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NDDO study of the coordination structure of M2+(S2CNH2)2 complexes (M = Ni, Cu)
Journal of Molecular Structure (Theochem), 139 (1986) 241-245 Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
NDDO STUDY OF THE COORDINATION STRUCTURE OF M2+(SzCNIIz)z COMPLEXES (M = Ni, Cu)
C. NIEKE Organisations- und Rechenzentrum, Karl-Marx-Universitiit, Leipzig (Deutsche Demokratische Republik)
Karl-Marx-Platz, DDR-7010
J. REINHOLD Sektion Chemie, Karl-Marx-Universitiit, Demo kratische Repu blik)
Talstrasse 35, DDR-7010
Leipzig (Deutsche
(Received 6 December 1985; in final form 13 March 1986)
ABSTRACT Quantum chemical NDDO calculations were performed with the aim of explaining the differing structures of copper( II) and Ni(II)bis( dithiocarbamate) complexes. Departure from planarity in copper complexes is reproduced by calculations, although the bent angle observed in the crystal is only reproduced when a sulfur atom of the neighbouring complex is included in the model system. An attempt was made to give a qualitative account of the bonding in the two complexes on the basis of the A0 picture of the central atom. INTRODUCTION
The crystal structures of the copper( II)bis(dithiocarbamate) and the corresponding nickel( II) compound exhibit characteristic differences. The central atom in the nickel complex respects a symmetry centre and the two ligand molecules are coordinated planar [l], while the copper complexes form binary units. In these binary units the two complexes are arranged in an approximately parallel fashion, whereby one sulfur atom is additionally coordinated to the neighbouring complex. They show a bent angle of about 6”, the chelate rings being bent away from the neighbouring complex. Additionally, the copper complex is twisted with an angle of about 10” [2, 31. The values amount to 3” and 8”, for the bent angle and the twisting angle, respectively, for the copper methyl complex [ 41. The reason for the distortion has been discussed by Bonamico et al. [2] in the following way. The central-Cu( II) ion strives to increase the coordination number, which causes an interaction between the copper and a sulfur atom of a neighbouring complex. Consequently, the copper has a tetragonalpyramidal coordination sphere. This cannot, however, explain the additional torsion. In the present paper, we try to calculate the possible distortions of the copper and nickel complexes by using the quantum-chemical NDDO method 0166-1280/86/$03.50
o 1986 Elsevier Science Publishers B.V.
242
which has been parametrized for transition metals [5]. The CNDO and INDO results are also included for comparison. The importance of the two-center two-electron integrals for the calculation of the chelate angles can be studied in this way because of the more consistent consideration of these integrals in the NDDO method as compared with other semiempirical methods. CALCULATIONS
AND DISCUSSION
The calculations were carried out on model compounds: single complexes in which the alkyl groups, R, have been replaced by H. Consequently, the real situation in the binary copper units cannot be comprehended. The influence of the neighbouring complex was simply simulated by a single sulfur atom additionally coordinated to the central ion. The parameters for Cu and Ni are described in [5] . For main-group elements the standard CNDO parameter values were used [6]. The geometry of the ligands and the metal-ligand distances are taken from the literature
The torsion of the complex Figure 1 shows the potential-energy curves for the torsion of the complexes. For the nickel complex, the calculations yield a large energy increase, although only for higher torsional angles (Fig. 1 b). The existence of planar molecules is, however, comprehensible. If the copper complex is twisted (Fig. la), the energy values are much more sensitive than for the nickel complex. The potential curves obtained by using the various semiempirical methods, point out, however, that only with the NDDO method is a minimum obtained (CX = 42”). The bending of the complex Figure 2 shows the potential curves depending on the bent angle 0 received by NDDO. Already, at small angles, for both M = Cu and M = Ni, a drastic increase in energy is calculated. From this result it follows that the bending of the complex is not based on the properties of a single molecule. The crystal structure [ 21 shows that the next intramolecular neighbour of a copper atom is a sulfur atom (Si) at a distance of 2.85 a. To simulate these conditions we repeated the calculations taking into account this sulfur atom. Figure 3 shows the resulting potential curves. The different behaviour of the copper and the nickel complexes could be discussed as follows. The sulfur atoms of the chelate rings (S,) coordinate to the px, py and the d,, orbitals of the central ion. The latter is empty in Ni(II), whereas it is singly occupied in Cu(I1). This results in a weaker coordinative bond, as can be seen from the Wiberg bond indices (Table 1). If we add a sulfur atom Si to the complex, the nickel-chelate bonds are only
243
I
b
60
30
90
a (“1 t
(b) I
,
0
.
60
30
90
a(“)
Fig. 1. Dependence of the total energy on the torsion angle, 01.(a) Cu( dtc),; (b) Ni(dtc),. (-) NDDO; (---) INDO; (-.-) CNDO.
Fig. 2. Dependence of the total energy on the bend angle, 0. (a) Cu(dtc),; (-) NDDO; (---> INDO.
(b) Ni( dtc),.
244
S~M-S - H_p&
Fig. 3. Dependence of the total energy on the bend angle, p. (a) Cu( dtc),-Si; Si. (-) NDDO; (-es) INDO.
