Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
COORDINATION COMPLEXES, PREPARATION AND USE
Document Type and Number:
WIPO Patent Application WO/1994/017083
Kind Code:
A1
Abstract:
A compound which is, or which contains at least two repeating units, represented by formula (1): (LnMn1)n2An3 or by formula (2): (LnMn1)n2L'n4An3 wherein L and L' are the same or different bis-lactam ligand represented by formula (3) or the same or different bis-pyridone ligand represented by formula (4) in which n, n1, n2, n3, n4 and n5 are the same or different integers; X is O or S; Y is O or S; Z is a straight or branched chain alkyl group or is -(CH2)n6-D-(CH2)n7- where D is O or a phenyl ring; R1 is optional and if present represents a straight or branched chain alkyl group on one or more of the methylene carbon atoms of the lactam ring; R2 is optional and if present represents a straight or branched chain alkyl group on one or more of the carbon atoms in the pyridone ring; n6 is zero or an integer; n7 is zero or an integer; A is at least one anion or a plurality of different anions; and M is at least one di- or other multivalent metal ion other than Hg, optionally bound to one or more anions A, provided that each metal ion M is bound to at least two said ligands. These compounds demonstrate inclusion of the metal ion(s) as an integral part of the ring structure and have the ability to form ordered arrays of chains, sheets or even three-dimensional networks. Potential industrial applications include uses in separations, purifications, absorptions, electrical processes, optical processes, chemical sensors or in catalysis of reactions.

