Marilyn M. Olmstead

A Distorted Tetrahedral Metal Oxide Cluster inside an Icosahedral Carbon Cage. Synthesis, Isolation, and Structural Characterization of Sc4(μ3-O)2@Ih-C80

The remarkably large cluster Sc4(mu3-O)2 has been obtained trapped inside an Ih-C80 cage by conducting the vaporization of graphite rods doped with copper(II) nitrate and scandium(III) oxide in an electric arc under a low pressure helium atmosphere with an added flow of air. The product has been isolated by chromatography and identified by high-resolution mass spectrometry. The structure of Sc4(mu3-O)2@Ih-C80 has been determined by X-ray crystallography on a crystal of Sc4(mu3-O)2@Ih-C80.NiII(OEP).2(C6H6). The Sc4(mu3-O)2 unit consists of a distorted tetrahedron of scandium atoms with oxygen atoms bridging two of its faces. The Sc-Sc distances range from 2.946(7) to 3.379(7) A.

Detection of a Family of Gadolinium-Containing Endohedral Fullerenes and the Isolation and Crystallographic Characterization of One Member as a Metal−Carbide Encapsulated inside a Large Fullerene Cage

A series of di-gadolinium endohedrals that extends from Gd(2)C(90) to Gd(2)C(124) has been detected by mass spectrometry of the o-dichlorobenzene extract of the carbon soot produced by direct current arcing of graphite rods filled with a mixture of Gd(2)O(3) and graphite powder. Chromatographic separation has led to the isolation of pure samples of two isomers of Gd(2)C(94) and the complete series from Gd(2)C(96) to Gd(2)C(106). Endohedral fullerenes of the type M(2)C(2n) can exist as the conventional endohedral, M(2)@C(2n), or as the carbide-containing endohedral, M(2)C(2)@C(2n-2). Crystallographic characterization of the more rapidly eluting isomer of Gd(2)C(94) reveals that it possesses the carbide structure, Gd(2)C(2)@D(3)(85)-C(92). Computational studies suggest that the more slowly eluting isomer of Gd(2)C(94) may be a conventional endohedral, Gd(2)@C(2)(121)-C(94).

Glowing gold rings: solvoluminescence from planar trigold(I) complexes

Abstract Colorless crystals of the cyclic trigold(I) complex, Au 3 (CH 3 OCNCH 3 ) 3 , that have previously been irradiated with low energy ultraviolet light, emit bright flashes of yellow light when they make contact with a solvent such as chloroform or acetone. Spectroscopic data as well as information on solvoluminescence for this trinuclear complex are presented herein. The origin of the solvoluminescence is considered in the context of the solid state structure of the complex which shows that these triangular complexes pack to form extended trigonal prismatic columns.

Sc2(μ2-O) Trapped in a Fullerene Cage: The Isolation and Structural Characterization of Sc2(μ2-O)@Cs(6)-C82 and the Relevance of the Thermal and Entropic Effects in Fullerene Isomer Selection

The new endohedral fullerene, Sc(2)(mu(2)-O)@C(s)(6)-C(82), has been isolated from the carbon soot obtained by electric arc generation of fullerenes utilizing graphite rods doped with 90% Sc(2)O(3) and 10% Cu (w/w). Sc(2)(mu(2)-O)@C(s)(6)-C(82) has been characterized by single crystal X-ray diffraction, mass spectrometry, and UV/vis spectroscopy. Computational studies have shown that, among the nine isomers that follow the isolated pentagon rule (IPR) for C(82), cage 6 with C(s) symmetry is the most favorable to encapsulate the cluster at T > 1200 K. Sc(2)(mu(2)-O)@C(s)(6)-C(82) is the first example in which the relevance of the thermal and entropic contributions to the stability of the fullerene isomer has been clearly confirmed through the characterization of the X-ray crystal structure.

Highly emitting near-infrared lanthanide "encapsulated sandwich" metallacrown complexes with excitation shifted toward lower energy.

