those of the citrato- compound already described. The molecular conductivities were higher, however: For v = 2048, the salt from the aquo-nitrate gave p = 177.9, and 215.4 after 1 hour in the cell, whilst the salt from the aquo-chloride gave p = 244.1, and 279.4 after 1 hour in the cell. All the foregoing results therefore show that the aquo- pentamminecobaltic nitrate solution used in this work had a specially reactive nature.

It has not so far been possible to obtain a series of chlorides or other salts corresponding to the nitrates described. The possi- bility of obtaining chlorides is still under investigation.

The author's thanks are due to Miss C. M. Butcher, B.Sc., for much valuable assistance during the preliminary stages of the work.

MUNICIPAL TECHNICAL SCHOOL, BIRMINGHAM. [Received, December 21st, 1922.1

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