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Study of bonding in some nickel complexes of isonitrosoketones
Specrrochimica
Arm. Vol
396. No
8. pp. 965-968,
1984
0
Pnnted,n GreatBnta~n
0584-8547/84 m.oo+ 00 1984. Persamon Press Ltd.
Study of bonding in some nickel complexes of isonitrosoketones S. V. SALVI, P. H. UMADIKAR, M. d. PATIL, P. M. DHADKE Institute of Science, M. Cama Road, Bombay-400032, India
N. V. BHAT Department of Chemical Technology, University of Bombay, Matunga, Bombay-400 019, India (Received 19 December 1983) Abstract-X-ray K-absorption edge analysis of nickel in some nickel complexes of isonitrosoketones has been carried out using a 400-mm bent crystal spectrometer. The analysis has been used to deduce information regarding the mode of bonding, the magnetic behaviour and the coordination of Ni in the complexes. On the basis of the results obtained, it has been concluded that Ni ions in Ni(HMAO), have square planar structure whereas Ni ions in Ni(HTGA)2 have tetrahedral structure. On the other hand Ni ions in Ni(EINA), and Ni(INACA)2 are surrounded by octahedra. Ni ions in Ni(INACA), are in the valence state higher than two and appear to be paramagnetic.
1. INTRODUCTION THE EDGE structure of transition metal ions in complexes has been widely investigated [l-3]. The analysis of edge structure is informative of the chemical bonding, e.g. the assignment of the bonding orbitals [4] and the bonding mode [S]. It is also possible, using the empirical classification of the edge structure of transition metal complexes by VAN NORDSTRAND[6], to determine the coordination of the absorbing ion. Our previous study of the K-absorption edge of some nickel(I1) complexes of isonitrosoketones [7] has given interesting information regarding their bonding and coordination. This has prompted us to investigate few more nickel complexes of isonitrosoketones and present the X-ray K-absorption edge analysis of all the nickel complexes of isonitrosoketones. The complexes include two forms of nickel bis(isonitrosoacetophenate): Ni(INAP)* green and brown [7], Ni(C6H9NZ03):, nickel-a-benzilmonoximate : Ni(a-BMO);, nickel-2-hydroxy-Smethylacetophenoneoxime : Ni(HMA0)2, nickel ethyl-a-isonitrosoacetoacetyl : Ni(EINA)2, nickel isonitrosoacetop-carboxyaniline : Ni(INACA)2 and nickel thioglycolicacidanilide : Ni(HTGA)2. The Kabsorption spectra of NiO and NiClz * 6H20 are included to facilitate comparison.
2. EXPERIMENTAL Spectra were recorded using a 400 mm bent crystal transmission spectrograph with mica crystal as an analyser. Spectra were obtained on INDU industrial X-ray film and were microphotometered using an MO-4 microphotometer. Absorption curves were rigorously averaged. Spectra of nickel and NiClz .6H20 were studied as standards and were compared with those appeared in literature. This was done in order to check the reliability of our experimental set up. The complexes were prepared by the procedure reported [8-131. [l] [2] [3] [4] [S] [6] [7] [S] [9] [lo] [11] [12] [13]
W. W. BEEMANand H. HANSON,Phys. Rev. 76, 118 (1949). F. A. COTTONand H. P. HANSON,J. Chem. Phys. 26, 1758 (1967). N. V. BHAT,A. SYAMAL,S. V. SALVIand P. H. UMADIKAR,Spectrochim. Acta 35B, 489 (1980). G. MITCHELLand W. W. BEEMAN,J. Chem. Phys. 20, 1298 (1952). B. D. PADALIA,C. S. GUFTA,A. V. PAIGANKAR and B. C. HALDAR,Curr. Sci. 38,490 (1969). R. A. VAN NORDSTRAND, Adv. Catalysis 12, 149 (1960). P. H. UMADIKAR,S. G. MESTRY,N. V. BHATand B. C. HALDAR,Spectrochim. Acta JlB, 411 (1976). N. V. THAKKAR,Ph.D. Thesis, Bombay University (1976). M. S. GAIKWAD,Ph.D. Thesis, Bombay University (1976). P. M. DHADKEand B. C. HALDAR,Proc. 15th Int. Coord. C/tern.Corlf. Moscow (1973). B. D. GUPTAand W. U. Malik, J. Znd. Chem. Sot. 48 79 (1971). S. B. KULKARNI,M.Sc., Thesis, Bombay University (1983). M. R. PATIL,Private communication.
