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Adduct formation by sub-coordinated metal complexes—VI. Synthesis and pyridine adducts of some nickel(II) chelates formally tri-coordinated
Notes exprriences prrliminaires nous permettent d'ailleurs de penser que AIC13 est incapable de drplacer AI(OCH(CF3)2)3 des complexes examinrs ici. J-.P. LAUSSAC J-.P. LAURENT Laboratoire de Chimie de Coordination C.N.R.S. B.P. 4142-31030 Toulouse Cedex France REFERENCES 1. J-.P. Laussac, J-.P. Laurent et G. Commenges, Org. Mag. Res. sous presse. 2. I. R. Beattie et G. A. Ozin, J. Chem. Soc. A, 2373 (1%8); 2535 (1%9).
599
3. T. N. Huckerby, J. W. Wilson et I. J. Worral, J. Chem. Soc. A, 1189 (1%9). 4. W. H. N. Vriezen et F. Jellinek, Rec. Tray. Chim. 89, 1306 (1970). 5. M. S. Bains et D. C. Bradley, Can. J. Chem. 40, 1350 (1%2); 40, 2218 (1%2). 6. V. J. Shiner, Jr. et D. Whittaker, J. Am. Chem. Soc. 87, 843 (1964). 7. J. G. Oliver et I. J. Worrall, J. Inorg. Nucl. Chem. 33, 1281 (1971). 8. T. Ueshima, S. Tonita et T. Saegusa, Bull. Chem. Soc. Japan 41, 1194 (1968). 9. K. S. Mazdiyasni, B. J. Schaper et L. M. Brown, Inorg. Chem. 10, 889 (1971). 10. W. Davies et W. Jones, J. Chem. Soc. 132, 1262 (1929). 11. J-.P. Laussac et J-.P. Laurent, J. Chem. Phys. 3,417 (1973).
J. inorg,nucl.Chem.,1976.Vol.38, pp. 599-601. PergamonPress. PrintedinGreatBritain
Adduct formation by sub-coordinated metal complexes--Vl. Synthesis and pyridine adducts of some nickel(H) chelates formally tri-coordinated (First received 11 March 1974; in revisedform 9 September 1975) PREVIOUS papers report studies concerning addition of N-ring bases (pyridine, mono and dimethylpyridines and cycIomethylenimines) to bis(salicylaldoximate)nickel(ll), a monomer substrate having a square-planar structure[I-4]. Similar studies with O-N-O and O-N-S donors are reported here. The ligand molecules are: (a) N-(2-hydroxyphenyl)-salicylaldimine(Hasap); (b) 2-pentanone-4-(2-benzothiazoline), (H~aat); (c) 2-(0hydroxiphenyl)benzothiazoline, (H2sat); they react with metal ions as dianions of the corresponding tridentate Schiff bases[5]. All the substrates and the corresponding pyridine addition products were synthesized and investigated by vibrational and electronic spectroscopy, magnetic measurements and differential thermal analysis. EXPERIMENTAL Preparation o.f the compounds and analysis. Analytical grade reagents were used through all the experiments. H2aat, Hasat and H2sap were synthesized as previously reported [5-7]. Nisap was prepared mixing a solution of Hasap (21 g) in ethanol (150 ml) with a solution of Ni(CH3COO)2.4HaO(25 g) in 1:1 water ethanol (100ml). The mixture was refluxed for 8hr until separation of a dark brown solid which was filtered from the hot solution, washed with ethanol-ether mixture and dried at 120°C. It is poorly soluble in the most common organic solvents. Nisap. 3py was synthesized refluxing Nisap (5 g) in an excess of pyridine (10 ml) until complete solution. The brown liquid was cooled at room temperature, then a small amount of benzene (30 ml) and a large excess of petroleum ether were added with stirring. The brown crystals separated were quickly pump filtered and washed with little petroleum ether. They smell strongly pyridine at room temperature, and require storing in a closed bottle. Nisap.py was obtained by refluxing nisap.3py in ethanol until complete solution. After cooling a yellow pink solid was separated, pump filtered, washed with ethanol and stored in a dessicator over NaOH. It smells but very little of pyridine. Niaat was prepared by mixing equimolar amounts of Ni(CH3COO)2.4HaO(6'2g) and H2aat (5.1g) just as for the preparation of Nisat. The dark solid obtained was recrystallized from aceton and dried over silica gel. Niaat.py was obtained as dark brown crystals following the same method as for Nisat.py. Nisat was prepared by mixing equimolar amounts of
