Synthesis of a Neutral Mixed-Valence Diferrocenyl Carborane for Molecular Quantum-Dot Cellular Automata Applications.

The preparation of 7-Fc(+) -8-Fc-7,8-nido-[C2 B9 H10 ](-) (Fc(+) FcC2 B9 (-) ) demonstrates the successful incorporation of a carborane cage as an internal counteranion bridging between ferrocene and ferrocenium units. This neutral mixed-valence Fe(II) /Fe(III) complex overcomes the proximal electronic bias imposed by external counterions, a practical limitation in the use of molecular switches. A combination of UV/Vis-NIR spectroscopic and TD-DFT computational studies indicate that electron transfer within Fc(+) FcC2 B9 (-) is achieved through a bridge-mediated mechanism. This electronic framework therefore provides the possibility of an all-neutral null state, a key requirement for the implementation of quantum-dot cellular automata (QCA) molecular computing. The adhesion, ordering, and characterization of Fc(+) FcC2 B9 (-) on Au(111) has been observed by scanning tunneling microscopy.

Hydrogen-bonded clusters of 1, 1'-ferrocenedicarboxylic acid on Au(111) are initially formed in solution.

Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of ferrocenedicarboxylic acid (Fc(COOH)2) on the Au(111) surface. The surface is prepared by pulse-deposition of Fc(COOH)2 dissolved in methanol, and the solvent is evaporated before imaging. While the rows of hydrogen-bonded dimers that are common for carboxylic acid species are observed, the majority of adsorbed Fc(COOH)2 is instead found in six-molecule clusters with a well-defined and chiral geometry. The coverage and distribution of these clusters are consistent with a random sequential adsorption model, showing that solution-phase species are determinative of adsorbate distribution for this system under these reaction conditions.

Hydrogen-bonded clusters of ferrocenecarboxylic acid on Au(111).

Self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH) contain two fundamental units, both stabilized by intermolecular hydrogen bonding: dimers and cyclic five-membered catemers. At surface coverages below a full monolayer, however, there is a significantly more varied structure that includes double-row clusters containing two to twelve FcCOOH molecules. Statistical analysis shows a distribution of cluster sizes that is sharply peaked compared to a binomial distribution. This rules out simple nucleation-and-growth mechanisms of cluster formation, and strongly suggests that clusters are formed in solution and collapse into rows when deposited on the Au(111) surface.

Self-assembly of hydrogen-bonded two-dimensional quasicrystals.

The process of molecular self-assembly on solid surfaces is essentially one of crystallization in two dimensions, and the structures that result depend on the interplay between intermolecular forces and the interaction between adsorbates and the underlying substrate. Because a single hydrogen bond typically has an energy between 15 and 35 kilojoules per mole, hydrogen bonding can be a strong driver of molecular assembly; this is apparent from the dominant role of hydrogen bonding in nucleic-acid base pairing, as well as in the secondary structure of proteins. Carboxylic acid functional groups, which provide two hydrogen bonds, are particularly promising and reliable in creating and maintaining surface order, and self-assembled monolayers of benzoic acids produce structure that depends on the number and relative placement of carboxylic acid groups. Here we use scanning tunnelling microscopy to study self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH), and find that, rather than producing dimeric or linear structures typical of carboxylic acids, FcCOOH forms highly unusual cyclic hydrogen-bonded pentamers, which combine with simultaneously formed FcCOOH dimers to form two-dimensional quasicrystallites that exhibit local five-fold symmetry and maintain translational and rotational order (without periodicity) for distances of more than 400 ångströms.

Adsorption of diferrocenylacetylene on Au(111) studied by scanning tunneling microscopy.