s&s) 39:8-B
965
s. v. SALVr et al.
966
3. RESULTSAND DISCUSSION The structural features of the X-ray K-absorption edge of nickel in the complexes are tabulated in Table 1 and also are shown in Fig. 1. The structural data of X-ray K-absorption edge for NiO and NiCl,.6H,O are also included for the sake of comparison. (Ar)ed*4s2 configuration of electrons in nickel indicates that the first allowed transition is 1s -+ 4~. The principal absorption maximum A is therefore, assigned to this transition. It is significant to note that the position of the principal absorption maximum lies in the range 22-30 eV for most of the complexes whereas it has a value in the region of 17-20 eV for ionic compounds such as NiO and NiC12 *6Hz0. Table 1. Structural data such as position of K-absorption edge, principal absorption maximum, edge width and structure suggested of nickel in various nickel compounds Structural feature
Compound Ni(INAP),Brown Ni(INAP)2 Green Ni(HTGA), NiC12.6H20 Ni(EINA)2 NiO NI(C,HgNzO,), Ni(HMAO)* Ni(INACA)2 Ni(aBMO)z
(et)
(et)
(et)
P -
9.4 9.4 10.0 12.2 12.5 13.3 15.0 15.5 15.0 16.5
22.6 17.8 25.0 17.2 22.5 20.3 27.2 28.0 30.0 24.5
P
P P
P
Structure suggested 13.2 8.4 15.0 5.0 10.0 7.0 12.2 12.5 fS.0 8.0
NiN,O., NiN,04 NiS,02 NiOs NiNBOJ NiO, NiN,O NiN,02 NiN,O, NiN,OB
[E,S(X,
* XL)I1” 11.1 8.8 8.7 7.2 9.3 8.4 8.2 8.4 11.8 8.4
3.1. Position of the absorption edge and magnetic property It is well known that the increase in the valency of the ion is associated with the shift in the position of the K-absorption edge towards high energy side, whereas the covalency is observed to suppress the shift. The position of the K-absorption edge, i.e. the half intensity point on the absorption curve, for most of these complexes lies in the range 12.5-16.5 eV. The K-edge of Ni2 + ion in NiC12 -6H2O is situated at 12.2 eV. It would be therefore, not improper to conclude that these complexes are as much ionic as NiC12 *6H2O if not more. However Ni ion in these complexes is in the divalent state and all these complexes are known to be covalent. Moreover these are coordination complexes containing nitrogen and oxygen donor. Therefore, the cause for the high K-absorption edge shift may be other than the charge on the ion. A careful examination of the other data (in particular the magnetic data of the nickel complexes, viz. Ni(INAP), green and brown, Ni(CsH9N203) and Ni(crBM0):) has revealed that the edge shift for paramagnetic complexes is found to be less than 10 eV, whereas that for diamagnetic complexes is in the vicinity of 15.5 eV. A similar trend was observed in the case of the compounds of yttrium, an element from the second transition series [14]. This can be very easily explained on the basis of the ligand field theory. The ee orbitals of a diamagnetic Ni ion are shifted to high energy side compared to the ee orbitals of a paramagnetic ion. A small transition probability exists as these orbitals combine with the p orbitals of the ion through the p orbitals of the ligand. As a result the edge-shift is higher for diamagnetic ions than for paramagnetic ones. It is interesting to note that the absorption edge for NiO (antiferromagnetic) lies approximately in the middle of this spread. It is therefore, concluded that Ni(HMA0)2 and Ni(INACA)2 are diamagnetic. Ni(EINA)2 and Ni(HTGA)2 may be, on the other hand, paramagnetic. The edge shift of Ni2+ ion in NiC12 .6H20 which is paramagnetic is also same as that for Ni(EINA)2. The comparison between the position of K-edge and the magnetic behaviour of the complexes is presented in Table 2. [14] V. G.
