Bridged and pseudo-octahedral complexes—I

J. inorg,nucl.Chem.,1971,Vol.33, pp. 3739-3748. PergamonPress. Printedin GreatBritain

BRIDGED

AND PSEUDO-OCTAHEDRAL COMPLEXES- I

SPECTRAL A N D M A G N E T I C S T U D I E S OF SOME COMPLEXES OF COBALT(II) A N D NICKEL(II) WITH N I T R O G E N DONORS* S. N. DAS, S. N. M O H A R A N A and KAILASH C. DASH Department of Chemistry, Utkal University, Vani Vihar, Bhubaneswar-4, India

(Received 15 March) Abstract-Complexes of the type ML2X~ are described (M = Co(ll) or Ni(II); L = o-, m-, p-toluidine. anisidine and phenetidine; X = CI, CNS or ½SO4). The compounds have been characterised and possible structures have been deduced on the basis of analytical data, molar conductivities, electronic and i.r. spectra, and magnetic susceptibility data in the temperature range 80-300°K. The i.r. spectra establish the coordination of the anion to two metal atoms, forming a bridged structure. The T,/ symmetry of the free sulphate ion is lowered to C2v in the complexes. All the compounds obey the Curie-Weiss law over the temperature range employed and the observed magnetic moments are dependent on temperature, suggesting a weak antiferromagnetic exchange interaction between the two metal atoms in the complex. All the compounds contain metal ions in a 6-coordinate environment. INTRODUCTION

A LARGE number of first-row transition metal halides are k n o w n [ l - 8 ] to react

with pyridines, anilines and other similar nitrogen donor ligands to form adducts of the type ML,,X2, where M = Mn, Co, Ni, Cu, Zn, and Cd; L = the nitrogen donor ligand; X = halide; and n -- l, 2 or 4. These adducts have been prepared by various preparative techniques[8]. The thermal stability, stereochemistry and empirical formulae of the complexes have been discussed in terms of steric hindrance, 7r-acceptor properties and ligand polarisability. The proposed structures for many of the adducts have been deduced from magnetic and spectral studies [9-12]. *Presented in part in the Chemistry Symposium of the Dept. of Atomic Energy (Govt. of India) held in Madras (November 1970). I. S. M. Nelson and T. M. Shepherd, J. chem. Soc. 3276 (1965). 2. J. R. Allan, D. H. Brown, R. H. Nuttal and D. W. A. Sharp, J. inorg, nucl. Chem. 27, 1305 (1965). 3. D. M. L. Goodgame, M. Goodgame, M. A. Hitchman and M. J. Weeks, J. chem. Soc. A. 1769 (1966). 4. J. R. Allan, D. H. Brown, R. H. Nuttal and D. W. A. Sharp, J. inorg, nucl. Chem. 27. 1529 (1965). 5. A. K. Majumdar, A. K. Mukherjee and A. K. Mukherji, J. inorg, nucl. Chem. 26, 2177 (1964). 6. N. S. Gill and J. Kingdon. Austral. J. Chem. 19, 2197 (1966). 7. L. M. Vallarino, W. E. Hill and J. V. Quagliano, lnorg. Chem. 4, 1598 (1965). 8. S. Buffagni, L. M. Vallarino and J. V. Quagliano, lnorg. Chem. 3, 67 t (1964). 9. D . M . L . Goodgame and M. Goodgame, J. chem. Soc. 207 (1963). 10. A. B. P. Lever, J. Lewis and R. S. Nyholm, J. chem. Soc. 5042 (1963). 11. A. B. P. Lever, J. inorg, nucl. Chem. 27, 149 (1965). 12. A. B. P. Lever, S. M. Nelson and T. M. Shepherd, lnorg. Chem. 4, 810 (1965). 3739

3740

S.N.

