Studies on di-pthiocyanato dithiocyanato nickel(I1) diisothiocyanato tin(IV) or titanium(IV) and related complexes

P. P. SINGH A N D S. B. SHARMA Clrer~~isrry Depnr.trrier~t. Mcrl~crr.(~t~i La1 K~rrrccrr.i College, Bcrlr~crniprrr (U.P.), It~ciici

Received July 31, 1975

P. P. SINGH and S. B. SHARMA. Can. J. Chem. 54, 1563 (1976). NiM(NCS),, [NiL,][M(NCS),], and [NiL6][M(NCS)6] (M = Sn(lV), Ti(1V); L = pyridine

(py), 3-cyanopyridine (cpy), nicotinamide (nia), ethylnicotinate (ent), and ethylenediamine (en)) have been prepared and characterised by elemental analysis, magnetic moment, and infrared and electronic spectral studies. These studies suggest a thiocyanate bridged structure for NiM(NCS), and a cationic-anionic structure for [NiL,][M(NCS),] and [NiL6][M(NCS)6].

P. P. SINGH et S. B. SHARMA. Can. J. Chem. 54, 1563 (1976). On a prepark et caractCrisC par analyse CICmentaire, moment magnitique et etudes spectrales

infrarouge et klectronique les complexes NiM(NCS),, [NiL,][M(NCS),] et [NiL,][M(NCS),] (M = Sn(IV), Ti(1V); L = pyridine (py), cyano-3 pyridine (cpy), nicotinamide (nia), nico- tinate d'kthyle (ent) et ethylknediamine (en)). Ces etudes suggkrent qu'il existe une structure pontie par le thiocyanate dans le NiM(NCS)6 et une structure cationique-anionique dans le [NiL,][M(NCS),] et le [NiL,][M(NCS),].

[Traduit par le journal]

Introduction

In this article we are presenting the synthesis and structure of a new class of hexathiocyanates. These are of the general formula NiM(NCS)6, [NiL4][M(NCS)6], and [NiL6][M(NCS)6] (M = Sn(IV), Ti(1V); L = a number of pyridine deriv- atives and ethylenediamine).

Experimental

Materials arld Mar~iprrlatiorls Tin(1V) and titanium(1V) chlorides were purified by

the method of Hildebrand and Caster (1). Reagent grade anhydrous nickel(I1) chloride and potassium thiocyanate (BDH) were used after drying in vacuum for 24 h. Ethylenediamine (en) and pyridine (py) (BDH) were purified by double distillation. Nicotinamide (nia) (BDH) was crystallized from alcohol and dried in vacuum. Ethylnicotinate (ent) and 3-cyanopyridine (cpy) were syn- thesized by standard methods (2), from nicotinic acid and nicotinamide respectively, and were purified by distilla- tion under reduced pressure. Solvents were purified and strictly dried by known methods. All reactions were carried out in a dry box flushed with nitrogen.

Preparatiori of the Complexes The whole apparatus (Fig. 1) along with the required

chemicals was placed in a dry box flushed with nitrogen. Tin(1V) chloride (1.3 g, 5 mmol), finely powdered po- tassium thiocyanate (2.9 g, 30 mmol), stringently dried acetonitrile (50 ml), and a teflon-coated magnetic stirring bar were placed in the flask A. The whole mass was stirred for 12 h at room temperature. The stop cocks (C and D) were closed and the apparatus was removed from the dry

box, and inverted. The stop cock D was connected to the vacuum pump, when quick filtration took place. The residue (KCI) remained on the sintered disc (E) and the filtrate came into the flask B. The apparatus was again transferred to the dry box. Anhydrous nickel(I1) chloride (0.65 g, 5 mmol) was added to the filtrate in flask B along with a Teflon-coated magnetic stirrer. The flask A and the disc arm (F) were replaced by fresh components. The stirring was done for 2 h, and the apparatus was brought out of the dry box and inverted. The filtration was done as described above, potassium chloride on the disc was rejected and the filtrate preserved in the flask A.

Following a similar procedure, about a dozen solutions in different flasks A were prepared. Solvent from one of the flasks was evaporated by vacuum, when yellowish green crystals separated. This was NiSn(NCS)6.