Ni(CH3COO)a.4HaO(6.2g) in water--ethanol 1 : 1 mixture (110 ml) and Hasat(5.5 g) in ethanol (100 ml). It precipitated immediately as dark brown dust which was separated by centrifugation, purified by recrystaUization from CH2CI2 and dried over silica gel. Nisat.py was obtained by dissolving Nisat (1.0g) in hot pyridine (5.0 ml), evaporation of the resulting dark solution till small volume and addition of petroleum ether while stirring. The dark solid, so separated, was pump filtered and washed with little petroleum ether. A survey of the analytical results is given in Table 1. Physical measurements. Vibrational spectra were carried out in the 4000-250 cm -~ range using KCI disk for the pyridine adducts, Nujol or KC1 disk for the other compounds. A Perkin-Elmer 457 Spectrometer was used in any case. Electronic and diffuse reflectance spectra were recorded in the 1000-250 m/~ range by using a Beckman DK 2A spectrometer. The solvents used were dichloroethane, methanol or N,N dimethylacetamide; MgO for the solids. Magnetic measurements[8] and differential thermal analysis (DTA)[111 were carried out, as previously reported. RESULTS AND DISCUSSION All the parent complexes investigated exhibit a ratio 1 '. 1 ligand to nickel. Solubilities in polar organic solvents followed the order Niaat,>Nisat>Nisap as found by previous workers[12]. Osmometric measurements indicate that Niaat is a dimer in CH2C12[12]; the solubilities of Nisat and Nisap were too low to permit measurement of molecular weights, suggesting cluster species in such complexes. To obtain information about which donor atoms of the ligands are bound to the metal atom in the complexes, IR spectra of Nisap, Nisat and Niaat were compared with those of the free ligands. So the absence of the OH stretch frequency and the shift of the CN stretch frequency (1630-1610 cm -~) can be seen in the Nisap spectrum when compared with that of Hasap. Free H:sat and Haaat have benzothiazoline structures as indicated by vibrational and electronic spectra [5]. The frequencies attributable to NH (at 3260 cm -~) and OH (at 3060 cm -~) in Hasat disappear in the Nisat IR spectrum while the formation of a C=N bond is evident from the appearance in the same spectrum of a band at 1600 cm -1. Analogously the Niaat vibrational spectrum does not exhibit any NH or C=O frequency, which are clearly visible in the H2aat spectrum, (at 3350 and 1705 cm -1) while it exhibits the vc-~
600
Notes Table 1. Analyticaldata C% fob~d (ealcd.)
H% fottnd (calcd.)
N% found (calcd.)
0% fotk~d (calcd.)
Nisap C13HgN02Ni
57.6 (57.8)
3.43 (3.36)
4.89 (5.19)
13.! (11.9)
Nisap.pyr 018H13N202Ni
62.2
(62.1)
3.99 (3.77)
8.09 (8.05)
NisaP.3pyr C28H24N402Ni
(66.3)
4.77 (4.77)
Nisat C13H9NOSNi
54.6 (54.6)
3.28 (3.17)
4.82 (4.90)
5.59 (5.59)
Nisat.pyr C18HI3N20SNi
60.1 (59.4)
3.75 (3.60)
7.51 (7.69)
4.38 (4.40)
Niaat C11H11NOSNi
49.9 (50.0)
4.41 (4.20)
5.11 (5-31)
6.20 (6.06)
Niaat C16H16N208Ni
55.2 (56.0)
4.55 (4.70)
7.99 (8.17)
(4.67)
Compound
66.5
11.3 (11.1)
(at 1600 cm-') which is absent in the H~aat spectrum. The above results confirm that all the ligands employed in this research behave as tridentate bi-anions of the corresponding Schiff bases[5]. In Fig. 1 are reported sketches of structures of the ligands and complexes investigated. Niaat and Nisat are diamagnetic in agreement with a square planar environment for the metal atom in dimer molecules. The magnetic behaviour of Nisap is completely different. In fact it is paramagnetic and, in the range 100-300°K the effective magnetic moment changes from 3.0 to 3.2 B.M. Consequently, considering the small orbital contribution to the effective magnetic moment and slight temperature dependence, we suggest a pseudo-octahedral structure for the metal atom environment. This configuration can be reached by axial polymerization of planar dimer moities through Ni-O-Ni bridges. On the other hand the rigidity of the ligand could hinder the formation of any tetrahedral dimer structure, in agreement with the resemblance of the vibrational spectra of H2sap and Nisap. Polymerization is shown by some copper(II) and nickel(II) complexes with tridentate dibasic ligands[15, 16]. It must be noticed that in the range in which the susceptibility measurements were carried Nisap does not seem to exhibit antiferromagnetic interaction which, on the other hand, have been reported for some metal complexes of trldentate ligands [17]. Concerning the absorbance and reflectance spectra of the complexes, Nisat and Niaat exhibit bands whose intensity is comparable to that of other nickel(II) complexes with sulphur containing ligands; in the visible range Nisap exhibits only one band which can be assigned to a d - d transition and exhibits a normal value for the molar extinction coefficient (e = 12) for octahedral complexes. It must be noticed also that our results concerning spectro-
S,% fo%L~d (calcd.)