DAS, S. N. M O H A R A N A and K A I L A S H

C. D A S H

Due to the ambidentate nature of thiocyanate ion, there has been considerable interest in complexes formed between this ion and transition metal salts, particularly with regard to their stereochemistry; as a result, a large number of nickel(II) and cobalt(II) thiocyanate complexes have been characterised [13-16]. The mode of metal thiocyanate bonding depends upon the metal itself, the nature of the other ligands in the coordination sphere, and electronic and steric factors [17, 18]. The i.r. spectra of metal thiocyanate complexes have been studied by several workers[19-22] to provide criteria for distinguishing between N- and S-coordination of the CNS group. Infra-red spectra have also been used to determine the nature of coordination of the simple sulphate ion, which may be either monodentate, bidentate or bridging[23], or may remain outside the coordination sphere. We report here results for some mixed ligand complexes containing bridged CNS and SO4 groups, in which nitrogen donor ligands such as toluidine(methyl aniline), anisidine(methoxy aniline) and phenetidine(ethoxy aniline) are present. These ligands contain the ring activator groups -CH3, -OCH3 and -OC2H5. The possibility of adduct formation between the transition metal salts and nitrogen donor ligands where the ring deactivator groups -Cl, Br and NO2 are present will be discussed later. Complexes of the type NiL2C12 (L = aniline or toluidine) were reported for the first time by Lever, Nelson and Shepherd[12] and their electronic spectra discussed. Ahuja e t al.[24] have reported the formation of the compound Ni(p-tol)2SO4, but present no detailed study of the coordination number and stereochemistry. In addition to the sulphato and thiocyanato complexes, chloro-complexes of Co(II) and Ni(II) with anisidine and phenetidine are reported, for the first time to our knowledge. EXPERIMENTAL Preparation of complexes The chloro complexes were prepared by mixing a hot ethanolic solution of the metal halide (1 mole) and aniline ( - 2.5 moles). On stirring the compounds were formed almost immediately. The cobalt compounds were blue and the nickel compounds green or pale green. The nickel sulphato complexes were prepared by mixing a hot methanolic solution of NiSO4"7H20 (1 mole) and aniline ( - 2'5 mole) and heating under reflux on a steam bath until fine microcrystalline pale green substances appeared ( - 30 min). The cobalt thiocyanate complexes were prepared as follows: alcoholic solutions of: Co(NOa)~.6Hz O (1 mole) and KSCN (2 moles) were mixed and the precipitated KNO3 was filtered off. The filtrate was somewhat concentrated by slow evaporation on a water bath, and on adding aniline ( - 2"5 moles) blue crystals separated out. 13. D. Forster and D. M. L. Goodgame, lnorg. Chem. 4, 715 (1965). 14. S. Buffagni, L. M. Vallarino andJ. V. Quagliano, lnorg. Chem. 3, 480 (1964). 15. H. Carbacho, B. Ungerer and G. Conteras, J. inorg, nucl. Chem. 32, 579 (1970). 16. S. Utsuno, J. inorg, nucl. Chem. 32, 183 (1970). 17. J. L. Burmeister and F. Basolo, lnorg. Chem. 3, 1587 (1964). 18. I. Bertini and A. Sabatini, Inorg. Chem. 5, 1025 (1966). 19. M. M, Chamberlain and J. C. Bailar, Jr.,J.Am. chem. Soc. 81, 6412 (1959). 20. P. C. H. Mitchell and R. J. P. Williams, J. chem. Soc. 1912 (1960). 21. J. Lewis, R. S. Nyholm and P. W. Smith, J. chem. Soc. 4590 (1960). 22. A. Turco and C. Pecile, Nature, Lond. 191, 66 (1961). 23. K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds pp. 163, Wiley, New York (1963). 24. I. S. Ahuja, D. H. Brown, R. H. Nuttal and D. W. A. Sharp, J. chem. Soc. A, 938 (1966).

Some bridged CNS and SO4 complexes of Co(ll) and Ni(ll)

3741

In all cases the compounds were filtered under suction, washed with the appropriate alcohol containing a little aniline, then with petroleum ether, and finally dried in vacuo. The compounds were characterised by analysis for the metal and the anion according to standard procedures[25]. with the results shown in Table 1. Table I. Analytical data, conductivities and magnetic moments (room temperature) for substituted aniline complexes ofcobalt(II) and nickel(lI)

