Structure and Luminescence Studies of Salts of the Helical Dication, [Au2(μ-bis(diphenylphosphine)ethane)2]2+ and Comparison with Salts of [Au2(μ-bis(diphenylphosphine)propane)2]2

Six salts ([Au2(μ-dppe)2](BF4)2·CHCl3, [Au2(μ-dppe)2](BF4)2·1,2-Cl2C2H4, [Au2(μ-dppe)2](PF6)2·CHCl3, [Au2(μ-dppe)2](PF6)2, [Au2(μ-dppe)2](SbF6)2, and [Au2(μ-dppe)2](OTf)2·2CHCl3), (dppe is bis(diphenylphosphine)ethane) containing the dication, [Au2(μ-dppe)2]2+, have been prepared and structurally characterized by single-crystal X-ray crystallography. Unlike the three-coordinate dppe-bridged dimers, Au2X2(μ-dppe)2 (X = Br, I), which show considerable variation in the distance between the gold(I) ions over the range 3.0995(10) to 3.8479(3) Å in various solvates, the structure of the helical dication, [Au2(μ-dppe)2], in the new salts is remarkably consistent with the Au···Au separation falling in the narrow range 2.8787(9) to 2.9593(5) Å. In the solid state, the six crystals display a green luminescence both at room temperature and at 77 K, which has been assigned as phosphorescence. However, solutions of the dication are not luminescent. Salts containing the analogous dication [Au2(μ-dppp)2](PF6)2 (dppp is bis(diphenylphosphine)propane) have been prepared to determine whether the longer bridging ligand might also twist into a helical shape. These salts include [Au2(μ-dppp)2](OTf)2 (OTf is triflate) and three crystalline forms of [Au2(μ-dppp)2](PF6)2: the solvate [Au2(μ-dppp)2](PF6)2·(CHCl3) and two polymorphs of the unsolvated salt. None of these crystals are luminescent, but all contain a similar dication, [Au2(μ-dppp)2]2+, that contains two nearly parallel, linear P-Au-P groups and a long separation between the gold ions that varies from 5.3409(4) to 5.6613(6)Å.

Tb2O@C2(13333)-C74: A Non-Isolated Pentagon Endohedral Fullerene Containing a Nearly Linear Tb-O-Tb Unit

Terbium has been added to the list of elements that form oxide clusters inside fullerene cages. Tb₂O@C₂(13333)-C₇₄ has been isolated as a byproduct of the electric arc synthesis of the azafullerene Tb₂@C₇₉N. Cocrystallization of Tb₂O@C₂(13333)-C₇₄ with Ni(OEP) (where OEP is the dianion of octaethylporphyrin) in toluene yielded black needles of Tb₂O@C₂(13333)-C₇₄·Ni^II(OEP)·1.5C₇H₈ that have been examined by single-crystal X-ray diffraction. The resulting structure shows that a nearly linear Tb-O-Tb unit is contained in a C₂(13333)-C₇₄, which has two sites where pentagons share an edge to form pentalene units at opposite ends of the fullerene. Unlike the usual situations where metal atoms in fullerenes that do not obey the isolated pentagon rule are situated within the folds of the pentalene units, the Tb atoms in Tb₂O@C₂(13333)-C₇₄ are positioned to the side of the pentalene units and near-neighboring hexagons. The magnetic properties of Tb₂O@C₂(13333)-C₇₄ have been examined starting from the experimental geometry, using ab-initio multiconfigurational methods. The computations predict that Tb₂O@C₂(13333)-C₇₄ will show strong axiality, which would make it a single-molecule magnet with a large magnetic anisotropy barrier.

