CSIRO PUBLISHING

Aust. J. Chem., 1984, 37, 281-91

Metal Complexes of 1,lO-Phenanthroline Derivatives. XIVT Complexes of 1,lO-Phenanthrolin-2-yl(pyridin-2-y1)amine Ahmad S. A b ~ s h a m l e h ,Harold ~ , ~ A. GoodwiqB Christopher G. BensonC and Gary J. on^' A

Australian International Award Scheme Scholar. School of Chemistry, University of New South Wales, P.O. Box 1, Kensington, N.S.W. 2033. Department of Chemistry, University of Missouri-Rolla, Rolla, Missouri 65401, U.S.A.

Abstract

],lo-Phenanthrolin-2-yl(pyridin-2-y1)aminehas been prepared in low yield from 2-chloro-1,lOphenanthroline and pyridin-2-amine. The molecule coordinates as a tridentate chelating agent of the ter-imine type and produces low-spin complexes with iron(11) in both its neutral and anionic forms. The bis(1igand) cobalt(11) complex is high-spin. Although the ligand provides a slightly weaker field than terpyridine, electronic and Mossbauer spectral data indicate a less distorted metal ion environment in its complexes, compared with those of terpyridine. This is correlated with the presence of the six-membered chelate ring.

Introduction Modification of the 2,2'-bipyridine system by the interposition of a single-atombridge between the pyridine nuclei produces a series of bidentate chelate groups with interesting structural and electronic properties, among which is the ability to generate variable spin-states in iron(^^).' Significant differences from bipyridine arise in the size of the chelate ring produced and in the non-planarity of systems in which the bridging group is saturated. The latter property has important electronic effects, notably in the extent of delocalization, but also introduces steric constraints both about the metal atom and between the coordinated ligands.'a3 Among the most studied chelates of this group is bis(pyridin-2-y1)amine which is readily formed by the interaction of pyridin-2-amine and 2-~hloropyridine.~ The same modification of the tridentate terpyridine system has not been reported although the molecule 2-(pyridin-2-yl)amino-4-(pyridin-2-yl)thiazole(1) does bear a close relationship to such a modification. In (1) the central thiazole ring, which is electronically closely akin to a pyridine ring, is separated from a terminal pyridine ring by a bridging amino group. This particular ligand is unusual in that it generates

t Part XIII, Aust. J.

Chem., 1982, 35, 1053.

' McWhinnie, W. R., Coord. Chem. Rev., 1970, 5, 293. Johnson, W. L., and Geldard, J. I?., Znorg. Chem., 1979, 18, 664. Geldard, J. F., and Lions, F., J. Am. Chem. Soc., 1962, 84, 2262. Steinhauser, E., and Diepolder, E., J. Chem. Soc., 1916, 110, 739.

A. S. Abushamleh, H. A. Goodwin, C. G. Benson and G. J. Long

a spin transition in iron(11) in both its neutral and anionic form^.^-^ In an attempt to obtain a more closely related analogue of bis(pyridin-2-y1)amine in a tridentate (2) (abbreviated system we have prepared l,l0-phenanthrolin-2-yl(pyridin-2-yl)amine LH in subsequent formulae of complexes) which is related to the hexa- and tetra-aza quadridentate macrocycles containing phenanthroline moieties reported by Ogawa and coworker^.^,^ Coordination of two molecules of (2) in meridional planes about an octahedral metal atom should not involve the inter-ligand repulsions evident in the tris complexes of bis(pyridin-2-y1)amine and in fact the bridging amino group should bring the pyridine nitrogen atom into a more favourable coordination position than in terpyridine where the terminal donor atoms are further from the metal atom than is the central nitrogen atom.10s11 On the other hand the extent of electron delocalization in (2) is limited by the amino group and this can be expected to influence the properties of its complexes. The acidity of this group should, however, be greatly enhanced in the coordinated molecule, and in the deprotonated form of (2) (abbreviated L in subsequent formulae of complexes) strict planarity and extensive electron delocalization are possible. The study of (2) therefore affords a means of examining the effects of replacement of a five-membered chelate ring as in chelates of terpyridine and related molecules by a six-membered ring and of deprotonation on the properties of such complexes. In the present work we report the properties of the bis(1igand) complexes of (2) with bivalent iron, cobalt and nickel. These afford a convenient measure of the electronic and structural features of the molecule.

