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Vickie McKee

Publications and source records attributed to Vickie McKee.

At least 19 recordsLinked to original sources
PubMed2006

Structural and magnetic diversity in cyano-bridged bi- and trimetallic complexes assembled from cyanometalates and [M(rac-CTH)]n+ building blocks (CTH = d,l-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane).

Seven new cyano-bridged heterometallic systems have been prepared by assembling [M'(rac-CTH)]n+ complexes (M' = CrIII, NiII, CuII), which have two cis available coordination positions, and [M(CN)6]3- (M = FeIII, CrIII) and [Fe(CN)2(bpy)2]+ cyanometalate building blocks. The assembled systems, which have been characterized by X-ray crystallography and magnetic investigations, are the molecular squares (meso-CTH-H2)[{Ni(rac-CTH)}2{Fe(CN)6)}2].5H2O (2) and [{Ni(rac-CTH)}2{Fe(CN)2(bpy)2}2](ClO4)4.H2O (5), the bimetallic chain [{Ni(rac-CTH)}2{Cr(CN)6)}2Ni(meso-CTH)].4H2O (3), the trimetallic chain [{Ni(rac-CTH)}2{Fe(CN)6)}2Cu(cyclam)]6H2O (4), the pentanuclear complexes [{Cu(rac-CTH}3{Fe(CN)6}2].2H2O (6) and [{Cu(rac-CTH)}3{Cr(CN)6)}2].2H2O (7), and the dinuclear complex [Cr(rac-CTH)(H2O)Fe(CN)6].2H2O (8). With the exception of 5, all compounds exhibit ferromagnetic interaction between the metal ions (JFeNi = 12.8(2) cm-1 for 2; J1FeCu= 13.8(2) cm-1 and J2FeCu= 3.9(4) cm-1 for 6; J1CrCu= 6.95(3) cm-1 and J2CrCu= 1.9(2)cm-1 for 7; JCrFe = 28.87(3) cm-1 for 8). Compound 5 exhibits the end of a transition from the high-spin to the low-spin state of the octahedral FeII ions. The bimetallic chain 3 behaves as a metamagnet with a critical field Hc = 300 G, which is associated with the occurrence of week antiferromagnetic interactions between the chains. Although the trimetallic chain 4 shows some degree of spin correlation along the chain, magnetic ordering does not occur. The sign and magnitude of the magnetic exchange interaction between CrIII and FeIII in compound 8 have been justified by DFT type calculations.

Journal Article↗
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.

Journal Article↗
PubMed2006

Unexpected ring expansion of an enantiopure imidazoline carbene ligand.

[reaction: see text] We report an unexpected ring expansion reaction of an enantiopure fenchone-derived imidazolinium salt during attempts to form copper complexes of the corresponding imidazoline carbene ligand. A N,N'-difenchyl piperazinone was formed in low yield together with the difenchyl-substituted five-membered urea.

Catalysis↗
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.

Journal Article↗
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.

Journal Article↗
PubMed2005

Dinuclear complexes of a pseudocalixarene macrocycle: structural consequences of intramolecular hydrogen bonding.

A series of dinuclear complexes of a pseudocalixarene macrocycle H6L containing two 2,2'-methylenediphenol groups have been synthesised and structurally characterised. Using divalent metal ions, complexes containing a common hyperbolic paraboloid (saddle) M2(H4L)2+ core are formed. The structure is controlled by two strong O-H-O interactions resulting from metal ion-promoted monodeprotonation of the methylenediphenol units. The metal ions are located in a cleft within which neutral or anionic guests can bind. Use of trivalent metal ions leads to complete deprotonation of the phenol groups and loss of the saddle conformation.

Journal Article↗
PubMed2004

5,5'-Di-tert-butyl-2,2'-dihydroxy-3,3'-methanediyldibenzaldehyde and its allyl-protected dialcohol and dialdehyde precursors.

5,5'-Di-tert-butyl-2,2'-dihydroxy-3,3'-methanediyldibenzaldehyde, C(23)H(28)O(4), (IV), has been structurally characterized in two polymorphic forms. The tetragonal form, (in I4(1)/a) has been reported previously but is redetermined and reinterpreted here, while the monoclinic form, (in C2/c) is reported for the first time. In both polymorphs, the molecule lies on a crystallographic twofold axis. Two precursors in the synthesis of (IV), namely 2,2'-bis(allyloxy)-5,5'-di-tert-butyl-3,3'-methanediyldibenzenemethanol (C(29)H(40)O(4)) and 2,2'-bis(allyloxy)-5,5'-di-tert-butyl-3,3'-methanediyldibenzaldehyde (C(29)H(36)O(4)) have also been characterized.