Self-Assembled Encapsulation of CuX2- (X = Br, Cl) in a Gold Phosphine Box-like Cavity with Metallophilic Au-Cu Interactions

Synthetic routes to the crystallization of two new box-like complexes, [Au6(Triphos)4(CuBr2)](OTf)5·(CH2Cl2)3·(CH3OH)3·(H2O)4 (1) and [Au6(Triphos)4 (CuCl2)](PF6)5·(CH2Cl2)4 (2) (triphos = bis(2-diphenylphosphinoethyl)phenylphosphine), have been developed. The two centrosymmetric cationic complexes have been structurally characterized through single-crystal X-ray diffraction and shown to contain a CuX2- (X = Br or Cl) unit suspended between two Au(I) centers without the involvement of bridging ligands. These colorless crystals display green luminescence (λem = 527 nm) for (1) and teal luminescence (λem = 464 nm) for (2). Computational results document the metallophilic interactions that are involved in positioning the Cu(I) center between the two Au(I) ions and in the luminescence.

Reactivity of Nitric Oxide and Nitrosonium Ion with Copper(II/I) Schiff Base Complexes: Mechanistic Aspects of Imine C═N Bond Cleavage and Oxidation of Pyridine-2-aldehyde to Pyridine-2-carboxylic Acid

Four Schiff base ligands of the general formulas [6-(R)-2-pyridyl-N-(2'-methylthiophenyl)methylenimine] (^RL1) and 6-p-chlorophenyl-2-pyridyl-N-(2'-phenylthiophenyl)methylenimine (^RL2), where R = H, Me, p-ClPh, and their bis-ligand copper(II) and copper(I) complexes, 1-4 and 1'-4', respectively, were synthesized and characterized. The reactivities of 1-4 with nitric oxide (NO) gas and of 1'-4' with solid NOBF₄ (NO⁺) were examined in dry acetonitrile in the presence and absence of water (H₂O). The results revealed that, in the absence of H₂O, complexes 1-4 (or 1'-4') reacts with NO (or NOBF₄), leading to imine C═N bond cleavage of both (or one) Schiff base(s) that generates 2 (or 1) equiv of 2-(methyl/phenyl)thiobenzenediazonium perchlorates (5/6) and the corresponding picolaldehyde (^RPial) via a copper nitrosyl of a {CuNO}¹⁰-type intermediate. In the presence of H₂O, the in situ formed ^RPial get oxidized to the corresponding picolinic acid (^RPicH) via an in situ formed LCu^IOH intermediate (LCu^I + HO-NO → LCu^IOH + NO⁺; L = ^RL1/^RL2/^RPic^- and ν_O-H of Cu^IOH = 3650 cm^-1) and subsequently produces, with the aid of NO⁺ oxidant, the picolinate-ligated copper(II) complexes (i) [(^HPic)₂Cu] (7), [(^MePic)₄Cu₃(NO₃)₂]_n·H₂O (8·H₂O), or [(^ClPhPic)₂Cu] (9) when NO reacts with 1-4 or (ii) [(^RPic)Cu^II(^RL1/^RL2)]⁺ when NO⁺ reacts with 1'-4'. The Cu^II to Cu^I reduction of [(^RPic)Cu^II(^RL1/^RL2)]⁺ is essential for C═N cleavage of the remaining ^RL1/^RL2 Schiff base; excess NO can do it. The X-ray structures (1, 1', 3', 5, 7, and 8) and spectroscopic results revealed the role of Cu^II/I, NO, NO⁺, and H₂O, shedding light on the mechanism of C═N bond cleavage and the oxidation of pyridine-2-aldehyde to pyridine-2-carboxylic acid. The reaction of 1 with ¹⁵NO revealed that the terminal N of the N₂⁺ group of 5 originates from ¹⁵NO [ν_{¹⁴N¹⁴N-} = 2248 cm^-1 and ν_{¹⁵N¹⁴N-} = 2212 cm^-1].

Introduction of a (Ph3P)2Pt group into the rim of an open-cage fullerene by breaking a carbon-carbon bond

Treatment of an open-cage fullerene, designated as MMK-9, with (Ph₃P)₄Pt in toluene solution at room temperature allows a (PPh₃)₂Pt unit to be incorporated into the rim of the cage so that it becomes an integral part of the carbon cage skeleton. The structure of the adduct has been determined by single crystal X-ray diffraction and reveals that the platinum atom has planar PtC₂P₂ coordination, rather than the usual η²-bonding to an intact C-C double bond of the fullerene.

