O2 activation by nonheme iron complexes: A monomeric Fe(III)-Oxo complex derived from O2.

Iron species with terminal oxo ligands are implicated as key intermediates in several synthetic and biochemical catalytic cycles. However, there is a dearth of structural information regarding these types of complexes because their instability has precluded isolation under ambient conditions. The isolation and structural characterization of an iron(III) complex with a terminal oxo ligand, derived directly from dioxygen (O2), is reported. A stable structure resulted from placing the oxoiron unit within a synthetic cavity lined with hydrogen-bonding groups. The cavity creates a microenvironment around the iron center that aids in regulating O2 activation and stabilizing the oxoiron unit. These cavities share properties with the active sites of metalloproteins, where function is correlated strongly with site structure.

Reversible cleavage and formation of the dioxygen O-O bond within a dicopper complex.

A key step in dioxygen evolution during photosynthesis is the oxidative generation of the O-O bond from water by a manganese cluster consisting of M2(mu-O)2 units (where M is manganese). The reverse reaction, reductive cleavage of the dioxygen O-O bond, is performed at a variety of dicopper and di-iron active sites in enzymes that catalyze important organic oxidations. Both processes can be envisioned to involve the interconversion of dimetal-dioxygen adducts, M2(O2), and isomers having M2(mu-O)2 cores. The viability of this notion has been demonstrated by the identification of an equilibrium between synthetic complexes having [Cu2(mu-eta2:eta2-O2)]2+ and [Cu2(mu-O)2]2+ cores through kinetic, spectroscopic, and crystallographic studies.

A Diazoalkane Derivative of a Polyoxometalate: Preparation and Structure of [Mo6 O18 (NNC(C6 H4 OCH3 )CH3 )](2-).

A new metathetical route to diazoalkane complexes is described which allows the introduction of such ligands into previously inaccessible environments. The method, which involves the exchange of oxo and [N2 CR2 ] ligands, is illustrated by the preparation of the first diazoalkane-polyoxometalate complex 1.

Solid-state behavior of cromolyn sodium hydrates.

Cromolyn sodium (CS, disodium cromoglycate) is an antiasthmatic and antiallergenic drug. The solid-state behavior of CS is still not completely understood. CS forms nonstoichiometric hydrates and sorbs and liberates water in a continuous manner, although with hysteresis. The reported continuous changes in crystal lattice parameters of CS, which are associated with the changes in water stoichiometry, renders CS physically variable, which may complicate formulation and processing. In addition, controversies still remain as to whether CS exists as different stoichiometric hydrates, mainly because of its variable powder X-ray diffraction (PXRD) patterns (Cox, J. S. G. et al. J. Pharm. Sci. 1971, 60, 1458-65), which indicates a variable crystal structure. The objectives of this study are (a) to understand this unusual water uptake in the light of the molecular and crystal structures of CS, (b) to understand the relationship between the crystal structure and the PXRD patterns using Rietveld analysis, and (c) to investigate whether CS exists as different stoichiometric hydrates. The crystal structure of CS containing 6.44 molecules of water per molecule of CS was determined at 295 and 173 K. The packing arrangements in these structures (space group P1) are similar to those in a previous report, in which the water stoichiometry is 5 to 6, but the bond lengths, bond angles, and lattice parameters are different, reflecting the different water stoichiometries. In the crystal structure solved at 295 K, the position of only one of the two sodium ions could be determined. In the crystal structure solved at 173 K, the previously undetermined sodium ion is disordered over three sites, while four of eight water positions are partially occupied. The 2-hydroxy-propane chain that links the two cyclic moieties of CS was found to be flexible, perhaps allowing the CS crystal to accommodate variable amounts of water. The lack of a fixed coordination site for the second sodium ion may contribute to the disorder of the water molecules. The nonstoichiometric water content of CS is mainly attributed to the water molecules that are associated with the two unoccupied sodium sites. From the PXRD patterns of CS powder, equilibrated at various relative humidities, the various lattice parameters, including previously unreported alpha, beta, and gamma values, were calculated using Rietveld analysis. The peak shifts in these PXRD patterns are quantitatively explained by slight changes in the unit cell parameters. The recently described solid forms of CS were prepared and were found to correspond to the original crystalline CS, described by Cox et al. (1971), but with contamination by the known M mesophase in various proportions. The present results support a variable crystal structure and not the existence of different stoichiometric hydrates of CS.

