Indian Journal of Chemistry Vol. 23A, January 1984, pp. 67-69 Nitrosyl Derivatives of Potassium Pentacyanocobaltate H P AGARWAL' & S B SHARMA Department of Chemistry, M A College of Technology. Bhopal 462007 Received 9 May 1983; revised and accepted 15 September 1983 Three nitrosyl derivatives of potassium pentacyanocobaltate have been prepared with NO (neutral), NO + and NO - ligands respectively. The magnetic, conductance and spectral studies indicate that the first two compounds have structural formulae K3 [CQ"(NO)(CN)sJ.4H 20 and K2[Co"(NO +XCN).(OH)].2H 2 0. The third compound (with NO -ligand) is found to be similar to that reponed in the literature i.e. K)[Co"1(NO -)(CNh].2H 2 0. Chemistry of nitrosocyano complexes of cobalt is still not well understood. Nitric oxide, which is an odd electron molecule, can form coordination compounds in four different ways.': (i) by loss of the odd electron followed by the coordination of the resultant NO + group; (ii) by the gain of an electron followed by the coordination of the resultant NO - group; (iii) by coordination of the neutral NO group; and (iv) by forming a double bond with the metal atom. The cyano derivatives are among the most frequently en- countered anionic nitrosyls and since the cyanide ion has one of the largest capacities for inducing spin- pairing in transition metal complexes, the majority of complexes are either diamagnetic or have low magnetic moments. Very few reports are available regarding the preparation of potassium penta- cyanonitrosylcobaltate(II). Nast and Rohmer? reported the preparation of an yellow compound, K3[CO lll (NO -)(CN)s].2H 2 0 by the reaction of [Co(NO -XNH 3 )s]CI 2 with excess ofKCN and KOH. The detailed studies of such compounds have been carried out by Griffith, Lewis and Wilkinson:', and Zhilinskaya and coworkers using UV /visible", IR s and Xvray" techniques. NMR studies on these compounds have been done by Suvorov and coworkers 7. In the present work potassium penta- cyanocobaltate(1I) has been prepared using the Adamson's method", and it has been used for the preparation of nitrosyl derivatives of potassium pentacyanocobaltate containing NO (neutral), NO + and NO - ligands. The characterisation of the new nitrosyl derivatives has been done on the basis of elemental analyses, molar conductance, magnetic moment, UV /visible and IR spectral studies. All the chemicals used were BDH reagent of AR grade or E Merck reagents of GR grade. KCN used was Riedel reagent of extrapure quality. Preparation by bubbling carbon dioxide Potassium pentacyanocobaltate(II) was prepared using the Adamson's method", but the sequence in which the reactants were added was changed. A solution containing 8.232 g of KCN was maintained at 3 ± I DC and pure nitrogen gas was bubbled through it to get rid of dissolved oxygen; then, a solution of cobalt nitrate (5.88 g) was added dropwise. During the course of addition of cobalt nitrate to potassium cyanide, an olive green precipitate appeared which rapidly got dissolved on shaking and an olive green solution of potassium pentacyanocobaltate(II) was formed. A solution of sodium nitrite (in I:1 molar proportion) was added to the olive green solution of potassium pentacyanocobaltate(II) and a stream of pure carbon dioxide gas was passed through it for an hour. The olive green colour of potassium pentacyanocobaltate(II) slowly changed into an orange red colour indicating the formation of a new compound. The resulting compound was isolated by precipitating it with 80% ethyl alcohol. The precipitate was quickly collected on a sintered glass filter. It was dissolved in doubly distilled water and reprecipitated with 80% ethyl alcohol. It was dried in vacuo. All the above operations were carried out in oxygen free nitrogen atmosphere and at 3 ± 1°C; yield, 85% [Found: K, 28.55; Co, 14.28; C, 14.95; N, 20.97; H 2 0, 17.34. Calc. for K3 [Co 1I(N0)(CN)s].4H 20: K, 28.73; Co, 14.28; C, 14.70; N, 20.57; H 2 0, 17.65%]. This compound(A) is of red colour. Preparation by the hydroxylamine method To an ice-cooled solution of potassium pentacyanocobaltate(II) prepared as above, potassium hydroxide (1 g) was added followed by the addition of hydroxylamine hydrochloride (1.407 g). The contents were thoroughly shaken and then heated on a steam- bath for one hour. The solution was filtered and cooled. The filtrate was poured, with stirring, into 80% ethanol. The precipitate was dissolved in the minimum quantity of water and the compound was again precipitated with ethanol. The precipitate was dried over anhydrous calcium chloride in vacuo; yield > 70% [Found: K, 24.10; Co, 18.40; C, 14.58; N, 21.60; H, 0.32; H 2 0, 10.99. Calc. for K2 [Co lI (NO)(CN)iOH)].2H 2 0: K, 24.12; Co, 18.18; C, 14.80; N, 21.59; H, 0.31; H 2 0, 11.15%]. This compound (B) is yellow in colour. 67