Bis(μ-thiolato)-dicopper Containing Fully Spin Delocalized Mixed Valence Copper-Sulfur Clusters and Their Electronic Structural Properties with Relevance to the CuA Site

With aromatic and aliphatic thiol-S donor Schiff base ligands, the copper-sulfur clusters, [(L1)₈Cu^I₆Cu^II₂](ClO₄)₂·DMF·0.5CH₃OH (1) and [(L2)₁₂Cu^I₅Cu^II₁₁(μ₄-S)(μ₄-O)₆](ClO₄)·4H₂O, respectively, have been reported ( Chem. Commun. 2017, 53, 3334); HL1/HL2 are 2-(((3-methylthiophen-2-yl)methylene)amino)benzene/ethanethiol). Complex 1 comprises a wheel shaped Cu₈S₈ framework, made up of interlinked Cu₂{μ-S(R)}₂ units. To understand the properties with relevance to the Cu_A site and to check whether self-assembly generates similar type clusters to 1, three complexes, [(L3)₈Cu^I₆Cu^II₂](ClO₄)₂·(C₂H₅)₂O·2.5H₂O (2), [(L3^Cl)₈Cu^I₆Cu^II₂](ClO₄)₂·1.25(C₂H₅)₂O·1.25CH₃OH·2H₂O (3), and [(L3^CF3)₈Cu^I₆Cu^II₂](ClO₄)₂·2(C₂H₅)₂O·H₂O (4) have been synthesized with supporting ligands HL3^X (HL3 = 2-((furan-2-ylmethylene)amino)benzenethiol when X = -H; X = -Cl or -CF₃ para to thiol-S are HL3^Cl and HL3^CF3 ligands, respectively). The X-ray structures of 3 and 4 feature a similar Cu₈S₈ architecture to 1. The spectroscopic properties and the X-ray structures revealed that 2-4 are fully spin delocalized mixed valence (MV) of class-III type clusters. The structural parameters of the N₂Cu₂{μ-S(R)}₂ units of 3 and 4 closely resemble those of the MV binuclear Cu_A site. With the aid of UV-vis-NIR, EPR, and spectroelectrochemical studies, the electronic properties of these complexes have been described in comparison with the MV model complexes and Cu_A site.

A non-luminescent polymorph of [(cyclohexyl isocyanide)2Au]PF6 that becomes luminescent upon grinding or exposure to dichloromethane vapor

The discovery of a third, non-luminescent crystalline polymorph of [(C6H11NC)2Au]PF6 is reported. Remarkably, crystals of this polymorph are sensitive to mechanical pressure or to exposure to dichloromethane vapor. In both cases, the conversion produces the yellow, green luminescent polymorph of [(C6H11NC)2Au]PF6 and not the colorless, blue luminescent polymorph.

Fullerene nanostructures: how the oblong shape of C70 forms a cocrystal with an enormous asymmetric unit and related cocrystals

Cocrystallization of NiII(OEP) (where OEP is the dianion of octaethylporphyrin) with C70 in p-xylene produces black plates of 12NiII(OEP)·12C70·18p-xylene (1). Single crystal X-ray diffraction at 90 K reveals that the crystal contains 42 individual, well-ordered molecules in the asymmetric unit with distinctive interactions between each NiII(OEP)/C70 pair and each pair of neighboring C70 molecules. Warming the crystal to 186 K produces a phase change so that only four NiII(OEP)/C70 sites and six p-xylene molecules are present. Under the same conditions CuII(OEP) cocrystallizes with C70 to form CuII(OEP)·C70·1.5p-xylene (2) with a much simpler structure consisting of one molecule of the porphyrin and the fullerene along with 1.5 molecules of p-xylene in the asymmetric unit. Crystallization of C70 from toluene in the presence of NiII(etioporphyrin-I) produces the black solvate 6C70·6toluene (3). It seems that C70 has a tendency to crystallize so that several orientations of the oblong molecule are present in the solid.