N i~o f olnqd (calcd.)
20.9 (21.7)
9.30 (9.20)
16.7 (16.9)
6.31 (6.31)
11.3 (11.6) 11.3 (11,2) 8.79
(8.81)
19.5
(20.5) 15.9
(16.1)
12.2 (12.6)
22.4 (22.2)
9.30
16.1 (17.1)
4.60
(9.35)
scopic data disagree with those reported by Brubaker. As a matter of fact, the usual C=N frequency assignments[13] for such complexes (1600 cm -~) differ from the authors assignments in the case of the Nisat and Niaat compounds[12]. Our data regarding the electronic spectra of the same complexes disagree too with those of the above authors as far as it concerns wavelengths and extinction coefficients at the maxima (see Table 3). These disagreements probably derive from the different procedure used by Brubaker et al. for preparing and purifying the complexes. We agree however with the structure of Niaat and Nisat proposed by them. Niaat, Nisat and Nisap react with pyridine giving stable 1:1 adducts of the hypothetical monomer tri-coordinated parent complexes. Vibrational spectra of these adducts show the peculiarity of the parent complexes and new bands (in the range 700-600cm -') which can be assigned to the pyridine ring vibrations[14]. All the monopyridine adducts are diamagnetic, suggesting a monomer square planar structure for them. Only in the case of Nisap it is possible to get a terpyridine adduct. It is paramagnetic (p.~= Y36B.M. at 278°K) and consequently for this adduct a pseudooctahedral structure can be inferred. Differential thermal analysis performed on Nisap.3py exhibit four endothermic peaks, at 130,181,240 and 390°C. The first seems consistent with the loss of two pyridine molecules (from the axial sites), changing Nisap.3py to Nisap.py; consequently the brown color of the substance turns to pink; then the monopyridine adduct looses pyridine changing to the monomer parent complex which polymerizes to the dark brown compound (Nisap) through the square planar dimer form and, finally, decomposes. The last three endothermic steps are found at the same temperatures in the DTA curves of Nisap.py. Nisat.py and Niaat.py loose pyridine at lower temperature. The
Table 2. Wavelengths in kK and molar absorbance @) of the parent complexes spectra maxima Complex
this paper
Reference(12)
25.0 36.6 38,5
(9.42.103) (2.59"104) (2,47"104 )
25.5 38.8 39.6
(8.30"103) (2.23"104) (2.09"104 )
Niaat in CH2C12
18.2 26.3 38.5
(9.75.102 ) (7.32"T03) (2.42-I04 )
19.2 32.2 34.5
(9.75402 ) (7-00"I03) (5-45"I04 )
NisaP in CH30H
11.4
(11.8)
Nisat
in CH2C12
Notes
Ni
601
L
.
/ n
sap- Nlsap
o
/=N\
~
NIIIp,3p v
S
cH~
o o/N~\L
L-~..,.,~.