Near-infrared (NIR) luminescent lanthanide complexes hold great promise for practical applications, as their optical properties have several complementary advantages over organic fluorophores and semiconductor nanoparticles. The fundamental challenge for lanthanide luminescence is their sensitization through suitable chromophores. The use of the metallacrown (MC) motif is an innovative strategy to arrange several organic sensitizers at a well-controlled distance from a lanthanide cation. Herein we report a series of lanthanide “encapsulated sandwich” MC complexes of the form Ln3+[12-MCZn(II),quinHA-4]2[24-MCZn(II),quinHA-8] (Ln3+[Zn(II)MCquinHA]) in which the MC framework is formed by the self-assembly of Zn2+ ions and tetradentate chromophoric ligands based on quinaldichydroxamic acid (quinHA). A first-generation of luminescent MCs was presented previously but was limited due to excitation wavelengths in the UV. We report here that through the design of the chromophore of the MC assembly, we have significantly shifted the absorption wavelength toward lower energy (450 nm). In addition to this near-visible inter- and/or intraligand charge transfer absorption, Ln3+[Zn(II)MCquinHA] exhibits remarkably high quantum yields, long luminescence lifetimes (CD3OD; Yb3+, QLnL = 2.88(2)%, τobs = 150.7(2) μs; Nd3+, QLnL = 1.35(1)%, τobs = 4.11(3) μs; Er3+, QLnL = 3.60(6)·10–2%, τobs = 11.40(3) μs), and excellent photostability. Quantum yields of Nd3+ and Er3+ MCs in the solid state and in deuterated solvents, upon excitation at low energy, are the highest values among NIR-emitting lanthanide complexes containing C–H bonds. The versatility of the MC strategy allows modifications in the excitation wavelength and absorptivity through the appropriate design of the ligand sensitizer, providing a highly efficient platform with tunable properties.

Is the Isolated Pentagon Rule Merely a Suggestion for Endohedral Fullerenes? The Structure of a Second Egg-Shaped Endohedral Fullerene—Gd3N@Cs(39663)-C82

The structure of Gd3N@Cs(39663)-C82 has been determined through single crystal X-ray diffraction on Gd3N@Cs(39663)-C82.NiII(OEP).2(C6H6) The carbon cage has a distinct egg shape because of the presence of a single pair of fused pentagons at one apex of the molecule. Although 9 IPR structures are available to the C82 cage, one of the 39709 isomeric structures that do not conform to the IPR was found in Gd3N@Cs(39663)-C82. The egg-shaped structure of Gd3N@Cs(39663)-C82 is similar to that observed previously for M3N@Cs(51365)-C84 (M = Gd, Tm, Tb). As noted for other non-IPR endohedral fullerenes, one Gd atom in Gd3N@Cs(39663)-C82 is nestled within the fold of the fused pentagons.

The Shape of the Sc2(μ2-S) Unit Trapped in C82: Crystallographic, Computational and Electrochemical Studies of the Isomers, Sc2(μ2-S)@Cs(6)-C82 and Sc2(μ2-S)@C3v(8)-C82

Single-crystal X-ray diffraction studies of Sc(2)(μ(2)-S)@C(s)(6)-C(82)·Ni(II)(OEP)·2C(6)H(6) and Sc(2)(μ(2)-S)@C(3v)(8)-C(82)·Ni(II)(OEP)·2C(6)H(6) reveal that both contain fully ordered fullerene cages. The crystallographic data for Sc(2)(μ(2)-S)@C(s)(6)-C(82)·Ni(II)(OEP)·2C(6)H(6) show two remarkable features: the presence of two slightly different cage sites and a fully ordered molecule Sc(2)(μ(2)-S)@C(s)(6)-C(82) in one of these sites. The Sc-S-Sc angles in Sc(2)(μ(2)-S)@C(s)(6)-C(82) (113.84(3)°) and Sc(2)(μ(2)-S)@C(3v)(8)-C(82) differ (97.34(13)°). This is the first case where the nature and structure of the fullerene cage isomer exerts a demonstrable effect on the geometry of the cluster contained within. Computational studies have shown that, among the nine isomers that follow the isolated pentagon rule for C(82), the cage stability changes markedly between 0 and 250 K, but the C(s)(6)-C(82) cage is preferred at temperatures ≥250 °C when using the energies obtained with the free encapsulated model (FEM). However, the C(3v)(8)-C(82) cage is preferred at temperatures ≥250 °C using the energies obtained by rigid rotor-harmonic oscillator (RRHO) approximation. These results corroborate the fact that both cages are observed and likely to trap the Sc(2)(μ(2)-S) cluster, whereas earlier FEM and RRHO calculations predicted only the C(s)(6)-C(82) cage is likely to trap the Sc(2)(μ(2)-O) cluster. We also compare the recently published electrochemistry of the sulfide-containing Sc(2)(μ(2)-S)@C(s)(6)-C(82) to that of corresponding oxide-containing Sc(2)(μ(2)-O)@C(s)(6)-C(82).

