Equatorial Coordination Research Articles

High-Affinity Uranyl-Specific Antibodies Suitable for Cellular Imaging

Monoclonal antibodies (mAbs) have proved to be valuable models for the study of protein-metal interactions, and previous reports have described very specific antibodies to chelated metal ions, including uranyl. We raised specific mAbs against UO2(2+)-DCP-BSA (DCP, 1,10-phenanthroline-2,9-dicarboxylic acid) to generate new sets of antibodies that might cross-react with various complexed forms of uranyl in different environments for further application in the field of toxicology. Using counter-screening with UO2(2+)-DCP-casein, we selected two highly specific mAbs against uranyl-DCP ( K D 10-100 pM): U04S and U08S. Competitive assays in the presence of different metal ions (UO2(2+), Fe (3+), Zn2+, Cu2+, and Ca2+) showed that uranyl in solution can act as a good competitor, suggesting some antibody ability to cross-react with chelating groups other than DCP in the UO2(2+) equatorial coordination plane. Interestingly, one of the antibodies could be used for revealing uranyl cations in cell samples. Fluorescence activated cell sorting analyses after immunolabeling revealed the interaction of uranyl with human kidney cells HK2. The intracellular accumulation of uranyl could be directly visualized by metal-immunostaining using fluorescent-labeled mAb. Our results suggest that U04S mAb epitopes mostly include the uranyl fraction and its paratopes can accommodate a wide variety of chelating groups.

Heterotapes: A Persistent, Dual‐Synthon Hydrogen‐Bonding Motif

The small dinitrile anion carbamoyldicyanomethanide, [C(CN)2-(CONH2)]- (cdm), reproducibly forms a hydrogen-bonded tape containing two different supramolecular synthons: a "heterotape". The tape incorporates both an amide dimer and a nitrile-containing ring. The robustness of the motif is confirmed by its persistence from an isolated tape in a separated ion-pair structure, [K(15c5)2](cdm) x H2O, to its incorporation into coordination complexes of octahedral metals, thus facilitating the formation of 2D sheets. Complexes containing coligands that occupy the equatorial coordination sites, [Cu(2,2'-py2NH)2(cdm)2] x 2 MeOH, [Ni(cyclam)(cdm)2], and [Cu(cyclam)(cdm)2] x 2 MeOH (cyclam = 1,4,8,11-tetraazacyclotetradecane, 2,2'-py2NH = di(2-pyridyl)amine), show retention of the heterotape motif, whilst the ethylene diamine complex [Cu-(en)2(cdm)2] (en = ethylene diamine) displays an alternative hydrogen-bonding motif due to interference from the diamine ligands.

Crystal structures, theoretical calculations, spectroscopic and electrochemical properties of Cr(III) complexes with dipicolinic acid and 1,10-phenantroline

The crystal structures of compounds Na[Cr(dipic) 2] · 2H 2O ( 1) and [Cr(dipic)(phen)Cl] · 1/2H 2O ( 2), dipic = dipicolinate, phen = 1,10-phenantroline, were determined. In both complexes, Cr(III) is in a distorted octahedral environment. In complex ( 1), the metal is coordinated to two nearly perpendicular dipic anions acting as tridentate ligands through one oxygen of each carboxylate group and the pyridinic nitrogen atom. In complex ( 2), Cr(III) ion is similarly coordinated to a dipic anion, defining a ligand equatorial plane. The phen molecule bridges the remaining equatorial coordination site and one of the axial positions through its N-atoms. The other axial position is occupied by a chloride ion. The optimized geometries of both compounds and their corresponding harmonic vibrational frequencies were calculated using methods of density functional theory. The infrared, Raman and electronic spectra of the complexes were recorded. Assignments of the most characteristic bands are reported and discussed. Their electrochemical properties were also investigated. Both compounds exhibit similar redox behavior; they undergo two main reduction processes involving the metal center and the dipicolinato ligand. No Cr(III) oxidation processes were found.