Scanning tunneling microscopy images of diferrocenylacetylene (DFA) coadsorbed with benzene on Au(111) show individual and close-packed DFA molecules, either adsorbed alongside benzene or on top of a benzene monolayer. Images acquired over a range of positive and negative tip-sample bias voltages show a shift in contrast, with the acetylene linker appearing brighter than the ferrocenes at positive sample bias (where unoccupied states primarily contribute) and the reverse contrast at negative bias. Density functional theory was used to calculate the electronic structure of the gas-phase DFA molecule, and simulated images produced through two-dimensional projections of these calculations approximate the experimental images. The symmetry of both experimental and calculated molecular features for DFA rules out a cis adsorption geometry, and comparison of experiment to simulation indicates torsion around the inter-ferrocene axis between 90° and 180° (trans); the cyclopentadienyl rings are thus angled with respect to the surface.

catena-Poly[[penta-µ-benzoato-µ-chlorido-dioxanedineodymium(III)] dioxane 2.5-solvate].

The asymmetric unit of the title compound, [Nd(2)(C(6)H(5)COO)(5)Cl(C(4)H(8)O(2))]·2.5C(4)H(8)O(2), consists of two Nd(III) ions bridged by one Cl(-) ion, five benzoate ions and one coordinating 1,4-dioxane mol-ecule. One Nd(III) ion is nine-coordinate, with a very distorted monocapped square-anti-prismatic geometry. It is coordinated by two chelating carboxyl-ate groups, three monodentate carboxyl-ate groups, one chloride ion and one dioxane mol-ecule. A second independent Nd(III) ion is eight-coordinated in a distorted square-anti-prismatic geometry by one chelating carboxyl-ate group, five monodentate carboxyl-ate groups and one chloride ion. The chains of the extended structure are parallel to the crystallographic b axis. There is a small amount of void space which is filled with five disordered dioxane solvent mol-ecules per unit cell. The intensity contribution of the disordered solvent molecules was removed by applying the SQUEEZE procedure in PLATON [Spek (2009). Acta Cryst. D65, 148-155].

Effects of the alkali-metal cation size on molecular and extended structures: formation of coordination polymers and hybrid materials in the homologous series [(4-Et-C6H4OM)·(diox)n], M = Li, Na, K, Rb, Cs.

The complete series of group 1 metal 4-ethylphenoxide (4-Et-C(6)H(4)O(-)) networks have been synthesized using 1,4-dioxane (diox) as a neutral linker. [{(4-Et-C(6)H(4)OLi)(4)·(diox)(2.5)}·diox](∞) (1) and [{(4-Et-C(6)H(4)ONa)(6)·(diox)(3)}(∞)] (2) form 2D and 3D networks, respectively, composed of discrete aggregates linked by diox. Compound 1 forms a hexagonal layered structure with Li(4)O(4) cubanes acting as nodes, whereas compound 2 forms a primitive cubic network (pcu) with Na(6)O(6) hexameric nodes. [{(4-Et-C(6)H(4)OK)(3)·diox}(∞)] (3), [{(4-Et-C(6)H(4)ORb)(2)·(diox)(0.5)}(∞)] (4), and [{(4-Et-C(6)H(4)OCs)(2)·(diox)(0.5)}(∞)] (5) are composed of isostructural 1D inorganic rods that are linked through diox to form pcu-type networks. Compound 5 is the first example of a network built from cesium inorganic rods.

Dramatic effect of aggregation on rates and thermodynamics of stereoisomerization of magnesium enolates.

Thermodynamic stereocontrol of the (hexamethyldisilazide)magnesium enolates of propiophenone in THF is reported. The overall stereoselectivity proves to be very sensitive to concentration, since dimeric species with bridging enolates show no stereoselectivity while monomeric enolates show a very strong thermodynamic preference for the Z enolate. Kinetically, interconversion among aggregates is remarkably slow, whereas stereoisomerization of the monomer, even in the absence of a proton source such as ketone or amine, is remarkably fast. Furthermore, stereoisomerization takes place in the absence of a proton source or excess ketone. These observations contrast with accepted views of these fundamentally important processes and have implications for understanding the identity and reactivity of metal enolates.

Synchrotron study of poly[[di-µ-aqua-(µ-2,2'-bipyridyl-5,5'-dicarboxyl-ato)di-potassium] dihydrate].