Nislp.py
/4
'Sc"
T
8.p,t
"c:,3
~
H
Nlllt.py
Nlaat
eat'-
Nlsat.p¥ ~$1""
-
Nlsat
Fig. 1. Sketch of structures of the ligands and complexes investigated. L = pyridine. impossibility of obtaining tris-pyridine adducts of Nisat and of Niaat seems in agreement with the lower stability of Nisat.py and Niaat.py in comparison to Nisap.py. In conclusion, the results reported in this paper confirm the weak tendency of nickel(II) to give tri-coordinated complexes. On the other hand the different type of coordination exhibited by ON-O (in sap 2-) and O-N-S (in sat2- and aat 2-) donor systems, can be ascribed to the higher polarizability of the sulphur atom compared with the oxygen atom. According to Pauling's e lectroneutrallity principle[18] it is expected than an ion, on bond formation, takes little charge from many difficult polarizable atoms and much charge from a few readily polarizable atoms [19]. This could be one of the factors which explains the impossibility of obtaining tris pyridine adducts of Nisat and Niaat.
Acknowledgements--We thank Italian CNR (Consiglio Nazionale deUe Richerche, Roma) for financial support. Gruppo Chimica di Coordinazione Universit?t degli Studi di Palermo Istituto di Chimica Generale Via Archirall 26 90123 Palermo, Italy
F. T. V. G.
MAGGIO PIZZINO ROMANO DIA
REFERENCES 1. F. Maggio, V. Romano, T. Pizzino and L. Pellerito, Ann. Chim. (Roma) 58, 725 (1968). 2. V. Romano, T. Pizzino, L. Pellerito and F. Maggio, Ann. Chim. (Roma) 59, 828 (1969).
3. V. Romano, F. Maggio and T. Pizzino, J. Inorg. Nucl. Chem. 33, 2622 (1971). 4. F. Maggio and V. Romano, J. lnorg. Nucl. Chem. 33, 3933 (1971). 5. R. Cefalh, R. Bosco, F. Bonati, F. Maggio and R. Barbieri, Z. Anorg. Allg. Chem. 376, 180 (1970); and refs. therein. 6. F. Maggio, R. Bosco, R. CefalO and R. Barbieri, Inorg. Nucl. Chem. lett. 4, 389 (1968). 7. M. Claasz, Ber. Dtsch. Chem. Ges. 49, 1141 (1916). 8. L. Sacconi, M. Ciampolini, F. Maggio and F. P. Cavasino, J. Inorg. Nucl. Chem. 19, 73 (1961). 9. B. N Figgs and R. S. Nyholm, J. Chem. Soc. 4190 (1958). 10. P. W. Selwood, Magnetochemistry. Interscience, New York (1956). 11. G. Werber and F. Maggio, Ann. Chim. (Roma) 53, 3 (1963). 12. G. R. Brubaker, J. C. Datta, Inorg. Chem. 9, 2608 (1970). 13. R. H. Holen and G. Everett, Jr., Progress in Inorganic Chemistry (Edited by F. A. Cotton), Vol. 7, p. 161. Wiley, New York (1966); and refs. therein. 14. D. M. Adams, Metal-Ligand and Related Vibrations. Arnold, London (1%7); and refs. therein. 15. J. A. Bertrand and C. E. Kirkwood, Inorg. Chim. Acta 4, 192 (1970). 16. M. Kato, H. B. Jonhassen andJ. C. Fanning, Chem. Rev. 64,99 (1964). 17. A. P. Ginsberg, R. C. Sherwood and E. Koubek, L Inorg. Nucl. Chem. 29, 353 (1967). 18. L. Pauling, J. Chem. Soc. 1461 (1948). 19. R. S. Nyholm, Proc. Chem. Soc. 273 (1961).
599
3. T. N. Huckerby, J. W. Wilson et I. J. Worral, J. Chem. Soc. A, 1189 (1%9). 4. W. H. N. Vriezen et F. Jellinek, Rec. Tray. Chim. 89, 1306 (1970). 5. M. S. Bains et D. C. Bradley, Can. J. Chem. 40, 1350 (1%2); 40, 2218 (1%2). 6. V. J. Shiner, Jr. et D. Whittaker, J. Am. Chem. Soc. 87, 843 (1964). 7. J. G. Oliver et I. J. Worrall, J. Inorg. Nucl. Chem. 33, 1281 (1971). 8. T. Ueshima, S. Tonita et T. Saegusa, Bull. Chem. Soc. Japan 41, 1194 (1968). 9. K. S. Mazdiyasni, B. J. Schaper et L. M. Brown, Inorg. Chem. 10, 889 (1971). 10. W. Davies et W. Jones, J. Chem. Soc. 132, 1262 (1929). 11. J-.P. Laussac et J-.P. Laurent, J. Chem. Phys. 3,417 (1973).
