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Showing papers by "J. Fraser Stoddart published in 1985"



Journal ArticleDOI
TL;DR: In this paper, the authors showed that the most stable 1 : 1 complex is formed between dibenzo-30crown-10 and diquat bis(hexafluorophosphate)(2) in acetonitrile.
Abstract: Spectrophotometric investigations of equimolar mixtures of diquat bis(hexafluorophosphate)(2) and a range of dibenzo-3n-crown-n ethers [n=6–12; (10)–(16)] in acetonitrile reveal the existence of charge-transfer absorption bands at ca.λmax. 400 nm. These absorptions are attributable to intermolecular π–π charge transfer between the electron-rich catechol units of the dibenzo-crown ethers and the electron-deficient bipyridinium ring system of the diquat dication. The qualitative conclusion from these experiments, that the most stable 1 : 1 complex is formed between dibenzo-30-crown-10 (14) and diquat bis(hexafluorophosphate)(2). led to the isolation from dichloromethane methanol–n-heptane of red crystals of [diquat.dibenzo-30-crown-10][PF6]2 suitable for X-ray crystallography. Although the crystal structure analysis revealed that there are two independent sets of 1 : 1 complexes (I and II) in the unit cell, the gross structural features of the two complexes are very similar. In addition to the parallel alignment of their three aromatic rings to accommodate the stabilising intermolecular π-π charge-transfer interaction, there is probably some further host–guest stabilisation to be gained on account of favourable electrostatic interactions between the phenolic oxygen atoms in the host and the nitrogen atoms in the pyridinium rings of the guest. Moreover, there is some evidence for weak C–H ⋯ O hydrogen bonding involving principally H-6 and H-6′ on the bipyridinium ring system of the guest and certain –CH2OCH2– oxygen atoms in the host. As evidenced by 1H n.m.r. spectroscopy in CD3COCD3, these non-covalent bonding interactions are probably responsible for the formation of stable and ordered 1 : 1 complexes with similar gross structural features in solution, at least in the cases where dibenzo-30- crown-10 (14). dibenzo-33-crown-11 (15), and dibenzo-36-crown-12 (16) are the hosts. Further evidence for the 1 : 1 stoicheiometry of these solution complexes, as well as for the complex involving dibenzo-27-crown-9 (13), has come from equilibrium constant measurements for the association between the dibenzo-3n-crown-n(n=9–12) hosts (13)–(16) and diquat bis(hexafluorophosphate)(2) in acetone. A quantitative treatment of the charge-transfer absorption bands at 400 nm, which affords Kavalues of 410, 17 500, 10 800, and 2 000 M–1 for n=9, 10, 11, and 12, respectively, provides convincing quantitative evidence for (a) 1 : 1 stoicheiometry and (b) the relative stabilities of the 1 : 1 complexes in solution. In the case of dibenzo-24-crown-8 (12), a complex of 2:l (guest:host) stoicheiometry is believed to be formed in acetone with a Kavalue of 385 000 M–2, as shown by a successful quantitative treatment of the charge-transfer absorption data by an independent method.

61 citations


Journal ArticleDOI
TL;DR: In the second sphere coordination of a cyclobitane-1,1-dicaroxy; atiammimeplatinum(II)µ-cyclodextrin, stabilisation of the crystalline adduct is achieved by the cyclobutane ring if the guest penetrating into the cavity of the hoist and the ammine ligands on the guest participating in the formation of two(N−H ··O) hydrogen bonds with secondary hydroxy group at C(3) on neighboring α-D-glucopyranosid
Abstract: In the second sphere co-ordination of a cyclobitane-1,1-dicaroxy;atiammimeplatinum(II)µ-cyclodextrin, stabilisation of the crystalline adduct is achieved by the cyclobutane ring if the guest penetrating into the cavity of the hoist and the ammine ligands on the guest participating in the formation of two(N–H ··O) hydrogen bonds with secondary hydroxy group at C(3) on neighboring α-D-glucopyranosidic units in the host.

