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Peter Y Zavalij

Publications and source records attributed to Peter Y Zavalij.

At least 19 recordsLinked to original sources
PubMed2006

High-oxidation-state neutral and cationic tantalum(IV) alkyl complexes that are stable toward beta-hydrogen and beta-methyl eliminations.

The synthesis and solid-state structural characterization of a family of homoleptic and mixed dialkyl d1Ta(IV) complexes of the formula, (eta5-C5Me5)TaR1R2[N(i-Pr)C(Me)N(i-Pr)], where R1 = R2 = i-Bu (3), n-Bu (4), and Et (7), and R1 = Me, R2 = i-Bu (10), neopentyl (Np) (11), are reported, along with those for the cationic d1Ta(IV) complex, {(eta5-C5Me5)TaNp[N(i-Pr)C(Me)N(i-Pr)]}[B(C6F5)4] (12). All of the new compounds displayed a remarkably high degree of solution stability toward beta-hydrogen and beta-methyl eliminations/abstractions. Thermolysis of 3 in toluene at 80 degrees C for 18 h provided the Ta(IV) trimethylenemethane (TMM) complex 13.

Journal Article↗
PubMed2006

Nor-seco-cucurbit[10]uril exhibits homotropic allosterism.

The condensation of glycoluril and formaldehyde in concentrated HCl at 50 degrees C delivers nor-seco-cucurbit[10]uril (ns-CB [10]). 1H NMR and X-ray crystallographic evidence indicates that the two cavities of ns-CB[10] accommodate guests that are typically bound within CB[6] or CB[7]. Several interesting types of selectivity are possible within these ternary complexes-top/center isomerism, diastereoselective complexation of chiral (but racemic) guest pairs, and guest size controlled homotropic allosterism.

Journal Article↗
PubMed2006

High fidelity kinetic self-sorting in multi-component systems based on guests with multiple binding epitopes.

The molecular recognition platforms of natural systems often possess multiple binding epitopes, each of which has programmed functional consequences. We report the dynamic behavior of a system comprising CB[6], CB[7], and guests cyclohexanediammonium (1) and adamantanealkylammonium (2) that we refer to as a two-faced guest because it contains two distinct binding epitopes. We find that the presence of the two-faced guest--just as is observed for protein targeting in vivo--dictates the kinetic pathway that the system follows toward equilibrium. The influence of two-faced guest structure, cation concentration, cation identity, and individual rate and equilibrium constants on the behavior of the system was explored by a combination of experiment and simulation. Deconstruction of this system led to the discovery of an anomalous host-guest complex (CB[6].1) whose dissociation rate constant (k(out) = 8.5 x 10(-10) s(-1)) is approximately 100-fold slower than the widely used avidin.biotin affinity pair. This result, in combination with the analysis of previous systems which uncovered extraordinarily tight binding events (K(a) > or = 10(12) M(-1)), highlights the inherent potential of pursuing a systems approach toward supramolecular chemistry.

Binding Sites↗
PubMed2006

A DFT computational study of spin crossover in iron(III) and iron(II) tripodal imidazole complexes. A comparison of experiment with calculations.

B3LYP* functionals were used to model the sixteen iron(II) (1A, LS and 5T, HS) and iron(III) (2T, LS and 6A, HS) complexes of the 1:3 Schiff base condensate of tris(2-aminoethyl)amine and imidazole-4-carboxaldehyde, H3L1, and its deprotonated forms, [H2L1]1-, [HL1]2-, and [L1]3-. This ligand system is unusual in that [FeH3L1]3+, [FeH3L1]2+ and [FeL1]- all exhibit a spin crossover between 100-300 K. This makes these complexes ideal for a hybrid DFT computational approach and provides an opportunity to refine the value of the exact exchange admixture parameter, c3, and to predict properties of partially protonated complexes that are not experimentally available. The accepted value of 0.20 is larger than the value of approximately 0.13 that was found to best reproduce experimental data in terms of spin state predictions. With iron(III) B3LYP calculations showed that all of the complexes were low spin at 298 K with the exception of [FeH3L1]3+ which is spin crossover in agreement with experimental results. It was also shown for iron(III) that the ligand field increased as the number of protons decreased. In contrast all of the iron(II) complexes were close to the spin crossover region regardless of protonation state. Experimental structures are fairly well modeled by this system in regard to the key structural indicators of spin state, which are the bite and trans angles. The calculated iron to nitrogen atom distances are always larger in the high spin form than the low spin form but all iron to nitrogen bond distances are larger than the experimental values. In general non-bonded interactions are not well modeled by this methodology.

Journal Article↗
PubMed2005

The inverted cucurbit[n]uril family.