(b) Ni( dtc),-
imperceptibly influenced. Si is an almost neutral atom and its bond to the central ion is therefore weaker than the Ni-Sci, bonds; thus the charge distribution in the chelate rings is essentially unchanged. In the copper complex, however, a part of the spin density is transferred from the central ion to Sj. The Cu-Sc,, bonds are more stable and are comparable in strength with the Cu-Si bond. Consequently, the Cu(I1) central ion has a tetragonal-pyramidal coordination sphere and for such systems it is energetically more favourable if the angle XbasaiMXapicd is greater than 90”, whereas the charge distribution and the bond strength are essentially unchanged, if this angle is varied. It should be possible to transfer the resulting Cu-Si bond to the dimer unit, thus explaining the observed bent angle and the tetragonal-pyramidal coordination sphere of the central ion in the crystal structure. The charge transfer of the Si atom, however, will not .appear in the real dimer, because this atom is part of a neighbouring chelate ring. CNDO and INDO calculations (shown in Figs. l-3 for comparison) do not give satisfactory results. The improvement obtained by using the NDDO method confirms our earlier statement [5, 71 that this method can be very useful for theoretical studies of the geometrical structure of coordination compounds. TABLE 1 Wiberg bond indices ( W) and sulfur charges (q) by the NDDO method P0 Ni( dtc), Ni( dtc),--Si Cu(dtc), Cu( dtc),-Si Cu( dtc),-Si
0 0 14
wM-sch 0.68 0.66 0.59 0.66 0.66
%h -0.06 -0.04 -0.19 0.02 -0.02
wM-Si
QSi
0.52
0.05
0.66 0.66
-0.59 -0.56
245 REFERENCES 1 M. Bonarnico, G. Dessy, C. Mariani, A. Viciago and L. Zambonelli, Acta Crystallogr., 19 (1965) 619. 2 M. Bonamico, G. Dessy, A. Mugnoli, A. Vaciago and L. Zambonelli, Acta Crystallogr., 19 (1965) 886. 3 B. H. Connor and E. N. Maslen, Acta Crystallogr., 21(1966) 828. 4 F. K. B. Einstein and J. S. Field, Acta Crystallogr., Sect. B: 30 (1974) 2928. 5 C. Nieke and J. Reinhold, Theor. Chim. Acta, 65 (1984) 99. 6 J. A. Pople and D. L. Beveridge, Approximate Molecular Orbital Theory, McGraw-Hill, New York, 1970. 7 C. Nieke and J. Reinhold, J. Mol. Struct. (‘Pheochem), 124 (1985) 87.
NDDO STUDY OF THE COORDINATION STRUCTURE OF M2+(SzCNIIz)z COMPLEXES (M = Ni, Cu)
C. NIEKE Organisations- und Rechenzentrum, Karl-Marx-Universitiit, Leipzig (Deutsche Demokratische Republik)
Karl-Marx-Platz, DDR-7010
J. REINHOLD Sektion Chemie, Karl-Marx-Universitiit, Demo kratische Repu blik)
Talstrasse 35, DDR-7010
Leipzig (Deutsche
(Received 6 December 1985; in final form 13 March 1986)
ABSTRACT Quantum chemical NDDO calculations were performed with the aim of explaining the differing structures of copper( II) and Ni(II)bis( dithiocarbamate) complexes. Departure from planarity in copper complexes is reproduced by calculations, although the bent angle observed in the crystal is only reproduced when a sulfur atom of the neighbouring complex is included in the model system. An attempt was made to give a qualitative account of the bonding in the two complexes on the basis of the A0 picture of the central atom. INTRODUCTION
The crystal structures of the copper( II)bis(dithiocarbamate) and the corresponding nickel( II) compound exhibit characteristic differences. The central atom in the nickel complex respects a symmetry centre and the two ligand molecules are coordinated planar [l], while the copper complexes form binary units. In these binary units the two complexes are arranged in an approximately parallel fashion, whereby one sulfur atom is additionally coordinated to the neighbouring complex. They show a bent angle of about 6”, the chelate rings being bent away from the neighbouring complex. Additionally, the copper complex is twisted with an angle of about 10” [2, 31. The values amount to 3” and 8”, for the bent angle and the twisting angle, respectively, for the copper methyl complex [ 41. The reason for the distortion has been discussed by Bonamico et al. [2] in the following way. The central-Cu( II) ion strives to increase the coordination number, which causes an interaction between the copper and a sulfur atom of a neighbouring complex. Consequently, the copper has a tetragonalpyramidal coordination sphere. This cannot, however, explain the additional torsion. In the present paper, we try to calculate the possible distortions of the copper and nickel complexes by using the quantum-chemical NDDO method 0166-1280/86/$03.50
o 1986 Elsevier Science Publishers B.V.