The title compound, {[K(2)(C(12)H(6)N(2)O(4))(H(2)O)(2)]·2H(2)O}(n), forms a three-dimensional coordination polymer in the solid state. The asymmetric unit consists of one K(+) ion, half of a 2,2'-bipyridyl-5,5'-dicarboxyl-ate ligand, one coordinated water mol-ecule and one solvent water mol-ecule. The K(+) ion is 7-coordinated by the oxygen atoms of two water mol-ecules and by five oxygen atoms of four carboxyl-ate groups, one of which is chelating. The extended structure can be described as a binodal network in which each K(+) is a six-connected node, bonding to four carboxyl-ate groups and two bridging water mol-ecules, and the 2,2'-bipyridyl-5,5'-dicarboxyl-ate linkers are eight-connected nodes, with each carboxyl-ate group bridging four metal centers. Overall, this arrangement generates a complex network with point symbol {3(4).4(12).5(12)}{3(4).4(4).5(4).6(3)}(2). Both of the bridging water mol-ecules participate as donors in hydrogen-bonding inter-actions; one to solvent water mol-ecules and a second to an oxygen atom of a carboxyl-ate group.

High-connectivity networks and hybrid inorganic rod materials built from potassium and rubidium p-halide-substituted aryloxides.

A series of complex networks have been synthesized from the association of potassium and rubidium p-halide-substituted aryloxides using 1,4-dioxane molecules as neutral linkers. The crystalline polymers [(4-F-C6H4OK)6 x (dioxane)4]infinity (1), [(4-I-C6H4OK)6 x (dioxane)6]infinity (2), and [(4-I-C6H4ORb)6 x (dioxane)6]infinity (3) are built from discreet, hexameric M6O6 aggregates. Compound 1 forms an unusual 16-connected framework involving both K-F and K-O(diox) interactions. Each hexamer connects to eight neighboring aggregates through double-bridging contacts, resulting in a body-centered cubic (bcu) topology. Compounds 2 and 3 are isostructural, 12-connected networks, where each aggregate utilizes six dioxane double bridges to form primitive cubic (pcu) nets. In contrast, the complexes [(4-Cl-C6H4OK)3 x (dioxane)]infinity (4), [(4-Br-C6H4OK)2 x (dioxane)0.5]infinity (5), and [(4-Br-C6H4ORb)5 x (dioxane)5]infinity (6) are built from one-dimensional (1D) inorganic rods composed solely of M-O(Ar) interactions. The extended structures of both 4 and 5 can be described as pcu nets, where parallel 1D inorganic pillars are connected through dioxane bridges. Compound 6 is also composed of parallel 1D inorganic rods, but in this instance the coordinated dioxane molecules do not bridge, resulting in isolated, close-packed chains in the solid state.

Manipulation of molecular aggregation and supramolecular structure using self-assembled lithium mixed-anion complexes.

A set of zero-, one-, two-, and three-dimensional materials have been synthesized by systematically varying the stoichiometry of the two components 2,4,6-Me3-C6H2OLi (ArOLi) and Me2N(CH2)(2)OLi (ROLi) within single aggregates, while using 1,4-dioxane (diox) as a ditopic linker. The homoleptic complex [{(ArOLi)4 x (diox)2} superset3(diox)](infinity) 1 forms a 3D diamondoid extended structure, where Li4O4 cubanes act as tetrahedral nodes. Attempts to rationally alter the dimensionality of the network through the sequential replacement of ArOLi vertices by potentially chelating ROLi units have succeeded. The mixed-anion complexes [{(ROLi)(ArOLi)3 x (diox)(1.5)} superset1/2(C6H14)](infinity) 2 and [(ROLi)4(ArOLi)2 x (diox)](infinity) 4 , adopt 2D hexagonal net and 1D chain structures respectively. Furthermore, the two complexes [{(ROLi)3(ArOLi)3 x (diox)(0.5)}(C6H14)](infinity) 3 and [(ROLi) 5(ArOLi) x (diox)(0.5)](infinity) 5 both form unusual 0D molecular dumbbell structures in the solid state. Incorporation of multiple ROLi units in the mixed-anion complexes not only results in reducing the number of possible sites for polymer extension through chelation, but also changes the aggregation state of the building block from tetrametallic Li4O4 units to hexametallic Li6O6 units.

