PtS-Related {[Cu^I(F₄TCNQ^II–)]⁻}_∞ Networks

A series of compounds of composition A­[Cu^I­(F₄­TCNQ^II–)] (A = a quaternary ammonium or phosphonium cation, F₄­TCNQ^II– = the dianionic form of 2,3,5,6-tetra­fluoro-7,7,8,8-tetra­cyano­quino­dimethane) have been synthesized and structurally characterized. In each structure, an anionic [Cu^I­(F₄­TCNQ^II–)]⁻ framework possessing the topology of PtS is formed with the Cu­(I) center serving as a tetrahedral 4-connecting center and the F₄­TCNQ^2– anion acting as a planar 4-connecting unit. Although a PtS topology is observed for six different compounds, the anionic framework shows significant geometric variation depending upon the identity of the cation. Very similar structures are obtained when the organic cation is NMe₄⁺, NMe₂­Pr₂⁺, or NMe₂­Bu₂⁺. A distorted anionic structure possessing the same connectivity is generated when the cation is NEt₄⁺, and anionic frameworks with a different connectivity, but still related to PtS, are obtained when the much larger quaternary phosphonium cations are employed. Of interest in the structures containing quaternary phosphonium cations are π-stacking interactions involving phenyl groups of the cation and F₄­TCNQ^2– ligands. These face-to-face interactions between the electron-rich F₄­TCNQ^2– ligands and a phenyl group of the cation appear to be responsible for the color exhibited by these compounds

PtS-Related {[Cu^I(F₄TCNQ^II–)]⁻}_∞ Networks

A series of compounds of composition A­[Cu^I­(F₄­TCNQ^II–)] (A = a quaternary ammonium or phosphonium cation, F₄­TCNQ^II– = the dianionic form of 2,3,5,6-tetra­fluoro-7,7,8,8-tetra­cyano­quino­dimethane) have been synthesized and structurally characterized. In each structure, an anionic [Cu^I­(F₄­TCNQ^II–)]⁻ framework possessing the topology of PtS is formed with the Cu­(I) center serving as a tetrahedral 4-connecting center and the F₄­TCNQ^2– anion acting as a planar 4-connecting unit. Although a PtS topology is observed for six different compounds, the anionic framework shows significant geometric variation depending upon the identity of the cation. Very similar structures are obtained when the organic cation is NMe₄⁺, NMe₂­Pr₂⁺, or NMe₂­Bu₂⁺. A distorted anionic structure possessing the same connectivity is generated when the cation is NEt₄⁺, and anionic frameworks with a different connectivity, but still related to PtS, are obtained when the much larger quaternary phosphonium cations are employed. Of interest in the structures containing quaternary phosphonium cations are π-stacking interactions involving phenyl groups of the cation and F₄­TCNQ^2– ligands. These face-to-face interactions between the electron-rich F₄­TCNQ^2– ligands and a phenyl group of the cation appear to be responsible for the color exhibited by these compounds

New Cu^I₂(TCNQ^–II) and Cu^I₂(F₄TCNQ^–II) Coordination Polymers

Coordination polymer strips of composition ...Cu⁺₂·lig^2–·Cu⁺₂·lig^2–·Cu⁺₂·lig^2–... (where lig^2– = TCNQ^2– or its 2,3,4,5-tetrafluoro analogue) are observed with a wide range of coligands (monodentate, bidentate, and tridentate). Interdigitation of “thin”, planar N-heteroaromatic coligands on one strip with those on a neighbor is a common structural feature. Coligands too bulky to allow interdigitation give either non-interdigitating strips or 2D sheet structures. Both strips and sheets have 2-connecting Cu centers and 4-connecting tetracynano ligands. As a consequence of the great flexibility of the Cu/tetracyano ligand association, the geometries of the sheet structures vary widely from almost coplanar to highly corrugated and convoluted, despite which the same topology is present in all

Role of NEt₄⁺ in Orienting and Locking Together [M₂lig₃]^2– (6,3) Sheets (H₂lig = Chloranilic or Fluoranilic Acid) to Generate Spacious Channels Perpendicular to the Sheets

