Homoleptic Rare-Earth-Metal Sandwiches with Dibenzo[,]cyclooctatetraene Dianions.

A family of rare-earth complexes [RE(III) = Y, La, Gd, Tb, Dy, and Er] with doubly reduced dibenzo[,]cyclooctatetraene (DBCOT) has been synthesized and structurally characterized. X-ray diffraction analysis confirms that all products of the [RE(DBCOT)(THF)][RE(DBCOT)] composition consist of the anionic sandwich [RE(DBCOT)] and the cationic counterpart [RE(DBCOT)(THF)]. Within the sandwich, two elongated π decks are slightly bent toward the metal center (avg.

Novel Chelating Agents for Zirconium-89-Positron Emission Tomography (PET) Imaging: Synthesis, DFT Calculation, Radiolabeling, and and Complex Stability.

We report the synthesis and evaluation of novel chelating agents for zirconium-89 (Zr) with positron emission tomography (PET) imaging applications. New chelating agents NODHA, NOTHA, and NODHA-PY were constructed on 1,4,7-triazacyclononane (TACN) and possess hydroxamic acid or a pyridine ring as an acyclic binding moiety. The new chelating agents were theoretically studied for complexation with Zr(IV).

Lanthanide-mediated tuning of electronic and magnetic properties in heterotrimetallic cyclooctatetraenyl multidecker self-assemblies.

The synthesis of a novel family of homoleptic COT-based heterotrimetallic self-assemblies bearing the formula [LnKCa(COT)(THF)] (Ln(iii) = Gd, Tb, Dy, Ho, Er, Tm, and Yb) is reported followed by their X-ray crystallographic and magnetic characterization. All crystals conform to the monoclinic 2/ space group with a slight compression of the unit cell from 3396.4(2) Å to 3373.

Doubly-Reduced Pentacene in Different Coordination Environments: X-ray Crystallographic and Theoretical Insights into Structural and Electronic Changes.

Chemical reduction of pentacene (C H , 1) with Group 1 metals ranging from Li to Cs revealed that 1 readily undergoes a two-fold reduction to afford a doubly-reduced 1 anion in THF. With the help of 18-crown-6 ether used as a secondary coordinating agent, five π-complexes of 1 with different alkali metal counterions have been isolated and fully characterized. This series of complexes enables the first evaluation of alkali-metal ion binding patterns and structural changes of the 1 dianion based on the crystallographically confirmed examples.

Stepwise Generation of Mono-, Di-, and Triply-Reduced Warped Nanographenes: Charge-Dependent Aromaticity, Surface Nonequivalence, Swing Distortion, and Metal Binding Sites.

The stepwise chemical reduction of a molecular warped nanographene (WNG) having a negatively curved π-surface and defined C H composition with Cs metal used as the reducing and complexing agent allowed the isolation of three different reduced states with one, two, and three electrons added to its π-conjugated system. This provided a unique series of nanosized carbanions with increasing negative charge for in-depth structural analysis of consequences of controlled electron charging of non-planar nanographenes, using X-ray crystallographic and computational tools. The 3D molecular electrostatic potential (MEP) maps identified the negative charge localization at the central part of the WNG surface where selective coordination of Cs ions is confirmed crystallographically.

Stretching [8]cycloparaphenylene with encapsulated potassium cations: structural and theoretical insights into core perturbation upon four-fold reduction and complexation.

The consequences of four-electron addition to [8]cycloparaphenylene ([8]CPP, ) have been evaluated crystallographically, revealing a significant core deformation. The structural analysis exposes an elliptical distortion observed upon electron transfer, with the deformation parameter (D.P.

Generation and Reactivity of a Ni(μ-1,2-peroxo) Complex.

High-valent transition metal-oxo, -peroxo, and -superoxo complexes are crucial intermediates in both biological and synthetic oxidation of organic substrates, water oxidation, and oxygen reduction. While high-valent oxygenated complexes of Mn, Fe, Co, and Cu are increasingly well-known, high-valent oxygenated Ni complexes are comparatively rarer. Herein we report the isolation of such an unusual high-valent species in a thermally unstable Ni(μ-1,2-peroxo) complex, which has been characterized using single-crystal X-ray diffraction and X-ray absorption, NMR, and UV-vis spectroscopies.

Incorporation of coinage metal-NHC complexes into heptaphosphide clusters.

Cu(i) and Au(i) ions, capped with an N-heterocyclic carbene (NHC), react with (TMS)3P7 (TMS = trimethyl-silyl) to afford an η4-coordinated anion [NHCDippCu-P7(TMS)]- and a neutral trinuclear complex (NHCDippAu)3P7. Protecting the P7 cage with the TMS groups is instrumental in controlling the course of these reactions.

Heterotrimetallic Mixed-Valent Molecular Precursors Containing Periodic Table Neighbors: Assignment of Metal Positions and Oxidation States.