We report the isolation, characterization, and recognition behavior of iCB[6] and iCB[7], which are diastereomers of CB[6] and CB[7], respectively, containing a single inverted glycoluril unit. Product resubmission experiments establish that these inverted CB[n] are intermediates in the mechanism of CB[n] formation. As a consequence of the inverted glycoluril ring, these inverted cucurbiturils possess a permanent dipole moment, are slightly smaller than their diastereomers, show distinctive selectivity in their recognition behavior, and report directly on the contents of their hydrophobic cavity.

Bridged-Ring Compounds↗
PubMed2005

Synthesis and characterization of manganese(II) and iron(III) d5 tripodal imidazole complexes. Effect of oxidation state, protonation state and ligand conformation on coordination number and spin state.

The 1 : 3 Schiff base condensates of tris(2-aminoethyl)amine (tren) or tris(3-aminopropyl)amine (trpn) with 4-methyl-5-imidazolecarboxaldehyde, H3L1 and H3L2, respectively, were generated in situ and used to prepare complexes with manganese(II) and iron(III). The resultant complexes, [MnH3L1](ClO4)2, [MnH3L1](ClO4)2.EtOH.H2O, [MnH3L2](ClO4)2, [FeH3L1](ClO4)3.1.5(EtOH) and [FeHL1](I3) (0.525)(I)(0.475).2.625H2O, have been characterized by EA, IR, ES MS, variable temperature magnetic susceptibility, X-ray crystallography, and Mössbauer spectroscopy for the iron complexes. The three manganese(II) complexes are high spin with [MnH3L2](ClO4)2 exhibiting coordination number seven while the others are six coordinate. [FeH3L1](ClO4)3.1.5(EtOH) has two iron sites, a seven coordinate and a pseudo seven coordinate site. The complex is high spin at room temperature but exhibits a magnetic moment that decreases with temperature corresponding to conversion of one of the sites to low spin. [FeHL1](I3) (0.525)(I)(0.475).2.625H2O is low spin even at room temperature. In the present complexes the apical nitrogen atom, N(ap), of the tripodal ligand is pyramidal and directed toward the metal atom. The data show that the M-N(ap) distance decreases as the oxidation state of the metal increases, as the number of bound imidazole protons on the ligand increases, and as the number of carbon atoms in the backbone of the ligand (tren vs. trpn) increases. In a limiting sense, short M-N(ap) distances result in high spin seven coordinate mono capped octahedral complexes and long M-N(ap) distances result in low spin six coordinate octahedral complexes.

Crystallography, X-Ray↗
PubMed2005

Cucurbit[10]uril.

Melamine diamine 1 is able to displace CB[5] from the CB[10].CB[5] complex resulting in CB[10].12 and precipitated CB[5].1. We were able to isolate free CB[10] by treatment of CB[10].1 with acetic anhydride followed by washing with MeOH, DMSO, and water. The spacious cavity of CB[10] is able to complex large guests, including a cationic calix[4]arene derivative in its 1,3-alternate form (CB[10].1,3-alt-3). The addition of adamantane carboxylic acid (4) to CB[10].3 triggers a conformational change during the formation of termolecular complex CB[10].cone-3.4.

Bridged-Ring Compounds↗
PubMed2005

The cucurbit[n]uril family: prime components for self-sorting systems.

We determined the values of Ka for a wide range of host-guest complexes of cucurbit[n]uril (CB[n]), where n = 6-8, using 1H NMR competition experiments referenced to absolute binding constants measured by UV/vis titration. We find that the larger homologues--CB[7] and CB[8]--individually maintain the size, shape, and functional group selectivity that typifies the recognition behavior of CB[6]. The cavity of CB[7] is found to effectively host trimethylsilyl groups. Remarkably, the values of Ka for the interaction of CB[7] with adamantane derivatives 22-24 exceeds 10(12) M(-1)! The high levels of selectivity observed for each CB[n] individually is also observed for the CB[n] family collectively. That is, the selectivities of CB[6], CB[7], and CB[8] toward a common guest can be remarkably large. For example, guests 1, 3, and 11 prefer CB[8] relative to CB[7] by factors greater than 10(7), 10(6), and 3000, respectively. Conversely, guests 23 and 24 prefer CB[7] relative to CB[8] by factors greater than 5100 and 990, respectively. The high levels of selectivity observed individually and collectively for the CB[n] family renders them prime components for the preparation of functional biomimetic self-sorting systems.

Biomimetic Materials↗
PubMed2005

Open metal-organic framework containing cuprate chains.