S. No. 1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19

Compound Co(o-anis)2Cl2 Co(m-anis)2Cl2 Co (p-anis)2Cl2 Co (p-phen)2Cl2 Co(m-tol)2(SCN)2 Co(p-tol)z(SCN)~ Co(p-anis)~ (SCN)2 Co (p-phen)._,(SCN) 2 Ni(o-anis)2Cl., Ni(m-anis)2Cl2 Ni(p-anis)~Cl2 Ni(p-phen)2Cl2 Ni(o-tol)2SO4 Ni (m-tol),.,SO4 Ni (p-tol)..,SO4 Ni(o-anis)2SO4 Ni(m-anis)2SO4 Ni(p-anis)2SO4 N i (p-phen) 2SO4

% metal Found Reqd. 15.5 15.7 15.2 14.2 14-8 14-9 14-0 13-0 16'5 16.1 16.3 14-8 15.8 15-7 15.9 14.8 14.8 14.9 14.1

15-6 15-6 15-6 14.6 15"5 15-5 13.9 13.1 15.6 15.6 15.6 14.5 15.9 15.9 15.9 14-6 14.6 14.6 13.7

% anion Found Reqd. 19.1 19.0 19.0 18.1 30'3 30.4 27.3 25.9 18"8 18.8 18.7 17.9 26.4 26.1 26.3 24.1 24.2 24.0 22.3

18-8 18.8 18.8 17.5 30'5 30-5 27.5 25.8 18'8 18.8 18-8 17-5 26.3 26-3 26-3 23.9 23.9 23-9 22.4

A.~I~

/zefdB.M.)¢

3.2 2.9 4.7 3.6 5.6 6"7 9-5 7-2 8'5 8-0 10. I 8-8 insol.

4-9 4.8 5.0 4.9 5"2 4.9 5.1 5.0 3.1 3.2 3.3 3.3 3.2 3.2 3.0 3.3 3.3 3-2 3.0

*Molar conductivity (mho mole -j cm 2) in acetone (approximately 0.001M) at room temperature. A 1 : 1 electrolyte has a molar conductivity of about 120 mhos mole -1 cm -~ in acetone. CEffective magnetic moment in Bohr magnetons at 23°C.

Magnetic" measurements The magnetic susceptibility determinations were carried out on solid samples using a Gouy apparatus with a semimicro-balance and tapered magnet pole tips. The sample tube was calibrated with HgCo(CNS)4126]. The room-temperature susceptibility was measured for all the compounds (Table I), and the values have been corrected for diamagnetism using Pascal's constants[27] for various atoms and groups. The susceptibilities shown are the average values of at least five independent measurements for each experimental configuration. The susceptibilities of all the compounds were measured at field strengths of approximately 4000, 6000 and 8000 Gauss and were found to be independent of field strength, indicating the absence of ferromagnetic impurities [28]. Low-temperature measurements were carried out for the nickel sulphato and cobalt thiocyanato compounds (Tables 2 and 3), using a Dewar vessel of special design fitting between the magnet pole pieces at a 2 in. pole gap. The vessel was filled with liquid nitrogen and sample temperatures were measured by a copper-constantan thermocouple placed in the inner wall of the vessel jacket along the 25. A. 1. Vogel, Quantitative lnorganic,4nalysis. Longmans, London (1959). 26. B. N. Figgis and R. S. Nyholm, J. chem. Soc. 4190 (1958). 27. B. N. Figgis and J. Lewis, in Modern Coordination Chemistry, (Edited by J. Lewis and R. G. Wilkins), pp. 400. Interscience, New York (1960). 28. A. Earnshaw, Introduction to Magnetochemistry pp. 87. Academic Press, London (1968).

3742

S.N.

D A S , S. N. M O H A R A N A

z © ""7.

r.~

gh

"d

e.~

.o

z e.,

L)

e-i

Z

~D ¢¢

[..,

5

and K A I L A S H C. D A S H

Some bridged CNS and SO4 complexes of Co(I I) and Ni(I I)

~ E

~

T

3743

3744

S.N. DAS, S. N. MOHARANA and KAILASH C. DASH

sample column ( - 6 in.). Magnetic moments were calculated using the formula/x~ft = 7.997 × ×M~°'~x 10 -8 [29].