Seeing luminescence appear as crystals crumble. Isolation and subsequent self-association of individual [(C6H11NC)2Au]+ ions in crystals

Non-luminescent, isostructural crystals of [(C6H11NC)2Au](EF6)·C6H6 (E = As, Sb) lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. Previous studies have shown that the two-coordinate cation, [(C6H11NC)2Au]+, self-associates to form luminescent crystals that contain linear or nearly linear chains of cations and display unusual polymorphic, vapochromic, and/or thermochromic properties. Here, we report the formation of non-luminescent crystalline salts in which individual [(C6H11NC)2Au]+ ions are isolated from one another. In [(C6H11NC)2Au](BArF24) ((BArF24)- is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) each cation is surrounded by two anions that prohibit any close approach of the gold ions. Crystallization of [(C6H11NC)2Au](EF6) (E = As or Sb, but not P) from benzene solution produces colorless, non-emissive crystals of the solvates [(C6H11NC)2Au](EF6)·C6H6. These two solvates are isostructural and contain columns in which cations and benzene molecules alternate. With the benzene molecules separating the cations, the shortest distances between gold ions are 6.936(2) Å for E = As and 6.9717(19) Å for E = Sb. Upon removal from the mother liquor, these crystals crack due to the loss of benzene from the crystal and form luminescent powders. Crystals of [(C6H11NC)2Au](SbF6)·C6H6 that powder out form a pale yellow powder with a blue luminescence with emission spectra and powder X-ray diffraction data that show that the previously characterized [(C6H11NC)2Au](SbF6) is formed. In the process, the distances between the gold(i) ions decrease to ∼3 Å and half of the cyclohexyl groups move from an axial orientation to an equatorial one. Remarkably, when crystals of [(C6H11NC)2Au](AsF6)·C6H6 stand in air, they lose benzene and are converted into the yellow, green-luminescent polymorph of [(C6H11NC)2Au](AsF6) rather than the colorless, blue-luminescent polymorph. Paradoxically, the yellow, green-luminescent powder that forms as well as authentic crystals of the yellow, green-luminescent polymorph of [(C6H11NC)2Au](AsF6) are sensitive to benzene vapor and are converted by exposure to benzene vapor into the colorless, blue-luminescent polymorph.

Unsymmetrical Coordination of Bipyridine in Three-Coordinate Gold(I) Complexes

The unsymmetrical coordination of gold(I) by 2,2'-bipyridine (bipy) in some planar, three-coordinate cations has been examined by crystallographic and computational studies. The salts [(Ph₃P)Au(bipy)]XF₆ (X = P, As, Sb) form an isomorphic series in which the differences in Au-N distances range from 0.241(2) to 0.146(2) Å. A second polymorph of [(Ph₃P)Au(bipy)]AsF₆ has also been found. Both polymorphs exhibit similar structures. The salts [(Et₃P)Au(bipy)]XF₆ (X = P, As, Sb) form a second isostructural series. In this series the unsymmetrical coordination of the bipy ligand is maintained, but the gold ions are disordered over two unequally populated positions that produce very similar overall structures for the cations. Although many planar, three-coordinate gold(I) complexes are strongly luminescent, the salts [(R₃P)Au(bipy)]XF₆ (R = Ph or Et; X = P, As, Sb) are not luminescent as solids or in solution. Computational studies revealed that a fully symmetrical structure for [(Et₃P)Au(bipy)]⁺ is 7 kJ/mol higher in energy than the observed unsymmetrical structure and is best described as a transition state between the two limiting unsymmetrical geometries. The Au-N bonding has been examined by natural resonance theory (NRT) calculations using the "12 electron rule". The dominant Lewis structure is one with five lone pairs on Au and one bond to the P atom, which results in a saturated (12 electron) gold center and thereby inhibits the formation of any classical, 2 e^- bonds between the gold and either of the bipy nitrogen atoms. The nitrogen atoms may instead donate a lone pair into an empty Au-P antibonding orbital, resulting in a three-center, four-electron (3c/4e) P-Au-N bond. The binuclear complex, [μ₂-bipy(AuPPh₃)₂](PF₆)₂, has also been prepared and shown to have an aurophillic interaction between the two gold ions, which are separated by 3.0747(3) Å. Despite the aurophillic interaction, this binuclear complex is not luminescent.