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Indian Journal of ChemistryVol. 23A, January 1984, pp. 67-69
Nitrosyl Derivatives of PotassiumPentacyanocobaltate
H P AGARWAL' & S B SHARMA
Department of Chemistry, M A College of Technology.Bhopal 462007
Received 9 May 1983; revised and accepted 15 September 1983
Three nitrosyl derivatives of potassium pentacyanocobaltate havebeen prepared with NO (neutral), NO + and NO - ligandsrespectively. The magnetic, conductance and spectral studiesindicate that the first two compounds have structural formulaeK3 [CQ"(NO)(CN)sJ.4H 20 and K2[Co"(NO +XCN).(OH)].2H20.The third compound (with NO -ligand) is found to be similar to thatreponed in the literature i.e. K)[Co"1(NO -)(CNh].2H20.
Chemistry of nitrosocyano complexes of cobalt is stillnot well understood. Nitric oxide, which is an oddelectron molecule, can form coordination compoundsin four different ways.': (i) by loss of the odd electronfollowed by the coordination of the resultant NO +
group; (ii) by the gain of an electron followed by thecoordination of the resultant NO - group; (iii) bycoordination of the neutral NO group; and (iv) byforming a double bond with the metal atom. The cyanoderivatives are among the most frequently en-countered anionic nitrosyls and since the cyanide ionhas one of the largest capacities for inducing spin-pairing in transition metal complexes, the majority ofcomplexes are either diamagnetic or have lowmagnetic moments.
Very few reports are available regarding thepreparation of potassium penta-cyanonitrosylcobaltate(II). Nast and Rohmer?reported the preparation of an yellow compound,K3[COlll(NO -)(CN)s].2H20 by the reaction of[Co(NO -XNH3)s]CI2 with excess ofKCN and KOH.The detailed studies of such compounds have beencarried out by Griffith, Lewis and Wilkinson:', andZhilinskaya and coworkers using UV /visible", IRs andXvray" techniques. NMR studies on these compoundshave been done by Suvorov and coworkers 7.
In the present work potassium penta-cyanocobaltate(1I) has been prepared using theAdamson's method", and it has been used for thepreparation of nitrosyl derivatives of potassiumpentacyanocobaltate containing NO (neutral), NO +
and NO - ligands. The characterisation of the newnitrosyl derivatives has been done on the basis ofelemental analyses, molar conductance, magneticmoment, UV /visible and IR spectral studies.
All the chemicals used were BDH reagent of ARgrade or E Merck reagents of GR grade. KCN usedwas Riedel reagent of extrapure quality.
Preparation by bubbling carbon dioxidePotassium pentacyanocobaltate(II) was prepared
using the Adamson's method", but the sequence inwhich the reactants were added was changed. Asolution containing 8.232 g of KCN was maintained at3 ± IDC and pure nitrogen gas was bubbled through itto get rid of dissolved oxygen; then, a solution of cobaltnitrate (5.88 g) was added dropwise. During the courseof addition of cobalt nitrate to potassium cyanide, anolive green precipitate appeared which rapidly gotdissolved on shaking and an olive green solution ofpotassium pentacyanocobaltate(II) was formed. Asolution of sodium nitrite (in I:1 molar proportion)was added to the olive green solution of potassiumpentacyanocobaltate(II) and a stream of pure carbondioxide gas was passed through it for an hour. Theolive green colour of potassiumpentacyanocobaltate(II) slowly changed into anorange red colour indicating the formation of a newcompound. The resulting compound was isolated byprecipitating it with 80% ethyl alcohol. The precipitatewas quickly collected on a sintered glass filter. It wasdissolved in doubly distilled water and reprecipitatedwith 80% ethyl alcohol. It was dried in vacuo. All theabove operations were carried out in oxygen freenitrogen atmosphere and at 3± 1°C; yield, 85%[Found: K, 28.55; Co, 14.28; C, 14.95; N, 20.97; H20,17.34. Calc. for K3 [Co 1I(N0)(CN)s].4H 20: K, 28.73;Co, 14.28; C, 14.70; N, 20.57; H20, 17.65%]. Thiscompound(A) is of red colour.