Inventors:
Goodgame
David
Martin
Lawrence, Williams
David
John
Application Number:
PCT/GB1994/000104
Publication Date:
August 04, 1994
Filing Date:
January 19, 1994
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
Imperial, College Science OF.
TECHNOLOGY & MEDICINE GOODGAME
David
Martin
Lawrence, Williams
David
John
International Classes:
C07D207/24; C07D207/27; C07D213/64; C07F3/00; C07F5/00; C07F13/00; C07F15/06; C07F19/00; C07D207/26; (IPC1-7): C07F19/00; C07D213/64; C07D227/087
Other References:
D.M.L. GOODGAME ET AL.: "Synthesis, X-Ray Characterization, and Q-Band Electron Spin Resonance Studies of Heterometallic, Polymeric Compounds formed by Yttrium and Lanthanides (III) Nitrates with HgL2 (L=C4H6NO, the Anion of 2-Pyrrolidinone); Crystal Structure of [{Hg2EuL4(NO3)3}n] and [{Hg3Tb2L6(NO3)6}n]", JOURNAL OF THE CHEMICAL SOCIETY, DALTON TRANSACTIONS, no. 8, August 1989 (1989-08-01), LETCHWORTH GB, pages 1439 - 1447
CHEMICAL ABSTRACTS, vol. 111, no. 19, 6 November 1989, Columbus, Ohio, US; abstract no. 173340z, V.D. KISELEV ET AL.: "N,N'-bismaleimides in Diels-Alder reactions. II. Catalytic effect of gallium chloride in reactions with trans,trans-1,4-diphenybutadiene" page 653;
G.A. DOYLE ET AL.: "Framework Coordination Chemistry; Generalised Entry in a New Class of Supramolecular Compounds exemplified by the Structure of [Mn2(epby)3(NO3)4]n [where epby=N,N'-ethylenebis(2-pyridone)] and [Er2(ebpyrr)3(NO3)6]n [where ebpyrr=N,N'-ethylenebis(2-pyrrolidone]", JOURNAL OF THE CHEMICAL SOCIETY, CHEMICAL COMMUNICATIONS, no. 2, 21 January 1993 (1993-01-21), LETCHWORTH GB, pages 207 - 209
D.M.L. GOODGAME ET AL.: "Ligand-induced Formation of a Triple Helical Bridge involving O-Donor Ligands in Dimeric Lanthanide Complexes", JOURNAL OF THE CHEMICAL SOCIETY, CHEMICAL COMMUNICATIONS, no. 12, 21 June 1993 (1993-06-21), LETCHWORTH GB, pages 1019 - 1021
G.A. DOYLE ET AL.: "Conversion of Atmospheric Dioxygen to a mu-eta2, eta2-Peroxo Bridge in a Dinuclear Uranium (VI) Complex", JOURNAL OF THE CHEMICAL SOCIETY, CHEMICAL COMMUNICATIONS, no. 14, 21 July 1993 (1993-07-21), LETCHWORTH GB, pages 1170 - 1172
D.M.L. GOODGAME ET AL.: "Formation of a Novel "Bedspring"-like Framework Structure by a Neodymium Nitrate complex with N,N'-ethylenebis(2-pyridone)", POLYHEDRON, vol. 12, no. 24, 1993, OXFORD GB, pages 2933 - 2939
Download PDF:
Claims:
CLAIMS
1. A compound which is, or which contains at least two repeating units, represented by: formula (1) (LnMnl>n2An3 (1) or by formula (2) (LnMnl)n2L'n4An3 (2) wherein L and L* are the same or different bislactam ligand represented by formula (3) or the same or different bispyridone ligand represented by formula (4) in which n, n , n , n , n and n are the same or different integers, X is 0 or S, Y is 0 or S, Z is a straight or branched chain alkyl group or is (CH2)n6D(CH2)n7 where D is 0 or a phenyl ring, R is optional and if present represents a straight or branched chain alkyl group on one or more of the methylene carbon atoms of the lactam ring, R2 is optional and if present represents a straight or branched chain alkyl group on one or more of the carbon atoms in the pyridone ring, is zero or an integer, n 7 is zero or an integer, A is at least one anion or a plurality of different anions, and M is at least one di or other multivalent metal ion other than Hg, optionally bound to one or more anions A, provided that each metal ion M is bound to at least two said ligands.
2. Compounds as claimed in claim 1 wherein A represents at least one inorganic ion.
3. Compounds as claimed in claim 2 wherein the ion(s) are one or more of the following : nitrate, chloride and bromide.
4. Compounds as claimed in any preceding claim wherein Z represents an ethylene, butylene or phenyl linking group.
5. Compounds as claimed in any preceding claim wherein R± and/or R2 are absent.
6. Compounds as claimed in any preceding claim wherein A is at least one metal ion from the following: main group metals, lanthanide metals, transition metals or actinide metals, in the form of ring framework compounds wherein the metal ion(s) is (are) an integral part of said ring framework.
7. Compounds as claimed in claim 6 wherein the metal ion is one or more from the following: manganese (II), erbium (III), cobalt (II), zinc (II), neodynmium (III) , terbium (III) and uranium (VI) .
8. Metallamacroyclic compounds as claimed in any preceding claim represented by the following empirical formulae: L2M2An3; L2MaMbAn3; LL'M2An3; LL'MaMbAn3; M6L6An3; M6L6L'6An3; (LnMnl)2An3; (LnMnl)3An3; wherein Ma and Mb represent different metal ions in the same compound.
9. Compounds of the formula [Mn2(EBPy)3 (N03)4]χ [Er2(EBPyrr) 3(N03)6]χ [Co(EBPy)Cl2]2 {[Zn(EBPyrr)3] (C104)2.2CH3CN}χ [U02μ(02)U02(EBPyrr)2] [Zn(EBPy)(N03)2]2 [Zn(oXBPy)Cl2]2 {[Tb2(EBPy)3(N03)6] .5MeCN}χ [Nd2(BBPy)3(N03)6]χ [Co(EBPyrrS)Br2]2 wherein EBPy is an ethylenebridge bis(2pyridone) , EBPyrr is an ethylene bridged bislactam BBpy is a butylene bridged bis(2pyridone) , oXBPy is an orthoxylyl bridged bis(2 pyridone) and EBPyrrS is an ethylene bridged bisthiolactam, x represents the number of repeating units of the molecule in the compound, and μ represents a number of oxygen molecules.
10. A method of making a compound of formula (1) or (2) as defined in claim 1, by mixing a solution of one or more said ligands L and/or L' as defined in claim 1 in an organic solvent with a solution of a salt of the metal M and separating the compounds formed.
11. Use of a compound as claimed in any one of claims 1 to 9, in separation or purification processes.
12. Use of a compound as claimed in any one of claims 1 to 9 in absorbtion of selective molecular or ionic species.
13. Use of a compound as claimed in any one of claims 1 to 9 in an electrical or optical process.
14. Use of a compound as claimed in any one of claims l to 9 as a chemical sensor.
15. Use of a compound as claimed in any one of claims 1 to 9 as a catalyst for a chemical process.
Description:
COORDINATION COMPLEXES, PREPARATION AND USE

This invention is concerned with novel coordination complexes, including precursors for molecular framework compounds, molecular ring framework compounds themselves and polymeric derivatives thereof. The principal compounds of interest with attractive potential applications are those with a molecular ring framework incorporating holes and/or channels in the molecular array. However, the invention is sufficiently broad in scope to embrace compounds whose molecular array is not of ring formation.

