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An anwser to the sprio versus ansa dilemma in cylophosphazenes Part XV. The first MACRO-diBINO and MEGA-diBINO non-geminal species from oxodiamines
Journal of Molecular Structure, 221 (1990) 245-252 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
245
AN ANSWER TO THE SPIRO VERSUS ANSA DILEMMA IN CYCLOPHOSPHAZENES Part XV. The first MACRO-diBIN0 and MEGA-diBIN0 nongeminal species from oxodiamines*
FRANCOIS SOURNIES, PIERRE CASTERA, JEAN-PAUL FAUCHER, MARCEL GRAFFEUIL and JEAN-FRANCOIS LABARRE** CNRS, Laboratoire Structure et Vie, FacultC de Pharmacie, 35 chemin des Maraichers, 31400 Toulouse (France) (Received 17 July 1989)
ABSTRACT Aminolysis of N3P,C1, by oxodiamines in ethyl ether-Na&O, saturated water (interface process) [ (1: 1) stoichiometric conditions] or in 2-propanol [ (1: 2) stoichiometric conditions] leads stereoselectively and/or stereospecifically to MACRO-diBIN0 and MEGA-diBIN0 species which constitute a new class of macrocyclic crown ethers.
INTRODUCTION
Reactions of the long oxodiamines 3,6-dioxaoctane-l,&diamine (20202)) 4,7-dioxadecane-l,lO-diamine (30203), 4,9-dioxadodecane-1,12-diamine (30403) and 4,7,10-trioxatridecane-1,13diamine (3020203), on N,P,Cl, lead (i) to MACRO-ANSA [ 2-41 and MEGA-ANSA [ 51 derivatives with THF as solvent, (ii) to MACRO-SPIRO [2-41 and MEGA-SPIRO [5-81 derivatives when reactions are performed in toluene-Na,CO, saturated water (interface process), and (iii) to MACRO-monoBIN and MEGA-monoBIN species [ 1 ] in ethyl ether-Na,CO, saturated water (interface process) when working in 2 : 1 stoichiometric conditions. These reactions are usually stereoselective and in some cases stereospecific. This is especially the case for the synthesis of the monoBIN compounds. In the present work we extended the use of the Et,O-water interface procedure to the production of polyBIN0 architectures. The present paper deals with the synthesis of diBIN0 non-geminal dicyclophosphazenes upon reaction of oxodiamines on N3PsClGin 1:1 conditions. *For Part XIV, see Ref. 1. **Author to whom correspondence should be addressed.
0022-2860/90/$03.50
0 1990 Elsevier Science Publishers B.V.
246 AMINOLYSIS
OF N3P3C& BY OXODIAMINES
(1: 1): THE diBIN0
NON-GEMINAL
COMPOUNDS
In addition to the previously mentioned 20202,30203 and 30403 dioxodiamines and to the 3020203 trioxodiamine, we also investigated the reaction of the simplest Lehn’s monooxodiamine, i.e. H,N- ( CH2)2-0- (CH,),-NH, (202; Aldrich, 17609-5). The diBIN0 derivatives were prepared by reaction at the Et,O-water interface according to the following pathway: 2N3P3 Cl, + 2 (oxodiamine) -&BIN0
(oxodiamino) + 2HC1
The two possible isomers, i.e. the geminal and the non-geminal species, which could be expected from the reaction in the case of dioxodiamines (mOnOm) are shown in Fig. 1.These two isomers are A,B systems in 31PNMR spectroscopy but the two expected NMR patterns are predicted to differ noticeably, according to the transferable 31PNMR rules recently proposed [ 91 for BASIC
‘P-P- I /
’
/
I
\
--p---P
NH
y4’
‘. m”., cH5\___y____y-:2 C-H*
CHZ
Fig. 1. The two possible geminal and non-geminal isomers for diBIN0 dioxodiamines.