A known trinuclear structure was used to design the heterobimetallic mixed-valent, mixed-ligand molecule [Co (hfac) -Na-Co (acac) ] (1). This was used as a template structure to develop heterotrimetallic molecules [Co (hfac) -Na-Fe (acac) ] (2) and [Ni (hfac) -Na-Co (acac) ] (3) via isovalent site-specific substitution at either of the cobalt positions. Diffraction methods, synchrotron resonant diffraction, and multiple-wavelength anomalous diffraction were applied beyond simple structural investigation to provide an unambiguous assignment of the positions and oxidation states for the periodic table neighbors in the heterometallic assemblies.

Coupling of two curved polyaromatic radical-anions: stabilization of dimers by counterions.

In this study, a comprehensive theoretical investigation of both kinetic and thermodynamic stabilities was performed for dimeric dianionic systems (CH) and (CH), neutralized by two alkali metal cations. The influence of the counterions was of primary interest. The impact of the additional/spectator ligand(s) was elucidated by considering adducts with four molecules of diglyme or two molecules of 18-crown-6 ether.

Homolytic Versus Heterolytic Bond Breaking in Functionalized [R-C H ] Systems.

The comprehensive theoretical investigation of stability of functionalized corannulene cations [R-C H ] with respect to two alternative bond-breaking mechanisms, namely, homolytic or radical ([R-C H ]  → R  + C H ) and heterolytic or cationic ([R-C H ]  → R  + C H ), was accomplished. The special focus was on the influence of the nature of R-group on the energetics of the bond cleavage. Detailed study of energetics of both mechanisms has revealed that the systems with small alkyl groups such as methyl tend to undergo bond breaking in accordance with homolytic mechanism.

Mono-reduced Corannulene: To Couple and Not to Couple in One Crystal.

One-electron reduction of corannulene, C H , with Li metal in diglyme resulted in crystallization of [{Li (diglyme) } (C H ) (C H -C H ) ] (1), as revealed by single-crystal X-ray diffraction. This hybrid product contains two corannulene monoanion-radicals along with a dianionic dimer, crystallized with four Li ions wrapped by diglyme molecules. The dimeric (C H -C H ) anion provides the first crystallographically confirmed example of spontaneous radical dimerization for C H .

Three to tango requires a site-specific substitution: heterometallic molecular precursors for high-voltage rechargeable batteries.

Design of heterometallic molecules, especially those containing at least two different metals with close atomic numbers, radii, and the same coordination number/environment is a challenging task. This quest is greatly facilitated by having a heterobimetallic parent molecule that features multiple metal sites with only some of those displaying substitutional flexibility. Recently, a unique heterobimetallic complex LiMn(thd) (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) has been introduced as a single-source precursor for the preparation of a popular spinel cathode material, LiMnO.

Modulating stability of functionalized fullerene cations [R-C ] with the nature of R-group.

In this study, the first comprehensive theoretical investigation of the stability of functionalized fullerene-based cations [R-C ] and its relationship with the nature of the attached R-group was performed. C -Fullerene core was functionalized with an alkyl group of different length (R = (CH ) CH , where n = 0-9). This set was further complemented by bulky isopropyl and tert-butyl and conjugated phenyl groups.

Comprehensive Theoretical Study of Interactions between Ag and Polycyclic Aromatic Hydrocarbons.

The first comprehensive and systematic theoretical exploration of the bonding nature and energetics of the interactions between Ag(I) cation and a wide set of π-ligands was accomplished. This set ranges from simple ethylene and aromatic benzene to planar and curved polyaromatic molecules and to closed-cage C -fullerene. Simultaneous application of two energy decomposition schemes based on different ideas, namely, NBO-NEDA and EDA-NOCV, allowed shedding light on the nature of the bonding and its energetics.

A three body problem: a genuine heterometallic molecule a mixture of two parent heterometallic molecules.

This work raises a fundamental question about the "real" structure of molecular compounds containing three different metals: whether they consist of genuine heterometallic species or of a mixture of parent heterometallic species. Heterotrimetallic complex LiCoNi(tbaoac) (, tbaoac = -butyl acetoacetate) has been designed based on the model tetranuclear structure featuring two transition metal sites in order to be utilized as a molecular precursor for the low-temperature preparation of the LiCoNiO battery cathode material. An investigation of the structure of appeared to be very challenging, since the Co and Ni atoms have very similar atomic numbers, monoisotopic masses, and radii as well as the same oxidation state and coordination number/environment.

Record Alkali Metal Intercalation by Highly Charged Corannulene.

The need for advanced energy storage technologies demands the development of new functional materials. Novel carbon-rich and carbon-based materials of different structural topologies attract significant attention in this regard. Attractive systems include a unique class of bowl-shaped polycyclic aromatic hydrocarbons that map onto fullerene surfaces and are thus often referred to as fullerene fragments, buckybowls, or π-bowls.

Power of Three: Incremental Increase in the Ligand Field Strength of N-Alkylated 2,2'-Biimidazoles Leads to Spin Crossover in Homoleptic Tris-Chelated Fe(II) Complexes.