Spectrophotometric measurements

Electronic spectra of the complexes were taken in acetone (where possible) using a Beckman DK 2 recording spectrophotometer. I.R. absorption spectra were run in the 4000-5000 cm-1 region as Nujol mulls on a Perkin Elmer 337 Grating I.R. Spectrophotometer, using a polystyrene strip for calibration. Conductance measurements

Conductance measurements were performed at room temperature (300°K) in acetone solutions ( - 10-3 M) with a Toshniwal electrolytic conductivity bridge, type CL 0102, and a dip-type cell which was previously calibrated with aqueous KCI solution. RESULTS AND DISCUSSION N i n e t e e n new aniline c o m p l e x e s have been studied; analytical data, molar conductivities and r o o m t e m p e r a t u r e magnetic m o m e n t s are presented in T a b l e 1. Analogous c o m p o u n d s of metal chlorides with toluidines h a v e also been p r e p a r e d and studied for the sake of c o m p l e t e n e s s and in order to assign the coordination numbers with confidence. T h e tetrakis-(aniline) c o m p l e x e s could not be prepared either by the m e t h o d reported here or by other preparative techniques. T h e nickel sulphato c o m p o u n d s are highly insoluble in c o m m o n organic solvents. T h e cobalt thiocyanato c o m p o u n d s are also not very soluble, but a dilute solution in acetone permitted a conductivity m e a s u r e m e n t which showed t h e m to be non-electrolytes. T h e conductivities and spectra leave little doubt that the thiocyanate and the sulphate groups in these complexes are covalently bound to the metal. T h e results in this p a p e r are discussed in two parts. T h e first aim is to establish the coordination n u m b e r of the central metal a t o m in the MLzXz c o m p l e x e s by means of conductivity values, magnetic properties and electronic spectra in solution (where possible). This evidence shows that these c o m p l e x e s are not 4-coordinate as indicated by the formula [ M L 2 X z ] , but are 6-coordinate complexes with pseudo-octahedral stereochemistry. T h e second aim is to identify the nature of the bridging-ligands f r o m the spectra. Coordination number C o b a l t t h i o c y a n a t o c o m p l e x e s . T h e experimental magnetic m o m e n t s of these c o m p o u n d s at r o o m t e m p e r a t u r e s (Table 1) fall in the range[30] 4.7-5.2 B.M. e x p e c t e d for octahedral c o b a l t ( I I ) complexes. F o r a C o ( I I ) ion in an octahedral environment, the ground state is three-fold orbitally degenerate (4T1~) and a large orbital contribution to the magnetic m o m e n t increases the spin-only value f r o m 3-89 to 4-7-5.2 B.M.. H o w e v e r , in order to account accurately for the experimental results it is necessary to consider electron delocalisation and a l o w - s y m m e t r y ligand field component. T h e electronic spectra in acetone solutions of all the CoL2 (CNS)2 complexes (L ~ p-toluidine, p-anisidine a n d p-phenitidine), show a band of m o d e r a t e intensity at ca. 18,200cm -1 with a shoulder on the high-frequency side, and

29. B.N. Figgis, Introduction to Ligand Fields. Interscience, New York (1966). 30. J. Lewis, Sci. Progr. 51,452 (1962).

Some bridged CNS and SO4 complexes of Co(II) and Ni(lI)

3745

another band at 16,400 cm -~. Assuming an Oh field, this band may be due to a 4T,,,(F) --~ 4A2o transition. According to Ferguson[31], this transition involves two electrons and is not frequently observed, but gains intensity in symmetries o f D4h o r lower. Nickel sulphato complexes. The ground state configuration of nickel(II) ion in a regular octahedral field is always 3A2o(tze) 6 and it follows from a simple energy level diagram that it will be paramagnetic with two unpaired electrons. Furthermore, since the predominant contribution to the magnetic susceptibility is given by the spin-only term (even though some minor corrections are necessary due to spin-orbit coupling, covalent character of the double bond and temperatureindependent paramagnetism, the magnetic moment should be close to the spinonly value of 2-83 B.M.. In fact, this is the case, and the observed magnetic moments of known octahedral Ni(II) compounds lie in the region 2.83-3-4 B.M. [32]. An explanation for this increase in magnetic moment of tetrahedral Co(II) and octahedral Ni(II), both of which have orbitally non-degenerate ground states, was first given by Schlapp and Penney[33]. The observed values of the magnetic moments for the NiL2SO4 (L ~ substituted aniline) complexes (Table 1) fall in this range, and hence they are high-spin tetragonal complexes of Ni(II). The magnetic susceptibility measurements of these complexes over the temperature range 80-300°K reveals a marked temperature dependence (Tables 2 and 3). Curie-Weiss behaviour was observed for all the compounds with negative Weiss constants. This deviation from the true Curie behaviour (i.e.) negative intercepts in the plot of 1Ix vs. T) may be explained by assuming antiferromagnetic interaction between the adjacent paramagnetic centres (i.e. the metal atoms, Co or Ni) where the exchange interaction is transmitted via the thiocyanate or sulphate bridges, the evidence for which is presented below.