In the presence of the Et₄N⁺ cation the chloranilate dianion (can^2–) associates with a range of divalent cations, M²⁺, to yield an isomorphous series of crystalline compounds of composition (Et₄N)₂[M₂(can)₃] (M = Mg, Mn, Fe, Co, Ni, Cu, and Zn). The fluoranilate dianion (fan^2–) likewise affords the closely related (Et₄N)₂[Zn₂(fan)₃]. The structures of (Et₄N)₂[Zn₂(can)₃], (Et₄N)₂[Fe₂(can)₃], and (Et₄N)₂[Zn₂(fan)₃] were determined by single crystal X-ray diffraction. Powder X-ray diffraction indicates that all the members of the can^2– series are isomorphous. The structure of (Et₄N)₂[Zn₂(fan)₃] is very closely related to the structures of the can^2– compounds. The [M₂(can)₃^2–]_<i>n</i> component is present as chicken-wire-like sheets with (6,3) topology. The Et₄N⁺ cation binds sheet to sheet and aligns them so that the large holes within the sheets are arranged one above another, thereby generating spacious channels running perpendicular to the sheets. The solvent molecules present in the channels are ill-defined and easily removed. The (Et₄N)₂[M₂(can)₃] structure remains intact after desolvation. The void spaces are calculated to be ∼39% in the case of the can^2– compounds and ∼43% in (Et₄N)₂[Zn₂(fan)₃]. Substantial amounts of CO₂ are sorbed at 273 K by (Et₄N)₂[Zn₂(can)₃] and (Et₄N)₂[Zn₂(fan)₃]. Spectroscopic evidence supports the presence of at least some of the chloranilate in the radical trianion form in (Et₄N)₂[Fe₂(can)₃]

Isomeric Ionic Lithium Isonicotinate Three-Dimensional Networks and Single-Crystal-to-Single-Crystal Rearrangements Generating Microporous Materials

Reaction between LiOH and isonicotinic acid (inicH) in the appropriate solvent or mixture of solvents affords a family of variously solvated forms of a simple ionic lithium salt, <i>viz</i>., Li⁺inic^–·S (where S = 0.5 morpholine, 0.5 dioxane, 0.25 <i>n</i>-hexanol, 0.5 <i>N</i>-methylpyrrolidinone, 0.5 <i><i>N,N</i></i>-dimethylformamide, 0.5 <i>n</i>-propanol, 0.5 cyclohexanol, 0.5 pyridine, 0.5 <i>t</i>-butanol, 0.5 ethanol, and 0.5 methanol). Three-dimensional Li⁺inic^– frameworks containing solvent-filled channels are present in all of these except for the MeOH and EtOH solvates. The nondirectional character of the electrostatic interactions between the Li⁺ and inic^– ions bestows an element of “plasticity” upon the framework, manifested in the observation of no less than five different framework structures within the family. Unusual single-crystal-to-single-crystal transformations accompany desolvation of Li⁺inic^–·S in which the Li⁺inic^– framework undergoes a major rearrangement (from a structure containing “8484 chains” to one with “6666 chains”). The “before and after” structures are strongly suggestive of the mechanism and the driving force for these solid state framework rearrangements: processes which further demonstrate the “plasticity” of the ionic Li­(inic) framework. A solid-state mechanism for these desolvation processes that accounts very satisfactorily for the formation of the channels and for the diverse geometrical/topological aspects of the transformation is proposed. The reverse process allows the regeneration of the solvated 8484 form. When the 6666 Li⁺inic^– form is immersed in carbon disulfide, a single-crystal-to-single-crystal transformation occurs to generate Li⁺inic^–·0.25CS₂. The hydrate, Li⁺inic^–·2H₂O which consists of discrete Li­(inic)·H₂O chains obtained by recrystallizing the salt from water, can also be obtained by hydration of the 6666 form. A dense 3D network with the formula, Li­(inic) can be obtained in a reversible process by the removal of the water from the hydrated form and also by crystallization from a <i>t</i>-amyl alcohol solution