Homoleptic complexes [Fe(L )]X (L = 1,1'-(α,α'- o-xylyl)-2,2'-biimidazole, L = 1,1'-(α,α'-3,4-dibromo- o-xylyl)-2,2'-biimidazole, L = 1,1'-(α,α'-2,5-dimethoxy- o-xylyl)-2,2'-biimidazole; X = BF or ClO) were synthesized by direct reactions of the Fe(II) precursor salts and bidentate ligands L, L, or L. All mononuclear complexes undergo gradual temperature-driven spin-crossover (SCO) between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states. Complexes with ligands L and L synthesized in methanol exhibit complete SCO with the midpoint of the LS↔HS conversion varying from 233 to 313 K, while complexes with ligand L, crystallized from an ethanol/dichloromethane mixture, exhibit incomplete SCO with the residual HS/LS ratio of ∼1:4 for [Fe(L)](BF) and ∼1:1 for [Fe(L)](ClO).

Site-Directed Dimerization of Bowl-Shaped Radical Anions to Form a σ-Bonded Dibenzocorannulene Dimer.

Designed site-directed dimerization of the monoanion radicals of a π-bowl in the solid state is reported. Dibenzo[a,g]corannulene (C H ) was selected based on the asymmetry of the charge/spin localization in the C H anion. Controlled one-electron reduction of C H with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs (diglyme)} (C H -C H ) ] (1), as revealed by single crystal X-ray diffraction study performed in a broad range of temperatures.

Fusing a Planar Group to a π-Bowl: Electronic and Molecular Structure, Aromaticity and Solid-State Packing of Naphthocorannulene and its Anions.

Molecular and electronic structure, reduction electron transfer and coordination abilities of a polycyclic aromatic hydrocarbon (PAH) having a planar naphtho-group fused to the corannulene bowl have been investigated for the first time using a combination of theoretical and experimental tools. A direct comparison of naphtho[2,3-a]corannulene (C H , 1) with parent corannulene (C H , 2) revealed the effect of framework topology change on electronic properties and aromaticity of 1. The presence of two reduction steps for 1 was predicted theoretically and confirmed experimentally.

A Naphtho-p-quinodimethane Exhibiting Baird's (Anti)Aromaticity, Broken Symmetry, and Attractive Photoluminescence.

We report a novel reductive desulfurization reaction involving π-acidic naphthalene diimides (NDI) 1 using thionating agents such as Lawesson's reagent. Along with the expected thionated NDI derivatives 2-6, new heterocyclic naphtho-p-quinodimethane compounds 7 depicting broken/reduced symmetry were successfully isolated and fully characterized. Empirical studies and theoretical modeling suggest that 7 was formed via a six-membered ring oxathiaphosphenine intermediate rather than the usual four-membered ring oxathiaphosphetane of 2-6.

Stepwise deprotonation of sumanene: electronic structures, energetics and aromaticity alterations.

The first comprehensive theoretical investigation of structural, energetic, and electronic changes in a sumanene skeleton, CH, upon a step-wise deprotonation process is performed. This study is complemented by a detailed consideration of aromaticity in target bowl-shaped systems, including neutral sumanene and its three deprotonated anions, namely CH, CH, and CH. In order to obtain the most reliable and method-independent characteristics, a set of aromatic descriptors of different nature has been applied.

Position Assignment and Oxidation State Recognition of Fe and Co Centers in Heterometallic Mixed-Valent Molecular Precursors for the Low-Temperature Preparation of Target Spinel Oxide Materials.

A series of mixed-valent, heterometallic (mixed-transition metal) diketonates that can be utilized as prospective volatile single-source precursors for the low-temperature preparation of MM'O spinel oxide materials is reported. Three iron-cobalt complexes with Fe/Co ratios of 1:1, 1:2, and 2:1 were synthesized by several methods using both solid-state and solution reactions. On the basis of nearly quantitative reaction yields, elemental analyses, and comparison of metal-oxygen bonds with those in homometallic analogues, heterometallic compounds were formulated as [Fe(acac)][Co(hfac)] (1), [Co(hfac)][Fe(acac)][Co(hfac)] (2), and [Fe(hfac)][Fe(acac)][Co(hfac)] (3).

Tuning the separation and coupling of corannulene trianion-radicals through sizable alkali metal belts.

The first heterobimetallic sandwich-type aggregate formed by bowl-shaped corannulene trianion-radicals, CH˙, has been synthesized using mixed-metal reduction of CH. The product was crystallographically characterized to reveal the self-assembly of [Cs//(CH)/4K/(CH)//Cs], in which two triply-charged corannulene decks encapsulate a rectangle of four potassium ions (the K···K separations are 4.212(4) and 5.

Double Concave Cesium Encapsulation by Two Charged Sumanenyl Bowls.

The controlled reaction of Na and Cs, two alkali metals of different ionic sizes and binding abilities, with sumanene (C H ) affords a novel type of organometallic sandwich [Cs(C H ) ] , which crystallized as a solvent-separated ion pair with a [Na(18-crown-6)(THF) ] cation (where THF=tetrahydrofuran). The unprecedented double concave encapsulation of a metal ion by two bowl-shaped sumanenyl anions in [Cs(C H ) ] was revealed crystallographically. Evaluation of bonding and energetics of the remarkable product was accomplished computationally (B2PLYP-D/TZVP/ZORA), providing insights into its formation.