The present invention seeks to provide such coordination complexes, including those with various ring framework sizes and orientations, wherein specified metal ions or combinations of different metal ions can be incorporated into and thereby become chemically bound into the ring framework. The holes and/or channels which are bounded by the ring framework have a retention capacity for other molecules or ions which may be shape, size or charge selective. Such ring framework compounds have potential use in, inter alia, separation or purification processes, selective molecular or ionic uptake, catalysts, electrical or optical processes, and chemical sensors amongst other industrially useful applications. The present compounds can form large ring systems such as, for example only, 8 to 80

membered rings. Alternatively, contiguous linking of the metallamacrocyles, which may be of the same or differing ring systems, may be linked to form chains, two-dimensional sheets or three-dimensional networks.

Well-defined arrays of metal ions shown by embodiments of the present compounds in their ring framework present opportunities for catalysis of chemical reactions, as the arrays are relatively open to smaller molecular substrates. A further feature of the compounds is their capacity to bring sets of metal ions, which can be the same or different, into ordered arrays of chains, sheets or three- dimensional networks.

Selection of metal ion(s) on the basis of their known characteristics could lead to compounds (or precursors therefor) with application in the optical or electronic fields.

There are already known metallamacrocyclic compounds with metals bonded within the ring framework, based on mercury/hetero etal combinations. For example J. Chem. Soc, Chemical Communications, 3, 1991, pp 175-6, discloses preparation and crystal structure of heterometallic polymeric complexes utilising 2-oxazolidone as bridging organic ligand. Arrays of contiguous 16- and 48- membered metallamacrocycles are disclosed but there is no suggestion of industrially significant utility.

Inclusion of mercury in such complexes as a key

building block not only limits synthetic developments but would also raise toxicological problems in any subsequent industrial applications. The present inventors have continued the quest for extended frameworks which incorporate metal ions other than mercury in the structure, using a wider range of organic bridging ligands, and with alternative organic metal-linking groups.

According to this invention we provide a compound which is, or which contains at least two repeating units, represented by:

formula (1) ( L n M nl>n2 A n3 (1) or by formula (2) ( n M nl>n2 L 'n4 A n3 (2)

wherein L and L' are the same or different bis-lactam ligand represented by formula (3)

R.'

or the same or different bis-pyridone ligand represented by formula (4)

in which n, n , n , n , n 4 and n are the same or different integers,

X is 0 or S,

Y is 0 or S,

Z is a straight or branched chain alkyl group or is -(CH 2 ) n6 -D-(CH 2 ) n7 - where D is 0 or a phenyl ring,

R 1 is optional and if present represents a straight or branched chain alkyl group on one or more of the methylene carbon atoms of the lactam ring,

R 2 is optional and if present represents a straight or branched chain alkyl group on one or more of the carbon atoms in the pyridone ring, n is zero or an integer, n 7 is zero or an integer,

A is at least one anion or a plurality of different \ anions, and

M is at least one di- or other multi-valent metal ion other than Hg, optionally bound to one or more anions A, provided that each metal ion M is bound to at least two said ligands.

The anion(s) can be inorganic ions such as nitrate, chloride, bromide and the like.

It is preferred that where n is 2 or greater, the compound or unit ( L n M nl ) 2 ; (L n M nl ) 3 and the like are cyclic.

We also provide, in another aspect of the present invention, methods for preparing compounds of formula (1) or (2) above, by mixing a solution of one or more said ligands L; L as defined above in an organic solvent with a solution of a salt of the metal M, and separating the compound(s) formed from solution by appropriate means.

Suitable solvents include alcohols such as ethanol, or acetonitrile, nitromethane, 2, 2-dimethoxypropane or mixtures of such solvents. The metal salt(s) can be halide(s) and/or nitrate(s) as example of the inorganic ions which can be bound to the metal(s) in the present compounds. Combinations of different metals and different salts thereof can be employed. Separation can be effected by, for example, crystallisation by either cooling or concentrating the solution after reaction.

