Comparison of N···I and N···O Halogen Bonds in Organoiodine Cocrystals of Heterocyclic Aromatic Diazine Mono-N-oxides.

A series of cocrystals of halogen bond donors 1,4-diiodotetrafluorobenzene (p-F4DIB) and tetraiodoethylene (TIE) with five aromatic heterocyclic diazine mono-N-oxides based on pyrazine, tetramethylpyrazine, quinoxaline, phenazine, and pyrimidine as halogen bonding acceptors were studied. Structural analysis of the mono-N-oxides allows comparison of the competitive occurrence of N···I vs O···I interactions and the relative strength and directionality of these two types of interactions. Of the aromatic heterocyclic diazine mono-N-oxide organoiodine cocrystals examined, six exhibited 1:1 stoichiometry, forming chains that utilized both N···I and O···I interactions. Two cocrystals presented 1:1 stoichiometry with exclusive O···I interactions. Two cocrystals displayed a 2:1 stoichiometry-one characterized solely by O···I interactions and the other solely by N···I interactions. We have also compared these interactions to those present in the corresponding diazines, some of which we report here and some which have been previously reported. In addition, a computational analysis using density functional theory (M062X/def2-SVPD) was performed on these two systems and has been compared to the experimental results. The calculated complex formation energies were, on average, 4.7 kJ/mol lower for the I···O halogen bonding interaction as compared to the corresponding N···I interaction. The average I···O interaction distances were calculated to be 0.15 Å shorter than the corresponding I···N interactions.

Developing Structural First Principles for Alkylated Triphenylphosphonium-Based Ionic Liquids.

While ionic liquids have proved to be versatile materials for a wide spectrum of applications, e.g., energy, materials, and medicine, several challenges remain concerning the rational design of novel materials. In light of this, a series of four triphenylphosphonium-based ionic liquids have been synthesized for the first time. These compounds exhibit high thermal stability with decomposition temperatures up to 450 °C. Their solid-state structures are characterized by single-crystal X-ray diffraction and the intermolecular interactions rigorously analyzed via Hirshfeld surface analysis. It was found that the unique geometries of the anions used in the study form distinct interactions with the cations. The interactions in the crystalline state are correlated with the thermal properties of the four ionic liquids to rationalize the melting points and phase transitions for each compound. The observed arrangements of the alkyl chains on the cations are investigated computationally to gain an understanding of how rotational freedom may impact the thermal properties of the compounds. By intention, each IL reported in this work offers a unique property profile and contributes to the ever-growing ionic liquid catalog.

Synthesis and Characterization of a Linear Triiron(II) Extended Metal Atom Chain Complex with Fe-Fe Bonds.

Extended metal atom chain (EMAC) complexes of first-row transition metals with metal-metal bonds have the potential to elicit unique magnetic properties and reactivities. Until now, the library of EMAC complexes with late-first-row transition metals was incomplete because of the omission of a triiron species with Fe-Fe bonding. Herein we report the synthesis and preliminary investigation of the first linear, triiron(II) complex containing close Fe-Fe interactions. The complex is supported by three dianionic 2,6-bis[(trimethylsilyl)amido]pyridine ligands (L), with an overall composition of Fe3L3, and pseudohelical ligand coordination stabilizing the local trigonal-planar geometry at each iron. Fe3L3 was characterized by X-ray diffraction, 1H NMR, cyclic voltammetry, electronic absorption, and Mössbauer spectroscopies. Evans method analysis indicated a large uncompensated spin and an S = 6 ground state, suggesting ferromagnetic coupling in the triiron chain, likely due to direct exchange.

Synthesis, characterization, and crystal structures of organonickel(II) complexes coordinated to novel 1-bromo-2,6-bis{[(λ5-phosphanylidene)imino]methyl}benzene NCN-pincer ligands.