Results and Discussion Characterization of the Ligand

The ligand (2) was formed in low yield only (approx. 10%) when 2-chloro-1,lOphenanthroline was heated with excess pyridin-2-amine in the presence of base. Its mass spectrum showed the parent ion peak at mle 272 and a base peak at 271 consistent with the loss of hydrogen. A peak at mle 179 indicated the loss of the pyridin-2-amine fragment and, characteristically for molecules such as (2), a doubly charged molecular ion peak was observed at mle 136. Tautomeric forms of (2) (such as (3)) are possible, similar to those postulated for the hexaaza macrocycle obtained from reaction of 2,9-dichloro-1,lO-phenanthroline with 1,lO-phenanthroline-2,9-diaminereported by Ogawa and coworker^.^ Ogawa Goodwin, H. A., Aust. J. Chem., 1964, 17, 1366. Sylva, R. N., and Goodwin, H. A,, Aust. J. Chem., 1967, 20, 479. ' Goodwin, 13. A,, and Sylva, R. N., Aust. J. Chem., 1968, 21, 1081. Ogawa, S., Yamaguchi, T., and Gotoh, N., J. Chem. Soc., Perkin Trans. 1, 1974, 976. Ogawa, S., J. Chem. Soc., Pevkin Trans. 1, 1977, 214. 'O Corbridge, D. E., and Cox, E. G., J. Chem. Soc., 1966, 594. Wickramasinghe, W. A , , Eird, P. H., and Serpone, N., Inovg. Chem., 1982, 21, 2694.

Metal Complexes of 1,lO-Phenanthroline Derivatives. XIV

found in these tautomers strong intramolecular hydrogen bonding giving rise to a rather low value for vNH in the infrared spectrum at 2780 cm-I. In the spectrum of (2) vN, appears as a strong band at 3280 cm-' in the solid and 3415 cm-' in chloroform solution. Unlike the rigid macrocyclic structures described by Ogawa which would favour intramolecular hydrogen bonding, (2) is much more flexible about the NH bridge and this would allow the molecule to adopt a trans configuration (4). In (4) interaction between the electron pairs of the azo-methine nitrogen atoms would be reduced and only intermolecular hydrogen bonding would occur, hence the relatively high value for vNH.

Table 1. Analytical data for complexes of (2) Cornplex

C

Found (%) H N

M

C

Required (%) H N

M

Table 2. Properties of complexes of (2) Complex [Ni(LH)21 [ B F ~ I z [Ni(LH)2] [C1O4I2 [NhI [Fe(LH)2] [BF4I2 [Fe(LH)2] [NO3], [FeL21 [Co(LHhI [BF4I2 A

Conductivity in

Colour

A (S cm2)A

pink pink brown red-brown red-brown deep violet orange

174 186 21 177 181 25 193

M

nitromethane solution.

The complexes of (2) isolated in the present work are listed in Table 1 together with their analytical data, and some of their properties are given in Table 2. In the infrared spectra of complexes of (2) v,, was somewhat weaker and was always shifted to lower frequencies (Table 2) and of course was absent in the spectra of the deprotonated complexes. Significantly, all complexes of (2) were found to be extensively solvated, very likely through hydrogen bonding with the bridging NH group, and the solvent molecules were not removed when the complexes were dried i n vacuum at elevated temperatures.


The electronic spectrum of (2) in nitromethane solution shows bands at 27300 14400), 28500 (E 14000), 31300 (8 22400) and 32300 cm-' (E26600 mol- ' cm-l). These are typical for n+n* transitions in molecules of this kind but interaction of the lone pair of the amino-nitrogen atom with the heterocyclic ring orbitals may give the bands some n-n* character. In the spectra of all the complexes of (2) a band was always observed at 26500 cm-I with E approx. 8000 mol-' cm-'. This is presumably the lowest energy intraligand transition shifted to lower energy by coordination. (E

Table 3. Magnetic data for complexes

Nickel(11) Complexes The pale pink complexes [Ni(LH),] [BF412 and [Ni(LH),] [CIO,], were readily obtained by interaction of the ligand (2) with the appropriate nickel salt in ethanol. Both complexes were found to be essentially identical in their spectral properties but differed significantly in their magnetism (Table 3). Thus the fluoroborate was found to have an unexpectedly high magnetic moment (3.7 BM at 303 K). The moment, which was found to be slightly temperature-dependent, was reproducible in a second sample. Since the complex is coordinatively saturated some sort of intermolecular electronic exchange seems unlikely. In any case the magnetism of the perchlorate is more or less normal and both salts have virtually identical X-ray diffraction patterns, indicating they are isostructural. An orbital contribution to the magnetism of six-coordinate nickel(11) can be provided through the 3T2, state by way of spin orbit coupling12 and the high value observed for the fluoroborate complex may arise at least in part from such a contribution but the value is certainly much higher than that normally found for nickel(11) in an octahedral field. lZ

Figgis, B. N., 'Introduction to Ligand Fields' (Interscience: New York 1967).