Electrochemically Directed Synthesis of Cu₂^I(TCNQF₄^II–)(MeCN)₂ (TCNQF₄ = 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane): Voltammetry, Simulations, Bulk Electrolysis, Spectroscopy, Photoactivity, and X‑ray Crystal Structure of the Cu₂^I(TCNQF₄^II–)(EtCN)₂ Analogue

The new compound Cu₂^I(TCNQF₄^II–)­(MeCN)₂ (TCNQF₄^2– = dianion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) has been synthesized by electrochemically directed synthesis involving reduction of TCNQF₄ to TCNQF₄^2– in acetonitrile containing [Cu­(MeCN)₄]⁺_(MeCN) and 0.1 M Bu₄NPF₆. In one scenario, TCNQF₄^2– is quantitatively formed by reductive electrolysis of TCNQF₄ followed by addition of [Cu­(MeCN)₄]⁺ to form the Cu₂^I(TCNQF₄^II–)­(MeCN)₂ coordination polymer. In a second scenario, TCNQF₄ is reduced in situ at the electrode surface to TCNQF₄^2–, followed by reaction with the [Cu­(MeCN)₄]⁺ present in the solution, to electrocrystallize Cu₂^I(TCNQF₄^II–)­(MeCN)₂. Two distinct phases of Cu₂^I(TCNQF₄^II–)­(MeCN)₂ are formed in this scenario; the kinetically favored form being rapidly converted to the thermodynamically favored Cu₂^I(TCNQF₄^II–)­(MeCN)₂. The postulated mechanism is supported by simulations. The known compound Cu^ITCNQF₄^I– also has been isolated by one electron reduction of TCNQF₄ and reaction with [Cu­(MeCN)₄]⁺. The solubility of both TCNQF₄^2–- and TCNQF₄^•–-derived solids indicates that the higher solubility of Cu^ITCNQF₄^I– prevents its precipitation, and thus Cu₂^I(TCNQF₄^II–)­(MeCN)₂ is formed. UV–visible and vibrational spectroscopies were used to characterize the materials. Cu₂^I(TCNQF₄^II–)­(MeCN)₂ can be photochemically transformed to Cu^ITCNQF₄^I– and Cu⁰. Scanning electron microscopy images reveal that Cu^ITCNQF₄^I– and Cu₂^I(TCNQF₄^II–)­(MeCN)₂ are electrocrystallized with distinctly different morphologies. Thermogravimetric and elemental analysis data confirm the presence of CH₃CN, and single-crystal X-ray diffraction data for the Cu₂^I(TCNQF₄^II−)­(EtCN)₂ analogue shows that this compound is structurally related to Cu₂^I(TCNQF₄^II–)­(MeCN)₂

Mixed Valency in a 3D Semiconducting Iron–Fluoranilate Coordination Polymer

A pair of coordination polymers of composition (NBu₄)₂[M₂(fan)₃] (fan = fluoranilate; M = Fe and Zn) were synthesized and structurally characterized. In each case the compound consists of a pair of interpenetrating three-dimensional, (10,3)-<i>a</i> networks in which metal centers are linked by chelating/bridging fluoranilate ligands. Tetrabutylammonium cations are located in the spaces between the two networks. Despite the structural similarity, significant differences exist between (NBu₄)₂[Fe₂(fan)₃] and (NBu₄)₂[Zn₂(fan)₃] with respect to the oxidation states of the metal centers and ligands. For (NBu₄)₂[Fe₂(fan)₃] the structure determination as well as Mössbauer spectroscopy indicate the oxidation state for the Fe is close to +3, which contrasts with the +2 state for the Zn analogue. The differences between the two compounds extends to the ligands, with the Zn network involving only fluoranilate dianions, whereas the average oxidation state for the fluoranilate in the Fe network lies somewhere between −2 and −3. Magnetic studies on the Fe compound indicate short-range ordering. Electrochemical and spectro-electrochemical investigations indicate that the fluoranilate ligand is redox-active in both complexes; a reduced form of (NBu₄)₂[Fe₂(fan)₃] was generated by chemical reduction. Conductivity measurements indicate that (NBu₄)₂[Fe₂(fan)₃] is a semiconductor, which is attributed to the mixed valency of the fluoranilate ligands