Physicochemical characterization of nedocromil bivalent metal salt hydrates. 3. Nedocromil calcium.

A crystalline pentahydrate and a crystalline 8/3 hydrate of nedocromil calcium (NC) were prepared. The relationships between these solid phases and the nature of the water interactions in their structures were studied through characterization by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Karl Fischer titrimetry (KFT), hot-stage microscopy (HSM), ambient- or variable-temperature powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, solid-state nuclear magnetic resonance (SSNMR) spectroscopy, water uptake at various relative humidities (RH), intrinsic dissolution rate (IDR) and solubility measurements. The solubility and intrinsic dissolution rate of the pentahydrate in water at 25 degrees C are approximately 17% greater than the corresponding values for the 8/3 hydrate, corresponding to a greater Gibbs free energy of only 380 J.mol-1 (91 cal.mol-1) for the pentahydrate. The results of DSC, TGA, and FTIR and SSNMR spectroscopy indicate that the water of hydration is more loosely bound in the pentahydrate than in the 8/3 hydrate. On increasing the temperature in open-pan DSC and TGA, the water in the pentahydrate is released in four steps (three steps in crimped pans), whereas the water in the 8/3 hydrate is released in three steps (three steps also in crimped pans). These three stepwise dehydrations are fundamentally explained by their different water environments in the crystal structure of the 8/3 hydrate, which was determined by single-crystal XRD [crystal data: triclinic, space group P1, a = 13.2381(3) A, b = 13.3650(2) A, c = 17.8224(2) A, alpha = 68.202(1) degrees, beta = 86.894(1) degrees, gamma = 82.969(1) degrees, Z = 6]. The asymmetric unit contains three nedocromil anions and three calcium cations associated with eight water molecules. The nedocromil anions act as polyfunctional ligands to the Ca2+ ions, coordinating through both the carbonyl oxygen and the carboxylate oxygen atoms. The molecular conformations of the three nedocromil anions in the asymmetric unit are almost identical. However, the crystal structure contains two different calcium environments, one of which has the Ca2+ ion hydrated by four water molecules in the equatorial plane and by two carbonyl oxygens in its axial coordination sites. In the second environment, the Ca2+ ion has four carboxylate oxygen atoms in its equatorial plane and two water molecules in its axial coordination sites. Two of the carboxylate ligands are twisted out of the tricyclic ring, and the other two carboxylate ligands are nearly coplanar with the tricyclic ring. All of the eight water molecules in the 8/3 hydrate are linked to calcium and carboxylate ions and none are linked to other water molecules.

Syntheses of four D- and L-hexoses via diastereoselective and enantioselective dihydroxylation reactions.

An expeditious approach to various protected hexoses has been developed by the use of the Sharpless catalytic asymmetric dihydroxylation reaction. Applying the Sharpless catalytic asymmetric dihydroxylation reaction on vinylfuran, diols with high enantioexcess are produced. The resulting diols can be stereoselectively transformed into either protected D- or L-mannose in five steps and approximately 39% yield from furfural. Similarly, both D- and L-talose and gulose have been synthesized in 19% overall yields, respectively. Using a modified strategy, both protected D- and L-gulo- and allo-sugar-delta-lactones were synthesized in eight steps and approximately 20%, overall yield from furfural.

Crystal structures of a family of silver cyanide complexes of thiourea and substituted thioureas.

