Indian Journal of ChemistryVol. ::!IA. November 19S::!.pp. 1049-10)::!

Studies on Bonding Modes of Cyanate & Thiocyanate Ionsin Bimetallic Complexes

S B SHARMA· & T N OJHADepartment of Chemistry. M.L.K. College. Balrampur 271 201

Received 29 April 1982; rerised and accepted 4 October 1982

Reactions of Ml4(NCOh (M = Mn, Fe. Co. Ni or Cu; l = pyridine) with Hg(SCNh or Agz{SCN)2 in 1:I molar ratio yieldcomplexes of the type l2M(NCOhHg(SCNh or l2M(NCOhAg2(SCN)2' These complexes are non-conducting in DMF anddecompose without melting. Magnetic moment values and electronic spectral data suggest an octahedral stereochemistryaround M2 + ion. Infrared spectral studies reveal the presence of only bridged. thiocyanatet - NCS -) and cyanatet - NCO -)groups, between M and Hg or Ag, indicating a polymeric structure for all the complexes. The proposed structures aresupported by Pearson's HSAB theory.

Studies on the bonding modes of arnbidentatepseudohalide ions like NCS -, NCSe - and NCO-'have evoked much interest! -3. The NCS and NCSeions can coordinate in three ways, viz., M-NCX, M-NCX-M' or M-XCN (X =S or Se)4. The cyanate ionpossesses two potential donor sites, Nand 0 atoms.Until recently, the only established bonding mode forthis ion was through N-end, thus giving rise to either

N-terminal (M-NCO) or N-bridged (~ NCO)

type structures.':". Recently, Hendrickson et al,'carried out a single crystal X-ray analysis of a'dinuclear Ni(IJ) complex di-u-cyanato-bis (2, 2', 2"-triaminotriethylarninejdinickel, and confirmed thatthe cyanate ion formed and end-to-end bridge of thetype,

<, /NCO -:N' N,' .....

,/ <, oeN'/ <,

Kohout et al.8 investigated some Cu(II) cyanatecomplexes and demonstrated that the N-end ofcyanate is coordinated to one Cu atom whereas the freeO-end forms an axial bond with another Cu atom,leading to Cu-NCO-Cu type bridging". These findingshave created further interest in the bonding behaviourof cyanate ion. In the present paper we report thesynthesis and structural elucidation of certainbimetallic dicyanatodithiocyanate complexes withpyridine.

Materials and MethodsMLiNCOh (M = Mn, Fe, Co, Ni, Cu) were

prepared with a slight modification of the reportedmethod". Metal nitrate (I mmo\) {manganese chloridefor Mn(IO and ferrous ammonium sulphate for Fe(IO}was stirred in ice-cooled demineralised water with2 mmol of potassium cyanate. To the resulting clear

solution, an ethanolic solution of 5 mmol of pyridine(L) was added and the precipitate formed in each caseWas worked up as described".

LzM(NCOhHg(SCN)l or L2M(NCO)2-Ag2(SCN)z-- These were prepared by stirringan acetone solution of ML4(NCO)2 (I mmol)with Hg(SCNh or Agz{SCN)z (slightly less thanI mmol) for about 30 hr. In each case, a solid complexwas precipitated which was filtered, washed withacetone and dry ether followed by drying in vacuo oversilica gel. Reactions of ML2(NCOh and Hg(SCN)2 orAgz(SCN)2 gave similar complexes. The complexeswere analysed for carbon, sulphur, nitrogen and metalby standard methods.

All the complexes decompose without melting andare insoluble in common organic solvents except DMFand DMSO. Carbon and nitrogen analyses were doneat RSIC, CDRI, Lucknow. All the complexes gavesatisfactory analytical results (Table 1).

IR spectra (mull) in the region 4000-400 cm -1 wererecorded on a Perkin-Elmer 621 spectrophotometer.Far IR spectra were recorded (650-50 em -1) aspolyethylene discs on a polytec FIR-30 spectro-photometer. Electronic spectra were recorded in thesolid state in mull on a Carl-Zeiss DMR-21spectrophotometer in the range 2500-200 nrn. Molarconductance values were measured in DMF using aPhilips-PR 9500 conductivity bridge. Magneticsusceptibilities were measured at room temperature ona Gouy balance which was precalibrated againstHg[Co(NCS)4]. Pascal's constants were used fordiamagnetic corrections.