T o the various other flasks, ligands in 1 :4 or 1 :6 molar ratio were added and stirred for 6 h. In each case solid complexes were formed which were filtered, washed with the solvent and dried in vacuum.

NiTi(NCS),, [NiL,l[Ti(NCS),], and [NiL,I[Ti(NCS)6] were prepared by a similar procedure.

Pl~ysicul Measirrernerrts The infrared spectra of ligands, metal hexathiocyanates,

and complexes were recorded on a Perkin-Elmer model 621 or 457 spectrophotometer in the range 4000-200 cm-1. Samples were run as Nujol mulls using Csl plates. Spectra of soluble ligands were also recorded in solution. Infrared spectral data are included in Tables 1 and 2.

Electronic spectra were obtained on a Cary-14 spectro- photometer between 1700-300 nm. Samples were run as their methanol, ethanol, or acetone solutions and as Nujol mulls. Electronic spectral data are included in Table 3.

Magnetic susceptibility measurements were made at

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TABLE 1. Assignment of infrared spectral bands and fundamental species of NiM(NCS), (ref. 20)'

Band positions (cm-1)

Schematic description Cz, Species No. Assignment of species N ~ S ~ I ( N C S ) ~ NiTi(NCS)6

NCS pseudo antisymm. st. degenerate (v(CN)) 3A1+2Bl+Bz 1 Al+B2(terminal N-bonded) 2050111 2060mb 2 A, +Bl(terminal S-bonded) 2120s 2120sh 3 AI + Bl(bridged) 2160s 2160s

NCS pseudo symm. st. degenerate (v(CS)) 3A1+2Bl +Bz 4 Al+Bz(terminal N-bonded) 770m 767m n 5 A1+ Bl(terminal S-bonded) 722m 720m 6 AI+BI(bridged)

5 760sh,740sh 760sh,735sh L

M-NCS deformation A* (G(MNC)) 2Al+Bl+Bz 7 A,+ Bz(terrninal N-bonded) 500m 495m n 8 Al+Bl(bridged) - - 2

- - z

Ni-SCN deformation A* (G(NiSc)) 2Al+2Bt 9 AI+Bl(terminal N-bonded) 435sh 430sh

< 10 A1 + Bl(bridged) o r

M-NCS and Ni-SCN deformation B" (8(NCS)) and (8(SCN)) ~ A I + ~ B I + B ~ 11 Al+Bz(terrninal N-bonded) 482w 480m VI

456s P

12 Al+Bl(bridged) 455s - 13 Al+ Bl(terminal S-bonded) 420w 120w w --,

m

M-N, degenerate stretch (u(M-N)) ~ A I + B I + B ~ 14 A1 +Bz(terminal N-bonded) 307s 305sb 15 Al+ Bl(bridged) 290sh 280sh

N i p s 4 degenerate stretch (u(Ni-S)) 2Al+2Bl 16 Al+ Bl(terminal S-bonded) 270sh 275sh 17 Al+Bl(bridged) 245w 250w

M-N4 deformation (G(NMN)) AI+BI+B~ 18 -~ - -

Ni-S4 deformation (8(SNiS)) AI+BI 19 - - -

t t 'A* involves M-N-C-S deformation and B* involves M-N-C-S deformation (20) st. = stretch, symm. = symmetric, s = strong, m = medium, w = weak, sh = slloulder.

1 1 1 1 1 I

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SINGH AND SHARMA

$ - a

g U

- --TnT-Tx-nT= X x s ~ n X s m 225.s m m ~ m G z ~ U m m ~ ~ U U U U U z_ z zEzzzZIEgg&. - zz c.y.*w m s+ hs + h inzT31a;?--~~ $ 5 5 pX5 2.2 2 2 5 ' ~ 3 n n r n . - n m X - n m X w V V V w V w V V w w w .-.-.-.- .-.-.-.-.-.- .- .- Z Z Z Z Z Z Z Z Z Z Z Z ------------

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CAN. J. CHEM. VOL. 54, 1976

FIG. 1. Apparatus for the preparation of NiM(NCS)6, [NiL41[M(NCS),I, and [NiL6][M(NCS)6] (M = Sn(IV), Ti(1V)).

room temperature by Gouy's method using HgCo(NCS), as standard. The diamagnetic corrections were made by the method outlined by Figgis and Lewis (3). Magnetic moment data are included in Table 3.