A three-dimensional Cu(II) metal-organic framework, copper hydroxide p-pyridinecarboxylate hydrate, [Cu(OH)(C5H4NCO2).H2O], was synthesized by hydrothermally reacting copper nitrate with p-pyridinecarboxylic acid. The crystals were suitable for single-crystal X-ray diffraction analysis, which showed that the Cu(II) centers adopt a slightly distorted square pyramidal geometry. They coordinate to both the pyridyl and carboxylate functionalities of the pyridinecarboxylate bridging ligands. Infinite copper oxide chains run through the structure and are connected by p-pyridinecarboxylate (p-PyC) ligands. Crystal data: monoclinic, space group P2(1)/n, a = 3.5521(2) A, b = 15.8665(11) A, c = 12.9977(9) A, beta = 95.285(2) degrees , and Z = 4. Thermogravimetric analysis (TGA) revealed that the guest H2O molecules in the channels may be removed, and the material is stable to ca. 245 degrees C. Magnetic measurements indicated the material has one-dimensional (1D) antiferromagnetic ordering within the Cu2+ chains with a Néel temperature of ca. 51 K. Data fitting to the Bonner-Fisher model yielded a coupling constant, J, of -7.3 cm(-1) and g factor of 2.15. The Curie tail below 20 K is due to a small amount of paramagnetic impurities, calculated to be approximately 0.2% in concentration. Further characterization of crystallinity and morphology are discussed, including powder X-ray diffraction (PXRD), elemental analysis, and optical microscopy.

Journal Article↗
PubMed2005

"Matched/mismatched" diastereomeric dirhodium(II) carboxamidate catalyst pairs. Structure-selectivity correlations in diazo decomposition and hetero-Diels-Alder reactions.

Homo-ligated dirhodium(II) carboxamidates provide well-defined structural frameworks with which to investigate catalyst-controlled multiple asymmetric induction ("match/mismatch" effects). Diastereomeric pairs of methyl 2-oxoimidazolidine-4(S)-carboxylate ligands containing 2-phenylcyclopropane (4S,2'S,3'S-HMCPIM and 4S,2'R,3'R-HMCPIM) and N-benzenesulfonylproline (4S,2'S-HBSPIM and 4S,2'R-HBSPIM) attachments at the 1-N-acyl site have been prepared; the resulting (cis-2,2)-Rh(2)L(4) compounds have been produced in good yields, and the X-ray crystal structure of each dirhodium(II) compound has been obtained. The incorporation of additional stereocenters into the dirhodium(II) ligands leads to recognizable levels of double asymmetric induction for C-H insertion, cyclopropanation, and hetero-Diels-Alder cycloaddition applications. The configurationally "matched" cases provide modest increases in enantioselectivity for intramolecular C-H insertion reactions relative to the model catalyst Rh(2)(MPPIM)(4), but applications of the configurationally mismatched catalysts result in significant lowering of enantioselectivity. The Rh(2)(BSPIM)(4) catalysts show the highest degree of differential selectivity. Hetero-Diels-Alder reactions show inverse behavior from the configurationally matched and mismatched Rh(2)L(4) catalysts to that found in the metal carbene transformations.

Catalysis↗
PubMed2004

Structural chemistry of new lithium bis(oxalato)borate solvates.

Recently lithium bis(oxalato)borate, LiB(C2O4)2, has been proposed as an alternative lithium salt for the electrolyte in rechargeable batteries that do not contain explosive perchlorate, reactive fluoride or toxic arsenic. This lithium salt crystallizes in the form of solvates from such solvents as water, acetonitrile, acetone, dimethoxyethane, 1,3-dioxolane and ethylene carbonate. Their crystal structures were determined in order to explore the crystal chemistry of this lithium salt. It was found that most of the solvents consist of a lithium bis(oxalato)borate dimer in which the ligand acts as both a chelating and a bridging agent. Lithium has octahedral coordination that typically includes one or, less commonly, two solvent molecules. An exception to this rule is the ethylene carbonate solvate where the lithium is tetrahedrally surrounded exclusively by the solvent and bis(oxalato)borate plays the role of counter-ion only. The ethylene carbonate solvates were also studied for LiPF6 and LiAsF6 salts and they have similar structures to the bis(oxalato)borate tetrahedral complexes.

Journal Article↗
PubMed2003

Structures of potassium, sodium and lithium bis(oxalato)borate salts from powder diffraction data.

The crystal structures of the alkali-metal bis(oxalato)borate salts A[B(C2O4)2] (A = K, Na, Li) have been determined ab initio using powder diffraction data obtained from a laboratory diffractometer. The K compound crystallizes in the orthorhombic space group Cmcm and its structure has been solved by direct methods applied to the integrated intensities from full pattern decomposition. The Na compound is isostructural with the K salt, while the crystal structure of the highly hydroscopic Li compound differs from the other two. It has an orthorhombic lattice, space group Pnma, and its structure was solved by the global optimization method using a parallel tempering approach. In the K and Na structures the metal ions and complex borate ions form chains with m2m symmetry. Metal-oxygen bonding between the chains links them into a layer and then a framework with square tunnels. The coordination number of both K and Na is eight. The Li compound also contains chains that have .m. symmetry and are bound together into a three-dimensional framework. The coordination polyhedron of the Li atom is a square pyramid with Li lying in its base. This square pyramidal coordination leads to its high reactivity with moisture to give Li[B(C2O4)2]H2O with lithium in six coordination.