The syntheses and crystal structures of a family of silver cyanide complexes of thiourea and substituted thioureas are reported. The sulfur ligands include thiourea (tu), 1-methyl-2-thiourea (mtu), 1,3-dimethyl-2-thiourea (dmtu), 1,1,3,3-tetramethyl-2-thiourea (tmtu), and 2-imidazolidinethione (N,N'-ethylenethiourea, etu). Synthesis was effected by dissolving AgCN in an aqueous solution of ligand. Two different complexes were obtained by the reaction of AgCN with tu. Complex 1a: (AgCN)(tu), monoclinic, P2(1)/c, a = 9.3851 (6) A, b = 8.2782 (5) A, c = 7.1178 (5) A, beta = 94.591 (1) degree, and Z = 4. Complex 1b: (AgCN)(tu)2, triclinic, P1, a = 7.9485 (14) A, b = 9.431 (2) A, c = 12.771 (2) A, alpha = 85.695 (3) degrees, beta = 81.210 (4) degrees, gamma = 77.987 (2) degrees, and Z = 4. Complex 2: (AgCN)(mtu), triclinic, P1, a = 4.113 (2) A, b = 9.472 (4) A, c = 9.679 (4) A, alpha = 113.918 (5) degrees, beta = 98.188 (6) degrees, gamma = 97.725 (6) degrees, and Z = 2. Complex 3 (AgCN)2(dmtu)2, monoclinic, P2(1)/m, a = 7.1482 (7) A, b = 14.776 (2) A, c = 7.3366 (7) A, beta = 92.418 (2) degrees, and Z = 2. Complex 4: (AgCN)(tmtu), orthorhombic, P2(1)2(1)2(1), a = 8.823(6) A, b = 10.209 (2) A, c = 10.362 (2) A, and Z = 4. Complex 5: (AgCN)2(etu)2, triclinic, P1, a = 6.8001 (2) A, b = 8.6154 (1) A, c = 13.4747 (3) A, alpha = 71.720 (1) degree, beta = 79.906 (1) degree, gamma = 75.885 (2) degrees, and Z = 2. All of the structures involve either one- or two-dimensional polymeric arrays held together by bridging S and CN groups. There is, however, no similarity between any two of the arrays. Four of the five ligands used also form similar complexes with CuCN. For one ligand, tmtu, the structures are isomorphous. For the other three, not only are the structures not isomorphous, the m/n ratio in (MCN)mLn when M is Ag is different from that when M is Cu.

Syntheses and structures of quinuclidine-stabilized amido- and azidogallanes.

Quinuclidine-stabilized amido- and azidogallanes, HGa[N(TMS)2]2(quin) (1), H2Ga[N(TMS)2](quin) (2), HGa-[N(H)(2,6-iPr2C6H3)]2(quin) (3), and H2GaN3(quin) (4), were synthesized from the quinuclidine adducts of mono- and dichlorogallane. Structural determinations revealed that all compounds were monomeric with four-coordinate gallium centers. Reactions of the five-coordinate compound, HGaCl2(quin)2, with 2 equiv of Li[N(TMS)2] or Li[N(H)(2,6-iPr2C6H3)] resulted in the isolation of compound 1 or 3. A ligand redistribution during the reaction of H2GaCl(quin) with Li[N(H)(2,6-iPr2C6H3)] produced compound 3 and H3Ga(quin) in a 1:1 molar ratio.

Construction of the tetracyclic skeleton of leucothol A. 1,2,4a,5,6,7,8,9,10,10a,11,11a-dodecahydro-11-hydroxy-11-methyl-7- phenylthiomethyl-5aH-5a,8-methano-cyclohepta[b] naphthalen-10-one.

The title compound, C24H30O2S, is a tetracyclic intermediate for the synthesis of leucothol A and the first example of an ethanoanthracene skeleton to be synthetized. The single-crystal X-ray structure of this compound is presented.

Assembly of the inorganic double helix Mg6(Et2NCO2)12 by fixation of carbon dioxide: crystal and solution structure.

The homoleptic magnesium carbamato complex Mg6(Et2NCO2)12, 1 (Et2NCO2- = diethylcarbamato anion), was prepared by the reaction of dibutylmagnesium with diethylamine, followed by carboxylation using gaseous carbon dioxide. Crystallographic characterization demonstrated that 1 has the standard M6(R2NCO2)12 structure and is a double helix of MgO(x)(x = 5, 6) coordination polyhedra with Delta or Lambda stereochemistry arising from the configuration around the six-coordinate Mg2+ cations. It crystallized in the orthorhombic space group Ccca with two molecules of Delta1 and two of Lambda1 per unit cell (a = 21.548 A, b = 25.094 A, c = 15.4485(11) A, alpha = beta = gamma = 90 degrees ). Extensive solution characterization of 1 by 1-dimensional proton and 13C NMR spectroscopy and by two-dimensional 1H-[13C] NMR correlation techniques verified that the helical structure is maintained in solution. Moreover, these measurements indicated that the intramolecular dynamics of 1 relating to motions of the ethyl groups was substantially hindered in solution. Correlation of the crystallographic and NMR structural studies indicated that this arises from a combination of hindered rotation about the carbamato C-N bond and efficient packing of the ethyl groups around the Mg6O24 core. The result is an inverted-micelle-like structure for 1 in which the hydrophobic ethyl groups form a sheath largely restricting access to the hydrophilic Mg6O24 core.