Dirhenium carbonyl complexes bearing 2-vinylpyridine, morpholine and 1-methylimidazole ligands

Treatment of the labile compound [Re 2(CO) 8(MeCN) 2] with 2-vinylpyridine in refluxing benzene affords exclusively the new compound [Re 2(CO) 8(μ-η 1:η 2-NC 5H 4CH CH 2)] ( 1) in 39% yield in which the μ-η 1:η 2-vinylpyridine ligand is coordinated to one Re atom through the nitrogen and to the other Re atom via the olefinic double bond. Reaction of [Re 2(CO) 8(MeCN) 2] with morpholine in refluxing benzene furnishes two compounds, [Re 2(CO) 9(η 1-NC 4H 9O)] ( 2) and [Re 2(CO) 8(η 1-NC 4H 9O) 2] ( 3) in 5% and 29% yields, respectively. Reaction of [Re 2(CO) 8(MeCN) 2] with 1-methylimidazole gives [Re 2(CO) 8{η 1-NC 3H 3N(CH 3)} 2] ( 4) and the mononuclear compound fac-[ReCl(CO) 3{η 1-NC 3H 3N(CH 3)} 2] ( 5) in 18% and 26% yields, respectively. In the disubstituted compounds 2 and 4, the heterocyclic ligands occupy equatorial coordination sites. The mononuclear compound 5 consists of three CO groups, two N coordinated η 1-1-methylimidazole ligands and a terminal Cl ligand. The XRD structures of complexes 1, 3 and 5 are reported.

Molecular Dynamics Simulations of Cu(II) and the PHGGGWGQ Octapeptide

The interaction between Cu2+ and the copper-binding octapeptide region in the human prion protein has been investigated by molecular dynamics simulations. In total four different nonbonded and bonded models were used in the study. Charge sets containing atomic partial charges were developed for these models. Out of the considered models, the bonded model performed physically in the most correct way. The simulations with the bonded model showed that the water molecules in the axial position are very labile. The tryptophan indole ring can remain in a stable position on top of the equatorial coordination plane of copper without water mediation. Strong aromatic interaction was observed between the imidazole and indole rings. The nonbonded models showed a tendency for water-mediated interaction between the copper ion and different carbonyl oxygen atoms. In the case of the bonded model, a carbonyl group could also interact directly with the copper ion in one of the apical position.

Toward modeling the high chloride, low pH form of sulfite oxidase: Ka-band ESEEM of equatorial chloro ligands in oxomolybdenum(V) complexes

Two oxomolybdenum(V) complexes, (dttd)MoOCl and [(bdt)MoOCl2]− (where dttd=2,3:8,9-dibenzo-1,4,7,10-tetrathiadecane and bdt=1,2-benzenedithiolate), which contain one or two equatorial chloro ligands, respectively, were studied by electron spin echo envelope modulation (ESEEM) spectroscopy in the microwave Ka-band (∼29GHz). The ESEEM amplitude from the chloro ligands in both compounds is significantly greater than that tentatively attributed to chloride in the vicinity of the oxomolybdenum active site in the high chloride, low-pH (lpH) form of sulfite oxidase (SO). Thus, these ESEEM results rule out equatorial coordination of chloride in the enzyme, although the possibility for a weakly bound chloride in the trans axial position or nearby non-coordinated chloride(s) remains for lpH SO in solution.

Crystal engineering of 3-D coordination polymers by pillaring ferromagnetic copper(ii)-methylmalonate layers