38 citations


Journal ArticleDOI
TL;DR: An X-ray structural investigation has shown that the macrobicyclic host (1), synthesised regiospecifcally from 3,4-dihydroxybenzaldehyde (2) in eight steps, forms a deep red 1 : 1 crystalline complex with Diquat in which the quest dication is encapsulated by the host as mentioned in this paper.
Abstract: An X-ray structural investigation has that the macrobicyclic host (1), synthesised regiospecifcally from3,4-dihydroxybenzaldehyde (2) in eight steps, forms a deep red 1 : 1 crystalline complex with Diquat in which the quest dication is encapsulated by the host.

35 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that Pt(NH3)2(CBDCA), cyclobutane-1,1-dicaboxylato and α-cylodextrin (α-CD) form a 1:1 adduct in water with a standard free energy change in the region of 10.4−13.0 kJ mol−1 at 22−25 °C.
Abstract: Microcalorimetry and 1H n.m.r. spectroscopy have established that Pt(NH3)2(CBDCA)(CBDCA = cyclobutane-1,1-dicaboxylato) and α-cylodextrin (α-CD)form a 1:1 adduct in water with a standard free energy change (–ΔG⊖) in the region of 10.4–13.0 kJ mol–1 at 22–25 °C.

34 citations



Journal ArticleDOI
TL;DR: X-ray structural investigations of the 1:1 crystalline complexes formed between [Diquat][PF 6 ] 2 and (i) the bisformyl dibenzo-30-crown-10 derivative 2 as discussed by the authors reveal that in both cases, charge transfer, as well as electrostatic binding and weak [C-···O] hydrogen bonding combine to give the cortlexes their remarkable stabilities.

21 citations


Journal ArticleDOI
TL;DR: In addition to hydrogen bonding and Coulombic forces, charge transfer interactions stabilise the 1:1 adducts formed between [Pt(bipy)(NH3)2] 2+ and a series of dibenzo-3n-crown-n (n = 6-12) ethers as evidenced by 1H NMR and UV-visible spectra in solution and by X-ray crystal structures (for n = 8 and 10) in the solid state as mentioned in this paper.
Abstract: In addition to hydrogen bonding and Coulombic forces, charge transfer interactions stabilise the 1:1 adducts formed between [Pt(bipy)(NH3)2] 2+ and a series of dibenzo-3n-crown-n (n = 6–12) ethers as evidenced by 1H NMR and UV-visible spectra in solution and by X-ray crystal structures (for n = 8 and 10) in the solid state. Mutual diamagnetic (ring current) shielding by the aromatic systems of host and guest results in dramatic upfield shifts of certain aromatic proton resonances on adduct formation, especially when n = 10 or 11. A broad charge-transfer absorption band at 350 nm attains its maximum intensity at n = 11 though stability constant measurements indicate optimum binding when n = 10. X-ray diffraction studies reveal that, when n = 8, only one of the crown ether benzo-rings interacts with the bipyridyl ligand in a charge-transfer sense. However, when n = 10, the macrocycle is sufficiently large and flexible to allow both benzo-rings to enter into stabilising interactions with the bipyridyl ligand such that the platinum complex is encapsulated by the host in a U-shaped cavity.

20 citations


Journal ArticleDOI
TL;DR: In this paper, the synthesis of octamethyl-18-crown-6 (BH 3 NH 3 ) 2 · 2 with borane-ammonia was reported.

19 citations



Journal ArticleDOI
TL;DR: The crystal structure of 2Li picrate was determined by X-ray diffraction methods as mentioned in this paper, and the 2H2O complex was shown to have a 2:1 crystal structure.