In the electronic spectra of both complex salts the two ligand field transitions v , (3A2, + 3 ~ 2 gand ) v, (3Az, + 3Tlg) were observed at 12500 and 19300 cm-',

respectively, both in the solid state and in solution. The low intensity of the bands associated with these transitions ( E approx. 15 mol-I cm-l) and the ratio v2:v, (1 54) are consistent with relatively little distortion from a regular octahedral environment about the nickel(11) ion.13 The third ligand field band was obscured by strong charge-transfer absorption (Fig. 1).

-

Fig. 1. Electronic spectrum of A , [NiL2] in chloroforn~; B. [Ni(LH)J [BF4I2in nitromethane

From the value of v, it can be seen that 10Dq (Ni2+)lies within the range (1040012750 cm-I) estimated by Robinson, Curry and Busch14 to encompass the spincrossover value for iron(11). The value is in fact very close to that of the model compound terpyridine15 (12740 cm-I) which effects spin-pairing in iron@) and a quartet-doublet transition in cobalt(11). The properties of the complexes of (2) with these metal ions are discussed below. Treatment of either complex nickel salt with base gave rise to the uncharged deprotonated complex [NIL,]. The solid-state and solution spectra of this complex show only a single band, associated with v,, at 12700cm-'. Charge-transfer absorption has moved much further into the visible region with the loss of a proton from the coordinated ligand (Fig. 1) and obscures both v, and v,. Deprotonation has, in this instance, resulted in a slight increase in the field strength as might be expected from the more extended delocalization of the n electron density possible in the deprotonated species. Ivon(11) Complexes Interaction of (2) with iron(11) fluoroborate in ethanol gave the deep red-brown complex [Fe(LH),] [BF,],. The magnetic moment for this complex indicates that it is essentially low-spin at room temperature but it is higher than that normally obtained for iron(11) in the lA,, state. Below room temperature a decrease in the moment is observed and this might suggest the presence of a small and temperaturedependent fraction of high-spin species. This would be consistent with the location of lODq (NiZ+)within, but near the upper limit of, the critical crossover region for iron(11). The experimental temperature range then encompasses only the initial l 3 Lever, l4 'j

A. B. P., 'Inorganic Electronic Spectroscopy' (Elsevier: Amsterdam 1968). Robinson, M. A,, Curry, J. D., and Busch, D. H., Znorg. Chem., 1963, 2, 1178. Henke, W. von, and Reinen, D., Z . Anorg. Allg. Chem., 1977, 436, 187.

A. S. Abushamleh, H. A. Goodwin, C . G. Benson and G. J. Long

stages of a thermally induced 'A,, + 5 ~ 2 transition. g The similar magnetic properties of the complex nitrate (Table 3) indicate the likely absence of any significant aniondependence of the spin state such as has been frequently observed with crossover systerns.16 It is possible that the magnetism arises not from a partial low-spin + highspin transition, but from mixing in some higher states as has been suggested for some other essentially low-spin iron(11) systems.17 For both the fluoroborate and the nitrate the magnetic moment increases essentially linearly with temperature (Fig. 2) as would be expected for a second-order Zeeman contribution to the susceptibility.

Fig. 2, Tcmpesatuse dependence of the magnetic moment of -4. [Fe(LH)>] [NO;]?: B , [WLH)21 [ B F J I ~ : C. [FeL?].