BHIDE
and N. V.
BHAT, .I. Ckm.
Phys. 48, 3103 (1968).
Bonding in nickel complexes I
NI Metal
J
Fig. 1. X-ray absorption fine structure of K-edge of some nickel(H) isonitrosoketones. The curves for Ni metal, NiCls.6HsO and NiO are also included to facilitate comparison. The zero of the energy scale has been chosen at the K-edge of nickel metal.
Table 2. Comparison of position of K-absorption edge with magnetic behaviour of nickel complexes Compound Ni(INAP),Brown Ni(INAP),Green Ni(HTGA)s NiCl,.6H,O Ni(EINA), NiO Ni(C,H9NsO& Ni(INACA), Ni(HMAO)s Ni(aBMO),
K(eV) 9.4 9.4 10.0 12.2 12.5 13.3 15.0 15.0 15.5 16.5
Magnetic data
Coordination
Paramagnetic Paramagnetic Paramagnetic Paramagnetic Paramagnetic Antiferro Diamagnetic Diamagnetic Diamagnetic Diamagnetic
Octahedral Octahedral Tetrahedral Octahedral Octahedral Octahedral Square planar Distorted octahedral Square planar Distorted octahedral
3.2. Determination of coordination On the basis of magnetic behaviour it is possible to decide upon the coordination of nickel ion in nickel complexes [4]. Diamagnetic complexes of nickel are generally’ square planar/penta coordinated and paramagnetic complexes are either octahedrally or tetrahedrally coordinated (Table 3). It is concluded therefore, that Ni(EINA)2 and Ni(HTGA)2 may be octahedral/tetrahedral and Ni(HMA0)2 may be square planar. However, empirical criterion of VAN NORDSTRAND[6] and MITCHELLand BEEMAN[4] on the shape of the
968
s. v.
SALVI
et al.
Table 3. Coordination and magnetic type of some Ni(II) complexes Coordination number
Compound NiC1,.6H20 Ni(en),(NO&
WW-bMBr~ K3CNiVW [Ni(PHPh2)&] [Ni(PHPh,),Br,]
WGH5LP12C~2 Ni-bis-salicylaldehyde-o-phenylene diamine Ni-bis-N-methylsalicylaldiamine
4 (Square planar) 4 (Square planar) 4 (Square planar) 4 (Tetrahedral) 4 (Tetrahedral)
Magnetic type Paramagnetic[ 171 Paramagnetic[17] Paramagnetic[ 171 Diamagnetic[ 171 Diamagnetic[ 181 Diamagnetic[ 181 Diamagnetic[ 171
Diamagnetic[4] Diamagnetic[4] Paramagnetic[ 171 Paramagnetic[17]
absorption edge has led to reliable determination of the coordination of the ion in a compound. On the basis of these criterion the presence of a low energy absorption maximum “a”, in the case of Ni(HMAO)? indicates that Ni ion in this complex has a square planar structure. A smooth monotonically rising curve of Ni(EINA)2 means octahedral surrounding for Ni ion in Ni(EINA)2. The spectroscopic and magnetic data for Ni(HMA0) and Ni(EINA)2 also agrees with these conclusions. The presence of a low energy absorption maximum “a” along with the paramagnetic nature of Ni(HTGA)2 favours tetrahedral coordination for Ni ions in Ni(HTGA)2. The smooth variation in the absorption coefficient near the edge of Ni(INACA)2 indicates octahedral coordination for this complex. Its diamagnetic behaviour may be ascribed to the distorted octahedra as in the case of Ni(aBM0):. 3.3. Determination of near neighbours and efective charge Edge width of the absorption curve is measured as the separation between the position of the K-absorption edge and the principal absorption maximum. From the knowledge of edge width, valuable information can be derived regarding the nature of ligands surrounding the central absorbing atom. According to the empirical relationship given by NIGAMet al. [15].