J. inorg,nucl.Chem.,1976.Vol.38, pp. 599-601. PergamonPress. PrintedinGreatBritain
Adduct formation by sub-coordinated metal complexes--Vl. Synthesis and pyridine adducts of some nickel(H) chelates formally tri-coordinated (First received 11 March 1974; in revisedform 9 September 1975) PREVIOUS papers report studies concerning addition of N-ring bases (pyridine, mono and dimethylpyridines and cycIomethylenimines) to bis(salicylaldoximate)nickel(ll), a monomer substrate having a square-planar structure[I-4]. Similar studies with O-N-O and O-N-S donors are reported here. The ligand molecules are: (a) N-(2-hydroxyphenyl)-salicylaldimine(Hasap); (b) 2-pentanone-4-(2-benzothiazoline), (H~aat); (c) 2-(0hydroxiphenyl)benzothiazoline, (H2sat); they react with metal ions as dianions of the corresponding tridentate Schiff bases[5]. All the substrates and the corresponding pyridine addition products were synthesized and investigated by vibrational and electronic spectroscopy, magnetic measurements and differential thermal analysis. EXPERIMENTAL Preparation o.f the compounds and analysis. Analytical grade reagents were used through all the experiments. H2aat, Hasat and H2sap were synthesized as previously reported [5-7]. Nisap was prepared mixing a solution of Hasap (21 g) in ethanol (150 ml) with a solution of Ni(CH3COO)2.4HaO(25 g) in 1:1 water ethanol (100ml). The mixture was refluxed for 8hr until separation of a dark brown solid which was filtered from the hot solution, washed with ethanol-ether mixture and dried at 120°C. It is poorly soluble in the most common organic solvents. Nisap. 3py was synthesized refluxing Nisap (5 g) in an excess of pyridine (10 ml) until complete solution. The brown liquid was cooled at room temperature, then a small amount of benzene (30 ml) and a large excess of petroleum ether were added with stirring. The brown crystals separated were quickly pump filtered and washed with little petroleum ether. They smell strongly pyridine at room temperature, and require storing in a closed bottle. Nisap.py was obtained by refluxing nisap.3py in ethanol until complete solution. After cooling a yellow pink solid was separated, pump filtered, washed with ethanol and stored in a dessicator over NaOH. It smells but very little of pyridine. Niaat was prepared by mixing equimolar amounts of Ni(CH3COO)2.4HaO(6'2g) and H2aat (5.1g) just as for the preparation of Nisat. The dark solid obtained was recrystallized from aceton and dried over silica gel. Niaat.py was obtained as dark brown crystals following the same method as for Nisat.py. Nisat was prepared by mixing equimolar amounts of
Ni(CH3COO)a.4HaO(6.2g) in water--ethanol 1 : 1 mixture (110 ml) and Hasat(5.5 g) in ethanol (100 ml). It precipitated immediately as dark brown dust which was separated by centrifugation, purified by recrystaUization from CH2CI2 and dried over silica gel. Nisat.py was obtained by dissolving Nisat (1.0g) in hot pyridine (5.0 ml), evaporation of the resulting dark solution till small volume and addition of petroleum ether while stirring. The dark solid, so separated, was pump filtered and washed with little petroleum ether. A survey of the analytical results is given in Table 1. Physical measurements. Vibrational spectra were carried out in the 4000-250 cm -~ range using KCI disk for the pyridine adducts, Nujol or KC1 disk for the other compounds. A Perkin-Elmer 457 Spectrometer was used in any case. Electronic and diffuse reflectance spectra were recorded in the 1000-250 m/~ range by using a Beckman DK 2A spectrometer. The solvents used were dichloroethane, methanol or N,N dimethylacetamide; MgO for the solids. Magnetic measurements[8] and differential thermal analysis (DTA)[111 were carried out, as previously reported. RESULTS AND DISCUSSION All the parent complexes investigated exhibit a ratio 1 '. 