The compounds obtained have been solids whose solid state molecular structure can be ascertained by X-ray diffraction studies. Accordingly metal ions M, or combinations of different metal ions (which may be referred to as Ma, Mb, Mc, Md and the like) can be linked by the

I ligands L with or without L as defined above to form metallamacrocycles as single rings in which L 1 is absent (equivalent to n = O) , for which the smallest ring would be

I I

4-membered, eg L 2 2 , L 2 a M jD ; LL M 2 ; LL M a b . Single rings can be connected to form frameworks of different size (L' is present and n can exceed 2) . Examples of single rings and connected frameworks are MgLg and gLgL'g.

Preferably the metal ions are any of a wide range of

main group metals, transition metals, lanthanides or actinideε. By way of example only, compounds can be prepared wherein one or more of the following ions form an integral part of the ring structure, namely manganese (II) , erbium (III) and cobalt (II) , zinc (II) , neodymium (III) , terbium (III) and uranium (VI) .

In order that the invention may be more easily understood and readily carried into effect, embodiments thereof will now be described by way of non-limiting example only.

Abbreviations used : for the bis-pyridone ligand (L and/or L') EBPy = the ethylene bridged bis (2-pyridone) , namely:N,N'-ethylenebis(2-pyridone) (compound 4a wherein n = 2) . This compound, and its preparation is described in C. Alberti, Gazz.Chim.Ital. , 1956, 86 « 1181. BBpy = the butylene bridged bis(2-pyridone) namely: N,N'-butylenebis(2- pyridone) (compound 4b wherein n = 4) . This compound, and its preparation, is described in J.A. Gautier and J. Renault, Compt. Rend; 1947, 225, 682. o-XBPY = ortho-xylyl bridged bis(2-pyridone) namely: N,N'-1,2-xylylbis(2- pyridone) (compound 4c) . This latter compound was obtained by refluxing α,α 1 -dibromo-ortho-xylene with 2 equivalents of the sodium salt of 2-pyridone for six hours at Ca. 145°C. The product was extracted with boiling toluene and recrystallised from the same solvent. It was characterised by microanalysis, IR spectroscopy, and Η and 13 C NMR.

: for the bis-lactam ligand (L and/or L 1 ) EBPyrr = the ethylene bridged bis-lactam, namely:N,N'-ethylenebis(2- pyrrolidone) (the compound 3a wherein X = O) . This compound and its preparation is described in W.Reppe, Annalen, 1955, 596, 1.

: for the bis-thiolactam ligand (L and/or L') EBPyrrs = the ethylene bridged bis-thiolactam, namely : N,N'- ethylenebis(pyrrolidin-2-thione) (the compound 3b wherein X = S) . This compound was obtained by reacting EBPyrr with Lawesson's Reagent following a standard method (Organic Syntheses. 1984, .62 . , 158) and was characterised by elemental analysis, NMR and mass spectroscopy.

(CH 2 ) 2 (3a, X=0; 3b, x=s)

I

Example 1

Preparation of the framework precursor or unit shown in Figure 1, for complexes of the type [Mn 2 (EBPy) 3 (N0 3 ) 4 ] χ .

A solution of EBPy in acetonitrile was added to and mixed with a solution of hydrated manganese (II) nitrate in the same solvent. After reaction, the solvent mixture was evaporated, isolating the above complex as a crystalline solid. A satisfactory microanalysis was obtained and the solid state molecular structure found to be in accord with that shown in Figure 1 by X-ray diffraction. Stoichiometry was found to be Mn(EBPy) 1 5 (N0 3 ) 2 . The manganese is six co-

ordinate, being bonded to the oxygen atoms of three different EBPy ligands, two oxygen atoms from a bidentrate nitrate and one from a monodentate nitrate.

Adjacent manganese centres in the complex comprising repeating units defined above are linked via the EBPy ligands in two essentially orthogonal directions, shown in Figure 2 as 36-member macrocyclic rings, each containing 4 Mn atoms linked by one edge to form a polymeric chain of macrocycles. Example 2

Preparation of the complex [Er 2 (EBPyrr) 3 (N0 3 ) 6 ] χ shown in Figure 3.

A solution of EBPyrr in acetonitrile was added to and mixed with a solution of hydrated erbium (III) nitrate in the same solvent. After reaction, the solvent mixture was evaporated, isolating the above complex as a crystalline solid. A satisfactory microanalysis was obtained and the solid state molecular structure found to be in accord with that shown in Figure 3 by X-ray diffraction. Stoichiometry was found to be Er(EBPyrr) 1 5 (N0 3 ) 3 ; excluding the trapped CH 3 CN solvent molecules.

The erbium atom is nine co-ordinate, being bonded to three different EBPyrr ligands and to three bidentate nitrate groups.