Results and DiscussionAnalytical data for the complexes conform to the

general formulae L2M(NCOhHg(SCNh andL2M(NCOhAgiSCN)2' Molar conductances of the

1049

INDIAN J. CHEM., VOL. 21A, NOVEMBER 1982

.------.~--~--.

Table I-Analytical Data of the Complexes

Complex Colour Found (Calc.), '!~(Dec. temp.) --_.

'C N C S Hg/Ag M

L2Mn(NCOhHg(SCNh White 13.69 27.41 10.45 32.68 8.95(187) (13.18) (2761) (10.31) (31.58) (8.29)

L2Fe(NCOhHg(SCNh Red 13.67 2736 10.43 32.63 9.08(211) (13.22) (27.03) (10.33) (31.30) (9.02)

LPJ(NCOhHg(SCN)2 Pink 13.60 27.18 10.38 32.47 9.50(233) (13.08) (2704) (10.23) (30.99) (9.54)

L2Ni(NCOhHg(SCNh Blue 13.60 27.23 10.39 32.58 9.51(213) (12.95) (2719) (10.36) (3U9) (937)

L2Cu(NCOhHg(SCN)2 Blue 13.50 2701 10.30 32.23 10.20(157) (12.91) (2711) (10.36) (31.95) (10.10)

L2Mn(NCOhAg2(SCN)2 White 13.36 26.70 10.19 34.30 8.70(196) (13.02) (26.75) (1020) (3414) (8.50)

L2Fe(Ncn),Ag2(SCNh Red 13.34 26.67 10.18 34.25 8.72(182) (12.83) (2667) (10.09) (34.22) (878)

L2Co(NCO)2Ag2(SCNh Pink 13.2X 26.54 10.13 34.09 8.68(195) (12.94) (26.61) (10.21) (34.20) (852)

L2Ni(NCO}zAg2(SCNh Blue 13.28 26.55 10.14 34.09 8.68(214) (13.~ I) (26.41) ( 10.18) (34.14) (877)

L2Cu(NCOhAg2(SCNh Blue 13.18 26.35 1000 33.84 8.62(153) ( 13.11) (2638) (10.16) (33.62) (8.50)

L =Pyridine, M = Mn, Fe, Co. Ni or Cu- -------- .- - --- ---

complexes in DMF at MIIOOO dilution were found tobe in the range 35-55 ohm I em/mol I which areindicative of non-conducting nature of the complexes.

Electronic spectra of cobalt complexes show thepresence of three bands in the ranges 20AOO-20,200;18,500-17,800; and 9,300-8,300 em I which may beassigned to the transitions ' TI g --> '" TI g(P) (1'3),4 TI g -",

4A2iF) (1'2) and -r., --> "'T2g(F) (1'1). respectively.Spectral parameters Dq, B' and Ii, calculated usingTanabe and Sugano matrices", appear in the ranges950-985, 859-867 and 0.88-0.89, respectively. Theelectronic spectral band positions, values of spectralparameters, pink colour and magnetic moment valuesof the complexes in the range 4.98-5.08 B.M., suggestan octahedral ligand field around Co(ll) in itscomplexes II.

The Ni(II) complexes exhibit absorption bands inthe regions 25,000-27.100; 16,700-13,900; and10.100-8,300 em I corresponding to the transitions3A

zg-->JTIg(P)(','3), 3A2g-->.1TliF)(;'2) and .1A2g-->

.1 T2iF) (1'1)' respectively. Spectral parameters Dq, B'and {i were calculated; these appear in the ranges 832-1044 ern 1,829-926 em I and 0.80-0.88, respectively.Colours of the complexes, electronic spectral bandpositions, spectral parameters and magnetic momentvalues in the range 3.12-3.21 B.M. indicate octahedralstereochemistry around Ni(II)II.

The magnetic moments of Cu(II) complexes (1.88-\. 92 B.M.) are much higher as compared to the spin-only value. This may be due to strong Jahn-Teller

1050

distortion operative in Cu(ll) complexes. The presentCu(II) complexes exhibit a broad band in the regionISAOO-15,800 ern I; but, no splitting is evident. Thus,it seems that the symmetry approximates to D4h ratherthan D 3 and a tetragonally distorted octahedral ligandfield is predicted around Cu(II).