1 ligand to nickel. Solubilities in polar organic solvents followed the order Niaat,>Nisat>Nisap as found by previous workers[12]. Osmometric measurements indicate that Niaat is a dimer in CH2C12[12]; the solubilities of Nisat and Nisap were too low to permit measurement of molecular weights, suggesting cluster species in such complexes. To obtain information about which donor atoms of the ligands are bound to the metal atom in the complexes, IR spectra of Nisap, Nisat and Niaat were compared with those of the free ligands. So the absence of the OH stretch frequency and the shift of the CN stretch frequency (1630-1610 cm -~) can be seen in the Nisap spectrum when compared with that of Hasap. Free H:sat and Haaat have benzothiazoline structures as indicated by vibrational and electronic spectra [5]. The frequencies attributable to NH (at 3260 cm -~) and OH (at 3060 cm -~) in Hasat disappear in the Nisat IR spectrum while the formation of a C=N bond is evident from the appearance in the same spectrum of a band at 1600 cm -1. Analogously the Niaat vibrational spectrum does not exhibit any NH or C=O frequency, which are clearly visible in the H2aat spectrum, (at 3350 and 1705 cm -1) while it exhibits the vc-~
600
Notes Table 1. Analyticaldata C% fob~d (ealcd.)
H% fottnd (calcd.)
N% found (calcd.)
0% fotk~d (calcd.)
Nisap C13HgN02Ni
57.6 (57.8)
3.43 (3.36)
4.89 (5.19)
13.! (11.9)
Nisap.pyr 018H13N202Ni
62.2
(62.1)
3.99 (3.77)
8.09 (8.05)
NisaP.3pyr C28H24N402Ni
(66.3)
4.77 (4.77)
Nisat C13H9NOSNi
54.6 (54.6)
3.28 (3.17)
4.82 (4.90)
5.59 (5.59)
Nisat.pyr C18HI3N20SNi
60.1 (59.4)
3.75 (3.60)
7.51 (7.69)
4.38 (4.40)
Niaat C11H11NOSNi
49.9 (50.0)
4.41 (4.20)
5.11 (5-31)
6.20 (6.06)
Niaat C16H16N208Ni
55.2 (56.0)
4.55 (4.70)
7.99 (8.17)
(4.67)
Compound
66.5
11.3 (11.1)
(at 1600 cm-') which is absent in the H~aat spectrum. The above results confirm that all the ligands employed in this research behave as tridentate bi-anions of the corresponding Schiff bases[5]. In Fig. 1 are reported sketches of structures of the ligands and complexes investigated. Niaat and Nisat are diamagnetic in agreement with a square planar environment for the metal atom in dimer molecules. The magnetic behaviour of Nisap is completely different. In fact it is paramagnetic and, in the range 100-300°K the effective magnetic moment changes from 3.0 to 3.2 B.M. Consequently, considering the small orbital contribution to the effective magnetic moment and slight temperature dependence, we suggest a pseudo-octahedral structure for the metal atom environment. This configuration can be reached by axial polymerization of planar dimer moities through Ni-O-Ni bridges. On the other hand the rigidity of the ligand could hinder the formation of any tetrahedral dimer structure, in agreement with the resemblance of the vibrational spectra of H2sap and Nisap. Polymerization is shown by some copper(II) and nickel(II) complexes with tridentate dibasic ligands[15, 16]. It must be noticed that in the range in which the susceptibility measurements were carried Nisap does not seem to exhibit antiferromagnetic interaction which, on the other hand, have been reported for some metal complexes of trldentate ligands [17]. Concerning the absorbance and reflectance spectra of the complexes, Nisat and Niaat exhibit bands whose intensity is comparable to that of other nickel(II) complexes with sulphur containing ligands; in the visible range Nisap exhibits only one band which can be assigned to a d - d transition and exhibits a normal value for the molar extinction coefficient (e = 12) for octahedral complexes. It must be noticed also that our results concerning spectro-
S,% fo%L~d (calcd.)
N i~o f olnqd (calcd.)