derivatives from
247
(BINO-ANSA-SPIRO in cyclophosphazenes) systems. The reactions were stopped when the 31P NMR singlet of N3P3CI, at 20.09 ppm (Brucker AC 200, CDCl,, H,PO, 85% as standard) remained unchanged with time, that is after a few hours at room temperature. The organic phase was dried over Na,SO, and the solvent was removed in vacua at 25°C to give colourless oils. The 31P NMR spectra of the crude final product is (A for 202, B for 20202, C for 30203, D for 30403 and E for 3020203) revealed features which depend on the nature of the oxodiamines as follows. (1) For A and B, only an A,B system (a triplet centred on 19.0 ppm and a and a midoublet centred on 21.7 ppm, ‘Jpp = 47.3 and 46.7 Hz, respectively) nor singlet at 20.09 ppm (unreacted N3P3C16) were observed. (2) For C, an A2B system was observed as for A and B, together with the singlet at 20.09 ppm but also a minor A,X system (a triplet around 9-11 ppm and a doublet around 21-22 ppm) which corresponds to the mono-SPIRO derivative [2,5] as a by-product. (3) For D and E, together with the singlet at 20.09 ppm and the minor A,X system of the mono-SPIRO by-products, it was observed that the expected A,B systems for the diBIN0 species actually collapsed in a unique “false” singlet at 21.78 and 21.60 ppm, respectively. Several techniques can be used to extract pure diBIN0 samples from these crude final products, depending on the oxodiamine reagent. (i) A single washing with n-heptane for A and B (N3P3C16 being highly soluble in this solvent whilst the two diBIN0 derivatives are not). (ii) Dissolving crude D in acetonitrile followed by slow evaporation (diBIN0 30403 precipitates on walls of the vessel whilst N3P3C16 and SPIRO 30403 remain in solution). (iii) Addition of a CH,Cl,-CH,CN (1: 1) mixture to the oily final product for C which precipitates the diBIN0 30203. (iv) HPLC quantitative separation with a ternary AcOEt : n-heptane: CH,Cl, (6 : 3 : 1) mixture for E (other techniques being unsuccessful in this case). In every case, a final washing with cold water is recommended in order to eliminate traces of chlorhydrate which induce slow oligomerization of the bulk in time. However, yields are commonly poor (from 10% for C to 30% for E) except for A and B which are obtained in a pure state with yields above 90%. In other words, it is much easier to obtain pure diBIN0 compounds when the oxodiamine length is short. The same reactions can also be achieved in 2-propanol as solvent in 1: 2 stoichiometric conditions (one molecule of oxodiamine being used here for removing the hydrogen chloride). Final yields are about the same, except for D which is obtained cleanly in this way, conversely to what was observed for the synthesis described above. Thus, polar “protic” solvents such as the biphasic ether-water system or alcohols give strong solute-solvent hydrogen interactions that prevail over the intramolecular hydrogen bonds which exist in free oxodiamines [2]. These intermolecular interactions make the oxodi-
248 TABLE 1 31PNMR chemical shifts and coupling constants for compounds A to E Compound
A B C D E
S(PC1,) (ppm)
2JPP
QClNH)
(ppm) 21.57 21.42 22.48 21.78 21.60
18.94 18.98 20.63 21.78 21.60
47.3 46.7 48.0 -
2.63 2.44 1.85 0 0
G(gClNH)
-a(pCl,)
(Hz)
I
amines prone to link two N3P3 rings to give BIN0 (bridged) configurations rather than one N3P, ring to give a constrained SPIRO or ANSA configuration. The chemical shifts and ‘Jpp coupling constants for compounds A to E (Bruker AC200, CDCl,) are gathered in Table 1 which calls for the following remarks. (i) First-order A,B patterns are revealed for A, B and C whilst a “false” singlet is only observed for D and E, at least at 81.015 MHz. (ii) The “Jpp values are similar within the series, i.e. within the range 46.7-48.0 Hz. (iii) Moreover, in connection with (i), the gap between the centres of each doublet-triplet system decreases slowly from 2.63 ppm for A to 1.85 ppm for C and then drops suddenly to zero for D and E. The break so observed between compounds C and D within the series could not be explained until now. The DC1 mass spectra of compounds A to E were recorded on a NERMAG RlO-10H quadrupole mass spectrometer. The spectra reveal molecular ions MH+ at m/z = 755,843,899,955 and 987 for A, B, C, D and E, respectively. Satellite distributions confirm the presence of eight chlorine atoms in the molecules (maximum peaks at MH+ + 4 mass units). Incidentally, the (M, NH+ ) peaks are not observed, as they are for the monoBIN parents [ 11. CRYSTAL AND MOLECULAR STRUCTURE OF THE diBIN0 (30203)
NON-GEMINAL
REPRESENTATIVE
This 30-crown-ether-like architecture crystallizes in a triclinic system: Pl bar, a=9.019(6), b=9.224(5), c=11.542(8) A, cx=94.87(4), /3=95.97(4), y=99.68(3), V=936.5(1) A3,Z=1,D,=1.599(1) Mgm-3,R=0.049for2862 unique reflections and 199 variable parameters. Details of the data collection, final positions and equivalent isotropic thermal parameters, fractional coordinates of hydrogen atoms, bond lengths and angles will be published shortly [lOI* A ball-and-stick drawing of a suitable perspective view of the title molecule
249
Fig. 2. A perspective view of the &BIN0 30203 non-geminal propound witfi N3F3 rings parallel to the plane of the figure.