P vhf
- XL). E,] ‘I* = constant
where Z (X, - X,) is the summation of difference of electronegativities (Pauling scale) of the central absorbing atom M and its various ligands L and E,is the corresponding edge width. The values of edge width for these complexes and the structures suggested for them are included in Table 1. The value of [E (X, - XL). E,]“* evaluated for each complex is also shown in Table 1. It is interesting to note that it is constant and is approximately 8.4 for all the compounds except for Ni(INAP)* brown, Ni(EINA)* and Ni(INACA), for which it is much greater than 8.4. The assignment of coordination and near neighbours is thus confirmed foi all except these three complexes. Our investigation of transition metal compounds has shown that the value of the constant evaluated tends to be high if the valency is higher [16]. Thus the high K-edge shift in the case of Ni(INACA)* may be due to a higher charge on Ni ion in this complex. This opens up an interesting possibility that Ni(INACA), may be weakly paramagnetic. Indeed the magnetic moments of the Ni(II1) complexes have been reported to be in the range 1.7-2.6 B.M. [17]. [15] [16] [17] [18]
H. L. NIGAM and U. C. SRIVASTAVA, Chem. Commun. 14, 761 (1971). S. V. SALVI, Ph.D. Thesis, Bombay University (1982). B. N. FIGGISand J. LEWIS, Progr. Inorg. Chem. 6, 37 (1964). J. LEWIS, R. S, NYHOLM and G. A. RODLEY, Nature 207, 72 (1965).
Arm. Vol
396. No
8. pp. 965-968,
1984
0
Pnnted,n GreatBnta~n
0584-8547/84 m.oo+ 00 1984. Persamon Press Ltd.
Study of bonding in some nickel complexes of isonitrosoketones S. V. SALVI, P. H. UMADIKAR, M. d. PATIL, P. M. DHADKE Institute of Science, M. Cama Road, Bombay-400032, India
N. V. BHAT Department of Chemical Technology, University of Bombay, Matunga, Bombay-400 019, India (Received 19 December 1983) Abstract-X-ray K-absorption edge analysis of nickel in some nickel complexes of isonitrosoketones has been carried out using a 400-mm bent crystal spectrometer. The analysis has been used to deduce information regarding the mode of bonding, the magnetic behaviour and the coordination of Ni in the complexes. On the basis of the results obtained, it has been concluded that Ni ions in Ni(HMAO), have square planar structure whereas Ni ions in Ni(HTGA)2 have tetrahedral structure. On the other hand Ni ions in Ni(EINA), and Ni(INACA)2 are surrounded by octahedra. Ni ions in Ni(INACA), are in the valence state higher than two and appear to be paramagnetic.
1. INTRODUCTION THE EDGE structure of transition metal ions in complexes has been widely investigated [l-3]. The analysis of edge structure is informative of the chemical bonding, e.g. the assignment of the bonding orbitals [4] and the bonding mode [S]. It is also possible, using the empirical classification of the edge structure of transition metal complexes by VAN NORDSTRAND[6], to determine the coordination of the absorbing ion. Our previous study of the K-absorption edge of some nickel(I1) complexes of isonitrosoketones [7] has given interesting information regarding their bonding and coordination. This has prompted us to investigate few more nickel complexes of isonitrosoketones and present the X-ray K-absorption edge analysis of all the nickel complexes of isonitrosoketones. The complexes include two forms of nickel bis(isonitrosoacetophenate): Ni(INAP)* green and brown [7], Ni(C6H9NZ03):, nickel-a-benzilmonoximate : Ni(a-BMO);, nickel-2-hydroxy-Smethylacetophenoneoxime : Ni(HMA0)2, nickel ethyl-a-isonitrosoacetoacetyl : Ni(EINA)2, nickel isonitrosoacetop-carboxyaniline : Ni(INACA)2 and nickel thioglycolicacidanilide : Ni(HTGA)2. The Kabsorption spectra of NiO and NiClz * 6H20 are included to facilitate comparison.