Three new copper(II) complexes of formula [Cu(Memal)(H2O)]n (1), [Cu2(pyz)(Memal)2] (2) and [Cu2(4,4′-bpy)(Memal)2(H2O)2] (3) (Memal = methylmalonate, pyz = pyrazine and 4,4′-bpy = 4,4′-bipyridine) were obtained and structurally characterized by X-ray diffraction. Complex 1 is a square grid of aquacopper(II) units which are linked by carboxylate-methylmalonate groups in the anti–syn (equatorial–equatorial) coordination mode. The crystal structures of 2 and 3 consist of corrugated layers of copper(II) (2) and aquacopper(II) (3) units with intralayer carboxylate-methylmalonate bridges in the anti–syn (equatorial–apical) coordination mode which are linked through pyrazine (2) and 4,4′-bipyridine (3) ligands; to build up a 3-D network. Magnetic susceptibility measurements of complexes 1–3 in the temperature range 2–300 K show the occurrence of an overall ferromagnetic behaviour with a weak intralayer ferromagnetic coupling (J = +1.61(1) cm−1) in 1 whereas two opposite magnetic interactions occur in 2 and 3, one ferromagnetic through the anti–syn carboxylate (2 and 3) and the other antiferromagnetic through pyz (2) and 4,4′-bpy) (3).

Crystal structure and dynamic properties of a bimetallic cyano complex Cd(C4H8O2)Cu(CN)3 with an interpenetrating 3D framework containing a 1,4-dioxane bridging ligand as a rotor

The title complex Cd(C(4)H(8)O(2))Cu(CN)(3) has a 3D twofold interpenetrating framework structure. The structural base of the framework is a planar hexagonal network complex of [Cu(CN)(3)Cd](infinity) ,which is formed with cyanides connecting the coordination sites of Cu(i) ions with a triangle planar form and the equatorial coordination sites of Cd(ii) ions with a trigonal bipyramid form. The networks are stacked and a 1,4-dioxane molecule coordinates to two Cd(ii) ions in alternate networks as a bridging ligand. The 1,4-dioxane ligand penetrates a hexagonal window of the network sandwiched between the bridged networks. This 1,4-dioxane bridge completes the 3D twofold interpenetrating framework structure. (2)H-NMR powder patterns of the deuterated complex Cd(C(4)D(8)O(2))Cu(CN)(3) revealed the dynamics of the 1,4-dioxane bridge as a rotor. Above 253 K, the 1,4-dioxane ligand undergoes rotational motion combined with a ring inversion between two chair conformations. The free energy of activation DeltaG(double dagger) for the ring inversion was calculated to be 41.4(7) kJ mol(-1) at 298 K.

Anhydrous Photochemical Uranyl(VI) Reduction: Unprecedented Retention of Equatorial Coordination Accompanying Reversible Axial Oxo/Alkoxide Exchange

In a dramatic reversal of the normal trend of observed reactivity in uranyl(VI) coordination chemistry, an unprecedented retention of the normally labile equatorial coordination plane accompanies facile and reversible axial oxo/alkoxide exchange during both the photochemical reduction of cationic uranyl(VI) phosphine-oxide complexes with organic substrates and subsequent hydrolysis of the uranium(IV) alkoxide complexes to regenerate the uranyl(VI) starting complex.

Even-Numbered Metal Chain Complexes: Synthesis, Characterization, and DFT Analysis of [Ni4(μ4-Tsdpda)4(H2O)2] (Tsdpda2- = N-(p-toluenesulfonyl)dipyridyldiamido), [Ni4(μ4-Tsdpda)4]+, and Related Ni4 String Complexes