(non-gem &BIN0 (30203)) is given in Fig. 2 (the hydrogen numbering is omitted for clarity). The molecule shows a centre of symmetry which coincides with one centre of symmetry of the unit cell. The most striking feature of Fig. 2 is that the two N3P3 rings adopt a trcans ~o~~~rstion with respect to the 3~-members macrocycle, as is clearly visualized in Fig. 3. Cons~uently, t.he two remaining PC& groups are quite‘distant
250
Fig. 3. A perspective view of the diBIN0 perpendicular to the plane of the figure.
30203 non-geminal compound with N3P, rings quasi-
for each other and are no longer accessible for the grafting of a third BIN0 stave upon reaction of a new molecule of 30203 on the non-gem diBIN0 30203. In other words, the non-gem diBIN0 30203 compound adopts, in the solid state at least, the “chair” configuration shown in Fig. 4. Thus, any hope of preparing a non-gem triBIN0 (coded as oxobarrelane by analogy with barrelanes from non-oxygenated diamines [ 111) will pass through the synthesis of the “boat” configuration (Fig. 4) of the corresponding non-gem diBIN0 parent. The synthesis of “boat” non-gem diBIN0 isomers from dioxodiamines is yet to be achieved; work is underway to meet this challenge. The X-ray structures of other non-gem diBIN0 derivatives, i.e. of compounds A, B, D and E,
Fig. 4. Simplified patterns
of the “chair” and “boat” forms of a diBIN0
non-geminal
“CHAIR” FORM
derivative.
~__ ..I
. I
.
...?
252
need to be determined to be certain of their “chair” or “boat” configuration. Studies are currently in progress for this purpose. CONCLUSION
Aminolysis
of N3P3C16 by oxodiamines at an E&O-water interface and in conditions leads to diBIN0 dicyclophosphazenic non-geminal architectures which adopt a tram configuration. Such diBIN0 bridged species, as well as their monoBIN analogues, are highly soluble in common organic solvents and they constitute prime candidates for further synthesis of cryptates with usual and/or exotic properties [ 121. 1: 1 stoichiometric
ACKNOWLEDGEMENTS
We are greatly indebted to Texaco and BASF for donating the oxodiamines and to Shin Nisso Kako for their gift of pure crystalline N,PJ&. The authors wish to thank the Conseil Regional de Midi-Pyrenees for its generous financial support of this project.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12
F. Sournies, P. Castera, A. el Bakili and J.-F. Labarre, J. Mol. Struct., 221 (1990) 239. A. el Bakili, P. Castera, J.-P. Faucher, F. Sournies and J.-F. Labarre, J. Mol. Struct., 195 (1989) 21. R. Enjalbert, J. Galy, A. el Bakili, P. Castera, J.-P. Faucher, F. Sournies and J.-F. Labarre, J. Mol. Struct., 196 (1989) 207. T.S. Cameron, A. Linden, A. el Bakili, P. Castera, J.-P. Faucher, M. Graffeuil, F. Sournies and J.-F. Labarre, J. Mol. Struct., 212 (1989) 281. F. Sournies, A. el Bakili, J.-F. Labarre and B. Perly, J. Mol. Struct., 196 (1989) 41. T.S. Cameron, A. Linden, F. Sournies, A. el Bakili and J.-F. Labarre, J. Mol. Struct., 197 (1989) 41. J. Jaud, F. Sournies and J.-F. Labarre, J. Mol. Struct., 212 (1989) 305. F. Sournies, A. el Bakili, B. Zanin, J.-F. Labarre and J. Jaud, J. Mol. Struct., 220 (1990) 63. J.-P. Bonnet and J.-F. Labarre, Inorg. Chim. Acta, 149 (1988) 187. R. Enjalbert, J. Galy, F. Sournies and J.-F. Labarre, J. Mol. Struct., in press. P. Castera, J.-P. Faucher, M. Granier and J.-F. Labarre, Phosphorus Sulfur, 22 (1987) 37. J.-F. Labarre, P. Castera, J.-P. Faucher, M. Graffeuil and F. Sournies, CNRS French Patent No. 89-15484,1989.