20.9 (21.7)
9.30 (9.20)
16.7 (16.9)
6.31 (6.31)
11.3 (11.6) 11.3 (11,2) 8.79
(8.81)
19.5
(20.5) 15.9
(16.1)
12.2 (12.6)
22.4 (22.2)
9.30
16.1 (17.1)
4.60
(9.35)
scopic data disagree with those reported by Brubaker. As a matter of fact, the usual C=N frequency assignments[13] for such complexes (1600 cm -~) differ from the authors assignments in the case of the Nisat and Niaat compounds[12]. Our data regarding the electronic spectra of the same complexes disagree too with those of the above authors as far as it concerns wavelengths and extinction coefficients at the maxima (see Table 3). These disagreements probably derive from the different procedure used by Brubaker et al. for preparing and purifying the complexes. We agree however with the structure of Niaat and Nisat proposed by them. Niaat, Nisat and Nisap react with pyridine giving stable 1:1 adducts of the hypothetical monomer tri-coordinated parent complexes. Vibrational spectra of these adducts show the peculiarity of the parent complexes and new bands (in the range 700-600cm -') which can be assigned to the pyridine ring vibrations[14]. All the monopyridine adducts are diamagnetic, suggesting a monomer square planar structure for them. Only in the case of Nisap it is possible to get a terpyridine adduct. It is paramagnetic (p.~= Y36B.M. at 278°K) and consequently for this adduct a pseudooctahedral structure can be inferred. Differential thermal analysis performed on Nisap.3py exhibit four endothermic peaks, at 130,181,240 and 390°C. The first seems consistent with the loss of two pyridine molecules (from the axial sites), changing Nisap.3py to Nisap.py; consequently the brown color of the substance turns to pink; then the monopyridine adduct looses pyridine changing to the monomer parent complex which polymerizes to the dark brown compound (Nisap) through the square planar dimer form and, finally, decomposes. The last three endothermic steps are found at the same temperatures in the DTA curves of Nisap.py. Nisat.py and Niaat.py loose pyridine at lower temperature. The
Table 2. Wavelengths in kK and molar absorbance @) of the parent complexes spectra maxima Complex
this paper
Reference(12)
25.0 36.6 38,5
(9.42.103) (2.59"104) (2,47"104 )
25.5 38.8 39.6
(8.30"103) (2.23"104) (2.09"104 )
Niaat in CH2C12
18.2 26.3 38.5
(9.75.102 ) (7.32"T03) (2.42-I04 )
19.2 32.2 34.5
(9.75402 ) (7-00"I03) (5-45"I04 )
NisaP in CH30H
11.4
(11.8)
Nisat
in CH2C12
Notes
Ni
601
L
.
/ n
sap- Nlsap
o
/=N\
~
NIIIp,3p v
S
cH~
o o/N~\L
L-~..,.,~.
Nislp.py
/4
'Sc"
T
8.p,t
"c:,3
~
H
Nlllt.py
Nlaat
eat'-
Nlsat.p¥ ~$1""
-
Nlsat
Fig. 1. Sketch of structures of the ligands and complexes investigated. L = pyridine. impossibility of obtaining tris-pyridine adducts of Nisat and of Niaat seems in agreement with the lower stability of Nisat.py and Niaat.py in comparison to Nisap.py. In conclusion, the results reported in this paper confirm the weak tendency of nickel(II) to give tri-coordinated complexes. On the other hand the different type of coordination exhibited by ON-O (in sap 2-) and O-N-S (in sat2- and aat 2-) donor systems, can be ascribed to the higher polarizability of the sulphur atom compared with the oxygen atom. According to Pauling's e lectroneutrallity principle[18] it is expected than an ion, on bond formation, takes little charge from many difficult polarizable atoms and much charge from a few readily polarizable atoms [19]. This could be one of the factors which explains the impossibility of obtaining tris pyridine adducts of Nisat and Niaat.
Acknowledgements--We thank Italian CNR (Consiglio Nazionale deUe Richerche, Roma) for financial support. Gruppo Chimica di Coordinazione Universit?t degli Studi di Palermo Istituto di Chimica Generale Via Archirall 26 90123 Palermo, Italy
F. T. V. G.
MAGGIO PIZZINO ROMANO DIA
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