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Jane Nelson

Publications and source records attributed to Jane Nelson.

15 recordsLinked to original sources
PubMed2006

Comparison of copper imine and amine podates: geometric consequences of podand size and donor type.

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.

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PubMed2006

Effect of methylation on the coordination of copper by small azacryptands; the role of geometrically constrained hydrogen bonding in stabilizing terminally coordinated oxygen species.

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.

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PubMed2006

Electronic structure of binuclear mixed valence copper azacryptates derived from integrated advanced EPR and DFT calculations.

Binuclear, mixed valence copper complexes with a [Cu(+1)(.5), Cu(+1)(.5)] redox state and S = (1)/(2) can be stabilized with rigid azacryptand ligands. In this system the unpaired electron is delocalized equally over the two copper ions, and it is one of the very few synthetic models for the electron mediating Cu(A) site of nitrous oxide reductase and cytochrome c oxidase. The spatial and electronic structures of the copper complex in frozen solution were obtained from the magnetic interactions, namely the g-tensor and the (63,65)Cu, (14)N, (2)H, and (1)H hyperfine couplings, in combination with density functional theory (DFT) calculations. The magnetic interactions were determined from continuous wave (CW) electron paramagnetic resonance (EPR), pulsed electron nuclear double resonance (ENDOR), two-dimensional TRIPLE, and hyperfine sublevel correlation spectroscopy (HYSCORE) carried out at W-band or/and X-band frequencies. The DFT calculated g and Cu hyperfine values were in good agreement with the experimental values showing that the structure in solution is indeed close to that of the optimized structure. Then, the DFT calculated hyperfine parameters were used as guidelines and starting points in the simulations of the various experimental ENDOR spectra. A satisfactory agreement with the experimental results was obtained for the (14)N hyperfine and quadrupole interactions. For (1)H the DFT calculations gave good predictions for the hyperfine tensor orientations and signs, and they were also successful in reproducing trends in the magnitude of the various proton hyperfine couplings. These, in turn, were very useful for ENDOR signals assignments and served as constraints on the simulation parameters.

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PubMed2005

Squeezing the [Cu-OH...H2O-Cu]3+ bridge by cryptate encapsulation.

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.

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PubMed2005

Cascade complexation: a single cyano bridge links a pair of Cu(II) cations.

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.

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PubMed2004

Ferromagnetic interaction in mu1,3-cyanamido-derived copper(II) cryptates.

The reaction of dinuclear copper(II) cryptates with calcium cyanamide, CaNCN, and sodium dicyanamide, Na[N(CN)(2)] results in dinuclear compounds of formulae [Cu(2)(HNCN)(R3Bm)](ClO(4))(3) (1), [Cu(2)(dca)(R3Bm)](ClO(4))(3)4H(2)O (2), and [Cu(2)(NCNCONH(2))(R3Bm)](CF(3)SO(3))(3) (3), in which R3Bm=N[(CH(2))(2)NHCH(2)(C(6)H(4)-m)CH(2)NH(CH(2))(2)](3)N and dca=dicyanamido ligand (NCNCN(-)). The X-ray diffraction analysis reveals for both 1 and 3 a dinuclear entity in which the copper atoms are bridged by means of the -NCN- unit. The molar magnetic susceptibility measurements of 1-3 in the 2-300 K range indicate ferromagnetic coupling. The calculated J values, by using theoretical methods based on density functional theory (DFT) are in excellent agreement with the experimental data. Catalytic hydration of a nitrile to an amide functional group is assumed responsible for the formation of 3 from a mu(1,3)-dicyanamido ligand.

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PubMed2004

Electrochemistry of a labile average-valence dicopper system.

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).

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PubMed2004

Dinegative tetrahedral oxoanion complexation; structural and solution phase observations.

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.

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PubMed2003

Steric complementarity in carboxylate anion recognition.

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.

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PubMed2003

Redox-adaptable copper hosts. Pyridazine-linked cryptands accommodate copper in a range of redox States.

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.

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PubMed2003

Caged oxoanions.

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.

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PubMed1998

Raman Spectroscopy of Three Average-Valence Dicopper Cryptates: Evidence for Copper-Copper Bonding.

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.

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