Molar conductance of the complexes were determined in alcohol with the help of a Philips conductivity bridge model PR-9500. Molar conductance data are included in Table 4.

Results and Discussion

NiSn(NCS)6 on(/ NiTi(~Vcs)~ (i) The infrared absorption bands assigned to

C-N stretching illode are observed at 2160, 2120, 2050, and 2080 cm-I. The positions of these bands indicate the presence of both bridged and termiilal thiocyanates (4,6, 16, 17). The posi- tion and number of bands in C-S stretching and NCS bending regions as presented in Table 1 also support the presence of both terminal and bridging thiocyanates (7, 9, 16, 17).

(ii) The electronic spectra of the complexes in solid phase show the presence of three bands a t about 9 100, 14 600, and 25 000 cm-I (Table 3), due to the transitions 3A2, + 3T2,, 3A2g -> 3T1,(F), and 3A2, + 3Tl,(P), respectively. The positions of these bands are typical of nickel(I1) in octahedral environment (10). The colour and Bohr magneton values also favour an octahedral geometry for nickel(I1). The Dq values suggest a weak interaction between nickel(I1) and thio- cyanate ion. Similarly, the Racah parameter (B') indicates less orbital overlap.

(iii) On the basis of the above observations we can tentatively propose the following structure (Fig. 2). In these complexes the sulphur end of thiocyanate has been shown attached to nickel(I1) and the nitrogen end, to tin(1V) or titanium(1V) according to H.S.A.B. theory (11). The octa- hedral configuration by nickel(I1) and tin(1V) or titanium(1V) is perhaps achieved by weak attachment of thiocyanates at the axial position, similar to nickel(I1) in NiHg(SCN)4 (12).

(iv) If the proposed structure is correct, the complexes will belong to the C2, point group. Assuming this point group, the number of normal modes along with their species have been calculated (Table 5). The comparison of the observed and calculated number of bands indi- cates that our proposed structure is correct.

TABLE 3. Electronic spectral band assignments, spectral parameters, and magnetic moment of Ni(I1) octahedral complexes

v I (cm-1) v L (cm-1) v3 (cm-1) lODq B ' Perf Complexes 3A2, -, jTzZ 3A2, --t 3TI,(F) 3A2, 4 3Tl,(P) (cm-1) (cm-1) B (B.M.)

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TABLE 4. Analytical results and molar conductance data

yo Tin or % % Molar conductance Melting :& Nickel titanium Thiocyanate Sulphur (A,,) (mhos cm-2 mol-1) point

Complexes Colour ("c) Obs. Calc. Obs. Calc. Obs. Calc. Obs. Calc. M/512 M/1020

Green Greenish yellow Blue Greenish yellow Yellow Blue Blue Yellowish green Light green Blue Blue Yellow Blue Blue

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T A ~ L E 5. Calculated normal modes of different point groups and their fundamental species' i! 2 No. of ir M-NCS and No. of ir -.

Complexes Point M-NCS and M-L active M-L, def. or active CI or ions group Vibrational species st. species st. species bend. species def. species 5 %

NiM(NCS), c20 19A1+Az+14_B~+6_B2 lOdt+7B,+6_B, 20 9Al+A2+7@1+3& 19 < 0

M(NCS)62- 0, 3Alg+3Eg+2Tlg+6_Tlu+3T2~+3Tlu 3A1g+3Eg+3_Tttl 3 3T2g+3z1,,S3Ta, 3 r

'st. = stretching: del. = dclormation; bend. = bending,

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SINGH AND SHARMA 1569

SCN NCS NCS\ j ,,SCN\ j /NCS

M NCS/~ ' \SCN/ i \NCS

SCN NCS

FIG. 2. Di-p-thiocyanato dithiocyanato nickel(I1) diiso- thiocyanato tin(1V) or titanium(1V).