1.R. spectra Spectra were recorded in the region 4000-5000 cm -1. and in all cases the spectra of the complexes was compared with that of the free ligand. It has been shown [34, 35] that the vibrational frequencies of pyridine do not change greatly when it is coordinated to a metal: the i.r. spectra of coordinated pyridine closely resembles that of the free ligand, when few bands are split in the spectra of the complexes, probably due either to lattice effects or to departures from idealised symmetry. It has now been found that the i.r. spectra of the substituted anilines when present as ligands in complexes are closely similar to those of the free bases. Thus it is possible to identify bands originating from the anilines, and hence these are omitted from the tables of spectra. The spectra of the sulphato and thiocyanato groups will therefore be discussed in detail. It has been observed that the i.r. spectra of the sulphato complexes are remarkably similar to each other with regard to the number of bands, band shapes, frequencies and relative 31. J. Ferguson,J. chem. Phys. 32,528 (1960). 32. F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry pp. 882. Interscience, New York (1964). 33. R. Schlapp andW. G. Penney, Phys. Rev. 42,666 (1932). 34. N. S. Gill, R. H. Nuttal, H. C. Scaife and D. W. A. Sharp, J. inorg, nucl. Chem. 18, 79 (1961). 35. M. Goldstein, E. F. Mooney, A. Anderson and H. A. Gebbie, SpectrochimActa 21,105 (1965).

3746

S . N . DAS, S. N. MOHARANA and KAILASH C. DASH

intensities. Hence, the same mode of coordination is present in all the sulphato complexes. In a similar manner, the spectra indicate the same mode of coordination in all the thiocyanate complexes.

Thiocyanato complexes Considerable interest has been shown in the ambidentate nature of the pseudohalide ions, in particular thiocyanate ion[36]. The thiocyanate ion may coordinate to a metal through either S or N, or may act as a bridge between two metal atoms ( M - C N S - M ) . It is known from X-ray data that metals of the first transition series (e.g. V, Cr, Mn, Co, Ni, Cu, Zn) form M - N bonds, whereas those of the second and third transition series (e.g. Rh, Pd, Ag, Cd, Pt, Hg) form M - S bonds with the thiocyanate group. Furthermore, both electronic and steric factors from the other ligands present in complexes containing coordinated thiocyanate appear to provide a delicate balance as to whether the thiocyanate ion bonds via nitrogen or sulphur [ 17, 22, 37]. The i.r. data [ 19-21,38], especially in the mid-region, have proved invaluable in elucidating the nature of binding in the thiocyanate complexes according to the assignments below:

M-NCS M-SCN Bridged-CNS

C = N stretching vl (era-0

N - C - S bending v2(cm -~)

C-S stretching v3(cm-0

2040-2100 2080-2100 2075-2150

450-490 410-470

780-860 690-720 775-790

However, this criterion for determining bond type based on any of these three bands should be used with caution. Assignments based on Vl are difficult, due to small variations in peak positions and to overlapping, va may be a better guide, due to the wide separation between the C - S frequencies for N and S bonding. Assignments based on v~ are perhaps the best, but the peaks are weak, and due to the limitations of the instrument used this method could not be used. When C N S is involved in bridging, i.e. in M - N C S - M , the pseudo-asymmetric stretch, vl, is generally observed to increase, and the pseudosymmetric stretch, va, to decrease relative to these frequencies in terminally bonded M - N C S complexes [20]. That this is also the case for bridging thiocyanate complexes containing anilines as the neutral ligands is illustrated in Table 4. Table 4. Frequencies of the fundamental NCS vibrations (cm-1)