The synthesis and the X-ray structure of two complexes exhibiting a linear chain of four nickel atoms is reported, following Ni4(mu4-phdpda)4 (1), which had been characterized previously. [Ni4(mu4-Tsdpda)4(H2O)2], where H2Tsdpda is N-(p-toluenesulfonyl)dipyridyldiamine (2), is axially coordinated to two water molecules, at variance with 1. One-electron oxidation of 2 resulted in the loss of the axial ligands, yielding [Ni4(mu4-Tsdpda)4]+, [3]+, which was also structurally characterized. Finally, we report the structure of Ni4(mu4-DAniDANy)4 (4), a complex synthesized starting from the new ligand N,N'-bis-p-anisyl-2,7-diamino-1,8-naphthyridine. Magnetic measurements concluded that 4 is diamagnetic, like 1, whereas 2 is antiferromagnetic (-2J(14) = 80 cm(-)(1), using the Heisenberg Hamiltonian H = -2J(14) S(1).S(4)), as are other axially coordinated chains with an odd number of nickel atoms. DFT calculations are reported on these complexes in order to rationalize their electronic structure and their magnetic behavior. The magnetic properties of the [Ni4]8+ complexes are governed by the electronic state of the Ni(II) atoms, which may be either low-spin (S = 0), or high-spin (S = 1). DFT calculations show that the promotion to high spin of two Ni atoms in the chain, either external or internal, depends on the interplay between axial and equatorial coordination. The synergy between axial coordination and the presence of electron-withdrawing toluenesulfonyl substituents in 2 favors the promotion to the high-spin state of the terminal Ni atoms, thus yielding an antiferromagnetic ground state for the complex. This is at variance with complexes 1 and 4, for which the lowest quintet state results from the promotion to high spin of the internal nickel atoms, together with an important ligand participation, and is destabilized by 9 to 16 kcal mol(-1) with respect to the diamagnetic ground state.

Structural and Magnetic Studies of Copper(II) and Zinc(II) Coordination Complexes Containing Nitroxide Radicals as Chelating Ligands

AbstractThe mononuclear transition metal complexes [Cu(CF3SO3)212](1a), [Zn(CF3SO3)212] (1b), [Cu(CF3SO3)222]·2CH3CN (2a), and [Zn(CF3SO3)222]·2CH3CN (2b) have been preparedfrom the newly synthesized doxyl nitroxide ligands 4,4‐dimethyl‐2,2‐di(2‐pyridyl)oxazolidine‐N‐oxyl (1) and 4,4‐dimethyl‐2,2‐bis[2‐(3‐methylpyridyl)]oxazolidine‐N‐oxyl (2) and M(CF3SO3)2 (M = CuII or ZnII). These metal–nitroxide complexes have been structurally and magnetically characterized. In all complexes, the four pyridyl groups coordinate in equatorial coordination sites and the two nitroxide groups in axial coordination sites, which means that the central metal ion acquires a distorted N4O2 octahedral configuration. The variable‐temperature magnetic susceptibility data show that complexes 1b and 2b exhibit paramagnetic behavior, and hence a very weak intraligand magnetic interaction could be estimated [JNO–NO = –0.64 (1b) and 0.14 cm–1 (2b)]. The χmT values of 1a and 2a decrease continuously with decreasing temperature until they reach a nearly constant value at around 50 K, thereby indicating an intramolecular antiferromagnetic interaction between the CuII ion and the nitroxide ligands for both 1a and 2a [JCu–NO = –81.6 (1a) and–78.1 cm–1 (2b)]. These magnetic behaviors are supported by density functional theory calculations and are discussed in connection with the specific structural features. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Relativistic Density Functional Theory Study of Dioxoactinide(VI) and -(V) Complexation with Alaskaphyrin and Related Schiff-Base Macrocyclic Ligands

Formation of complexes of alaskaphyrin 1, bi-pyen 2 and bi-tpmd 3 ligands with actinyl ions AnO2(n+), An = U, Np, Pu and n = 1, 2, was studied using density functional theory (DFT) within the scalar relativistic four-component approximation. The alaskaphyrin complexes of the uranyl are predicted to have a bent conformation, in contrast to the experimentally available X-ray data. This deviation is likely due to crystal packing effects. Apart from these conformational differences, calculated geometry parameters and vibrational frequencies are in agreement with the available experimental data. The character of bonding in the complexes is investigated using bond order analysis and extended transition states (ETS) energy decomposition. Metal-to-ligand bonds can be described as primarily ionic although substantial charge transfer is observed as well. Based on ETS analysis, it is shown that steric and/or fit/misfit requirements of actinyl cations to the ligand cavities, among the studied complexes, are the most favorable for the bi-pyen ligand 2, because its flexibility allows for optimal metal-to-donor-atom distances. Planarity of the equatorial coordination sphere of the actinide atom is found to be less important than the ability of a ligand to provide optimal uranium-to-nitrogen bond lengths. Experimental differences in demetalation rates between similar alaskaphyrin, bi-pyen and bi-tpmd uranyl complexes are explained as a result of easier protonation of the Schiff-base nitrogen of the latter. Reduction potentials calculated for the uranium complexes show a good agreement with the experiment, both in relative and in absolute terms.