Bond length of perchlorate at different temperatures: X-ray and neutron comparison

The averages (average deviations from the mean are given in square brackets) of uncorrected Cl-O bond distances in a perchlorate anion from an X-ray diffraction analysis of (N-{2-[bis(pyridin-2-ylmethyl)amino]ethyl}pyridine-2-carboxamidato)(nitric oxide)manganese perchlorate acetonitrile disolvate, [Mn(C₂₀H₂₀N₅O)(NO)]ClO₄·2CH₃CN or [Mn(PaPy₃)(NO)]ClO₄·2CH₃CN, decrease from 1.447 [4] Å at 10 K to 1.428 [4] Å at 170 K. The 10 K value is close to the neutron value (1.441 [1] Å) at 18 K. Comparisons are made with a second X-ray study at 30 K [1.444 (8) Å] and to libration-corrected, density functional theory (DFT), and Cambridge Structural Database (CSD) values.

Isolation and Crystallographic Characterization of Two, Nonisolated Pentagon Endohedral Fullerenes: Ho3 N@C2 (22010)-C78 and Tb3 N@C2 (22010)-C78

Purified samples of Ho₃ N@C₂ (22010)-C₇₈ and Tb₃ N@C₂ (22010)-C₇₈ have been isolated by two distinct processes from the rich array of fullerenes and endohedral fullerenes present in carbon soot from graphite rods doped with Ho₂ O₃ or Tb₄ O₇ . Crystallographic analysis of the endohedral fullerenes as cocrystals with Ni(OEP) (in which OEP is the dianion of octaethylporphyrin) shows that both molecules contain the chiral C₂ (22010)-C₇₈ cage. This cage does not obey the isolated pentagon rule (IPR) but has two sites where two pentagons share a common C-C bond. These pentalene units bind two of the metal ions, whereas the third metal resides near a hexagon of the cage. Inside the cages, the Ho₃ N or Tb₃ N unit is planar. Ho₃ N@C₂ (22010)-C₇₈ and Tb₃ N@C₂ (22010)-C₇₈ use the same cage previously found for Gd₃ N@C₂ (22010)-C₇₈ rather than the IPR-obeying cage found in Sc₃ N@D_3h -C₇₈ .

Cleavage of Carbon Disulfide by n-Propyldiphenylphosphine and Nickel(II) Bromide

Carbon disulfide is cleaved by n-propyldiphenylphosphine and nickel(II) bromide in a one-step process, to form two unprecedented complexes: orange, [Ni(S₂ C₂ (Pⁿ PrPh₂ )₂ )Br(Pⁿ PrPh₂ )]Br⋅CS₂ (1) and purple [Ni{η² -SC(Pⁿ PrPh₂ )₂ }Br(Pⁿ PrPh₂ )]Br⋅0.5CS₂ (2). Orange (1) contains a dithiolene-related ligand that results from carbon-carbon bond formation, while purple (2) contains a remarkable ligand in which two n-propyldiphenylphosphine molecules have added to a carbon atom of a CS unit that is coordinated to nickel.

Vapoluminescent Behavior and the Single-Crystal-to-Single-Crystal Transformations of Chloroform Solvates of [Au2 (μ-1,2-bis(diphenylarsino)ethane)2 ](AsF6 )2

The mono- and di-chloroform solvates of [Au₂ (μ-1,2-bis(diphenylarsino)ethane)₂ ](AsF₆ )₂ undergo single-crystal-to-single-crystal transformations that result in gain (over 12 hours) or slow loss (over five years) of only one chloroform molecule. The change in solvation results in changes in the structure and luminescence of the digold cation. The cation consists of a pair of slightly bent As-Au-As units that are connected through the two bridging dpae ligands and by aurophilic interactions with Au⋅⋅⋅Au contacts of 3.05152(15) Å in the disolvate or 2.9570(5) Å in the monosolvate.