In similar fashion to the complex of example 1, these organic ligands link, to form repeating units in the complex specified above, between adjacent metal centres in a macrocyclic array. This is illustrated in Figure 4. Both the macrocyle ring size and nature of the array are, however, quite different from the complex shown in Figure 2.

In the present example, 54- membered rings are formed, containing six erbium atoms. The macrocyclic rings are not self-filling and they accommodate acetonitrile solvent molecules. Adjacent rings are fused in a "parquet-like" pattern to form a two-dimensional sheet (Fig.6). In one direction the sheets stack in register so that continuous

channels are formed, permitting solvent molecule diffusion through the lattice. Example 3

Preparation of the complex [Co(EBPy)Cl 2 ] 2 shown in Figure 5.

A solution of EBPy in acetonitrile was added to and mixed with a solution of hydrated cobalt (II) chloride in the same solvent. After reaction, the solvent mixture was evaporated until a blue crystalline solid was formed, which was collected by filtration. A satisfactory microanalysis was obtained and the solid state molecular structure found to be in accord with that shown in Figure 5 by X-ray diffraction. The stoichiometry was found to be Co(EBPy)Cl 2 - The cobalt is four-coordinate, each cobalt being bound to two oxygen atoms, one from each of two different EBPy ligands and two chloride ions. The EBPy ligands bridge pairs of cobalt atoms to form the cyclic structure illustrated in Figure 5. Example 4 - A framework with rings of different size

Preparation of the complex { [Zn(EBPyrr) 3 ] (C10 4 ) 2 .2CH 3 CN} χ shown in Figure 7.

A solution of EBPyrr in acetonitrile was added to and mixed with a solution of hydrated zinc(II) perchlorate in the same solvent. After reaction, the solvent mixture was allowed to stand for a day when a colourless crystalline solid was formed, which was collected by filtration. A satisfactory microanalysis was obtained and the solid state molecular structure found to be in accord with that shown in Figure 7 by X-ray diffraction. The stoichiometry was found to be [Zn(EBPyrr) 3 ] (C10 4 ) 2 excluding trapped acetonitrile molecules. The zinc is six coordinate, each zinc atom being bound to six oxygen atoms, one from each of six different EBPyrr ligands. The EBPyrr ligands bridge adjacent zinc atoms so as to form a complex system in which in both 18- membered metallamacrocyclic rings (Figure 7a which is a view along the b-axis showing the framework based on two Zn, four

0, four N and eight C-atoms) and 36-membered rings (Figure 7b which is a view along the C-axis showing the framework based on four Zn, eight O, eight N and sixteen C-atoms) are formed.

Example 5 below demonstrates use of the present co¬ ordination complexes for the absorption and subsequent reaction of small molecules by uptake of atmospheric dioxygen by a uranium (VI) complex of EBPyrr and its conversion to coordinated peroxide ion. Example 5

Exposure of an acetonitrile solution of EBPyrr and uranyl nitrate to air resulted in the formation of both a yellow compound and an orange complex, the latter of which has been shown by X-ray diffraction studies to have the stoichiometry [U0 2 -μ(0 2 ) -U0 2 (EBPyrr) 2 ] (Figure 8) . This complex forms a metallamacrocyclic ring in which a dioxygen molecule has been converted to a coordinated peroxide ion forming a symmetrical bridge between the pair of uranium atoms. Example 6

Preparation of the complex [Zn(EBPy) (N0 3 ) 2 ] 2 shown in Figure 9.

A solution of hydrated zinc nitrate in acetonitile was added, with stirring, to an acetonitrile solution of EBPy. The resulting solution was evaporated, at room temperature in a desiccator over concentrated sulphuric acid, until a white crystalline solid was formed. This was collected by filtration. A satisfactory micronanalysis was obtained and the solid state molecular structure found by X-ray diffraction to be in accord with that shown in Figure 9. The stoichiometry was found to be Zn(EBPy) (N0 3 ) 2 . Each zinc atom is bound to four oxygen atoms; two oxygens are from two monodentate nitrate groups and two from different EBPy ligands. The EBPy ligands bridge pairs of zinc atoms to form the cyclic structure. This example demonstrates that the cyclic structure shown in example 3, may also be

obtained with metals other than cobalt (II) and anions other than chloride. Example 7

Preparation of the complex [Zn(o-XBPy)Cl 2 ] 2 shown in Figure 10.