A Hofmann pyridine complex: poly[tetra-μ-cyano-dipyridinemanganese(II)nickel(II)

The title compound, [MnNi(CN)4(C5H5N)2], has a layered structure of a two-dimensional network complex Mn(py)2Ni(CN)4, in which linkages of cyanide between the equatorial coordination sites of octahedral MnII ions (site symmetry 2/m) and those of square planar NiII ions (site symmetry 2/m) form a square mesh network. Pyridine ligands (located on mirror planes) coordinate to the axial sites of the MnII ions from both sides of the network.

A novel drug delivery system for type 1 diabetes: Insulin-mimetic vanadyl-poly(γ-glutamic acid) complex

Insulin-mimetic vanadyl-poly(γ-glutamic acid) complex, VO-γ-PGA, is proposed as a novel drug delivery system for treating type 1 diabetic animals. The structure of VO-γ-PGA in solution as well as in solid state was analyzed by electronic absorption, infra-red, and electron spin resonance spectra, and proposed that the equatorial coordination mode of VO 2+ is in either carboxylate(O)–VO–(OH 2) 3 or 2 carboxylate(O 2)–VO–(OH 2) 2. In vitro insulin-mimetic activity, metallokinetic feature in the blood of healthy rats, and in vivo normoglycemic effect of the complex prepared in solution were evaluated in streptozotocin(STZ)-induced type 1 diabetic mice, and these effects were compared with those of a solution containing only VOSO 4 as a positive control. The in vitro insulin-mimetic activity of VO-γ-PGA was examined by determining both inhibition of free fatty acid (FFA) release and glucose uptake in isolated rat adipocytes, in which the concentration of VO-γ-PGA for 50% inhibition of FFA release was significantly lower than that of VOSO 4. Metallokinetic study suggested that the bioavailability of VO-γ-PGA complex was much higher than that of VOSO 4. The complex showed a significant hypoglycemic activity within at least 4 h after a single oral administration, the effect being sustained for at least 24 h. Furthermore, VO-γ-PGA normalized the hyperglycemia in STZ-mice within 3 days when it was given orally at doses of 5–10 mg V kg −1 body mass for 16 days. The improvement in diabetes was also supported by the results on oral glucose tolerance test, HbA 1c levels, and blood pressure.

Nitridorhenium(V) Complexes with 1,3‐Dialkyl‐4,5‐dimethylimidazole‐2‐ylidenes

AbstractThe nitridorhenium(V) complexes [ReNCl2(PR2Ph)3] (R = Me, Et) react with the N‐heterocyclic carbenes (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐5‐ylidene (LEt) or 1,3,4,5‐tetramethylimidazole‐2‐ylidene (LMe) in absolutely dry THF under complete replacement of the equatorial coordination sphere. The resulting [ReNCl(LR)4]+ complexes (LR = LMe, LEt) are moderately stable as solids and in solution, but decompose in hot methanol under formation of [ReO2(LR)4]+ complexes. With 1,3‐diisopropyl‐4,5‐dimethylimidazole‐5‐ylidene (Li‐Pr), the loss of the nitrido ligand and the formation of a dioxo species is more rapid and no nitridorhenium intermediate could be isolated.The Re‐C bond lengths in [ReNCl(LEt)4]Cl of approximately 2.195Å are relatively long and indicate mainly σ‐bonding in the electron‐deficient d2 system under study.The hydrolysis of the nitrido complexes proceeds via the formation of [ReO3N]2− anions as could be verified by the isolation and structural characterization of the intermediates [{ReN(PMe2Ph)3}{ReO3N}]2 and [{ReN(OH2)(LEt)2}2O][ReO3N].