Utilization of a Nonemissive Triphosphine Ligand to Construct a Luminescent Gold(I)-Box That Undergoes Mechanochromic Collapse into a Helical Complex

Luminescent gold(I) complexes ([Au₆(Triphos)₄Cl](PF₆)₅·2(CH₃C₆H₅), [Au₆(Triphos)₄Cl](AsF₆)₅·8(CH₃C₆H₅), and [Au₆(Triphos)₄Cl](SbF₆)₅·7(CH₃C₆H₅) where Triphos = bis(2-diphenylphosphinoethyl)phenylphosphine) with a boxlike architecture have been prepared and crystallographically characterized. A chloride ion resides at the center of the box with two of the six gold(I) ions nearby. Mechanical grinding of blue luminescent crystals containing the cation, [Au₆(Triphos)₄Cl]⁵⁺, results in their conversion into amorphous solids with green emission that contain the bridged helicate cation, [μ-Cl{Au₃(Triphos)₂}₂]⁵⁺. A mechanism of the mechanochromic transformation is proposed. The structures of the blue-emitting helicate, [Au₃(Triphos)₂](CF₃SO₃)₃·4(CH₃C₆H₅)·H₂O, and the green-emitting bridged-helicate, [μ-Cl{Au₃(Triphos)₂}₂](PF₆)₅·3CH₃OH have been determined by single crystal X-ray diffraction.

Mixed valence copper-sulfur clusters of highest nuclearity: a Cu8 wheel and a Cu16 nanoball

Fully spin delocalized mixed valence copper-sulfur clusters, 1 and 2, supported by μ₄-sulfido and NS^thiol donor ligands are synthesized and characterized. Wheel shaped 1 consists of Cu₂S₂ units. The unprecedented nanoball 2 can be described as S@Cu₄(tetrahedron)@O₆(octahedron)@Cu₁₂S₁₂(cage) consisting of both Cu₂S₂ and (μ₄-S)Cu₄ units. The Cu₂S₂ and (μ₄-S)Cu₄ units resemble biological Cu_A and Cu_Z sites respectively.

The directional character of the piperazine double addition product, e{N(CH2CH2)2N}2C60, as a building block for forming crystalline fullerene polymers

The piperazine double addition product, ^e{N(CH₂CH₂)₂N}₂C₆₀, has its donor atoms positioned to bind Lewis acids in two orthogonal directions. It has been used to construct crystalline, 1-d and 2-d polymers through reactions with diiodine and the rhodium(ii) acetate dimer.

Insertion of a Transient Tin Nitride into Carbon-Carbon and Boron-Carbon Bonds

A simple exchange reaction between [Ar^iPr4Sn(μ-Cl)]₂ (1) and sodium azide afforded the doubly bridged Sn(II) azide, [Ar^iPr4Sn(μ-N₃)]₂ (2) (Ar^iPr4 = C₆H₃-2,6(C₆H₃-2,6-ⁱPr₂)₂) in 85% yield. Photolysis of a diethyl ether solution of 2 for ca. 16 h yielded an azepinyl-substituted insertion product, [C₆H₃-2-(C₆H₃-2,6-ⁱPr₂)-6-(C₆H₃N-3,7-ⁱPr₂)Sn]₂ (3). The reaction of the Lewis acid, B(C₆F₅)₃ (BCF), or the Lewis base, pyridine, with 2 dissociates the dimer to afford the corresponding complexed monomeric Sn(II) azide, Ar^iPr4SnN₃BCF (4) in which BCF coordinates the α-nitrogen, or Ar^iPr4Sn(pyridine)N₃ (6) in which pyridine coordinates to the tin atom. Photolysis of 4 in diethyl ether for 12 h results in the insertion of the α-nitrogen of the azide group into one of the B-C bonds of the BCF acceptor to yield the tin(II) amide, Ar^iPr4SnN(C₆F₅)B(C₆F₅)₂ (5). In contrast, photolysis of 6 for over 36 h afforded no apparent reaction. A highly reactive Sn nitride intermediate, Ar^iPr4Sn≡N, is proposed as part of the mechanistic pathway for the formation of 3 and 5 as a result of trapping the tin-centered radical isomers. This was effected by immediate freezing the samples of 2 or 4 after ca. 30 min of UV photolysis and recording their electron paramagnetic resonance spectra. These exhibited a rhombic g tensor of [g₁, g₂, g₃] = [2.029, 1.978, 1.933]. This radical intermediate could be related to the valence isomers of the nitride [-Sn^IV≡N] intermediate, in isomeric equilibrium with the nitrene [-Sn^II-N] and nitridyl [-Sn^III═N·] forms, but with the spin density on the nitrogen being quenched, possibly by the H atom abstraction to form an S = 1/2 species of formula -Sn·═N(H).