A novel family of four 1-bromo-2,6-bis{[(λ5-phosphanylidene)imino]methyl}benzene ligands has been synthesized and characterized. The phosphiniminomethyl substituents are decorated with either three phenyl groups, two phenyl and one cyclohexyl group, one phenyl and two cyclohexyl groups, or three cyclohexyl groups. Each ligand was metallated using zero-valent nickel through an oxidative addition to form a family of organonickel(II) complexes, namely (2,6-bis{[(triphenyl-λ5-phosphanylidene)imino]methyl}phenyl-κ3N,C1,N')bromidonickel(II) dichloromethane hemisolvate, [NiBr(C44H37N2P2)]·0.5CH2Cl2, (2,6-bis{[(cyclohexyldiphenyl-λ5-phosphanylidene)imino]methyl}phenyl-κ3N,C1,N')bromidonickel(II) diethyl ether hemisolvate, [NiBr(C44H49N2P2)]·0.5C4H10O, (2,6-bis{[(dicyclohexylphenyl-λ5-phosphanylidene)imino]methyl}phenyl-κ3N,C1,N')bromidonickel(II), [NiBr(C44H61N2P2)], and (2,6-bis{[(tricyclohexyl-λ5-phosphanylidene)imino]methyl}phenyl-κ3N,C1,N')bromidonickel(II), [NiBr(C44H73N2P2)]. This family of complexes represents a useful opportunity to investigate the impact of incrementally changing the steric characteristics of a complex on its structure and reactivity.

A family of tri- and dimetallic pyridine dicarboxamide cryptates: unusual O,N,O-coordination and facile access to secondary coordination sphere hydrogen bonding interactions.

A series of tri- and dimetallic metal complexes of pyridine dicarboxamide cryptates are reported in which changes to the base and metal source result in diverse structure types. Addition of strong bases, such as KH or KN(SiMe3)2, followed by divalent metal halides allows direct access to trinuclear complexes in which each metal center is coordinated by a dianionic N,N,N-chelate of each arm. These complexes bind a guest K(+) cation within the central cavity in a trigonal planar coordination environment. Minor changes to the solvent and equivalents of base used in the syntheses of the triiron(II) and tricobalt(II) complexes affords two trinuclear clusters with atypical O,N,O-coordination by each pyridine dicarboxamide arm; the amide carbonyl O atoms are oriented toward the interior of the cavity to coordinate to each metal center. Finally, varying the base enables the selective synthesis of dinuclear nickel(II) and copper(II) complexes in which one pyridine dicarboxamide arm remains protonated. These amide protons are at one end of a hydrogen bonding network that extends throughout the internal cavity and terminates at a metal bound hydroxide, carbonate, or bicarbonate donor. In the dinickel complex, the bicarbonate cannot be liberated as CO2 either thermally or upon sparging with N2, which differs from previously reported monometallic complexes. The carbonate or bicarbonate ligands likely arise from sequestration of atmospheric CO2 based on the observed reaction of the di(hydroxonickel) analog.

Preorganized assembly of three iron(II) or manganese(II) ß-diketiminate complexes using a cyclophane ligand.

A trinucleating cyclophane bearing three ß-diketimine arms, and the corresponding iron(II) and manganese(II) complexes have been synthesized and characterized. The three metal ions are oriented towards the internal void space, and are coordinated by a N2Br2 donor set, in which a unique combination of µ(3), µ, and terminal coordination modes are observed for the halide donors.

Synthesis and characterization of a tris(2-hydroxyphenyl)methane-based cryptand and its triiron(III) complex.

Reaction of tris(5-amino-2-ethoxy-3-isopropylphenyl)methane and pyridine-2,6-dicarbonyl-dichloride affords a multi-dentate cryptand in 48% yield. Metallation with iron(III) chloride results in a substantial conformational change of this ligand to give a trianionic triiron(III) complex. Ferric cations line the periphery of the internal cavity with each adopting a square pyramidal N(3)Cl(2) coordination environment.