245
AN ANSWER TO THE SPIRO VERSUS ANSA DILEMMA IN CYCLOPHOSPHAZENES Part XV. The first MACRO-diBIN0 and MEGA-diBIN0 nongeminal species from oxodiamines*
FRANCOIS SOURNIES, PIERRE CASTERA, JEAN-PAUL FAUCHER, MARCEL GRAFFEUIL and JEAN-FRANCOIS LABARRE** CNRS, Laboratoire Structure et Vie, FacultC de Pharmacie, 35 chemin des Maraichers, 31400 Toulouse (France) (Received 17 July 1989)
ABSTRACT Aminolysis of N3P,C1, by oxodiamines in ethyl ether-Na&O, saturated water (interface process) [ (1: 1) stoichiometric conditions] or in 2-propanol [ (1: 2) stoichiometric conditions] leads stereoselectively and/or stereospecifically to MACRO-diBIN0 and MEGA-diBIN0 species which constitute a new class of macrocyclic crown ethers.
INTRODUCTION
Reactions of the long oxodiamines 3,6-dioxaoctane-l,&diamine (20202)) 4,7-dioxadecane-l,lO-diamine (30203), 4,9-dioxadodecane-1,12-diamine (30403) and 4,7,10-trioxatridecane-1,13diamine (3020203), on N,P,Cl, lead (i) to MACRO-ANSA [ 2-41 and MEGA-ANSA [ 51 derivatives with THF as solvent, (ii) to MACRO-SPIRO [2-41 and MEGA-SPIRO [5-81 derivatives when reactions are performed in toluene-Na,CO, saturated water (interface process), and (iii) to MACRO-monoBIN and MEGA-monoBIN species [ 1 ] in ethyl ether-Na,CO, saturated water (interface process) when working in 2 : 1 stoichiometric conditions. These reactions are usually stereoselective and in some cases stereospecific. This is especially the case for the synthesis of the monoBIN compounds. In the present work we extended the use of the Et,O-water interface procedure to the production of polyBIN0 architectures. The present paper deals with the synthesis of diBIN0 non-geminal dicyclophosphazenes upon reaction of oxodiamines on N3PsClGin 1:1 conditions. *For Part XIV, see Ref. 1. **Author to whom correspondence should be addressed.
0022-2860/90/$03.50
0 1990 Elsevier Science Publishers B.V.
246 AMINOLYSIS
OF N3P3C& BY OXODIAMINES
(1: 1): THE diBIN0
NON-GEMINAL
COMPOUNDS
In addition to the previously mentioned 20202,30203 and 30403 dioxodiamines and to the 3020203 trioxodiamine, we also investigated the reaction of the simplest Lehn’s monooxodiamine, i.e. H,N- ( CH2)2-0- (CH,),-NH, (202; Aldrich, 17609-5). The diBIN0 derivatives were prepared by reaction at the Et,O-water interface according to the following pathway: 2N3P3 Cl, + 2 (oxodiamine) -&BIN0
(oxodiamino) + 2HC1
The two possible isomers, i.e. the geminal and the non-geminal species, which could be expected from the reaction in the case of dioxodiamines (mOnOm) are shown in Fig. 1.These two isomers are A,B systems in 31PNMR spectroscopy but the two expected NMR patterns are predicted to differ noticeably, according to the transferable 31PNMR rules recently proposed [ 91 for BASIC
‘P-P- I /
’
/
I
\
--p---P
NH
y4’
‘. m”., cH5\___y____y-:2 C-H*
CHZ
Fig. 1. The two possible geminal and non-geminal isomers for diBIN0 dioxodiamines.