For M n(ll) complexes, observed magnetic momentvalues are very close to spin-only value!". Absorptionmaxima are too poorly resolved to allow anysatisfactory interpretation.

Fe(II) complexes show magnetic moment valuessomewhat higher than those expected for a cf' system;which may be due to the presence of some Fe(III). Theelectronic spectrum of the complex.L2Fe(NCOhHg(SCNh. shows a broad. poorlydefined band which splits into two components, onearound 9,700 ern I and the other around11.200 em I. These components are believed torepresent transitions to the 5Eg state e T2g --> 5EJwhose degeneracy has been lifted by the Jahn-Tellereffect. An intense charge-transfer band is seen around27,600 ern I.

All the complexes show IR bands for CN stretching,CS stretching and NCS bending modes in the regions2,158-2,140, 800-780 and 467-443 cm -I, respectively,indicating the presence of only bridged thio-cyanatesl,13. vM-NCS, vHg-SCN or vAg-SCN andother low frequency vibrational modes are recorded inTable 2. All these bands appear in the ranges specifiedfor bridged NCS groups in bimetallic tetrathiocyanate

SHARMA & OJHA: BIMETALLIC COMPLEXES OF NCO & SCN

Table 2 -- Important Far Infrared Spectral Assignments (400-50 cm .1)

Complexes vM-LjvM-NCS vM'-SCN "N-M-N vL-M-L

L,Mn(NCO}zHg(SCN), 264sh.234sh 221m 178s 166sL,Fe(NCO),Hg(SCN), 266m 233bL,Co(NCO),Hg(SCN), 260m. 238m 222s, 212wL1Ni(NCO),Hg(SCN), 278sh. 252w 225sh, 220sL1Cu(NCOhHg(SCNh 284m. 268m 224s, 218sL1Mn(NCO),Ag1(SCN), 267m 226bL,l"e(NCO),Agz(SCN), 27Jw 228bL,Co(NCOhAgz(SCN}z 272w. 235s 228mL,Ni(NCO),Agz(SCN), 276h. NOsh 232mL,Cu(NCOhAgz(SCN), 2565 236b

M=Mn, Fe. Co. Ni or Cu: M'=Hg or Ag

complexes '. Further, all these complexes exhibit astrong to medium intensity band in the region 2,260-2,240 em I which is often split into two components .:No band assignable to CO stretch for N-terminal or N-bridged cyanates could be noticed. Further, the aboveband occurs at a much higher position than thatexpected for N-bridged cyanates 7 (below 2.200 em I).

Shifts in pyridine ring vibrations show features ofcoordination through ring nitrogen. M(l1) can acquirean octahedral geometry coordinating through twopyridine molecules, only when the molecule acquires apolymeric structure, as there is no infrared evidence toindicate coordination of solvent. Spectral bands due tocyanate groups are consistent with the presence ofbridging cyanate coordinating via both nitrogen andoxygen ends" ( - NCO -). A close comparison with theIR data reported by Duggan 7 indicates that thecyanates are end-to-end bridged forming a polymericstructure {Ia and Ib for Hg( II) complexes & lla and II bfor Ag(I) complexes}.

The possibility of the formation of structure like M- ONC - Hg + • as a result of isomerization of cyanateion, is completely ruled out due to the absence of NOstretching bands and the presence of CO stretchingbands around 1.220 em 1 in the range of bridgedcyanates (- NCO -) 7 The splitting of the eN

Py: SCN \ NCO SCN"/. '-..../' <, / :: M /Hg :l' SCN/ \ <,NCO "SCW·.:-

Py(M'Mn,Fe,Co,Ni or Cu)

I,I

Py NCO-A'l,\ 1//

SCN - M -NCS

OCN/ \ \Ag_

1 Py

(M=Mn,F~,Co,Nior Cu)

II,

176s180sh156s

168m167wl77s

15351565155m

170sh176s168w

stretching band is attributed to a slight lowering of theperfect Oh symmetry.

M - Land M - NCS stretching vibrations could notbe distinguished clearly due to overlapping of thebands. NCO bending vibrations also overlap withthe pyridine ring vibrations which appear above400 em I. In the overall three dimensional geometryof the complexes, the Hg-SCN or Ag-SCN bonds arebent 15.