Convenient syntheses of uranyl(VI) cis-dihalide complexes as anhydrous starting materials

The targeted syntheses of uranyl(VI) complexes UO 2X 2L (X = Cl, Br) possessing halide ligands exclusively at cis equatorial coordination sites are reported, supported by a neutral tridentate ligand (L), N,N, N′, N′-tetraalkylpyridine-2,6-dicarboxamide ( 1). A monomeric pentagonal bipyramidal geometry is observed in the solid state for the isostructural chloride ( 2a) and bromide ( 3a) derivatives as determined by X-ray crystallography.

Axial versus equatorial coordination of thioether sulfur: Mixed ligand copper(II) complexes of 2-pyridyl- N-(2′-methylthiophenyl)-methyleneimine with bidentate diimine ligands

The synthesis, structure and spectral and redox properties of the copper(II) complexes [Cu(pmtpm)Cl 2] ( 1) and [Cu(pmtpm) 2](ClO 4) 2 ( 6), where pmtpm is the linear tridentate ligand 2-pyridyl- N-(2′-methylthiophenyl)methyleneimine containing a thioether and two pyridine donors, are described. Also, the mixed ligand complexes [Cu(pmtpm)(diimine)](ClO 4) 2 ( 2– 5), where the diimine is 2,2′-bipyridine ( bpy) ( 2), 1,10-phenanthroline ( phen) ( 3), 2,9-dimethyl-1,10-phenanthroline ( 2,9-dmp) ( 4) or dipyrido-[3,2-d:2′,3′- f]-quinoxaline ( dpq) ( 5), have been isolated and studied. The X-ray crystal structures of the complexes 1, [Cu(pmtpm)(2,9-dmp)](ClO 4) 2 4 and 6 have been successfully determined. The complex 1 possesses a trigonal bipyramidal distorted square based pyramidal (TBDSBP) coordination geometry in which three corners of the square plane are occupied by two nitrogens and thioether s of pmtpm ligand and the remaining equatorial and the axial positions by two chloride ions. The complex 4 contains a CuN 4S chromophore also with a TBDSBP coordination geometry in which two nitrogens and the thioether sulfur of pmtpm ligand occupy three corners of the square plane. One of the two nitrogens of 2,9-dmp ligand is equatorially coordinated and the other axially to copper. On the other hand, the complex 6 is found to possess a square based pyramidal distorted trigonal bipyramidal (SPDTBP) coordination geometry. The CuN 2S trigonal plane in it is comprised of the pyridine and imine nitrogens and the thioether sulfur of the pmtpm ligand. The pyridine nitrogens of the ligand occupy the axial positions and the second thioether sulfur remains uncoordinated. On long standing in acetonitrile solution the mixed ligand complexes 2 and 3 undergo ligand disproportionation to provide the corresponding bis-complexes of bpy and phen, respectively, and 6. The electronic and EPR spectral parameters and the positive redox potential of complex 4 are consistent with the equatorial location of the thioether sulfur in the square-based coordination geometry around copper(II). On the other hand, the higher g ∥ and lower A ∥ values and lower E 1/2 values for the complexes 2, 3 and 5 are consistent with the axial coordination of the thioether sulfur. Also, the Cu(II)/Cu(I) redox potentials increase with increase in number of aromatic rings of the diimine ligand. The steric and electronic effects of the bidentate diimine ligands in orienting the thioether coordination to axial or equatorial position are discussed.