Journal Article↗
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).

Journal Article↗
PubMed2004

Synthesis and X-ray crystal structure of [Ag(phendio)2]ClO4 (phendio = 1,10-phenanthroline-5,6-dione) and its effects on fungal and mammalian cells.

The Cu(II) and Ag(I) complexes, [Cu(phendio)3](ClO4)2 x 4H2O and [Ag(phendio)2]ClO4 (phendio = 1,10-phenanthroline-5,6-dione), are prepared in good yield by reacting phendio with the appropriate metal perchlorate salt. The X-ray crystal structure of the Ag(I) complex shows it to have a pseudo tetrahedral structure. 'Metal-free' phendio and the Cu(II) and Ag(I) phendio complexes strongly inhibit the growth of the fungal pathogen Candida albicans, and are more active than their 1,10-phenanthroline analogues. The simple Ag(I) salts, AgCH3CO2, AgNO3 and AgClO4 x H2O display superior anti-fungal properties compared to analogous simple Cu(II) and Mn(II) salts, suggesting that the nature of the metal ion strongly influences activity. Exposing C. albicans to 'metal-free' phendio, simple Ag(I) salts and [Ag(phendio)2]ClO4 causes extensive, non-specific DNA cleavage. 'Metal-free' phendio and [Ag(phendio)2]ClO4 induce gross distortions in fungal cell morphology and there is evidence for disruption of cell division. Both drugs also exhibit high anti-cancer activity when tested against cultured mammalian cells.

Animals↗
PubMed2004

Synthesis, antimicrobial activity and chemotherapeutic potential of inorganic derivatives of 2-(4'-thiazolyl)benzimidazole[thiabendazole]: X-ray crystal structures of [Cu(TBZH)2Cl]Cl.H2O.EtOH and TBZH2NO3 (TBZH=thiabendazole).

Thiabendazole (TBZH) reacts with iron(III) nitrate causing protonation of the ligand to yield the nitrate salt [TBZH(2)NO(3)] (1). Reaction of TBZH with copper(II) acetate results in the deprotonation of the ligand yielding [Cu(TBZ)2.(H2O)2] (2). Reactions of TBZH with the chloride, nitrate and butanedioate salts of copper(II) yields [Cu(TBZH)2Cl]Cl.H2O.EtOH (3), [Cu(TBZH)(2)(NO(3))(2)] (4) and [Cu(TBZH)(O(2)C-CH(2)CH(2)-CO(2))] (5), respectively. The TBZH acts as a neutral chelating ligand in 3-5. Molecular structures of 1 and 3 were determined crystallographically. In 1, the asymmetric unit contains one TBZH(2)(+) cation and one NO(3)(-) anion. The structure of 3 comprises a five coordinate copper centre with the metal bound to two chelating TBZH ligands and one chloride. The geometry is best described as trigonal bipyramidal. Hydrogen bonding connects the complex cation with the uncoordinated chloride anion and the water and ethanol solvate molecules. Compound 1 and the copper complexes 2-5, the metal free ligands and a number of simple copper(II) salts were each tested for their ability to inhibit the growth of Candida albicans. The metal free TBZH and its nitrate salt (1) exhibited very poor activity. Complex 2, in which the TBZH is present as an anionic ligand (TBZ(-)), exhibits moderate activity towards the pathogen. Chelation of the neutral TBZH to copper centres (complexes 3-5) results in potent anti-candida activity. The dimethyl sulphoxide (DMSO) soluble complexes 3 and 4, along with metal free TBZH were assessed for their cancer chemotherapeutic potential towards two human epithelial-derived cancer model cell lines. Complexes 3 and 4 displayed similar dose-dependent cytotoxicity in both cell lines with IC(50) values of approximately 50 microM, which were found to be significantly lower than that for metal free TBZH.

Antifungal Agents↗
PubMed2004

Synthesis, X-ray crystal structure, anti-fungal and anti-cancer activity of [Ag2(NH3)2(salH)2] (salH2=salicylic acid).