The first noncoordinated phosphonium diylide, [Me2P(C13H8)2]-, and its ylidic and cationic counterparts: synthesis, structural characterization, and interaction with the heavy group 2 metals.

Treatment of potassium or lithium fluorenide with MePCl2 generates the organophosphine MeP(C13H9)2, which on reaction with methyl iodide produces the phosphonium species [Me2P(C13H9)2]I in 74% yield. In the solid state, H...I contacts of < 3.3 A help generate a layered structure in which the fluorenyl rings are nearly parallel. On subsequent reaction of [Me2P(C13H9)2]I with either KH or K[N(SiMe3)2], the corresponding neutral phosphoylide, Me2P(C13H9)(C13H8), forms in 67% yield and was structurally characterized. The phosphonium iodide [Me2P(C13H9)2]I was allowed to react with Ae[N(SiMe3)2]2 (Ae = Ca, Ba), and the product from the reaction with the calcium complex was structurally identified as the salt [CaI(thf)5][Me2P(C13H8)2]. The anion, which is outside the coordination sphere of the calcium, represents the first structurally authenticated example of a free phosphonium diylide. The P-C(ylidic) bond length of 1.748(4) A reflects some partial multiple bond character. 1H and 31P NMR spectra suggest that the barium analogue is similar. Density functional theory calculations were performed on representative phosphonium diylides as an aid to interpreting the bonding in this class of compounds. Despite the strong electrostatic attraction that usually drives metal-ligand binding in highly ionic systems, calcium and barium prefer to coordinate to a single iodide ion and several neutral oxygen donors rather than to the charged diylide.

LiEuPSe4 and KEuPSe4: novel selenophosphates with the tetrahedral [PSe4]3- building block.

LiEuPSe4, the first quaternary lithium-containing selenophosphate, was synthesized as red polyhedra by reacting Eu with a molten mixture of Li2Se/P2Se5/Se at 750 degrees C. Similarly, the reaction of Eu with a molten mixture of K2Se/P2Se5/Se at 495 degrees C produced red polyhedral crystals of KEuPSe4. Both compounds are unstable in moist air. In addition, both compounds were plagued with crystal twinning. Acceptable crystal structure refinements could only be obtained by identifying the type of twinning and taking it into account in the final refinement. LiEuPSe4 crystallizes in the noncentrosymmetric space group Ama2 (no. 40) with a = 10.5592 (9) A, b = 10.415 (1) A, c = 6.4924(7) A, and Z = 4. The structure is three-dimensional and composed of EuSe8 distorted square antiprisms and PSe4 tetrahedral building blocks that create tunnels, running down the a axis, in which the Li ions reside. The Li ions are in a highly distorted tetrahedral coordination. KEuPSe4 crystallizes in the space group P2(1)/m (no. 11) with a = 6.8469(6) A, b = 6.9521(6) A, c = 9.0436(8) A, beta = 107.677(2) degrees, and Z = 2. The structure has two-dimensional character with layers composed of EuSe6 trigonal prisms and PSe4 tetrahedral units. Between the [EuPSe4]nn- layers the K ions reside in a bicapped trigonal prism of Se atoms. The structure of the [EuPSe4]nn- framework is similar to that found in CsPbPSe4. Both compounds are semiconductors with band gaps of 2.00 and 1.88 eV, respectively. Differential thermal analysis and infrared spectroscopic characterization are also reported.

Addition and metathesis reactions of zirconium and hafnium imido complexes.

The zirconium and hafnium imido metalloporphyrin complexes (TTP)M = NArtPr (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion; M = Zr (1), Hf; AriPr = 2,6-diisopropylphenyl) were used to mediate addition reactions of carbonyl species and metathesis of nitroso compounds. The imido complexes react in a stepwise manner in the presence of 2 equiv of pinacolone to form the enediolate products (TTP)M[OC(tBu)CHC(tBu)(Me)O] (M = Zr (2), Hf (3)), with elimination of H2NAriPr. The bis(mu-oxo) complex [(TTP)ZrO]2 (4) is formed upon reaction of (TTP)Zr = NAriPr with PhNO. Treatment of compound 4 with water or treatment of compound 2 with acetone produced the (mu-oxo)bis(mu-hydroxo)-bridged dimer [(TTP)Zr]2(mu-O)(mu-OH)2 (5). Compounds 2, 4, and 5 were structurally characterized by single-crystal X-ray diffraction.