The various bonding modes of NCO and NCSmoieties shown here are also in agreement with thePearson's HSAB principle 1 0 which predicts that theharder end of the pseudohalide ion should be linked tothe harder metal (M) and the softer end to the softermetal (Hg or Ag). Thus the softer S-end of NCS willcoordinate to Hgt l I) or Ag(l) and the harder N-end tothe metal M(II). The hard base. pyridine, willcoordinate to M(l1) rather than to Hg(lI) or Ag(l).

We made a rough estimate of the softness values ofthe nitrogen and oxygen ends of cyanate ion byK loprnans method I - using partial values of chargesgiven by Wagner!" on each atom of cyanate ion andreached the conclusion tha t the O-end is softer than theN-end of NCO ion. Thus. we suggest that thesepolymers contain Hg(II) or Ag( I) coordinated to O-endofNCO and S-end of thiocyanate ions. This additional

Py

/SCN I NCO SCN"/. "'-/' "--/ :---..; M Hg :" /' <, '/" V'"I'OCN 1 'NCS OCN-:

IPy

(M'Mn,F~,Co,NI or Cu)

l b Ag/

Py Nc6\ 1/

SCN- M-NCS

OCN/ I "-I

/' Ag Py(M'Mn,Fe,Co,Ni orCu)

lib

1051

INDIAN J. CHEM .. VOL. 21A. NOVEMBER 1982

evidence corroborates the probable structures I and II.Two isomeric structures are possible (Ia, Ib and IIa,lIb). but the available evidences do not indicate clearlywhether only one of them is formed or a mixture of thetwo isomers is formed. A final confirmation can bemade only on the basis of single crystal X-ray analysiswhich we could not carry out.

AcknowledgementWe express our sincere thanks to Prof. J.L.

Burmeister, Chairman, Department of Chemistry,University of Delware. Newark, USA, for suggestingstructure and correcting the manuscript; to Dr. P.P.Singh, Head of the Department of Chemistry, M.L.K.College, Balrampur for providing research facilities; tothe authorities of the R:;IC, lIT, Madras forinstrumentation; and to CSIR, New Delhi for financialassistance.

ReferencesI Burmeister J L. The chemistry and biochemistry ofthiocyanic acid

and its derivatives. edited by A A Newman (Academic Press.

.'

1052

London) 1975.68; Norbury A H. Adrancesin lnorg chemRadiochem, 17 (1975) 23l.

2 Balahura RJ & Lewis N A, Coord chem Rev, 20(1976) 109; BaileyR A. Kozak S L, Michelsen T W & Mills W N. Coord chemReI', 6 (1971) 407.

3 Singh P P. Coord chem ReI'. 32 (1980) 33.4 Mitchel PC H & Williams R J P. J chem Soc. (1960) 1912.5 Norbury A H & Sinha A I p. J chem SOl. (\968) 1598.6 Nelson J & Nelson S M. J chem Soc\A). (1969) 1597.7 Duggan D M & Hendrickson D N,/norg Chern, 13(1974) 2056.8 Kohout J, Hvastijova M, Gazo J & Nadrornik M. Inorg chim

Acta. 37 (1979) 225.9 Tanabe Y & Sugano S. J phys Soc. Japan. 9 (1954) 753.

10 Cotton FA. Goodgame D M L. Goodgame M & Sacco A. J Amchem Soc. 83 (1961) 4157.

II Lever A B P. Inorganic electronic spectroscopy (Elsevier. NewYork) 1968. 320. 333. 355.

12 Forster D & Goodgame D M L. J chem Soc. (\ 965) 268; lnorgChern. 4 (1965) 823.

13 Nelson S M & Shepherd T M. J inorg IIUel Chem, 27 (1965) 2123.14 Makhija R. Pazdernik L & Rivest R. C{[IIJ Chern, 51 (1973) 438.

~071.15 Lindqvist I. Acta Crystallogr, 10 (1957) 29.16 Pearson R G. J chem Educ. 45 (1968) 581.643.17 Klopman G. J Am chem Soc. 90 (1968) 223.18 Wagner E L, J chem Phys, 43 (1965) 2728 .