2. EXPERIMENTAL Spectra were recorded using a 400 mm bent crystal transmission spectrograph with mica crystal as an analyser. Spectra were obtained on INDU industrial X-ray film and were microphotometered using an MO-4 microphotometer. Absorption curves were rigorously averaged. Spectra of nickel and NiClz .6H20 were studied as standards and were compared with those appeared in literature. This was done in order to check the reliability of our experimental set up. The complexes were prepared by the procedure reported [8-131. [l] [2] [3] [4] [S] [6] [7] [S] [9] [lo] [11] [12] [13]
W. W. BEEMANand H. HANSON,Phys. Rev. 76, 118 (1949). F. A. COTTONand H. P. HANSON,J. Chem. Phys. 26, 1758 (1967). N. V. BHAT,A. SYAMAL,S. V. SALVIand P. H. UMADIKAR,Spectrochim. Acta 35B, 489 (1980). G. MITCHELLand W. W. BEEMAN,J. Chem. Phys. 20, 1298 (1952). B. D. PADALIA,C. S. GUFTA,A. V. PAIGANKAR and B. C. HALDAR,Curr. Sci. 38,490 (1969). R. A. VAN NORDSTRAND, Adv. Catalysis 12, 149 (1960). P. H. UMADIKAR,S. G. MESTRY,N. V. BHATand B. C. HALDAR,Spectrochim. Acta JlB, 411 (1976). N. V. THAKKAR,Ph.D. Thesis, Bombay University (1976). M. S. GAIKWAD,Ph.D. Thesis, Bombay University (1976). P. M. DHADKEand B. C. HALDAR,Proc. 15th Int. Coord. C/tern.Corlf. Moscow (1973). B. D. GUPTAand W. U. Malik, J. Znd. Chem. Sot. 48 79 (1971). S. B. KULKARNI,M.Sc., Thesis, Bombay University (1983). M. R. PATIL,Private communication.
s&s) 39:8-B
965
s. v. SALVr et al.
966
3. RESULTSAND DISCUSSION The structural features of the X-ray K-absorption edge of nickel in the complexes are tabulated in Table 1 and also are shown in Fig. 1. The structural data of X-ray K-absorption edge for NiO and NiCl,.6H,O are also included for the sake of comparison. (Ar)ed*4s2 configuration of electrons in nickel indicates that the first allowed transition is 1s -+ 4~. The principal absorption maximum A is therefore, assigned to this transition. It is significant to note that the position of the principal absorption maximum lies in the range 22-30 eV for most of the complexes whereas it has a value in the region of 17-20 eV for ionic compounds such as NiO and NiC12 *6Hz0. Table 1. Structural data such as position of K-absorption edge, principal absorption maximum, edge width and structure suggested of nickel in various nickel compounds Structural feature
Compound Ni(INAP),Brown Ni(INAP)2 Green Ni(HTGA), NiC12.6H20 Ni(EINA)2 NiO NI(C,HgNzO,), Ni(HMAO)* Ni(INACA)2 Ni(aBMO)z
(et)
(et)
(et)
P -
9.4 9.4 10.0 12.2 12.5 13.3 15.0 15.5 15.0 16.5
22.6 17.8 25.0 17.2 22.5 20.3 27.2 28.0 30.0 24.5
P
P P
P
Structure suggested 13.2 8.4 15.0 5.0 10.0 7.0 12.2 12.5 fS.0 8.0
NiN,O., NiN,04 NiS,02 NiOs NiNBOJ NiO, NiN,O NiN,02 NiN,O, NiN,OB
[E,S(X,
* XL)I1” 11.1 8.8 8.7 7.2 9.3 8.4 8.2 8.4 11.8 8.4