derivatives from
247
(BINO-ANSA-SPIRO in cyclophosphazenes) systems. The reactions were stopped when the 31P NMR singlet of N3P3CI, at 20.09 ppm (Brucker AC 200, CDCl,, H,PO, 85% as standard) remained unchanged with time, that is after a few hours at room temperature. The organic phase was dried over Na,SO, and the solvent was removed in vacua at 25°C to give colourless oils. The 31P NMR spectra of the crude final product is (A for 202, B for 20202, C for 30203, D for 30403 and E for 3020203) revealed features which depend on the nature of the oxodiamines as follows. (1) For A and B, only an A,B system (a triplet centred on 19.0 ppm and a and a midoublet centred on 21.7 ppm, ‘Jpp = 47.3 and 46.7 Hz, respectively) nor singlet at 20.09 ppm (unreacted N3P3C16) were observed. (2) For C, an A2B system was observed as for A and B, together with the singlet at 20.09 ppm but also a minor A,X system (a triplet around 9-11 ppm and a doublet around 21-22 ppm) which corresponds to the mono-SPIRO derivative [2,5] as a by-product. (3) For D and E, together with the singlet at 20.09 ppm and the minor A,X system of the mono-SPIRO by-products, it was observed that the expected A,B systems for the diBIN0 species actually collapsed in a unique “false” singlet at 21.78 and 21.60 ppm, respectively. Several techniques can be used to extract pure diBIN0 samples from these crude final products, depending on the oxodiamine reagent. (i) A single washing with n-heptane for A and B (N3P3C16 being highly soluble in this solvent whilst the two diBIN0 derivatives are not). (ii) Dissolving crude D in acetonitrile followed by slow evaporation (diBIN0 30403 precipitates on walls of the vessel whilst N3P3C16 and SPIRO 30403 remain in solution). (iii) Addition of a CH,Cl,-CH,CN (1: 1) mixture to the oily final product for C which precipitates the diBIN0 30203. (iv) HPLC quantitative separation with a ternary AcOEt : n-heptane: CH,Cl, (6 : 3 : 1) mixture for E (other techniques being unsuccessful in this case). In every case, a final washing with cold water is recommended in order to eliminate traces of chlorhydrate which induce slow oligomerization of the bulk in time. However, yields are commonly poor (from 10% for C to 30% for E) except for A and B which are obtained in a pure state with yields above 90%. In other words, it is much easier to obtain pure diBIN0 compounds when the oxodiamine length is short. The same reactions can also be achieved in 2-propanol as solvent in 1: 2 stoichiometric conditions (one molecule of oxodiamine being used here for removing the hydrogen chloride). Final yields are about the same, except for D which is obtained cleanly in this way, conversely to what was observed for the synthesis described above. Thus, polar “protic” solvents such as the biphasic ether-water system or alcohols give strong solute-solvent hydrogen interactions that prevail over the intramolecular hydrogen bonds which exist in free oxodiamines [2]. These intermolecular interactions make the oxodi-
248 TABLE 1 31PNMR chemical shifts and coupling constants for compounds A to E Compound
A B C D E
S(PC1,) (ppm)
2JPP
QClNH)
(ppm) 21.57 21.42 22.48 21.78 21.60
18.94 18.98 20.63 21.78 21.60
47.3 46.7 48.0 -
2.63 2.44 1.85 0 0
G(gClNH)
-a(pCl,)
(Hz)
I
amines prone to link two N3P3 rings to give BIN0 (bridged) configurations rather than one N3P, ring to give a constrained SPIRO or ANSA configuration. The chemical shifts and ‘Jpp coupling constants for compounds A to E (Bruker AC200, CDCl,) are gathered in Table 1 which calls for the following remarks. (i) First-order A,B patterns are revealed for A, B and C whilst a “false” singlet is only observed for D and E, at least at 81.015 MHz. (ii) The “Jpp values are similar within the series, i.e. within the range 46.7-48.0 Hz. (iii) Moreover, in connection with (i), the gap between the centres of each doublet-triplet system decreases slowly from 2.63 ppm for A to 1.85 ppm for C and then drops suddenly to zero for D and E. The break so observed between compounds C and D within the series could not be explained until now. The DC1 mass spectra of compounds A to E were recorded on a NERMAG RlO-10H quadrupole mass spectrometer. The spectra reveal molecular ions MH+ at m/z = 755,843,899,955 and 987 for A, B, C, D and E, respectively. Satellite distributions confirm the presence of eight chlorine atoms in the molecules (maximum peaks at MH+ + 4 mass units). Incidentally, the (M, NH+ ) peaks are not observed, as they are for the monoBIN parents [ 11. CRYSTAL AND MOLECULAR STRUCTURE OF THE diBIN0 (30203)
NON-GEMINAL
REPRESENTATIVE
This 30-crown-ether-like architecture crystallizes in a triclinic system: Pl bar, a=9.019(6), b=9.224(5), c=11.542(8) A, cx=94.87(4), /3=95.97(4), y=99.68(3), V=936.5(1) A3,Z=1,D,=1.599(1) Mgm-3,R=0.049for2862 unique reflections and 199 variable parameters. Details of the data collection, final positions and equivalent isotropic thermal parameters, fractional coordinates of hydrogen atoms, bond lengths and angles will be published shortly [lOI* A ball-and-stick drawing of a suitable perspective view of the title molecule
249
Fig. 2. A perspective view of the &BIN0 30203 non-geminal propound witfi N3F3 rings parallel to the plane of the figure.