Synthesis and characterization of iridium 1,3,5-triaza-7-phosphaadamantane (PTA) complexes. X-ray crystal and molecular structures of [Ir(PTA)4(CO)]Cl and [Ir(PTAH)3(PTAH2)(H)2]Cl6.

The first 1,3,5-triaza-7-phosphaadamantane (PTA) ligated iridium compounds have been synthesized. The reaction of PTA with [Ir(COD)Cl]2 (COD = 1,5-cyclooctadiene) under a CO atmosphere produces an inseparable mixture of [Ir(PTA)3(CO)Cl] (1) and the PTA analogue of Vaska's compound, [Ir(PTA)2(CO)Cl] (2). Compound 1 and [Ir(PTA)4(CO)]Cl (3) were prepared via ligand substitution reactions of PTA with Vaska's compound, trans-Ir(PPh3)2(CO)Cl, in absolute and 95% ethanol, respectively. Complex 3 crystallizes in the orthorhombic space group Pbca with a = 20.3619(4) A, b = 14.0345(3) A, c = 24.1575(5) A, and Z = 8. Single-crystal X-ray diffraction studies show that 3 has a trigonal bipyramidal structure in which the CO occupies an axial position. This is the first crystallographically characterized [IrP4(CO)]+ complex in which the CO is axially ligated. Compound 1 was converted into 3 by ligand substitution with 1 equiv of PTA in water. Interestingly, the reaction of 3 with excess NaCl did not result in the production of 1, but instead the formation of the dichloro species, [Ir(PTAH)2(PTA)2Cl2]Cl3 (4) (PTAH = protonated PTA). Dissolution of 1 or 3 in dilute HCl produced 4 and a dihydrido species, [Ir(PTAH)4(H)2]Cl5 (5), which were readily separated by inspection due to their different crystal habits. Compound 5 crystallizes in the triclinic space group P1 with a = 12.4432(9) A, b = 12.5921(9) A, c = 16.3231(12) A, alpha = 76.004(1) degrees, beta = 71.605(1) degrees, gamma = 69.177(1) degrees, and Z = 2. Complex 5 exhibits a distorted octahedral geometry with two hydride ligands in a cis configuration. A rationale consistent with these reactions is presented by consideration of the steric and electronic properties of the PTA ligand.

Cationic aluminum alkyl complexes incorporating aminotroponiminate ligands.

