RELATIONSHIP BETWEEN THE PIXY SICAL PROPERTIES ETC. 5 1 VII.-Relationship between the Physical Properties of Isomeric Cobaltammines and the Electm-valencies of their Co-ordination Complexes. By RAJENDRA LAL DE. ACCORDING to Richards ( J . Anier. Chem. Soc. 1914 36 2417), elements are compressible substances and he has shown from indirect evidence that chemical affinity is responsible f o r the con-traction in volume which occurs when two different elements form a compound. Thus according to him chemical affinity instead of merely holding the atoms together exerts pressure in their inter-action. The primary object in undertaking the work described below was to study the chemical affinity (valency) in connexion with this attractive force. The above-mentioned attractive force is directly connected with molecular volume (that is density) and attempts have been made to study the influence of these forces by determining the densities of a few isomerides of a complex cobalt compound.(i) Triamminecobalt nitrite [(H3N)3C~(N02)3]. The isomerides chosen were : (ii) Dinitrotetra-amminecobalti-tetranitrodiamminecobaltiate, (iii) Hexa-am mine cob a1 t i-hexani t r ocob a1 t ia t e , For the sake of comparison double the molecular formulae of the isomeride (i) will be taken. It will then be observed that the number of NH3-groups NO,-groups and cobalt atoms is the same in the case of all the isomerides. Moreover the number of auxiliary valencies in them is the same but on account of a difference in the number of NH3- and NO,-groups around the respective cobalt atoms there is a variation in the number of electro-valencies.I n the isomeride (i) there is an absence of electro-valency in (ii) there is only one electro-valency whilst in (iii) there are three. Now if chemical affinity (valency) exerts an attraction the densities of the isomerides according to the hypo-thesis of compressible atoms ought to increase gradually as we pass from (i) to- (iii) for the number of electro-valencies has increased in the isomerides in the same order. It will be seen later that such a gradual increase in density has been found t o occur. I n preparing these isomerides it was noticed that their solu-0 52 DE RELATIONSHIP BETWEEN THE PHYSICAL bilities differed appreciably from one another. It was therefore desirable to make quantitative measurements of this property in order to find a relation between electro-valency and solubility.The results of these measurements go t o show that the solubility of the isomeride decreases as the number of its electro-valencies increases. E X P E R I M E N T A L. Triammi?aecobalt Nitrite.-This was prepared according to Jorgensen's method (Zeitsch. anorg. Chem. 1896 13 172). The salt obtained was a crystalline brownish-yellow substance. Its constitution was determined by Werner who has shown from con-ductivity measurements that i t is non-ionisable (Zeitsch. physiknl. Chenz. 1893 12 35; 1896 21 227). To confirm Werner's state-ment an aqueous solution of the salt was added to a ferric hydr-oxide sol; no precipitate could be detected; the salt was therefore a non-electrolyte.The cobalt in the compound was estimated as sulphate and the total nitrogen was determined by Dumas's method. As regards nitritic nitrogen although Jorgensen (Zoc. cit.) has stated that he was able to estimate it by simple titration with potassium per-manganate it was found impossible to do so mainly owing to its sparing solubility. The salt was therefore heated with potassium hydroxide to expel ammonia the cobalt precipitated as oxide and the nitro-groups converted into nitrite. The solution was then filtered and the filtrate made up to a definite volume. The amount of nitrite was determined by titration with permanganate and also calculated from the volume of nitrogen evolved when the solution was treated with carbamide in a nitrometer.(Found: Co=23'67; N=33*22; NO,=18.12. Calc. Co=23'76; N=33*86; NO,= 18.55 per cent.) Dinitrotetra-amminecobalti-tetra,Litro~~amminecoba~tiate. - This compound exists in two stereoisomeric forms. One was prepared by double decomposition of potassium tetranitrodiamminecobaltiate, K[Co(NO,),(NH,),] with flavocobalt nitrite (1 2-dinitritotetra-amminecobalt nitrate [Co(NH,),(NO,),]NO, and the other with croceocobalt chloride (1 6-dinitritotetra-amminecobalt chloride, [Co(NH,),(NO,),]Cl according to the equation given below (Jorgensen Zoc. cit.) : %here X= acid radicle. (Found for 1 2-derivative co1=23'51, N .=33*19 NO = 18.82 j f o r 1 6-derivative Co =23-62 N = 33-52 PROPERTIES OF ISOMERIC COBALTAMMINES ETC. 53 NO,= 18-48.Calc. Co= 23-76 ; N = 33-86 ; NO,= 18.55 per cent.) Hexa-amminecobalti-hexanitrocoba1tiate.-This compound was prepared by double ilecomposition of luteocobalt chloride (hexa-amminecobaltic chloride [Co(NH,),]Cl with sodium cobalti-nitrite according to the equation given below (Jorgensen Zoc. c i t . ) : PWNH,),IC~~ + ~ ~ ~ c ~ ( N o ) I = [ co( N H3),]I1' - [ c 0 (N O2),]II1 -t 3 Na C1 . (Found Co = 23.54 ; N = 32.98 ; NO = 18-02. N=33*86; NO,=18.55 per cent.) Calc. Co= 23-76 ; D e t er nzinn t io 1% of D ensi t y . The densities of the isomerides were determined a t 32-33O, compared with water a t 4O and with xylene as a filling liquid in the same way as was done in the case of the hyponitrites (T. 1916, 109 128). In the following table are given the densities and molecular volumes of the isomerides : Name of isomeride.Tria.mminecobalt nitrite . . . . . . . . 1 2-Dinitrotetramminecobalti-tetranitrodiamminecobaltiate 1 6-Dinitrotetramminecobalti-tetranitrodiamminecobalt iate Hexamminecobaltihexanitroco -baltiate Mol. V O ~ . = Mean MoI. Wt. Density. density Density { 2.0006 248.0 { 2.0323 I 3.0324 344.3 {%I%!!