Unusual C2h -Symmetric trans-1-(Bis-pyrrolidine)-tetra-malonate Hexa-Adducts of C60 : The Unexpected Regio- and Stereocontrol Mediated by Malonate-Pyrrolidine Interaction

A totally unanticipated regio- and stereoisomerically pure C_2h -symmetric trans-1-(bis-pyrrolidine)-tetra-malonate hexa-adduct of C₆₀ was obtained via a topologically controlled method, followed by a 1,3-dipolar cycloaddition reaction. The structures of the products were elucidated by ¹ H and ¹³ C NMR and by X-ray crystallography. The unexpected regio- and stereoselectivity observed, supported by theoretical calculations, was found to be a consequence of malonate-pyrrolidine interactions.

A temperature-dependent phase transformation of (E)-2-[(4-chloro-phen-yl)imino]-ace-naphthylen-1-one

The crystal structure determination based on 90 K data of the title imine ligand revealed non-merohedral twinning with three twin domains. In our experience, this is an indication of an ordering phase transition. Consequently, the structure was redetermined with higher temperature data, and a reversible phase transition was discovered.

The crystal structure determination based on 90 K data of the title imine ligand, C₁₈H₁₀ClNO, revealed non-merohedral twinning with three twin domains. In our experience, this is an indication of an ordering phase transition. Consequently, the structure was redetermined with higher temperature data, and a reversible phase transition was discovered. The higher temperature phase is indeed an ordered structure. At the higher temperature, the 4-chloro­phenyl group has rotated by ca 7° into a crystallographic mirror plane. Warming the crystal from 90 K to 250 K changes the space group from triclinic P-1, to monoclinic P2₁/m. Diverse non-classical inter­actions are present in the crystal packing, and these are described for the phase change reported in this work. The crystal structure of the title imine ligand, measured at 100 K, has been reported on previously [Kovach et al. (2011 ▸). J. Mol. Struct.992, 33–38].

An ordering phase transition, short hydrogen bonds and high Z' in the structure of Ni(Hpydc)2·3H2O

The structure of Ni(Hpydc)₂·3H₂O (H₂pydc = pyridine-2,6-dicarboxylic acid, also known as dipicolinic acid) has been reinvestigated at variable temperatures. At room temperature, it matches the known structure in the space group P2₁/c, but at 180 K it undergoes a phase transformation to a twinned structure in Cc. By 120 K, the structure is ordered and twinned with Z' = 4, and shows interesting short hydrogen-bonding interactions that include the formation of hydroxonium species.