Preparation by the hydroxylamine methodTo an ice-cooled solution of potassium
pentacyanocobaltate(II) prepared as above, potassiumhydroxide (1 g) was added followed by the addition ofhydroxylamine hydrochloride (1.407 g). The contentswere thoroughly shaken and then heated on a steam-bath for one hour. The solution was filtered andcooled. The filtrate was poured, with stirring, into 80%ethanol. The precipitate was dissolved in the minimumquantity of water and the compound was againprecipitated with ethanol. The precipitate was driedover anhydrous calcium chloride in vacuo; yield >70%[Found: K, 24.10; Co, 18.40; C, 14.58; N, 21.60; H,0.32; H20, 10.99. Calc. forK2 [ColI(NO)(CN)iOH)].2H20: K, 24.12; Co, 18.18;C, 14.80; N, 21.59; H, 0.31; H20, 11.15%]. Thiscompound (B) is yellow in colour.
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INDIAN J. CHEM., VOL. 23A, JANUARY 1984
Preparation by bubbling pure nitric oxide gasA stream of pure NO gas was bubbled through the
potassium pentacyanocobaltate(II) solution (preparedas above) for 45 min. After completion of the reaction,the compound was precipitated by the addition of 80(~~ethyl alcohol. The precipitate was redissolved indoubly distilled water and was reprecipitated with 80~/()ethyl acohol as above. It was subsequently dried invacuo over anhydrous calcium chloride; yield > 73°"[Found: K, 31.40; Co, 15.92; e, 15.98; N, 22.76: H20,9.88. Calc. for K3[Colll(NOXCN)s].2H20: K, 31.51;Co, 15.83; C, 16.12; N, 22.56; H20, 9.68';%',].The colourof this compound (C) is golden yellow.
The elemental analyses were carried out at NCL,Poona. The analyses of metal constituents and of waterof crystallization were carried out using atomicemission spectral technique. Electrolytic conductancemeasurements were carried out at 24' C in watersolution at infinite dilution. The Uv.visibleabsorption spectra were recorded in aqueous solutionon a Shimadzu spectrophotometer-240. The IRspectra were scanned in nujol on a Perkin Elmer IRspectrophotometer-599. Magnetic measurements weremade on solid samples at room temperature (24GC) forall the complexes using Gouy's method. For somesamples the DTA was got done from BARe, Bombay.
Compound AThis compound shows two absorption bands at 202
and 290 nm corresponding to tt= t:" transitions of CNand NO groups respectively?'! ''. The observed value ofNO band is somewhat lower than the usual value(302 nm), which may be due to coordination of NOligand.
In the IR spectrum of this compound, the v(OH) andb(HOH) bands appear in the ranges 3200-3700cm I
and 1575-1640 cm-I respectively showing the presenceof water of crystallization II. The v(CN) mode isobserved at 2125cm -I with a shoulder at 2200 em I.
The band at 415cm -I corresponds to Co-CNbending 12. The bands at 610 and 725 cm ::' correspondto Co-C and Co-N stretching respectively. The bandfor v(NO) is observed at 1150 cm -I which may beeither due to NO - or NO (neutral) ligand 13.
The magnetic moment of this compound, afterapplying diamagnetic corrections from Pascal'sconstants, is found to be 3.01 B.M. This indicates thatthe compound has two unpaired electrons ~-one dueto neutral NO and the other due to Co(lI), its analyticaland molar conductance data (408.4ohm -I cm2 mol -I) are in agreement with thestructural formula K3 [Coll(NO)(CN)s].4H20.