Journal Article↗
PubMed2003

Highly sensitive luminescent metal-complex receptors for anions through charge-assisted amide hydrogen bonding.

Two structurally simple and easily synthesized luminescent anion receptors featured with an amide-type anion binding site and rhenium(I) tricarbonyl pyridine signaling units have been developed, and they display outstanding sensitivity and selectivity toward a variety of anionic species. These complexes are highly emissive in solution. Upon anion binding, the emission intensity was significantly quenched. The sensitivities of these complexes are so high that the emission intensity can be effectively quenched by as much as 10% even in the presence of only 10(-8) M cyanide or fluoride anions. The ability of formation of intramolecular hydrogen bonding between the amide protons and central pyridine is believed to be responsible for the observed high selectivity.

Amides↗
PubMed2003

Structural diversity and polytypism of lead phenylphosphonates: BING-6 and BING-9.

We report the solvothermal synthesis and characterization of a series of layered lead phenylphosphonates. The crystals were suitable for single crystal X-ray diffraction data, and the two new structures we denote BING-6 [SUNY at Binghamton, Structure No. 6, Pb(PO(3)C(6)H(5)).0.25C(5)H(5)N, triclinic space group Ponemacr;, Z = 2, a = 7.0770(4) A, b = 9.3113(6) A, c = 14.6785(9) A, alpha = 80.456(1) degrees, beta = 78.023(1) degrees, gamma = 73.265(1)(o)] and BING-9 [Pb(PO(3)HC(6)H(5))(PO(3)HC(6)H(4)CH(3)), monoclinic space group C2/c, Z = 4, a = 32.663(8) A, b = 5.6220(13) A, c = 8.3307(19) A, beta = 101.419(4)(o)]. The third structure, a polytype of BING-9, was previously known only from powder X-ray diffraction methods and is denoted 3 [Pb(PO(3)HC(6)H(5))(2), monoclinic space group C2/c, Z = 4, a = 31.681(6) A, b = 5.5639(11) A, c = 8.2515(16) A, beta = 101.814(4)(o)]. All three structures possess Pb(II) and P centers connected by doubly and triply bridging oxygens. The phenyl groups cap and separate the charge-neutral layers. The phosphonates of BING-6 are nonprotonated, and the structure therefore has a Pb/P ratio of 1:1. Neutral, partially disordered pyridine solvent molecules also reside in the interlamellar space, increasing the layer to layer distance. BING-9 and 3 are polytypes and contain singly protonated phosphonates, for a Pb/P ratio of 1:2. Further characterization methods are discussed, including powder X-ray diffraction, in-situ variable temperature powder X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Related work in the Ge, Sn, and Mn systems is also discussed. These low-dimensional materials may be useful intercalation compounds for ion-exchange or sensor applications.

Journal Article↗
PubMed2002

New iron(III) phosphate phases: crystal structure and electrochemical and magnetic properties.

Two new iron(III) phosphates, FePO(4), have been synthesized from the dehydration of hydrothermally prepared monoclinic and orthorhombic hydrated phosphates FePO(4).2H(2)O. The structures of both hydrates were redetermined from single crystal data. On dehydration, a topotactic reaction takes place with only those bonds associated with the water molecules being broken, so that both FePO(4) phases have essentially the same Fe-P backbone frameworks as the corresponding hydrates. They are, respectively, monoclinic FePO(4), space group P2(1)/n, a= 5.480(1) A, b = 7.480(1) A, c= 8.054(1) A, beta = 95.71(1) degrees, and Z = 4; and orthorhombic FePO(4), space group Pbca, a = 9.171(1) A, 9.456(1) A, c = 8.675(1) A, and Z = 8. Both of these phases are thermally unstable relative to the trigonal quartz-like FePO(4). The electrochemical studies find that the orthorhombic iron phosphate is more active than the monoclinic phase, while both are more active than trigonal FePO(4). Both phases approach Curie-Weiss behavior at room temperature, with the monoclinic phase exhibiting stronger antiferromagnetic interactions due to Fe-O-Fe interactions. The electrochemical and magnetic data are consistent with the structures of these two compounds. The properties of these new iron phosphate structures are compared with other iron phosphate phases.

Journal Article↗