Homo- and heterodimetallic geminal dianions derived from the bis(phosphinimine) {Ph2P(NSiMe3)}2CH2 and the alkali metals Li, Na, and K.

The geminal organodimetallic complexes [({Ph2P(NSiMe3)}2C)2M4], where M4=Na4, 3; Li2Na2, 4; LiNa3, 5; Li2K2, 6; Na2K2, 7, and Na3K, 8, have been prepared through a variety of methods including direct or sequential deprotonation of the neutral ligand with strong bases (tBuLi, nBuNa, (Me3Si)2NNa, PhCH2K or (Me3Si)2NK), transmetalation of the homometallic derivatives (M4=Li4, 2 or Na4, 3) with tBuONa or tBuOK, and by cation exchange upon mixing the homometallic complexes in an arene solution. Complexes 3-8 have been characterized by single-crystal X-ray diffraction and are found to form a homologous series of dimeric structures in the solid-state, in accord with the previously reported structure of 2. Each complex is composed of a plane of four metals, M4, in which the ligands adopt capping positions to form distorted M4C2 octahedral cores. The metals in homometallic complexes 2 and 3 define an approximate square, whereas the heterometallic derivatives 4-8 have distinctly rhombic arrangements. The lighter metals in 4-8 interact strongly with the carbanions and the heavier metals are pushed towards the periphery of the structures. 1H, 13C, 7Li, 31P, and 29Si multinuclear NMR spectroscopic studies, cryoscopic measurements, and electrospray ionization-mass spectroscopic studies are consistent with the dimers being retained in solution. Dynamic solution behavior was discovered for Li2Na2 complex 4, in which all five possible tetrametallic derivatives Li4, Li3Na, Li2Na2, LiNa3 and Na4 coexist. Density functional theory (DFT) and natural bond order (NBO) calculations in association with natural population analyses (NPA) reveal significant differences in the electronic structures of the variously metalated dianions. The smaller cations are more effective in localizing the double negative charge on the carbanion (in the form of two lone pairs), leading to differences in the distribution of the electron density within the ligand backbones. In turn, a complex interplay of hyperconjugation, electrostatics and metal-ligand interactions is found to control the resulting electronic structures of the geminal organodimetallic complexes.

High-connectivity networks: characterization of the first uninodal 9-connected net and two topologically novel 7-connected nets.

Ring and cage aggregates containing the large alkali metals potassium or rubidium have proven to be excellent building blocks for the creation of high-connectivity nets, as demonstrated by their use as septahedral and nonahedral nodes in synthesis of two new types of 7-connected nets and the first ever example of a 9-connected net.

X-ray and neutron diffraction studies of water-encapsulated inside potassium aryloxide aggregates: complementary host-guest stabilization of mono- and dihydrated cages.

The controlled hydrolysis of potassium 2-tert-butylphenoxide or 2-isopropylphenoxide leads to the unexpected encapsulation of the water inside K6O6 hexameric drum aggregates. Encapsulation of the neutral molecules is enabled in these instances through the formation of strong hydrogen bonds and dative interactions between the host and guest.

Assembly of a homochiral, body-centered cubic network composed of vertex-shared Mg12 cages: use of electrospray ionization mass spectrometry to monitor metal carboxylate nucleation.