A solution of zinc chloride was dissolved in a 1:1 mixture of methanol and 2,2-dimethoxypropane and added to a solution of o-XBP in the same solvent mixture. The resulting solution was evaporated, at room temperature in a desiccator over concentrated sulphuric acid, until a white crystalline solid was formed. This was collected by filtration. A satisfactory microanalysis was obtained and the solid state molecular structure found by X-ray diffraction to be in accord with that shown in Figure 10. The stoichiometry was found to be Zn(o-XBPy)Cl 2 . Each zinc atom is bound to two chloride ions and to two oxygens, one from each of two different o-XBPy ligands. The o-XBPy ligands bridge pairs of zinc atoms to form the cyclic structure. This example demonstrates that the cyclic structure shown in examples 3 and 6 may also be obtained with linking groups (Z) other than -(CH 2 ) 2 ~- Example 8

Preparation of the complex { [Tb 2 (EBPy) 3 (N0 3 ) 6 ] .5MeCN} χ shown in Figure 11.

A solution of hydrated terbiu (III) nitrate in acetonitrile was added, with stirring, to an acetonitrile solution of EBPy. The resulting solution was evaporated, at room temperature in a desiccator over concentrated sulphuric acid, until a crystalline solid was formed. This was collected by filtration. A satisfactory microanalysis was obtained and the solid state molecular structure found by X- ray diffraction to be in accord with that shown in Figure 11. The stoichiometry was found to be {[Tb 2 (EBPy) 3 (N0 3 ) 6 ].5MeCN}.

The terbium atom is nine coordinate, being bonded to three different EBPy ligands and to three bidentate nitrate

groups (Fig. 11a) . The EBPy ligands bridge between terbium atoms so as to form 54-membered metallomacrocylic rings (Fig. lib) , which are yet further linked to form a two- dimensional sheet of rings. The acetonitrile molecules are accommodated within the ring structure.

This example demonstrates that structures comprising sheets of rings, such as that given in example 2, are not limited to complexes with bis-lactam ligands but can be obtained with bis-pyridone ligands. Example 9

Preparation of the complex [Nd 2 (BBPy) 3 (N0 3 ) 6 ] χ shown in Figure 12.

A solution of hydrated neodymium(III) nitrate in methanol was added to a methanol solution of BBPy. The resulting solution was evaporated, at room temperature in a desiccator over concentrated sulphuric acid, until a crystalline solid was formed. This was collected by filtration. A satisfactory microanalysis was obtained and the solid state molecular structure found by X-ray diffraction to be in accord with that shown in Figure 12. The stoichiometry was found to be Nd 2 (BBPy) 3 (N0 3 ) g .

The neodymium atom is nine coordinate, being bonded to three different BBPy ligands and to three bidentate nitrate groupds (Fig. 12a) . The BBPy ligands bridge between neodymium atoms so as to form 66-membered metallomacrocylic rings (Fig. 12b, in which, for clarity of presentation the nitrate groups and one of the pyridone units bonded to each Nd atom have been omitted) . These rings are further linked by BBPy ligand bridges. This example demonstrates the difference in ring sizes that can be obtained by altering the length of the bridging unit (Z) between the pyridone units in the bis-pyridone ligands. Example 10

Preparation of the complex [Co(EBPyrrS)Br 2 ] 2 shown in Figure 13.

A solution of hydrated cobalt(II) bromide in hot

ethanol was added to one of EBPyrrS also in hot ethanol and the resulting solution maintained at reflux for 1 to 2 minutes. An equal volume of 2,2-dimethoxypropane was added and the reflux continued for a further 1 to 2 minutes. The resulting solution was evaporated, at room temperature in a desiccator over concentrated sulphuric acid, until a crystalline solid was formed. This was collected by filtration. A satisfactory microanalysis was obtained and the solid state molecular structure was found by X-ray diffraction to be in accord with that shown in Figure 13.

The stoichiometry was found to be Co(EBPyrrS)Br 2 . Each zinc atom is bound to two bromide ions and to two sulphur atoms, one from each of two different EBPyrrS ligands. The EBPyrrS ligands bridge pairs of cobalt atoms to form the cyclic structure. This example demonstrates that large metallocyclic structures can also be obtained with the sulphur analogues of the bis-lactam ligands.

These results illustrate both the versatility and potential of the bis-lactam, bis-thiolactam and bis-pyridone organic ligands, L; L to form framework coordination compounds with potentially significant industrial applications.