The synthesis, structures, and reactivity of cationic aluminum complexes containing the N,N'-diisopropylaminotroponiminate ligand ((i)Pr(2)-ATI(-)) are described. The reaction of ((i)Pr(2)-ATI)AlR(2) (1a-e,g,h; R = H (a), Me (b), Et (c), Pr (d), (i)Bu (e), Cy (g), CH(2)Ph (h)) with [Ph(3)C][B(C(6)F(5))(4)] yields ((i)()Pr(2)-ATI)AlR(+) species whose fate depends on the properties of the R ligand. 1a and 1b react with 0.5 equiv of [Ph(3)C][B(C(6)F(5))(4)] to produce dinuclear monocationic complexes [([(i)Pr(2)-ATI] AlR)(2)(mu-R)][(C(6)F(5))(4)] (2a,b). The cation of 2b contains two ((i)()Pr(2)-ATI)AlMe(+) units linked by an almost linear Al-Me-Al bridge; 2a is presumed to have an analogous structure. 2b does not react further with [Ph(3)C][B(C(6)F(5))(4)]. However, 1a reacts with 1 equiv of [Ph(3)C][B(C(6)F(5))(4)] to afford ((i Pr(2)-ATI)Al(C(6)F(5))(mu-H)(2)B(C(6)F(5))(2) (3) and other products, presumably via C(6)F(5)(-) transfer and ligand redistribution of a [((i)()Pr(2)-ATI)AlH][(C(6)F(5))(4)] intermediate. 1c-e react with 1 equiv of [Ph(3)C][B(C(6)F(5))(4)] to yield stable base-free [((i)Pr(2)-ATI)AlR][B(C(6)F(5))(4)] complexes (4c-e). 4c crystallizes from chlorobenzene as 4c(ClPh).0.5PhCl, which has been characterized by X-ray crystallography. In the solid state the PhCl ligand of 4c(ClPh) is coordinated by a dative PhCl-Al bond and an ATI/Ph pi-stacking interaction. 1g,h react with [Ph(3)C][B(C(6)F(5))(4)] to yield ((i)Pr(2)-ATI)Al(R)(C(6)F(5)) (5g,h) via C(6)F(5)(-) transfer of [((i)Pr(2)-ATI)AlR][(BC(6)F(5))(4)] intermediates. 1c,h react with B(C(6)F(5))(3) to yield ((i)Pr(2)-ATI)Al(R)(C(6)F(5)) (5c,h) via C(6)F(5)(-) transfer of [((i)Pr(2)-ATI)AlR][RB(C(6)F(5))(3)] intermediates. The reaction of 4c-e with MeCN or acetone yields [((i)Pr(2)-ATI)Al(R)(L)][B(C(6)F(5))(4)] adducts (L = MeCN (8c-e), acetone (9c-e)), which undergo associative intermolecular L exchange. 9c-e undergo slow beta-H transfer to afford the dinuclear dicationic alkoxide complex [(((i)Pr(2)-ATI)Al(mu-O(i)()Pr))(2)][B(C(6)F(5))(4)](2) (10) and the corresponding olefin. 4c-e catalyze the head-to-tail dimerization of tert-butyl acetylene by an insertion/sigma-bond metathesis mechanism involving [((i)Pr(2)-ATI)Al(C=C(t)Bu)][B(C(6)F(5))(4)] (13) and [((i)Pr(2)-ATI)Al(CH=C((t)()Bu)C=C(t)Bu)][B(C(6)F(5))(4)] (14) intermediates. 13 crystallizes as the dinuclear dicationic complex [([(i Pr(2)-ATI]Al(mu-C=C(t)Bu))(2)][B(C(6)F(5))(4)](2).5PhCl from chlorobenzene. 4e catalyzes the polymerization of propylene oxide and 2a catalyzes the polymerization of methyl methacrylate. 4c,e react with ethylene-d(4) by beta-H transfer to yield [((i)Pr(2)-ATI)AlCD(2)CD(2)H][B(C(6)F(5))(4)] initially. Polyethylene is also produced in these reactions by an unidentified active species.

Hydrogen-bonding cavities about metal ions: synthesis, structure, and physical properties for a series of monomeric M-OH complexes derived from water.

The tripodal ligand N[CH2CH2NHC(O)NHC(CH3)3]3 ([H61]) was used to synthesize a series of monomeric complexes with terminal hydroxo ligands. The complexes [Co(II/III)H31(OH)](2-/1-), [Fe(II/III)H31(OH)](2-/1-), and [Zn(II)H31(OH)](2-) have been isolated and characterized. The source of the hydroxo ligand in these complexes is water, which was confirmed with an isotopic labeling study for [Co(III)H31(OH)](1-). The synthesis of [M(II)H31(OH)](2-) complexes was accomplished by two routes. Method A used 3 equiv of base prior to metalation and water binding, affording yields of < or = 40% for [Co(II)H31(OH)](2-). When 4 equiv of base was used (method B), yields ranged from 50% to 70% for all of the M(II)H31(OH)](2-) complexes. This improvement is attributed to the presence of an intramolecular basic site within the cavity, which scavenges protons produced during formation of the M(II)-OH complexes. The molecular structures of [Zn(II)H31(OH)](2-), [Fe(II)H31(OH)](2-), [Co(II)H31(OH)](2-), and [Co(III)H31(OH)](1-) were examined by X-ray diffraction methods. The complexes have trigonal bipyramidal coordination geometry with the hydroxo oxygen trans to the apical nitrogen. The three M(II)-OH complexes crystallized with nearly identical lattice parameters, and each contains two independent anions in the asymmetric unit. The complexes have intramolecular H-bonds from the urea cavity of [H31](3-) to the coordinated hydroxo oxygen. All the complexes have long M-O(H) bond lengths (>2.00 A) compared to those of the few previously characterized synthetic examples. The longer bond distances in [M(II)H31(OH)](2-) reflect the intramolecular H-bonds in the complexes. The five-coordinate [Zn(II)H31(OH)](2-) has an average Zn-O(H) distance of 2.024(2) A, which is similar to that found for the zinc site in carbonic anhydrase II (2.05(2) A). The enzyme active site also has an extensive network of intramolecular H-bonds to the hydroxo oxygen. [Co(II)H31(OH)](2-) and [Fe(II)H31(OH)](2-) have one-electron redox processes at -0.74 and -1.40 V vs SCE. Both complexes can be chemically oxidized to yield their corresponding M(III)-OH complexes. [Co(III)H31(OH)](1-), with an S = 1 ground state, is a rare example of a paramagnetic Co(III) complex.