(non-gem &BIN0 (30203)) is given in Fig. 2 (the hydrogen numbering is omitted for clarity). The molecule shows a centre of symmetry which coincides with one centre of symmetry of the unit cell. The most striking feature of Fig. 2 is that the two N3P3 rings adopt a trcans ~o~~~rstion with respect to the 3~-members macrocycle, as is clearly visualized in Fig. 3. Cons~uently, t.he two remaining PC& groups are quite‘distant
250
Fig. 3. A perspective view of the diBIN0 perpendicular to the plane of the figure.
30203 non-geminal compound with N3P, rings quasi-
for each other and are no longer accessible for the grafting of a third BIN0 stave upon reaction of a new molecule of 30203 on the non-gem diBIN0 30203. In other words, the non-gem diBIN0 30203 compound adopts, in the solid state at least, the “chair” configuration shown in Fig. 4. Thus, any hope of preparing a non-gem triBIN0 (coded as oxobarrelane by analogy with barrelanes from non-oxygenated diamines [ 111) will pass through the synthesis of the “boat” configuration (Fig. 4) of the corresponding non-gem diBIN0 parent. The synthesis of “boat” non-gem diBIN0 isomers from dioxodiamines is yet to be achieved; work is underway to meet this challenge. The X-ray structures of other non-gem diBIN0 derivatives, i.e. of compounds A, B, D and E,
Fig. 4. Simplified patterns
of the “chair” and “boat” forms of a diBIN0
non-geminal
“CHAIR” FORM
derivative.
~__ ..I
. I
.
...?
252
need to be determined to be certain of their “chair” or “boat” configuration. Studies are currently in progress for this purpose. CONCLUSION
Aminolysis
of N3P3C16 by oxodiamines at an E&O-water interface and in conditions leads to diBIN0 dicyclophosphazenic non-geminal architectures which adopt a tram configuration. Such diBIN0 bridged species, as well as their monoBIN analogues, are highly soluble in common organic solvents and they constitute prime candidates for further synthesis of cryptates with usual and/or exotic properties [ 121. 1: 1 stoichiometric
ACKNOWLEDGEMENTS
We are greatly indebted to Texaco and BASF for donating the oxodiamines and to Shin Nisso Kako for their gift of pure crystalline N,PJ&. The authors wish to thank the Conseil Regional de Midi-Pyrenees for its generous financial support of this project.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12
F. Sournies, P. Castera, A. el Bakili and J.-F. Labarre, J. Mol. Struct., 221 (1990) 239. A. el Bakili, P. Castera, J.-P. Faucher, F. Sournies and J.-F. Labarre, J. Mol. Struct., 195 (1989) 21. R. Enjalbert, J. Galy, A. el Bakili, P. Castera, J.-P. Faucher, F. Sournies and J.-F. Labarre, J. Mol. Struct., 196 (1989) 207. T.S. Cameron, A. Linden, A. el Bakili, P. Castera, J.-P. Faucher, M. Graffeuil, F. Sournies and J.-F. Labarre, J. Mol. Struct., 212 (1989) 281. F. Sournies, A. el Bakili, J.-F. Labarre and B. Perly, J. Mol. Struct., 196 (1989) 41. T.S. Cameron, A. Linden, F. Sournies, A. el Bakili and J.-F. Labarre, J. Mol. Struct., 197 (1989) 41. J. Jaud, F. Sournies and J.-F. Labarre, J. Mol. Struct., 212 (1989) 305. F. Sournies, A. el Bakili, B. Zanin, J.-F. Labarre and J. Jaud, J. Mol. Struct., 220 (1990) 63. J.-P. Bonnet and J.-F. Labarre, Inorg. Chim. Acta, 149 (1988) 187. R. Enjalbert, J. Galy, F. Sournies and J.-F. Labarre, J. Mol. Struct., in press. P. Castera, J.-P. Faucher, M. Granier and J.-F. Labarre, Phosphorus Sulfur, 22 (1987) 37. J.-F. Labarre, P. Castera, J.-P. Faucher, M. Graffeuil and F. Sournies, CNRS French Patent No. 89-15484,1989.