/ 2.0291 241.6 I i:::;? 2.0626 310.5 2-0001 j 2.0348 2.0300 I 2-0652 [ For the sake of comparison twice the usual molecular formula has been employed in the case of triamminecobalt nitrite. The densities of 1 2-dinitrotetra-ammiiiecobalti-tetranitrodiammi~~e-cobaltiate and its stereoisomeride are practically equal but the table shows that the density increases as we pass froin triammine-cobalt nitrite t o hexa-amminecobalti-hexanitrocobaltiate.Further, from the data of molecular volumes i t will be noticed that the difference between the molecular volume of triamminecobalt nitrite and that of dinitrotetra-amminecobalti-tetranitrodiamminecobaltiate is about 4 which is also practically the difference f o r hexa-ammine-cobalti-hexanitrocobaltiate and dinitrotetra-amminecobalti-tetra-nitrodiamininecobaltiate. The difference in the number of electro-valencies of triamminp 54 DE RELATIONSHIP BETWEEN THE PHYSICAL cobalt nitrite and dinitrotetra-amminecobalti-tetranitrodiammine-cobaltiate is 1 whilst in the case of hexa-amminecobalti-hexanitro-cobaltiate and the latter compound it is 2. If the contraction of molecular volume had been proportional to the number of electro-valencies in the isomeride the difference between the molecular volume of hexa-amminecobalti-hexanitrocobaltiate and that of dinitrotetra-amminecobalti-tetranitrodiamminecobaltiate would have been doubled.The decrease in molecular volume however, along with the increase in the number of electro-valencies seems t o indicate that chemical affinity (valency) exerts an attaraction. From compressibility measurements Richards (Zoc. cit.) has calculated the amount of contraction which an alkali metal under-goes during the formation of its chloride. The contractions are recorded below in order to compare them with those of the above isomerides. Hypothetical contraction of metal Alkali metal. on combination.Lithium ........................... 5.1 Sodium ............................ 9.0 Potassium ......................... 20.6 Rubidium .......................... 24.3 Csesium ............................. 41.1 It will be noticed that the contraction for lithium is small and is comparable with the small contractions found in the isomerides. Solubility Determirta,tions. The isomerides were only sparingly soluble in water so that the determination of their solubilities from the amount of cobalt dis-solved in the solutions could not be trusted. The amount of the compound dissolved was therefore determined from the estimation of ammonia combined with cobalt atoms in the compound. The substance was shaken with a small quantity of water f o r some time until a saturated solution was obtained.The solution was then filtered and to a definite amount of the filtrate sodium hydr-oxide was added. Ammonia which was then distilled off was absorbed in sulphuric acid of known strength and was estimated by nesslerisation and also by titration of the acid in the receiver when possible. Water free from ammonia was always used in these experiments . The solubilities of the isomerides were determined a t the ordinary temperature. The data are given below PROPERTIES OF ISOMERIC COBALTAMMINES ETC. 55 Ammonium chloride found in 1 litre of the solution. Name of isomeride. Grams. Mean value. [ 1-8821 \ Triamminecobalt nitrate ... ... . . . 11.84861 1 2-Dinitrotetra-amminecobalti- f 2.3806 1- 2.3848 tetranitrodiamminecobaltiate..\ 2.38901 1 6-Dinitrotetra-amminecobalti- 0.2564) 0.2572 tetranitrodiamminecobaltiate.. { 0.25791 Hexa-amminecobaltihexanitroco-baltiate ...... ... ... .. ......... ...... {:} 0*0139 Weight of isomerides dissolved in 1 litre. Grams. 2-8820 3-6800 0.3977 0.0215 The ratio between the solubilities of triamminecobalt nitrite and 1 6-dinitrotetra-am1ninecobalti-tetranitrodiamminecobaltiate is 7.3:1 and that between the solubilities of the latter compound and hexa-amminecobalti-hexanitrocobaltiate is 18.5 1. The ratio between the solubilities of 1 2-dinitrotetra-amminocobalti-tetra-nitrodiamminecobaltiate and its stereoisomeride is 9.3 1. This great difference in the solubilities of the stereoisomerides is prob-ably due to the difference in their spacial configurations.1 N On N On Flavocobalt radicle. Croceocobalt radicle. (1 2-Dinitrotetra-ammine- (1 6-Dinitrotetra-cobalt radicle.) amminecobalt radicle.) It will be observed that in the flavocobalt radicle the two nitro-groups are in contiguous positions whilst in the croceocobalt radicle they are widely apart from each other. In organic sub-stances acid radicles in contiguous positions have been found to impart greater reactivity to the compound. The high solubility of the isomeride obtained f rom flavocobalt nitrate in comparison with that of its isomeride obtained from croceocobalt chloride may therefore be due t o the contiguous positions of the two nitro-groups in the flavocobalt radicle of the former compound. Exceptc ing the abnormal behaviour of the isomeride obtained from flavo-cobalt nitrate the solubilities of the isomerides will be observed t o decrease as the number of electro-valencies in them increases. For studying the change which is produced by valency alone, these isomerides are very suitable as the physical properties possessed by elements and groups of elements in them remain th 56 CHAPMAN SPTNACENE A NEW HYDROCARBON same. in this line employing isomerides of other complex compounds. The author therefore wishes to cont,inue his investigations I n conclusion my thanks are due t o Prof. P. C. R2y for the encouragement I received from him during the above investigation. CHEMICAL LABORATORY, PRESIDENUY COLLEGE, CALCUTTA. [Received December 21d 1916.