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ABSTRACT: The beta-dialdiminate cryptand L(4) can be isolated in the tris protonated state, [H(3)L(4)](3+), from the condensation of malonaldehyde (generated in situ from its tetraacetal derivative) with tris-2-aminoethylamine (tren) in [3 + 2] mode. The cryptate cannot be deprotonated under aqueous conditions, but the neutral cryptand can be made by treatment with KOH in dry methanol. This cryptand is water-sensitive, but may be treated with copper salts under anhydrous conditions to generate highly insoluble copper(II) derivatives. The reduced form of the cryptand L(5) can be isolated upon borohydride reduction, and used to make dicopper mu-hydroxo cryptates, where strong interaction between the pair of encapsulated paramagnetic cations leads to effective magnetic silence. Crystal structures of L(4) in three of its tris protonated salts and of the solvated neutral ligand L(4) are presented, together with that of a mu-hydroxo dicopper(II) cryptate of the fully reduced cryptand, [Cu(2)(OH)L(5)] x 3 ClO(4) x MeCN.
Dalton Transactions 09/2009; · 3.84 Impact Factor
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ABSTRACT: N-methylation alters the conformation of octa-azacryptands leaving them unable to use all potential N-donors to coordinate copper(II) and anionic guests. This restriction, in the presence of other donors, normally results in exogenous coordination, with the exception of carbonate complexes, where two O-donors from the bridging anion along with three N-donors from the cryptand serve, in this series uniquely, to retain a pair of copper(II) ions within the "basket-shaped" cavity.
Dalton Transactions 06/2007; · 3.84 Impact Factor
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03/2007: pages 167 - 316; , ISBN: 9780470166482
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ABSTRACT: The imine podands tris[(2-nitrobenzylidene)aminoethyl]amine and tris[(2-nitrobenzylidene)aminopropyl]amine both stabilize copper(I), forming {tris[(2-nitrobenzylidene)aminoethyl]amine-kappa4N}copper(I) perchlorate acetonitrile disolvate, [Cu(C27H27N7O6)]ClO4.2CH3CN, (II), and {tris[(2-nitrobenzylidene)aminopropyl]amine-kappa4N}copper(I) perchlorate, [Cu(C30H33N7O6)]ClO4, (VI), respectively. The larger propyl-based ligand is a poorer fit for the CuI ion. The reduced amine podand tris[(2-nitrobenzyl)aminoethyl]amine binds CuII and the resulting compound, chloro{tris[(2-nitrobenzyl)aminoethyl]amine-kappa4N}copper(II) chloride ethanol solvate, [Cu(C27H33N7O6)Cl]Cl.C2H5OH, (IV), shows both intra- and intermolecular hydrogen bonding, which gives rise to RRS or SSR conformations in the podand strands rather than the expected pseudo-threefold symmetry.
Acta Crystallographica Section C Crystal Structure Communications 11/2006; 62(Pt 10):m472-6. · 0.52 Impact Factor
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ABSTRACT: Treatment of N-methyl substituted aminocryptand hosts with copper(II) generates monocopper(II) cryptates where copper(II) coordinates an oxygen-centered species, formally H3O+, which is also strongly hydrogen bonded to three aminocryptand N-methyl atoms via bonds which may best be viewed as NH(delta+)...O(delta-) in consequence of charge transfer. The strength of this hydrogen bonding precludes successful competition of another copper ion for the second coordination site thus suppressing formation of any Cu-Cu bonded average-valent system.
Dalton Transactions 08/2006; · 3.84 Impact Factor
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ABSTRACT: Treatment of cryptand L(1) with Cu(II) generates a H3O2(-)-bridged dicopper(II) cryptate, 2, where the guest anion has responded to steric constraint by a significant shortening of the O-O distance to 2.325(9) A; computational optimization at the B3LYP/6-31(d) level suggests that the bridging O-H...O H-bond is bent (approximately 157 degrees) but that the barrier to interchange of the bridging H atom is low (<4 kJ mol(-1)). This cryptate, rather than the [Cu2L(1)muCN]3+ species recently claimed to derive from cleavage of the C-C bond of the solvent, is the product of acetonitrile recrystallization of the initially formed reaction product, 1.