3.1. Position of the absorption edge and magnetic property It is well known that the increase in the valency of the ion is associated with the shift in the position of the K-absorption edge towards high energy side, whereas the covalency is observed to suppress the shift. The position of the K-absorption edge, i.e. the half intensity point on the absorption curve, for most of these complexes lies in the range 12.5-16.5 eV. The K-edge of Ni2 + ion in NiC12 -6H2O is situated at 12.2 eV. It would be therefore, not improper to conclude that these complexes are as much ionic as NiC12 *6H2O if not more. However Ni ion in these complexes is in the divalent state and all these complexes are known to be covalent. Moreover these are coordination complexes containing nitrogen and oxygen donor. Therefore, the cause for the high K-absorption edge shift may be other than the charge on the ion. A careful examination of the other data (in particular the magnetic data of the nickel complexes, viz. Ni(INAP), green and brown, Ni(CsH9N203) and Ni(crBM0):) has revealed that the edge shift for paramagnetic complexes is found to be less than 10 eV, whereas that for diamagnetic complexes is in the vicinity of 15.5 eV. A similar trend was observed in the case of the compounds of yttrium, an element from the second transition series [14]. This can be very easily explained on the basis of the ligand field theory. The ee orbitals of a diamagnetic Ni ion are shifted to high energy side compared to the ee orbitals of a paramagnetic ion. A small transition probability exists as these orbitals combine with the p orbitals of the ion through the p orbitals of the ligand. As a result the edge-shift is higher for diamagnetic ions than for paramagnetic ones. It is interesting to note that the absorption edge for NiO (antiferromagnetic) lies approximately in the middle of this spread. It is therefore, concluded that Ni(HMA0)2 and Ni(INACA)2 are diamagnetic. Ni(EINA)2 and Ni(HTGA)2 may be, on the other hand, paramagnetic. The edge shift of Ni2+ ion in NiC12 .6H20 which is paramagnetic is also same as that for Ni(EINA)2. The comparison between the position of K-edge and the magnetic behaviour of the complexes is presented in Table 2. [14] V. G.
BHIDE
and N. V.
BHAT, .I. Ckm.
Phys. 48, 3103 (1968).
Bonding in nickel complexes I
NI Metal
J
Fig. 1. X-ray absorption fine structure of K-edge of some nickel(H) isonitrosoketones. The curves for Ni metal, NiCls.6HsO and NiO are also included to facilitate comparison. The zero of the energy scale has been chosen at the K-edge of nickel metal.
Table 2. Comparison of position of K-absorption edge with magnetic behaviour of nickel complexes Compound Ni(INAP),Brown Ni(INAP),Green Ni(HTGA)s NiCl,.6H,O Ni(EINA), NiO Ni(C,H9NsO& Ni(INACA), Ni(HMAO)s Ni(aBMO),
K(eV) 9.4 9.4 10.0 12.2 12.5 13.3 15.0 15.0 15.5 16.5
Magnetic data
Coordination
Paramagnetic Paramagnetic Paramagnetic Paramagnetic Paramagnetic Antiferro Diamagnetic Diamagnetic Diamagnetic Diamagnetic
Octahedral Octahedral Tetrahedral Octahedral Octahedral Octahedral Square planar Distorted octahedral Square planar Distorted octahedral
3.2. Determination of coordination On the basis of magnetic behaviour it is possible to decide upon the coordination of nickel ion in nickel complexes [4]. Diamagnetic complexes of nickel are generally’ square planar/penta coordinated and paramagnetic complexes are either octahedrally or tetrahedrally coordinated (Table 3). It is concluded therefore, that Ni(EINA)2 and Ni(HTGA)2 may be octahedral/tetrahedral and Ni(HMA0)2 may be square planar. However, empirical criterion of VAN NORDSTRAND[6] and MITCHELLand BEEMAN[4] on the shape of the
968
s. v.