Mossbauer effect data also reveal the low-spin nature of the metal atom in both salts. At room temperature only a single doublet is observed (Fig. 3A) with parameters normal for low-spin iron@) (Table 4). No unusual temperature-dependence of these parameters was observed but the recoil-free fraction is very much greater at 78 K (Fig. 3B), which indicates a relatively low Debye temperature for the solids. The lower value of AEQ for these salts compared with those obtained for low-spin complexes of terpyridine18 and of related tridentateslg suggests a less distorted environment for the iron(11) ion which can be accounted for by the particular spatial freedom available in this ligand. The deprotonated complex [FeL2], readily formed by reaction of the cationic species with base, has magnetic properties (Table 3) similar to those discussed above for the complex salts from 89 to 303 K. Above room temperature the moment appears to increase sharply with temperature, which suggests the onset of the thermal occupation of the high-spin state (Fig. 2). This behaviour is not observed in the l6 l7

l8 l9

Goodwin, H. A,, Coord. Chem. Rev.,1976, 18, 293. Konig, E., and Kremer, S., Theor. Chim. Acta, 1971, 22, 45. Epstein, L. N., J. Chem. Phys., 1964, 40, 435. Eaggio-Saitovitch, E., and De Paoli, M. A., Inorg. Chim. Actn, 1978, 27, 15.


complex salts. At room temperature the Mossbauer spectrum of [FeL,] exhibits a simple, sharp doublet of low intensity. The spectral parameters for this compound are indicative of low-spin iron(11). At room temperature there is no indication of any high-spin component in the Mossbauer spectrum (see Fig. 4A). This indicates that at room temperature either the high-spin state is not populated or, if populated, the site has such a low recoil-free fraction that it is not observed. The magnetic results indicate that the first possibility is the more likely. Confirmation of the presence of a high-spin component at higher temperatures would require examination of a sample enriched in 57Fe, in an attempt to overcome the difficulties created by the expected small recoil-free fraction for any high-spin species above room temperature.

Fig. 3. Mijssbauer spectrum of [Fe(W21 m0312. A , 296 K; B, 7 8 K.

90 O L

I 88'Otl

, -3

1

,

-2

,

3

I

t

-

1

L0

d 1

2

3

4

Source velocity (mm/s)

Table 4. Mossbauer-effect spectral parameters for the iron complexes All data in mm s - ' relative to room temperature natural cr-iron foil Compound

T (K)

6

AEQ

rA

A(%)~

" Line width at half weight. Contribution of the doublet to the total area.

At 78 K the Mossbauer spectrum of [FeL,] shows two lines which are considerably broadened, compared with those observed at room temperature (Fig. 4B). The results are consistent with either a distribution of isomer shifts or, more likely, a distribution of quadrupole interactions. In the latter case, the spectrum may be fitted


with two symmetric doublets of virtually the same relative area and with the same isomer shift. This may indicate that [FeL,] undergoes a phase change or structural rearrangement between room temperature and 78 K to produce either two, or perhaps more, inequivalent iron sites. The resulting Mossbauer spectral parameters are presented in Table 4. An alternative assignment would produce two doublets with the same quadrupole interaction of 1 a08 mm s-I and isomer shifts of 0.30 and 0.48 mm s-l. This assignment, although possible, seems less likely because of the small value of 6 observed for one of the doublets compared to the room temperature value. 100 0

99 8 -

Fig. 4. Mossbauer spectrum of [FeL2] at A , 297 K, B, 78 K.

99 6 -

g

99 4 ,000

1

i

98598 0 1

97 5 97

1

or

1

96 5 96 Oc 955CI

I

I

I

1

Source velocity (mm/s)

The quadrupole interaction in the deprotonated complex is higher than that found in the cationic complex and this probably reflects the greater rigidity of the deprotonated system in which ri-electron delocalization is apparently greater. The extent of back-bonding from the metal d, orbitals is also expected to be greater in the deprotonated complex and the overall reduction in the isomer shift, which is indicative of increased s-electron density at the nucleus, is consistent with this observation. The electronic spectrum of [Fe(LH)JZf shows intense n+n* charge transfer absorption. This appears as a very broad peak centred at approx. 21000 cm-' in the diffuse reflectance spectrum of the solid salts but is clearly resolved into the typical two-line absorption associated with the low-spin iron(11)-ter-imine chromophore," with maxima at 25000 ( E 5700) and at 19340 cm-' ( E 4980 mol-I cm-l). The solid state spectrum of [FeL,] shows an intraligand transition at somewhat lower energy (24000 cm-') than in complexes of the neutral ligand, and a second rather broad band centred at 18000 cm-' which is presumably due to metal-ligand charge transfer. The solution spectrum of this deep purple complex reveals at least Krumholz, P., Znorg. Chem., 1965, 4, 612.