It may be pointed out that a compound of similarmolecular formula i.e. K3[CollXNO -XCN)sJ.2H20has been prepared by Nast and Rohmer ' and studied
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by Griffith, Lewis and Wilkinson". This compound isyellow in colour and is quite different from thepresently prepared red compound. It will beworthwhile to mention that newly prepared compoundis stable under an inert atmosphere and at lowtemperatures ( ~ O°C).
Differential thermal analysis study show that thereaction is endothermic in the temperature range 26-99C and the compound gives out water ofcrystallization. On subsequent heating above 300eC,the compound is decomposed giving first NO at 392Cand then cyanogen at 417"C. An exothermic peak isobtained at 417 C, and the compound completelydecomposes in 58 min on heating up to 484'C. At thistemperature the final products formed are oxides ofcobalt and potassium.
Compound BThis compound shows two absorption bands at 202
and 258 nm corresponding to n -rtt" transitions. Thefirst transition may be assigned to CN absorption andthe second to NO absorption. The observed value forNO band is shifted towards lower value (higherenergy) and it may be due to the presence of N == 0+moiety.
The IR spectrum of this compound clearly showsv(OH) and b(HOH) modes in the regions 3200-3700and 1600-1640 em I respectively, indicating thepresence of water of crystallization II. The v(CN) bandappears at 2140 em I. The bands corresponding toCo-CN bending, Co-C stretching and Co-N stretchingare observed at 420, 520 and 730 cm :" respectively. Asharp and strong peak at 1770 cm -I indicates thepresence of NO + moiety 13.The diamagnetic characterof the compound as indicated by negative value ofmagnetic susceptibility also supports the presence ofNO' ligand. The elemental analyses and theconductance measurements(290.22 ohms -I em? moll) support the assignedformula, Kz[Coll(NO+)(CN)iOH)].2H20.
Compound CLike compound A, this compound also gives two
bands at 201 and 300 nm corresponding to rr-->rr*transitions of eN and NO groups respectively9.1 o. TheI R spectrum of this compound exhibits the v(OH) and('j(HOH) bands in the ranges 3200-3700 and 1500-1700 cm'' respectively showing the presence of waterof crystallization. The v(CN) mode is obtained at2135 cm: I with a shoulder at 2200 cm I. The Co-CNbending, Co-C stretching and Co-N stretching bandsare observed at 420, 570 and 730cm -I respectively.The band for \{NO) is obtained at 1140 cm -I whichmay be assigned to NO or NO (neutral) ligand.
The magnetic susceptibility measurements of thiscompound indicate that it is a diamagnetic compound,
so it should contain NO - moiety. The analytical datasupport the structural formulaK3[COlll(NO -XCN)s].2H20. This compound is ofM3A type ail corroborated by the observed molarconductance value (376.00 ohms ·-1 em? mol :"). Thechemical composition of this compound is similar tothat of compound A, but in this compound anionic(NO -) group is present.
It may be pointed out that a similar compound hasbeen prepared by Nast and Rohmer? by a differentmethod, and the earlier spectral analyses given byGriffith, Lewis and Wilkinson, although reportedunder the name of this compound, were actually I 4 forK2[HCo(CN)s(NO)].2H 20. The detailed spectralstudies of K3[Coll~NO -XCN)s].2H20 have beendone recently by Zhilinskaya and coworkers" ·-6 andby Suvorov and coworkers 7.
The authors thank Dr B.L. Mehrotra, Principal, fornecessary facilities and the CSIR, New Delhi, for theaward of a Junior Research fellowship to one of them(S.B.S.). Thanks are also due to Dr R.N. Dubey,Physics Department, for assisting in magneticsusceptibility measurements.
149; Z anorg Chern. 249(1942) 321.2 Nast R & Rohmer M, Z anorg a/lg Chern. 285 (1956) 27L3 Griffith W P, Lewis J & Wilkinson G. J chern Soc, (1961) 775.4 Zhilinskaya V V, Kozlov G A, Nazarenko Yu P & Yatsimirskii