Near-Infrared Light Activated Release of Nitric Oxide from Designed Photoactive Manganese Nitrosyls: Strategy, Design, and Potential as NO Donors

Two new manganese complexes derived from the pentadentate ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-quinoline-2-carboxamide, PaPy2QH, where H is dissociable proton), namely, [Mn(PaPy2Q)(NO)]ClO4 (2) and [Mn(PaPy2Q)(OH)]ClO4 (3), have been synthesized and structurally characterized. The Mn(III) complex [Mn(PaPy2Q)(OH)]ClO4 (3), though insensitive to dioxygen, reacts with nitric oxide (NO) to afford the nitrosyl complex [Mn(PaPy2Q)(NO)]ClO4 (2) via reductive nitrosylation. This diamagnetic {Mn-NO}6 nitrosyl exhibits nuNO at 1725 cm-1 and is highly soluble in water, with lambdamax at 500 and 670 nm. Exposure of solutions of 2 to near-infrared (NIR) light (810 nm, 4 mW) results in bleaching of the maroon solution and detection of free NO by an NO-sensitive electrode. The quantum yield of 2 (Phi = 0.694 +/- 0.010, lambdairr = 550 nm, H2O) is much enhanced over the first generation {Mn-NO}6 nitrosyl derived from analogous polypyridine ligand, namely, [Mn(PaPy3)(NO)]ClO4 (1, Phi = 0.385 +/- 0.010, lambdairr = 550 nm, H2O), reported by this group in a previous account. Although quite active in the visible range (500-600 nm), 1 exhibits very little photoactivity under NIR light. Both 1 and 2 have been incorporated into sol-gel (SG) matrices to obtain nitrosyl-polymer composites 1.SG and 2.SG. The NO-donating capacities of the polyurethane-coated hybrid materials 1.HM and 2.HM have been determined. 2.HM has been used to transfer NO to reduced myoglobin with 780 nm light. The various strategies for synthesizing photosensitive metal nitrosyls have been discussed to establish the merits of the present approach. The results of the present study confirm that proper ligand design is a very effective way to isolate photoactive manganese nitrosyls that could be used to deliver NO to biological targets under the control of NIR light.

Molecular Accordion: Vapoluminescence and Molecular Flexibility in the Orange and Green Luminescent Crystals of the Dimer, Au2(μ-bis-(diphenylphosphino)ethane)2Br2

Solutions containing the components Au(+), dppe (dppe is bis(diphenylphosphino)ethane), and Br(-) in a 1:1:1 ratio can produce three different types of crystals: type A, orange luminescent solvates of the dimer Au(2)(dppe)(2)Br(2) (Au(2)(μ-dppe)(2)Br(2)·2(OSMe(2)), Au(2)(μ-dppe)(2)Br(2)·2(OCMe(2)), Au(2)(μ-dppe)(2)Br(2)·2(CH(2)Cl(2)), Au(2)(μ-dppe)(2)Br(2)·2(HC(O)NMe(2))); type B, green luminescent solvates of the same dimer (Au(2)(μ-dppe)(2)Br(2)·(NCMe) and Au(2)(μ-dppe)(2)Br(2)·0.5(C(4)H(10)O)); and type C, orange luminescent solvates of a polymer ({Au(μ-dppe)Br}(n)·0.5(C(4)H(10)O) and {Au(μ-dppe)Br}(n)·(CH(2)Cl(2))). Some crystals of types A are solvoluminescent. Exposure of type A crystals of Au(2)(μ-dppe)(2)Br(2)·2(OCMe(2)) or Au(2)(μ-dppe)(2)Br(2)·2(CH(2)Cl(2)) to air or vacuum results in the loss of the orange luminescence and the formation of new green luminescent crystals. Subsequent exposure of these crystals to acetone or dichloromethane vapor results in the reformation of crystals of type A. The dimeric complexes in crystals of types A and B are all centrosymmetric and share a common ring conformation. Within these dimers, the coordination geometry of each gold center is planar with a P(2)Br donor set. In other respects, the Au(2)(μ-dppe)(2)Br(2) molecule is remarkably flexible and behaves as a molecular accordion, whose dimensions depend upon the solvate content of a particular crystalline phase. In particular, the dimer Au(2)(μ-dppe)(2)Br(2) is able to accommodate Au···Au separations that range from 3.8479(3) to 3.0943(2) Å, and these variations along with alterations in the Au-Br distances and in the P-Au-P angles are the likely causes of the differences in the luminescence properties of these crystals.

The Correct Structure of Aquatolide—Experimental Validation of a Theoretically-Predicted Structural Revision

Aquatolide has been reisolated from its natural source, and its structure has been revised on the basis of quantum-chemical NMR calculations, extensive experimental NMR analysis, and crystallography.