Reaction of Mg(NO3)2.6H2O with (+)-camphoric acid (H2cam) in acetonitrile results in the immediate formation of soluble, dimetallic [Mg2(Hcam)3]+ cations. The formation of these stable cations in solution was determined by electrospray ionization mass spectrometry (ESI-MS). These dimers are 3-fold paddle-wheels, which associate together through the neutral acid units to build the metal-organic framework [Mg2(Hcam)3.3H2O].NO3.MeCN, 1. The network consists of a series of fused Mg12 cages that have 12 water molecules at their centers, creating isolated 0D cavities within the structure. Overall, the extended structure of 1 is a body-centered cubic (bcu) lattice, with the Mg12 cages being utilized as eight-connected nodes. The framework of 1 is chiral and adopts the very unusual space group I23. Use of 1,3-propanediol as an additive results in the formation of the simple 1D polymer [Mg(cam){HO(CH2)3OH}2], 2. In 2, each carboxylate-bridged metal center is chelated by two diols. ESI-MS studies confirm the formation of new ions in these solutions. The identities of 1 and 2 were confirmed by a combination of single-crystal X-ray diffraction, elemental analyses, IR, NMR, themogravimetric analyses, and ESI-MS data. ESI-MS has proven to be a valuable technique in the identification of stable SBUs in solution prior to network formation.

Synthesis, structure, and computational studies of the tetrameric magnesium imides [2,4,6-Cl3C6H2NMg.S]4 (S=1,4-dioxane and tetrahydrofuran).

The magnesium imide complexes [(ArNMg.diox)4.3(diox)] (4) and [(ArNMg.THF)4.tol] (5) (where Ar=2,4,6-Cl3C6H2, diox=1,4-dioxane, and THF=tetrahydrofuran) were prepared by the equimolar reaction of Bu2Mg with the primary amine in suitable solvent mixtures. The successful synthesis of the halide-substituted imides is notable because similar reactions with the less acidic organo-substituted anilines cease upon monodeprotonation. Both 4 and 5 form unusual Mg4N4 cubane aggregates in the solid state. Computational studies (HF/6-31G*) indicate that a combination of sterics and metal solvation determines the aggregation state adopted.

Organometallic polymers assembled from cation-pi interactions: use of ferrocene as a ditopic linker within the homologous series [{(Me3Si)2NM}2.(Cp2Fe)]infinity (M=Na, K, Rb, Cs; Cp=cyclopentadienyl).

Addition of ferrocene to solutions of alkali metal hexamethyldisilazides M(HMDS) in arenes (in which M=Na, K, Rb, Cs) allows the subsequent crystallization of the homologous series of compounds [{(Me(3)Si)(2)NM}(2) (Cp(2)Fe)](infinity) (1-4). Similar reactions using LiHMDS led to the recrystallization of the starting materials. The crystal structures of 1-4 reveal the formation of one-dimensional chains composed of dimeric [{M(HMDS)}(2)] aggregates, which are bridged through neutral ferrocene molecules by eta(5)-cation-pi interactions. In addition, compounds 3 and 4 also contain interchain agostic M--C interactions, producing two-dimensional 4(4)-nets. Whereas 1 and 2 were prepared from toluene, the syntheses of 3 and 4 required the use of tert-butylbenzene as the reaction media. The attempted crystallization of 3 and 4 from toluene resulted in formation of the mixed toluene/ferrocene solvated complexes [{(Me(3)Si)(2)NM)(2)}(2) (Cp(2)Fe)(x)(Tol)(y)](infinity) (in which M=Rb, x=0.6, y=0.8, 5; M=Cs, x=0.5, y=1, 6). The extended solid-state structures of 5 and 6 are closely related to the 4(4)-sheets 3 and 4, but are now assembled from a combination of cation-pi, agostic, and pi-pi interactions. The charge-separated complex [K{(C(6)H(6))(2)Cr}(1.5)(Mes)][Mg(HMDS)(3)] (15) was also structurally characterized and found to adopt an anionic two-dimensional 6(3)-network through doubly eta(3)-coordinated bis(benzene)chromium molecules. DFT calculations at the B3 LYP/6-31G* level of theory indicate that the binding energies of both ferrocene and toluene to the M(HMDS) dimers increases in the sequence Li

Direct and efficient one-pot preparation of ketones from aldehydes using N-tert-butylphenylsulfinimidoyl chloride.