Inorganic Chemistry 08/2005; 44(17):5987-9. · 4.60 Impact Factor
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ABSTRACT: A series of structurally characterised mu-cyanodicopper(II) cryptates shows moderately strong antiferromagnetic interaction in the range -2J= 150-200 cm(-1), at the high end of the observed range for such assemblies. The lowest magnetic exchange coupling parameter is displayed where there is slight bending of the M-CN-M assembly, enforced by the constraints of cryptate encapsulation. Thermally accessible triplet EPR spectra are observed with zero-field splittings of the order of 0.13-0.14 cm(-1), confirming collinear ground-state dz2 orbitals for Cu(II), consistent with their trigonal-bipyramidal coordination geometries.
Dalton Transactions 08/2005; · 3.84 Impact Factor
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ABSTRACT: Electrochemical studies on an average-valent dicopper cryptate demonstrate the existence of a solvent-assisted disproportionation in acetonitrile, which is absent in water. The existence of this process was confirmed via absorption spectroscopy, which allowed the evaluation of thermodynamic parameters. The disproportionation equilibrium is enthalpically controlled, and the results suggest an upper limit for the bond energy of the one-electron Cu-Cu bond of 200 kJ mol(-1).
Dalton Transactions 09/2004; · 3.84 Impact Factor
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ABSTRACT: A structural and solution phase study of complexation of dinegative oxoanionic guests by protonated azacryptand hosts is presented. The interactions involve a complex balance of competing factors: anion free energy of hydration, host basicity and solvation, and complementarity of steric matching between host and guest. The formation constants of dinegatively charged anion cryptates are much larger than the analogous values for the mononegative analogues perchlorate or perrhenate.
Dalton Transactions 09/2004; · 3.84 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 04/2004; 2004(12):2570 - 2584. · 2.94 Impact Factor
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ABSTRACT: A 2,6 pyridino-linked aminocryptand acts as a good host for carboxylate anions, oxalate, malonate, acetate and lactate at low protonation levels as shown by aqueous complexation constants. With oxalate, at the hexaprotonated level of the host, the crystal structure shows formation of a dimeric unit linked by an oxalate/semioxalate short (2.474 A) H-bond. The protonated cryptand uses a cleft-binding mode in preference to the cavity-binding mode used by other aminocryptand hosts.
Dalton Transactions 02/2004; · 3.84 Impact Factor
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ABSTRACT: The association between azacryptand hosts and oxoanion guests is reviewed. Positively charged hosts are the most effective; we focus on protonated azacryptands. Assessment of quantitative data suggests an anion cryptate effect and provides clear evidence for charge-based selectivity. Crystal structures show both cavity and cleft binding sites for anions within the series of cryptands studied. These two binding modes exhibit different pH dependence offering the possibility for design of monitoring/clean-up strategies based on a variation of appropriate host(s) and pH conditions.
Chemical Society Reviews 10/2003; 32(5):309-25. · 28.76 Impact Factor
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ABSTRACT: A series of structurally characterized copper complexes of two pyridazine-spaced cryptands in redox states + (I,I), (II,I), (II), (II,II) are reported. The hexaimine cryptand L(I) [formed by the 2 + 3 condensation of 3,6-diformylpyridazine with tris(2-aminoethyl)amine (tren)] is able to accommodate two non-stereochemically demanding copper(I) ions, resulting in [Cu(I)(2)L(I)](BF(4))(2) 1, or one stereochemically demanding copper(II) ion, resulting in [Cu(II)L(I)()](BF(4))(2) 3. Complex 3 crystallizes in two forms, 3a and 3b, with differing copper(II) ion coordination geometries. Addition of copper(I) to the monometallic complex 3 results in the mixed-valence complex [Cu(I)Cu(II)L(I)](X)(3) (X = PF(6)(-), 2a; X = BF(4)(-), 2b) which is well stabilized within this cryptand as indicated by electrochemical studies (K(com) = 2.1 x 10(11)). The structurally characterized, octaamine cryptand L(A), prepared by sodium borohydride reduction of L(I), is more flexible than L(I) and can accommodate two stereochemically demanding copper(II) ions, generating the dicopper(II) cryptate [Cu(II)(2)L(A)](BF(4))(4) 4. Electrochemical studies indicate that L(A) stabilizes the copper(II) oxidation state more effectively than L(I); no copper redox state lower than II,II has been isolated in the solid state using this ligand.