Carborane-containing liquid crystals: synthesis and structural, conformational, thermal, and spectroscopic characterization of diheptyl and diheptynyl derivatives of p-carboranes.

Molecular and electronic structures for four p-carborane derivatives were studied in the context of their liquid crystalline properties. Thus molecular and crystal structures of diheptyl and diheptynyl derivatives of 10- and 12-vertex bi-p-carboranes were determined by X-ray crystallography and compared to the results of ab initio calculations at the HF/6-31G level of theory. Experimentally observed significant positional disorder of one of the substituents in the 10-vertex derivatives, 2[2]a and 2[2]b, was related to conformational properties of the alkyl-carborane bond. Experimental and theoretical studies of the electronic structures were conducted for the four compounds using UV and NMR spectroscopies. The nature of the unique long wavelength absorption band at 232 nm in the diheptynyl derivative 2[2]b was explained using INDO/2//HF/6-31G analysis. The complete assignment of the (13)C signals was accomplished using a long-range coupling technique and was supported by the calculated (HF/6-31G) isotropic shielding tensors. Analysis of absorption spectra, NMR substituent effects, and trends in bond lengths shows generally strong cage-acetylene electronic interactions for the 10-vertex p-carborane, while the 12-vertex p-carborane remains largely electronically isolated. Ab initio calculations revealed that 12-vertex p-carborane has significantly larger electronic polarizability and quadrupole moments than the 10-vertex analogues, which are larger than those for bicyclo[2.2.2]octane compounds. All these results on packing, conformational, and electronic properties form the basis for the discussion of thermal behavior of the four carborane compounds, bicyclo[2.2.2]octane analogues, and some related compounds.

Variable-temperature x-ray structural investigation of [Fe[HC(3,5-Me2pz)3]2](BF4)2 (pz= pyrazolyl ring): observation of a thermally induced spin state change from all high spin to an equal high spin-low spin mixture, concomitant with the onset of nonmerohedral twinning.

The complex [Fe[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2) (pz = pyrazolyl ring) undergoes a phase transition that occurs concomitantly with a thermally induced spin conversion between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states. Above 204 K the compound is completely HS with the structure in the C2/c space group with Z = 4. A crystal structure determination of this phase was performed at 220 K yielding the cell constants a = 20.338(2) A, b = 10.332(1) A, c = 19.644(2) A, beta = 111.097(2) degrees, and V = 3851.5(6) A(3). There is one unique iron(II) site at this temperature. Below 206 K the compound converts to a 50:50 mixture of HS and LS. The radical change in the coordination sphere for half of the iron(II) sites, most notably a shortening of the Fe-N bond distances by ca. 0.2 A, that accompanies this magnetic transition causes a phase transition. The crystal system changes from C-centered monoclinic to primitive triclinic with Z = 2 with two half-molecules on independent inversion centers. A crystal structure determination was performed at 173 K in space group P1 with a = 10.287(2) A, b = 11.355(3) A, c = 18.949(4) A, alpha = 90.852(4) degrees, beta = 105.245(4) degrees, gamma = 116.304(4) degrees, and V = 1892.3(8) A(3). All specimens investigated below the phase transition temperature were determined to be nonmerohedral twins. Temperature cycling between these two forms does not appear to degrade crystal quality. Previous magnetic susceptibility measurements indicate a second, irreversible increase in the magnetic moment the first time the crystals are cooled below 85 K. A crystal structure determination at 220 K of a specimen precooled to 78 K was not significantly different from those not cooled below 220 K.