Steric Control of Bacteriochlorophyll Ligation

The axial coordination of central Mg(2+) ion in chlorophylls is of great structural and functional importance for virtually all photosynthetic chlorophyll proteins; however, little thermodynamic data are available on the ligand binding to these pigments. In the present study, spectral deconvolution of the bacteriochlorophyll Q(X) band serves to determine the ligand binding equilibria and relationships between thermodynamic parameters of ligand binding, ligand properties, and steric interactions occurring within the pigment. On the basis of the temperature effects on coordination, DeltaH degrees, DeltaS degrees, and DeltaG degrees of binding various types of ligands (acetone, dimethylformamide, imidazole, and pyridine) to diastereoisomeric bacteriochlorophylls were derived from respective van't Hoff's plots. At ambient temperatures, only ligation by imidazole and pyridine occurs spontaneously while DeltaG degrees becomes positive for ligation by acetone and dimethylformamide, due to a relatively large entropic effect, which is dominating when the energetic effects of ligation are small. It reflects, in quantitative terms, the control of the equatorial coordination of the Mg(2+) ion via the axial coordination: a "hard" free Mg(2+) ion is made into a softer center through the coordination of tetrapyrrole. Pigment structural features have comparable effects on the energetic and entropic contributions to the difference of ligation free energy between the diastereoisomers of bacteriochlorophyll. DeltaS degrees and DeltaH degrees values are consistently lower for the S epimer, most likely due to the steric crowding between bulky substituents. The two epimers show a 5 J.mol(-1).K(-1) difference in DeltaS degrees values, regardless of the ligand type, while the difference in DeltaH degrees amounts to 1.7 kJ.mol(-1), depending on the ligand. Such steric control of ligation would relate to the partial diastereoselectivity of chlorophyll self-assembly and, in particular, the very high diastereoselectivity of the ligation of chlorophylls in photosynthetic proteins.

Structure and Conformation of Bis(acetylacetonato)oxovanadium(IV) and Bis(maltolato)oxovanadium(IV) in Solution Determined by Electron Nuclear Double Resonance Spectroscopy

The structure and conformation of bis(acetylacetonato)oxovanadium(IV) [VO(acac)(2)] and bis(maltolato)oxovanadium(IV) [VO(malto)(2)] in frozen methanol have been determined by application of electron nuclear double resonance (ENDOR) spectroscopy. The positions of inner- and outer-sphere-coordinated solvent were assigned by ENDOR through use of selectively deuterated analogues of methanol. Similarly, the methyl and methylinyl proton resonance features of VO(acac)(2) were identified by site-selective deuteration. For VO(acac)(2), the ENDOR-determined metal-proton distances were best accounted for by a complex of tetragonal-pyramidal geometry, essentially identical to that determined by X-ray crystallography [Dodge, R. P.; Templeton, D. H.; Zalkin, A. J. Chem. Phys. 1961, 35, 55] but with an inner-sphere solvent molecule coordinated trans to the vanadyl oxygen and an axially positioned solvent molecule hydrogen-bonded to the vanadyl oxygen. In contrast to its trans conformation in crystals [Caravan, P.; et al. J. Am. Chem. Soc. 1995, 117, 12759], the VO(malto)(2) complex was found in a cis conformation whereby the donor oxygen atoms of one maltolato ligand occupied equatorial coordination sites. One of the donor oxygen atoms of the second maltolato ligand occupied the axial coordination site opposite the vanadyl oxygen atom, and the other an equatorial position. An inner-sphere-coordinated methanol molecule in the equatorial plane and a solvent molecule hydrogen-bonded to the vanadyl oxygen were also identified. No evidence for the trans isomer was observed.

Directed Supramolecular Assembly of Infinite 1-D M(II)-Containing Chains (M = Cu, Co, Ni) Using Structurally Bifunctional Ligands

The directed assembly of six different M(II) complexes (M = Cu, Co, and Ni) into infinite chains has been achieved by combining anionic chelating ligands (for controlling the coordination geometry) with bifunctional ligands containing a metal-coordinating pyridyl moiety and a self-complementary hydrogen-bonding moiety. Six crystal structures are presented, and in each case, the chelating acac ligand occupies the four equatorial coordination sites leaving room for the bifunctional ligand to coordinate in the axial positions. The supramolecular chemistry, which organizes the coordination complexes into the desired infinite 1-D chains, is driven by a combination of N-H...N and N-H...O hydrogen bonds.