Inorganic Chemistry 05/2003; 42(8):2764-73. · 4.60 Impact Factor
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ABSTRACT: Exceptionally large complexation constants for oxalate encapsulated within azacryptand hosts are partly explained by pi-stacking interactions between C=O and aromatic rings.
Chemical Communications 11/2002; · 6.17 Impact Factor
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04/2002;
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04/2002;
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ABSTRACT: Comparison of the X-ray structures of two pairs of dicopper(I) and dicopper(1.5) cryptates provides evidence (over 0.5 Å contraction of the internuclear distance in one pair) for copper-copper bond formation. Although resonance Raman spectroscopy fails to identify a pure copper-copper stretching mode, because of extensive mixing of several low-frequency stretching and bending modes, isotopic substitution experiments indicate significant Cu-Cu character in a band around 250 cm(-)(1). A normal coordinate analysis broadly supports the spectroscopic findings. X-ray crystal structures are presented for the dicopper(1.5) complex Cu(2)imBT(ClO(4))(3), C(18)H(30)Cl(3)Cu(2)N(8)O(12), a = 9.140(4) Å, c = 30.35(3) Å, rhombohedral, R32, Z = 3, and the dicopper(I) Cu(2)imbistrpn(ClO(4))(2), C(24)H(42)Cl(2)Cu(2)N(8)O(8), a = 9.279(2) Å, c = 32.846(9) Å, rhombohedral, R32, Z = 3.
Inorganic Chemistry 08/1998; 37(14):3567-3574. · 4.60 Impact Factor
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ABSTRACT: The different tendencies of dinuclear azacryptates of the m-CH2C6H4CH2 and 2,5-furano-spaced hosts L1 and L2 to catalyse CO2 uptake-reactions within these sterically-protected host cavities are examined. Bridging methylcarbonates are generated catalytically upon exposure of methanol solutions of L1, but not L2, di-transition cation cryptates to atmospheric CO2. X-Ray crystallographic structures of homodinuclear µ-carbonato cryptates of both ligands and µ-methylcarbonato cryptates of L1 with later first transition series cations are reported. ESI-MS spectra show loss of H2CO3 from µ-carbonato cryptates in collision activation experiments.
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ABSTRACT: 3,6-Diformylpyridazine has been incorporated into a crypt ligand (L) for the first time by condensation with tris(2-aminoethyl)amine (tren). This crypt is shown to be an accommodating host, being able to encapsulate none, one or two metal ion guests. The free crypt, disilver(I) complex and monocobalt(II) complex have been structurally characterised. Electrochemical studies establish that the pi -acceptor ligand L effectively stabilises the cobalt ion in the +2 oxidation state. (C) 2001 Elsevier Science B.V. All rights reserved.
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ABSTRACT: The -dialdiminate cryptand L4 can be isolated in the tris protonated state, [H3L4]3+, from the condensation of malonaldehyde (generated in situ from its tetraacetal derivative) with tris-2-aminoethylamine (tren) in [3 + 2] mode. The cryptate cannot be deprotonated under aqueous conditions, but the neutral cryptand can be made by treatment with KOH in dry methanol. This cryptand is water-sensitive, but may be treated with copper salts under anhydrous conditions to generate highly insoluble copper(II) derivatives. The reduced form of the cryptand L5 can be isolated upon borohydride reduction, and used to make dicopper -hydroxo cryptates, where strong interaction between the pair of encapsulated paramagnetic cations leads to effective magnetic silence. Crystal structures of L4 in three of its tris protonated salts and of the solvated neutral ligand L4 are presented, together with that of a -hydroxo dicopper(II) cryptate of the fully reduced cryptand, [Cu2(OH)L5]·3ClO4·MeCN.