Atom transfer reactions of (TTP)Ti(eta 2-3-hexyne): synthesis and molecular structure of trans-(TTP)Ti[OP(Oct)3]2.

Atom and group transfer reactions were found to occur between heterocumulenes and (TTP)Ti(eta 2-3-hexyne), 1 (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion). The imido derivatives (TTP)Ti=NR (R = iPr, 2; tBu, 3) were produced upon treatment of complex 1 with iPrN=C=NiPr, iPrNCO, or tBuNCO. Reactions between complex 1 and CS2, tBuNCS, or tBuNCSe afforded the chalcogenido complexes, (TTP)Ti=Ch (Ch = Se, 4; S, 5). Treatment of complex 1 with 2 equiv of PEt3 yielded the bis(phosphine) complex, (TTP)Ti(PEt3)2, 6. Although (TTP)Ti(eta 2-3-hexyne) readily abstracts oxygen from epoxides and sulfoxides, the reaction between 1 and O=P(Oct)3 did not result in oxygen atom transfer. Instead, the paramagnetic titanium(II) derivative (TTP)Ti[O=P(Oct)3]2, 7, was formed. The molecular structure of complex 7 was determined by single-crystal X-ray diffraction: Ti-O distance 2.080(2) A and Ti-O-P angle of 138.43(10) degrees. Estimates of Ti=O, Ti=S, Ti=Se, and Ti=NR bond strengths are discussed.

Three-coordinate copper(II)-phenolate complexes.

The reactions of LCuCl (L = 2,4-bis((2,6-diisopropylphenyl)imido)pentane (L(iPr)), 2,4-bis((2,6-diisopropylphenyl)imido)-3-chloropentane (L(CliPr))) with the phenolates TlOAr (Ar = C(6)H(3)Me(2), C(6)H(4)OMe, C(6)H(4)tBu) and NaOC(6)H(3)(tBu)(2) were explored. Novel three-coordinate Cu(II)-phenolates, LCuOAr, were isolated from the reactions with the thallium phenolates and were characterized by X-ray crystallography and spectroscopy (UV-vis, EPR). The complexes feature short Cu-O(phenolate) distances (average Cu-O = 1.81 A) and, with one exception, irregular N-Cu-O(phenolate) angles that differ within each compound (15 degrees < Delta < 28 degrees, where Delta = angleN(1)-Cu-O - angleN(2)-Cu-O). The exception is L(iPr)Cu(OC(6)H(4)tBu), for which X-ray structures at -100 and 25 degrees C differed due to an unusual reversible phase change with nonmerohedral twinning (2:1 ratio) in the low-temperature form. The high-temperature form has local C(2)(v) symmetry (Delta = 0 degrees ), and upon cooling below the phase transition temperature (-8 +/- 5 degrees C) lateral movement of the phenolate ligand (Delta = 17.6 degrees ) and rotation of the phenolate plane by 10.7 degrees occurs. Resonance Raman spectroscopic data acquired for L(iPr)Cu(OC(6)H(4)tBu) corroborated assignment of phenolate --> Cu(II) LMCT character in the UV-vis spectra. Cyclic voltammetry experiments (THF, 0.5 M NBu(4)PF(6)) revealed negative E(1/2) values for the Cu(II)/Cu(I) couples relative to NHE, consistent with enhanced stabilization of the Cu(II) state by both the strongly electron donating beta-diketiminate ligand and the phenolates. Although thermally stable, the Cu(II)-phenolates are unusually reactive with dioxygen, albeit to give product(s) that have yet to be identified. In the reaction of L(iPr)CuCl with NaOC(6)H(3)(tBu)(2) no Cu(II)-phenolate was observed. Instead, a Cu(I) complex was generated quantitatively by trapping with added isocyanide, [L(iPr)CuNC(C(6)H(3)Me(2))], along with 3,3',5,5'-tetra-tert-butyl-4,4'-dibenzoquinone and 2,6-di-tert-butylphenol in 27 +/- 3% and 46 +/- 6% yields, respectively, corresponding to the overall reaction 4L(iPr)Cu(II)Cl + 4NaOAr --> 4L(iPr)Cu(I) + 4NaCl + dibenzoquinone + 2(phenol).