A general, one-pot process has been established to prepare ketones from aldehydes using N-tert-butylphenylsulfinimidoyl chloride. By employing the developed protocol, a range of unsymmetrical ketones has been prepared in good yields from aldehydes in one simple synthetic operation. [reaction: see text]

Kinetics and mechanism of ketone enolization mediated by magnesium bis(hexamethyldisilazide).

Magnesium bis(hexamethyldisilazide), Mg(HMDS)(2), reacts with substoichiometric amounts of propiophenone in toluene solution at ambient temperature to form a 74:26 mixture of the enolates (E)- and (Z)-[(HMDS)(2)Mg(2)(mu-HMDS){mu-OC(Ph)=CHCH(3)}], (E)-1 and (Z)-1, which contain a pair of three-coordinate metal centers bridged by an amide and an enolate group. The compositions of (E)-1 and (Z)-1 were confirmed by solution NMR studies and also by crystallographic characterization in the solid state. Rate studies using UV-vis spectroscopy reveal the rapid and complete formation of a reaction intermediate, 2, between the ketone and magnesium, which undergoes first-order decay with rate constants independent of the concentration of excess Mg(HMDS)(2) (DeltaH++ = 17.2 +/- 0.8 kcal/mol, DeltaS++ = -11 +/- 3 cal/mol.K). The intermediate 2 has been characterized by low-temperature (1)H NMR, diffusion-ordered NMR, and IR spectroscopy and investigated by computational studies, all of which are consistent with the formulation of 2 as a three-coordinate monomer, (HMDS)(2)Mg{eta(1)-O=C(Ph)CH(2)CH(3)}. Further support for this structure is provided by the synthesis and structural characterization of two model ketone complexes, (HMDS)(2)Mg(eta(1)-O=C(t)Bu(2)) (3) and (HMDS)(2)Mg{eta(1)-O=C((t)Bu)Ph} (4). A large primary deuterium isotope effect (k(H)/k(D) = 18.9 at 295 K) indicates that proton transfer is the rate-limiting step of the reaction. The isotope effect displays a strong temperature dependence, indicative of tunneling. In combination, these data support the mechanism of enolization proceeding through the single intermediate 2 via intramolecular proton transfer from the alpha carbon of the bound ketone to the nitrogen of a bound hexamethyldisilazide.

Synthesis, structural characterization, gas sorption and guest-exchange studies of the lightweight, porous metal-organic framework alpha-[Mg3(O2CH)6].

Unsolvated magnesium formate crystallizes upon reaction of the metal nitrate with formic acid in DMF at elevated temperatures. Single-crystal XRD studies reveal the formation of [Mg3(O2CH)6 [symbol: see text] DMF], 1, a metal-organic framework with DMF molecules filling the channels of an extended diamondoid lattice. The DMF molecules in 1 can be entirely removed without disruption to the framework, giving the guest-free material alpha-[Mg3(O2CH)6], 2. Compound 2 has been characterized by both powder and single-crystal XRD studies. Thermogravimetric analyses of 1 show guest loss from 120 to 190 degrees C, with decomposition of the sample at approximately 417 degrees C. Gas sorption studies using both N2 and H2 indicate that the framework displays permanent porosity. The porosity of the framework is further demonstrated by the ability of 2 to uptake a variety of small molecules upon soaking. Single-crystal XRD studies have been completed on the six inclusion compounds [Mg3(O2CH)6 [symbol: see text] THF], 3; [Mg3(O2CH)6 [symbol: see text] Et2O], 4; [Mg3(O2CH)6 [symbol: see text] Me2CO], 5; [Mg3(O2CH)6 [symbol: see text] C6H6], 6; [Mg3(O2CH)6 [symbol: see text] EtOH], 7; and [Mg3(O2CH)(6) [symbol: see text] MeOH], 8. Analyses of the metrical parameters of 1-8 indicate that the framework has the ability to contract or expand depending on the nature of the guest present.