Tin(II) Hydrides as Intermediates in Rearrangements of Tin(II) Alkyl Derivatives

Reactions of the Sn(II) hydrides [ArSn(μ-H)]₂ (1) (Ar = Ar^iPr4 (1a), Ar^iPr6 (1b); Ar^iP4 = C₆H₃-2,6-(C₆H₃-2,6-ⁱPr₂)₂, Ar^iPr6 = C₆H₃-2,6-(C₆H₂-2,4,6-ⁱPr₃)₂) with norbornene (NB) or norbornadiene (NBD) readily generate the bicyclic alkyl-/alkenyl-substituted stannylenes, ArSn(norbornyl) (2a or 2b) and ArSn(norbornenyl) (3a or 3b), respectively. Heating a toluene solution of 3a or 3b at reflux afforded the rearranged species ArSn(3-tricyclo[2.2.1.0^2,6]heptane) (4a or 4b), in which the norbornenyl ligand is transformed into a nortricyclyl group. ¹H NMR studies of the reactions of 4a or 4b with tert-butylethylene indicated the existence of an apparently unique reversible β-hydride elimination from the bicyclic substituted aryl/alkyl stannylenes 2a or 2b and 3a or 3b. Mechanistic studies indicated that the transformation of 3a or 3b into 4a or 4b occurs via a β-hydride elimination of 1a or 1b to regenerate NBD. Kinetic studies showed that the conversion of 3a or 3b to 4a or 4b is first order. The rate constant k for the conversion of 3a into 3b was determined to be 3.33 × 10^-5 min^-1, with an activation energy E_a of 16.4 ± 0.7 kcal mol^-1.

Adamantylidene Addition to M3 N@Ih -C80 (M=Sc, Lu) and Sc3 N@D5h -C80 : Synthesis and Crystallographic Characterization of the [5,6]-Open and [6,6]-Open Adducts

Additions of adamantylidene (Ad) to M₃ N@I_h -C₈₀ (M=Sc, Lu) and Sc₃ N@D_5h -C₈₀ have been accomplished by photochemical reactions with 2-adamantyl-2,3'-[3H]-diazirine (1). In M₃ N@I_h -C₈₀ , the addition led to rupture of the [6,6]- or [5,6]-bonds of the I_h -C₈₀ cage, forming the [6,6]-open fulleroid as the major isomer and the [5,6]-open fulleroid as the minor isomer. In Sc₃ N@D_5h -C₈₀ , the addition also proceeded regioselectively to yield three major isomeric Ad mono-adducts, despite the fact that there are nine types of C-C bonds in the D_5h -C₈₀ cage. The molecular structures of the seven Ad mono-adducts, including the positions of the encaged trimetallic nitride clusters, have been unambiguously determined through single-crystal XRD analyses. Furthermore, results have shown that stepwise addition of Ad to Lu₃ N@I_h -C₈₀ affords several Ad bis-adducts, two of which have been isolated and characterized. The X-ray structure of one bis-adduct clearly revealed that the second Ad addition took place at a [6,6]-bond close to an endohedral metal atom. Theoretical calculations have also been performed to rationalize the regioselectivity.

Piperazine-functionalized C60 and diiodine or iodine monochloride as components in forming supramolecular assemblies

The reaction of the piperazine mono-adduct, N(CH₂CH₂)₂NC₆₀, with diiodine produced well ordered, black crystals of (I₂N(CH₂CH₂)₂NI₂)C₆₀·2.884(C₆H₆)·0.116I₂, which contains two nearly linear N-I-I units. Reaction of N(CH₂CH₂)₂NC₆₀ with iodine monochloride produced two materials: the dihalogen adduct, (ClIN(CH₂CH₂)₂NICl)C₆₀·2.3(CS₂)·0.7(CH₂Cl₂), when crystallization occurred rapidly from carbon disulfide/dichloromethane solution or the salt, [(N(CH₂CH₂)₂NH)C₆₀⁺][ICl₂^-]·CS₂, when crystallization happened more slowly from toluene/dichloromethane solution where hydrolysis of the iodine monochloride by adventitious water presumably occurred.

The design of synthetic superoxide dismutase mimetics: seven-coordinate water soluble manganese(ii) and iron(ii) complexes and their superoxide dismutase-like activity studies

Manganese(ii) and iron(ii) complexes derived from a pentadentate ligand have been characterized and these were utilized for superoxide dismutase-like activity studies.