'

two components to this band (Fig. 5) withamaximum at 20080 cm- (8 8260mol-' cm- ') and a prominent shoulder at 17390 cm-l. The charge transfer absorption in this deprotonated species is more intense and again extends further into the visible than in the charged complex. This again is indicative of the greater n-electron delocalization on the ligand.

Fig. 5. Electronic spectrum of A , [FeL2] in chloroform;

R, [Fe(LH)2] [BF4I2 in ethanol

Cobalt Complexes The relatively high ligand field strength of (2) as indicated by the properties of the nickel and iron complexes described above has prompted an examination of the properties of the corresponding cobalt(11) complexes since strong field ter-imine type chelate groups have been shown in many instances to effect a 2Eg 4Tlg spin transition in c o b a l t ( ~ ~ ) .This ~ l is consistent with the higher spin-pairing energy for d7 Co1' than for d6 Fe". No evidence for a spin transition in [Co(LH),I2+ has been found, however. The complex fluoroborate has been found to be magnetically normal for a high-spin, octahedral cobalt(11) complex (Table 2). In addition its electronic spectrum is typical for such systems. In the diffuse reflectance spectrum of the solid the 4T,, -+ 4T2g and 4T1g+ 4Tlg (P) transitions appear well resolved at 10800 and 22000 cm-', respectively. For the complex in solution the first transition remains undisplaced and with characteristically low intensity ( E 10 mol-' cm-l) but the high-energy transition is observed only as a shoulder at 22000 cm-I on an intense charge transfer band. Comparison with the spectrum of [Co(trpy),12+ indicates a displacement to lower energies of the main ligand field bands in the complex of (2) but the spectrum of the terpyridine complex is complicated by the contributions arising from the doublet ground state species.22 In order to check whether or not a spin transition in [Co(LH),I2+ does in fact occur but is obscured in the fluoroborate by a pronounced anion-dependence such as that which occurs in [Co(trpy),12+, a second salt, the bromide, was prepared. This salt has virtually the same magnetic properties as the fluoroborate, however, and it thus seems unlikely that (2) can effect spin-pairing in cobalt(11). This may be a consequence of the rather greater flexibility of (2) and the lower distortion of the 21 2Z

Barefield, E. K., Busch, D. H., and Nelson, S. M., Q. Rev.,Chem. Soc., 1968, 22, 457. Judge, J . S., and Baker, W. A., Inorg. Chirn. Acta, 1967, 1, 68.


metal ion environment compared to terpyridine and related molecules and their complexes in which the importance of low-symmetry components to the ligand field in increasing the accessibility of the doublet state has been r e ~ o g n i z e d . ~ ~ , ~ ~ Attempts to obtain the deprotonated complex [CoL,] were not successful; oxidation of the metal to Co"' always accompanied the deprotonation reaction. This behaviour is typical of that of complexes of similar ligands which can undergo deprotonation.'' The amine (2) thus represents an extension of the phenanthroline tridentate systems known in that it allows a study of the effects of increasing the size of one of the chelate rings from five-membered (as in most known systems) to six-membered. The properties of the complexes of (2) described above demonstrate important differences in (2) and its bidentate analog bis(pyridin-2-y1)amine. In the bidentate system the six-membered ring introduces steric crowding and the ligand field is relatively week. In the tridentate molecule, however, the effects are somewhat more favourable and the present study has revealed the relatively high-field nature of the ligand and provided evidence for lower distortion in its complexes than in those of related tridentates where both chelate rings are five-membered. The influence of the particular donor atom arrangement in (2) on the structural and thermodynamic properties of its complexes is being further studied. Experimental I n a 100-ml round-bottomed flask equipped with a reflux condenser (air jacket) a mixture of