Co(m-tol)2(CNS) z Co(p-tol)2 (CNS)2 Co(p-anis)2 (CNS)z Co(p-phen)z (CNS)2

v1(C-N)

va(C-S)

2108 2110 2105 2105

778 780 780 755

36. J. L. Burmeister, Coordn. chem. Rev. 1,205 (1966). 37. M. F. Farona and A. Wojocicki, lnorg. Chem. 4, 1402 (1965). 38. A. Sabatini and I. Bertini, Inorg. Chem. 4, 959 (1965); ibid. 4, 1665 (1965).

3747

Some bridged CNS and S04 complexes of Co(I1) and Ni(ll)

Sulfato complexes The simple inorganic anion SO4 belongs to the high-symmetry point-group

Ta; on coordination to the metal ion the s y m m e t r y of this ion will be lowered, since the o x y g e n a t o m bonded to a metal is different from the other oxygen atoms. T h e SO4 ion m a y coordinate in one o f three ways: M--O

O

U nidentate

Bidentate

Bridging

(C3,,)

(C2,,)

(C2,,)

In unidentate coordination, the symmetry becomes C3v, whereas in bidentate coordination the symmetry of the SO4 ion is C2v (both for chelating as well as for bridging) [23] and accordingly the i.r. and Raman selection rules are changed [39]. When the coordinated sulphato group belongs to C2~, four SO stretching bands at 1211, 1176, 1075 and 793 cm -1 are expected [40], and it is difficult to distinguish between the bridging and chelating sulphato groups. However, Eskenzi et al. [41 ] have shown that the SO stretching frequencies, together with an examination of the solubility of the compound, may be useful in distinguishing a bridging from a chelating sulphato group; the latter is expected to be more soluble. The SO stretching frequencies of the complexes (Table 5) and their high insolubility in common organic solvents indicate the presence of bridging sulphato groups. The evidence presented in this paper indicates that in these complexes the Table 5. SO stretching frequencies in sulphato complexes (cm ~) I/'1

Ni(o-tol)2SO4

970 (m)

Ni(m-tol)2SO4

985 (m)

N i (p-tol) 2 5 0 4

988 (s)

Ni (o-anis)2SO4

970 (m)

Ni (m-anis) zSO4

960 (m)

N i (p-anis) ~SO4

985 (m)

Ni(p-phen)2SO4

988 (s)

/)2

~3

P4

1040 (s) 1105 (sh) 1160 (sh) 1040 (s) 1143 (sh) 1030 (s) 1110 (w) 1035 (s) 1140 (s) 1040 (m) 1140 (s) 1032 (s) 1115 (w) 1140 (sh) 1048 (s) 1135 (sh)

620 (m) 645 (sh)

585 (s) 640 (m)

585 (s)

582 (s)

39. K. Nakamoto, J. Fujita, S. Tanaka and M. Kabayishi, J. Am. chem. Soc. 79, 4904 (1957). 40. C. G. Barraclough and M. L. Tobe, J. chem. Soc. 1993 (1961). 41. R. Eskenzi, J. Raskovan and R. Levitus, J. inorg, nucl. Chem. 21, 33 ( 1961 ).

3748

S . N . DAS, S. N. M O H A R A N A and K A I L A S H C. D A S H

metal atom (Co or Ni) is 6 coordinate. All have high melting points (> 250°C) and are relatively insoluble in common organic solvents. Hence they are all high-spin, polymeric and (pseudo) octahedral compounds of Co(II) or Ni(II), where 6-coordination of the central ion is achieved through anion bridging. Acknowledgement-The authors thank the U.G.C. for financial assistance to carry out this work. Thanks are also due to Professor C. R. Kanekar of the Tata Institute of Fundamental Research, Bombay, for permission to use the Gouy apparatus for determining susceptibility at low temperatures, and to Dr. S. N. Mohapatra of the Regional Research Laboratory, Bhubaneswar, for kindly recording the i.r. spectra.