Journal ArticleDOI
TL;DR: In this paper, 1 ∵ 1 (guest: host) crystalline complexes with borane ammonia as guest were shown to yield enantiomeric excesses of 5, 13, and 10% respectively.
Abstract: Whereas 1 ∶ 1 crystalline complexes have been isolated between borane ammonia and methyl 4,6-O-benzylidene-2,3-dideoxy-α-d-galactopyranosido [2,3-b]-1,4,7,10,13,16-hexaoxacyclo-octadecane (1), methyl 4,6-O-benzylidene-2,3-dideoxy-α-d-mannopyranosido [2,3-b] (methyl 4′,6′-O-benzylidene-2′,3′-dideoxy-α-d-mannopyranosido [2′,3′-k]-1,4,7,10,13,16-hexaoxacyclo-octadecane (3), and (1R,2R,7R,24R)-3,5,8,11,14,17,20,23,26,28-decaoxatricyclo-[21.4.0.02,7]octacosane (4), the hosts, methyl, 4,6-O-benzylidene-2,3-dideoxy-α-d-mannopyranosido[2,3-b] 1,4,7,10,13,16-hexaoxacyclo-octadecane (2) and 1,4 ∶ 1′,4′ ∶ 3,6 ∶ 3′,6′-tetra-anhydro-2,2′ ∶ 5,5′-bis-O-oxydiethylenedi-d-mannitol (5) have yielded 2 ∶ 1 (guest:host) crystalline complexes with borane ammonia as guest. X-ray analyses of the supramolecular structures of BH3NH3 ·1, (BH3NH3)2 ·2, BH3NH3 ·3, BH3NH3 ·4, and (BH3NH3)2 ·5 have been carried out and BH3NH3 ·1, BH3NH3 ·2, and (BH3NH3)2 ·5 have been shown to reduce acetophenone with enantiomeric excesses of 5, 13, and 10% respectively.

Journal ArticleDOI
TL;DR: In this article, the disubstituted derivatives 2 - 4 of dibenzo-30-crown-10 (5) form strong 1:1 complexes in CD3COCD3 solution with the diquat dication.


Journal ArticleDOI
TL;DR: The X-ray structure of the crystalline complex formed between 18crown-6 and 2 mol. equiv. of cisplatin and dimethylacetamide reveals hydrogen bonding which involves all three hydrogen atoms on both ammine ligands of Cisplatin forming bonds to (i) all six oxygen atoms of 18c Crown-6, (ii) one chlorine atom on a symmetry-translated CisPlatin, and (iii) the carbonyl oxygen atom of Dacetamide.
Abstract: The X-ray structure of the crystalline complex formed between 18-crown-6 and 2 mol. equiv. of cisplatin and dimethylacetamide reveals hydrogen bonding which involves all three hydrogen atoms on both ammine ligands of cisplatin forming bonds to (i) all six oxygen atoms of 18-crown-6, (ii)one chlorine atom on a symmetry-translated cisplatin, and (iii)the carbonyl oxygen atom of dimethylacetamide.

Journal ArticleDOI
TL;DR: In this paper, the quest is encapsulated within the host and the complexation strength is enhanced by the macrobicyclic cryptate effect in the 1 : 1 complex.
Abstract: Variable-temperature 1H n.m.r. spectroscopic studies in CD3COCD3 and u.v. spectroscopic measurements in Me2CO demonstrate that in the 1 : 1 complex, [Diquat·(1)]2+, the quest is encapsulated within the host and that the complexation strength (ΔG°=–7.4 Kcal mol–1) is enhanced by the macrobicyclic cryptate effect.



Journal ArticleDOI
TL;DR: In this paper, the diaza-18-crown-6 derivatives (1) and (2) incorporating methyl 4,6-O-benzylidene and methyl 4 6-O-[(S)-phenylethylidenes]-α-D-mannopyranosidic residues, have been shown, by variable-temperature high-field 1H n.m.r. spectroscopy, to form strong anisometric 1 : 1 complexes with substituted ammonium cations in CD2Cl2 solutions.
Abstract: Two diaza-18-crown-6 derivatives (1) and (2), incorporating methyl 4,6-O-benzylidene- and methyl 4,6-O-[(S)-phenylethylidene]-α-D-mannopyranosidic residues, have been shown, by variable-temperature high-field 1H n.m.r. spectroscopy, to form strong anisometric 1 : 1 complexes with substituted ammonium cations in CD2Cl2 solutions. Although there are a few examples of almost equally populated anisometric complexes, in most cases the major complex is associated with the β-face of the macrocyclic ring. Relevant thermodynamic data have been obtained from integration of appropriate signals in the low-temperature spectra. Approximate kinetic data have been evaluated using appropriate equations for site exchange between unequally populated sites.