2-chloro-1,lO-phenanthroline (2 g) (9.3 mmol) (prepared by the method of Halcrow and KermackZ6), barium oxide (0.77 g, 5 mmol) and freshly distilled pyridin-2-amine (1 .8 g, 19 mmol) was stirred magnetically and heated in an oil bath at 200-210" for 7 h. At the end of the reflux time the mixture was allowed to cool to about 100" and then the dark tarry material was treated with ice. The aqueous layer was decanted carefully and the residue was dissolved in chloroform (300 ml). The chloroform solution was refluxed for 15 min then cooled and anhydrous sodium sulfate added. The mixture was filtered and the filtrate was refluxed for a further 10 min with charcoal (6 g), then filtered. The orange-yellow filtrate was evaporated to dryness and the residue dissolved in absolute ethanol (100 ml) and refluxed with Kieselguhr (5 g) for 15 min and filtered. The filtrate was again refluxed with charcoal and filtered. The filtrate was then evaporated to dryness and water (20 ml) was added. A pale yellow, oily emulsion was obtained. Ethanol was added dropwise until a clear solution was obtained. This was cooled in the refrigerator overnight; yellow crystals of the product separated. These were dried in vacuum over P,O,,. Yield 0 . 2 g (10%). A sample recrystallized from benzene hadm.p. 212" (Found: C, 75.1; H, 4.6; N, 20.5. CI7H,,N4requires C, 75.0; H, 4 . 4 ; N, 20.6%).

Preparation of Complexes (Ail iron complexes were prepared under an atmosphere of nitrogen.) (A) [M(LH),] Xz (M = Fe, Co, Ni; X = BF,, CI04).-A hot solution of MX,.6Hz0 (1 mmol) in ethanol (20 ml) was added to a solution of (2) (2 mmol) in ethanol (30 ml). The reaction mixture was heated on the water bath for 30 min after which the volume was reduced to 20 ml. The crystalline product separated on cooling. This was washed with ethanol and dried in vacuum over P4OI0. Hogg, R., and Wilkins, R. G., J. Chem. Soc., 1962, 341. Williams, D. L., Smith, D. W., and Stoufer, R. C., Znorg. Chem., 1967, 10, 590. 2 5 Geldard, J. F., and Lions, F., Znorg. Chem., 1963, 2, 270. 2 6 Figgis, B. N., and Lewis, J., in 'Modern Coordination Chemistry' (Eds J. Lewis and R. G. Wilkins) (Interscience: New York 1960). 23 24


(B) [Fe(LH)2][NOs12.-Freshly prepared iron(11) chloride tetrahydrate (1 mmol) in water (IS ml) was added to a solution of (2) (2 n~mol)in hot ethanol (10 ml). The mixture was heated on the water bath for a few minutes to dissolve completely the ligand then it was filtered. A concentrated aqueous solution of ammonium nitrate was added and the mixture cooled in ice, whereupon the product crystallized. It was washed with a little cold water and dried over P,O,, in vacuum. (c) [ML,] (M = Fe, Ni).-Water (10 ml) and 5 M ammonia solution (5 ml) were added to a suspension of [M(LH),] [BF,], (1 mmol) in chloroform (50 ml). The mixture was shaken and an intense colour developed in the chloroform layer which was separated. The mixture was further extracted with chloroform (3 x 50 ml). The combined extracts were dried over anhydrous sodium sulfate and filtered. The volume was reduced to 10 ml and cooled. Light petroleum (b.p. 40-60") (60 ml) was slowly added and the product crystallized. It was dried at 100' for 24 h in vacuum.

Magnetic Data The magnetic data for solid samples were obtained by using a Newport Instruments variable temperature Gouy balance. Diamagnetic corrections were calculated from Pascal's constants listed by Figgis and Lewis.'= Curie-Weiss 0 values listed in Table 3 were obtained from an extrapolation of a plot of l/xl, against T. Values of X I , were measured at 89 and 303 K and at six intermediate temperatures. Electronic Spectra Electronic spectra were obtained with a Zeiss PMQ I1 spectrophotometer with an RA3 reflectance attachment calibrated against magnesium oxide. Infrared Spectra Infrared spectra were obtained for halocarbon mulls with a Perkin-Elmer 580B instrument. Mossbauer Spectra Mossbauer-effect spectra were measured with a Ranger Scientific Corp. constant-acceleration spectrometer equipped with a room-temperature rhodium matrix source and calibrated with natural a-iron foil. The spectral parameters were evaluated by means of standard least-squares techniques. Analyses Carbon, hydrogen and nitrogen analyses were performed by Dr P. Pham, University of New South Wales microanalytical laboratory. Metals were estimated by standard gravimetric techniques after decomposition of the complexes with concentrated sulfuric and nitric acids.

Acknowledgments G.J.L. and C.G.B. would like to thank the U.S. National Science Foundation ) the Petroleum Research Foundation for their support (Grant 1 ~ ~ 4 2 0 2 4 0 3and of this work. Manuscript received 9 August 1983