( u ) Unlike polymeric bridged tetrathiocyanates (12), these complexes are sharp melting and soluble in polar organic solvents. This shows that they are perhaps monomeric in nature. Attempts to find out the molecular weight were not successful as the complexes get solvated with the solvent molecules, and probably a species of the type [Ni(Solv)il[M(NCS)6] is formed. The forma- tion of such a species is justified by the molar conductance and infrared spectral measurements. The complexes in ethanol have molar conduc- tance values equivalent to 1 : 1 electrolyte and the solution spectra show the presence of only nitrogen bonded thiocyanates.

[NiL4][M(NCS)6] and [NiL6][M(NCS)6] (L = nia, ent, py, cpy; M = Sn(IV), Ti(IV))

(i) The infrared spectra of these complexes, show the presence of only one band in C-N stretching region. The position of this band indicates that thiocyanate is nitrogen bonded. The position and number of bands in C-S stretching and NCS bending regions also support the presence of only nitrogen bonded thiocyanates (5, 9, 13).

(ii) The colour and magnetic moment values of [NiL6][M(NCS)6] show that the nickel(I1) in these complexes is in octahedral configuration. The position of the electronic spectral bands and various ligand field parameters as presented in Table 3, also support the octahedral configura- tion of nickel(I1) in these complexes. The Dq values of this series of complexes are higher than NiSn(NCS)6 and NiTi(NCS)6, showing greater interaction of ligands with the metal ion. The Dq values also vary from ligand to ligand. This shows that the ligands (L) are attached to nickel(I1) and not to tin(1V) or titanium(1V). The complexes [NiL4:I[M(NCS)6] are diamagnetic and yellow in colour. This shows that nickel(I1) in these complexes is in the square planar geometry. The electronic spectral band positions also support this configuration of nickel(I1).

(iii) The molar conductance values of these complexes in ethanol are typical of I : 1 electro- lyte (Table 4).

(iu) On the basis of the above results we can propose a cationic-anionic type of formula for these complexes. The cation will consist of nickel(I1) with four or six ligand n~olecules, and the anion, of tin(1V) or titanium(1V) with six isothiocyanate ions. Hence the complexes can be formulated as [NiL41[M(NCS)6] and [NiL6]- [M(NCS)6] (M = Sn(lV), Ti(1V)).

Since the thiocyanate is nitrogen bonded it will prefer Sn(IV) or Ti(lV) for coordination accord- ing to H.S.A.B. theory (1 1).

(u) We have assumed D4, point group for [NiL4lW, Oh for [NiL612+ and [M(NCS)6]2+ and have calculated the number of normal modes and their species, the results of which, along with the observed number are presented in Tables 2 and 5. The comparison of calculated and observed number of bands also supports the proposed formulae.

Conclusions (i) The MPt(SCN)6 (14) and MHg(SCN)4 (5:

6, 12, 15), (M = Fe, Co, Ni, Zn, Pb) have generally a polynleric thiocyanate bridged struc- ture. NiM(NCSl6 (M = Sn(IV), Ti(1V)) how- ever, appear to be monomeric in nature.

(ii) The thiocyanate bridging in NiM(NCS)6 is perhaps the weakest of all known tetra or hexathiocyanates.

(iii) It has been shown recently (18,19) that the thiocyanate bridge in MM1(NCS)4 is weak when M and M' belong to class a type metals and the bridge is stable if one of the two metals belongs to class b type metals. On reaction with bases the thiocyanate bridge is ruptured more easily when both M and M' belong to class a type, and with difficulty when one of them belongs to class b type of metal. It has also been shown that in the presence of ligands of weak basicity the bridge is not ruptured even when both M and M' are class a type (18). The thiocyanate bridge in NiM(NCS)6, however, appears to be very weak as it breaks even in polar solvents like ethanol or acetonitrile.

Acknowledgements

The authors gratefully acknowledge the finan- cial support of U.G.C. New Delhi and instru-

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1570 CAN. J. CHEM. VOL. 54. 1976

mentat ion facilities by University o f Mont rea l , Montreal, Quebec.

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