242
which has been parametrized for transition metals [5]. The CNDO and INDO results are also included for comparison. The importance of the two-center two-electron integrals for the calculation of the chelate angles can be studied in this way because of the more consistent consideration of these integrals in the NDDO method as compared with other semiempirical methods. CALCULATIONS
AND DISCUSSION
The calculations were carried out on model compounds: single complexes in which the alkyl groups, R, have been replaced by H. Consequently, the real situation in the binary copper units cannot be comprehended. The influence of the neighbouring complex was simply simulated by a single sulfur atom additionally coordinated to the central ion. The parameters for Cu and Ni are described in [5] . For main-group elements the standard CNDO parameter values were used [6]. The geometry of the ligands and the metal-ligand distances are taken from the literature
The torsion of the complex Figure 1 shows the potential-energy curves for the torsion of the complexes. For the nickel complex, the calculations yield a large energy increase, although only for higher torsional angles (Fig. 1 b). The existence of planar molecules is, however, comprehensible. If the copper complex is twisted (Fig. la), the energy values are much more sensitive than for the nickel complex. The potential curves obtained by using the various semiempirical methods, point out, however, that only with the NDDO method is a minimum obtained (CX = 42”). The bending of the complex Figure 2 shows the potential curves depending on the bent angle 0 received by NDDO. Already, at small angles, for both M = Cu and M = Ni, a drastic increase in energy is calculated. From this result it follows that the bending of the complex is not based on the properties of a single molecule. The crystal structure [ 21 shows that the next intramolecular neighbour of a copper atom is a sulfur atom (Si) at a distance of 2.85 a. To simulate these conditions we repeated the calculations taking into account this sulfur atom. Figure 3 shows the resulting potential curves. The different behaviour of the copper and the nickel complexes could be discussed as follows. The sulfur atoms of the chelate rings (S,) coordinate to the px, py and the d,, orbitals of the central ion. The latter is empty in Ni(II), whereas it is singly occupied in Cu(I1). This results in a weaker coordinative bond, as can be seen from the Wiberg bond indices (Table 1). If we add a sulfur atom Si to the complex, the nickel-chelate bonds are only
243
I
b
60
30
90
a (“1 t
(b) I
,
0
.
60
30
90
a(“)
Fig. 1. Dependence of the total energy on the torsion angle, 01.(a) Cu( dtc),; (b) Ni(dtc),. (-) NDDO; (---) INDO; (-.-) CNDO.
Fig. 2. Dependence of the total energy on the bend angle, 0. (a) Cu(dtc),; (-) NDDO; (---> INDO.
(b) Ni( dtc),.
244
S~M-S - H_p&
Fig. 3. Dependence of the total energy on the bend angle, p. (a) Cu( dtc),-Si; Si. (-) NDDO; (-es) INDO.
(b) Ni( dtc),-
imperceptibly influenced. Si is an almost neutral atom and its bond to the central ion is therefore weaker than the Ni-Sci, bonds; thus the charge distribution in the chelate rings is essentially unchanged. In the copper complex, however, a part of the spin density is transferred from the central ion to Sj. The Cu-Sc,, bonds are more stable and are comparable in strength with the Cu-Si bond. Consequently, the Cu(I1) central ion has a tetragonal-pyramidal coordination sphere and for such systems it is energetically more favourable if the angle XbasaiMXapicd is greater than 90”, whereas the charge distribution and the bond strength are essentially unchanged, if this angle is varied. It should be possible to transfer the resulting Cu-Si bond to the dimer unit, thus explaining the observed bent angle and the tetragonal-pyramidal coordination sphere of the central ion in the crystal structure. The charge transfer of the Si atom, however, will not .appear in the real dimer, because this atom is part of a neighbouring chelate ring. CNDO and INDO calculations (shown in Figs. l-3 for comparison) do not give satisfactory results. The improvement obtained by using the NDDO method confirms our earlier statement [5, 71 that this method can be very useful for theoretical studies of the geometrical structure of coordination compounds. TABLE 1 Wiberg bond indices ( W) and sulfur charges (q) by the NDDO method P0 Ni( dtc), Ni( dtc),--Si Cu(dtc), Cu( dtc),-Si Cu( dtc),-Si
0 0 14
wM-sch 0.68 0.66 0.59 0.66 0.66
%h -0.06 -0.04 -0.19 0.02 -0.02
wM-Si
QSi
0.52
0.05
0.66 0.66
-0.59 -0.56
245 REFERENCES 1 M. Bonarnico, G. Dessy, C. Mariani, A. Viciago and L. Zambonelli, Acta Crystallogr., 19 (1965) 619. 2 M. Bonamico, G. Dessy, A. Mugnoli, A. Vaciago and L. Zambonelli, Acta Crystallogr., 19 (1965) 886. 3 B. H. Connor and E. N. Maslen, Acta Crystallogr., 21(1966) 828. 4 F. K. B. Einstein and J. S. Field, Acta Crystallogr., Sect. B: 30 (1974) 2928. 5 C. Nieke and J. Reinhold, Theor. Chim. Acta, 65 (1984) 99. 6 J. A. Pople and D. L. Beveridge, Approximate Molecular Orbital Theory, McGraw-Hill, New York, 1970. 7 C. Nieke and J. Reinhold, J. Mol. Struct. (‘Pheochem), 124 (1985) 87.