[Ag(2)(NH(3))(2)(salH)(2)] (salH(2)=salicylic acid) was synthesised from salicylic acid and Ag(2)O in concentrated aqueous NH(3) and the dimeric Ag(I) complex was characterised using X-ray crystallography. The complex is centrosymmetric with each metal coordinated to a salicylate carboxylate oxygen and to an ammonia nitrogen atom in an almost linear fashion. The two [Ag(NH(3))(salH)] units in the complex are linked by an Ag-Ag bond. Whilst metal-free salH(2) did not prevent the growth of the fungal pathogen Candida albicans [Ag(2)(NH(3))(2)(salH)(2)], [Ag(2)(salH)(2)] and some simple Ag(I) salts greatly inhibited cell reproduction. SalH(2), [Ag(2)(NH(3))(2)(salH)(2)] [Ag(2)(salH)(2)] and AgClO(4) produced a dose-dependent cytotoxic response against the three human derived cancer cell lines, Cal-27, Hep-G2 and A-498, with the Ag(I)-containing reagents being the most effective.

Animals↗
PubMed2003

A perchlorate salt of an octaprotonated cryptand.

The title compound, 1,4,8,11,14,18,23,27-octaaza-6,16,25(2,6)- tripyridinabicyclo[9.9.9]nonacosaphane(8+) octaperchlorate pentahydrate, C(33)H(59)N(11)(8+) x 8ClO(4)(-) x 5H(2)O, is a salt of an octaprotonated cryptand in which one of the pyridine groups and the bridgehead tertiary amines remain unprotonated. The central cavity of the cryptand is not occupied, although the perchlorate ions are hydrogen bonded in clefts formed between the arms of the cryptand.

Journal Article↗
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.

Journal Article↗
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.

Journal Article↗
PubMed1998

Self-Assembled Dinuclear Lanthanide Helicates: Substantial Luminescence Enhancement upon Replacing Terminal Benzimidazole Groups by Carboxamide Binding Units.

The segmental ligands bis{1-alkyl-2-[6'-(N,N-diethylcarbamoyl)pyridin-2'-yl]benzimidazol-5-yl}methane (alkyl = methyl (L(5)), ethyl (L(6))) react with lanthanide perchlorates (Ln = La, Eu, Gd, Tb) in acetonitrile to yield the f-f dinuclear homotopic triple-stranded helicates [Ln(2)(L(i)())(3)](6+) (i = 5, 6) under thermodynamic control. The crystal structure of [Tb(2)(L(6))(3)](ClO(4))(3)(MeCN)(2)(THF)(0.5)(EtOH)(0.5) (11a, C(124)H(145)N(26)O(31)Cl(6)Tb(2), triclinic, P&onemacr;, Z = 2) shows the wrapping of the ligands about a pseudo-C(3) axis passing through the metal ions. The Tb ions are 9-coordinate in facial pseudo-tricapped trigonal prismatic sites and are separated by 9.06 Å. (1)H-NMR and ES-MS data establish that the triple helical structure is maintained in solution. Spectrophotometric titrations (Ln = La, Eu) indicate log beta(23) = 24-25 and the formation of a 2:2 complex [Ln(2)(L(5))(2)](6+) (log beta(22) = 19-20). Quantum yield determination in acetonitrile shows that the terminal N,N-diethylcarboxamide groups in L(5) favor efficient intramolecular L(5) --> Eu(III) energy transfers leading to strong Eu-centered red luminescence, 50 times as intense as the luminescence observed when the carboxamide groups are replaced by substituted benzimidazole units in [Eu(2)(L(4))(3)](6+). Resistance toward hydrolysis also results from the use of carboxamide groups, and no quenching of luminescence is observed for [Eu(2)(L(5))(3)](6+) in moist acetonitrile up to 2.5 M water. The crucial role played by carboxamide groups for the control of structural, electronic, and photophysical properties is discussed. Replacing perchlorates by triflates allows the isolation of the dinuclear double-stranded helicate [Eu(2)(L(6))(2)(CF(3)SO(3))(4)(H(2)O(2))(2)](CF(3)SO(3))(2)(MeOH)(2)(H(2)O)(5)(.5), whose crystal structure (13a, C(85)H(106)Eu(2)F(18)N(16)O(30)S(6), monoclinic, C2/m, Z = 2) reveals a side-by-side arrangement of the two strands and 9-coordinate Eu ions linked through hydrogen-bonded water molecules.

Journal Article↗