SALVI
et al.
Table 3. Coordination and magnetic type of some Ni(II) complexes Coordination number
Compound NiC1,.6H20 Ni(en),(NO&
WW-bMBr~ K3CNiVW [Ni(PHPh2)&] [Ni(PHPh,),Br,]
WGH5LP12C~2 Ni-bis-salicylaldehyde-o-phenylene diamine Ni-bis-N-methylsalicylaldiamine
4 (Square planar) 4 (Square planar) 4 (Square planar) 4 (Tetrahedral) 4 (Tetrahedral)
Magnetic type Paramagnetic[ 171 Paramagnetic[17] Paramagnetic[ 171 Diamagnetic[ 171 Diamagnetic[ 181 Diamagnetic[ 181 Diamagnetic[ 171
Diamagnetic[4] Diamagnetic[4] Paramagnetic[ 171 Paramagnetic[17]
absorption edge has led to reliable determination of the coordination of the ion in a compound. On the basis of these criterion the presence of a low energy absorption maximum “a”, in the case of Ni(HMAO)? indicates that Ni ion in this complex has a square planar structure. A smooth monotonically rising curve of Ni(EINA)2 means octahedral surrounding for Ni ion in Ni(EINA)2. The spectroscopic and magnetic data for Ni(HMA0) and Ni(EINA)2 also agrees with these conclusions. The presence of a low energy absorption maximum “a” along with the paramagnetic nature of Ni(HTGA)2 favours tetrahedral coordination for Ni ions in Ni(HTGA)2. The smooth variation in the absorption coefficient near the edge of Ni(INACA)2 indicates octahedral coordination for this complex. Its diamagnetic behaviour may be ascribed to the distorted octahedra as in the case of Ni(aBM0):. 3.3. Determination of near neighbours and efective charge Edge width of the absorption curve is measured as the separation between the position of the K-absorption edge and the principal absorption maximum. From the knowledge of edge width, valuable information can be derived regarding the nature of ligands surrounding the central absorbing atom. According to the empirical relationship given by NIGAMet al. [15].
P vhf
- XL). E,] ‘I* = constant
where Z (X, - X,) is the summation of difference of electronegativities (Pauling scale) of the central absorbing atom M and its various ligands L and E,is the corresponding edge width. The values of edge width for these complexes and the structures suggested for them are included in Table 1. The value of [E (X, - XL). E,]“* evaluated for each complex is also shown in Table 1. It is interesting to note that it is constant and is approximately 8.4 for all the compounds except for Ni(INAP)* brown, Ni(EINA)* and Ni(INACA), for which it is much greater than 8.4. The assignment of coordination and near neighbours is thus confirmed foi all except these three complexes. Our investigation of transition metal compounds has shown that the value of the constant evaluated tends to be high if the valency is higher [16]. Thus the high K-edge shift in the case of Ni(INACA)* may be due to a higher charge on Ni ion in this complex. This opens up an interesting possibility that Ni(INACA), may be weakly paramagnetic. Indeed the magnetic moments of the Ni(II1) complexes have been reported to be in the range 1.7-2.6 B.M. [17]. [15] [16] [17] [18]
H. L. NIGAM and U. C. SRIVASTAVA, Chem. Commun. 14, 761 (1971). S. V. SALVI, Ph.D. Thesis, Bombay University (1982). B. N. FIGGISand J. LEWIS, Progr. Inorg. Chem. 6, 37 (1964). J. LEWIS, R. S, NYHOLM and G. A. RODLEY, Nature 207, 72 (1965).