Experimental and Theoretical Investigation for the Level of Conjugation in Carbazole-Based Precursors and Their Mono‑, Di‑, and Polynuclear Pt(II) Complexes

A series of trimethylsilyl-protected monoalkynes (Me₃SiCC–R) and bis-alkynes (Me₃ SiCC–R–CCSiMe₃) incorporating carbazole spacer groups (R = carbazole-2-yl, carbazole-3-yl, carbazole-2,7-diyl, <i>N</i>-(2-ethylhexyl)­carbazole-2,7-diyl, carbazole-3,6-diyl, <i>N</i>-(2-ethylhexyl)­carbazole-3,6-diyl), together with the corresponding terminal monoalkynes (H–CC–R) and bis-alkynes (H–CC–R–CC–H), have been synthesized and characterized. The CuI-catalyzed dehydrohalogenation reaction between <i>trans</i>-[(Ph)­(Et₃P)₂PtCl], <i>trans</i>-[(Et₃P)₂PtCl₂], and <i>trans</i>-[(P^<i>n</i>Bu₃)₂PtCl₂] and the terminal alkynes in ^<i>i</i>Pr₂NH/CH₂Cl₂ affords a series of Pt­(II) mono- and diynes, while the dehydrohalogenation polycondensation reactions with <i>trans</i>-[(P^<i>n</i>Bu₃)₂PtCl₂] under similar reaction conditions yields four Pt­(II) poly-ynes of the form <i>trans</i>-[(P^<i>n</i>Bu₃)₂Pt–CC–R–CC−]_<i>n</i>. The acetylide-functionalized carbazole ligands and the mono-, di-, and polynuclear Pt­(II) σ-acetylide complexes have been characterized spectroscopically, with a subset analyzed using single-crystal X-ray diffraction. The Pt­(II) mono-, di-, and poly-ynes incorporating the carbazole spacers are soluble in common organic solvents, and solution absorption spectra show a consistent red-shift between the 2- and 2,7- as well as 3- and 3,6-carbazole complexes. Computational modeling is used to explain the observed spectral shifts, which are related to the enhanced electronic delocalization in the latter systems. These results also indicate that the inclusion of carbazole-2,7-diyl units into rigid-rod organometallic polymers should enhance electronic transport along the chains

New Multi-Ferrocenyl- and Multi-Ferricenyl- Materials via Coordination-Driven Self-Assembly and via Charge-Driven Electro-Crystallization

Three new tetra-ferrocenylethynylpyridinyl copper complexes, L₄(CuI)₄ (<b>3</b>), L₄(CuBr)₂ (<b>4</b>), and L₄(CuCl)₂ (<b>5</b>) have been prepared from the reaction of ferrocenyl­ethynyl­pyridine (L)­(<b>2</b>) with copper halides CuX (with X = I^–, Br^–, Cl^–).The ligand <b>2</b> and the complexes <b>3</b>–<b>5</b> have been fully characterized by spectroscopic methods. The structures of <b>2</b>–<b>4</b> have been confirmed by single-crystal X-ray crystallography. <b>2</b> forms a dimer in the crystalline-state through C–H··N hydrogen bonds. <b>4</b> and <b>5</b> are dimers and <b>3</b> a tetramer, in all cases linked through Cu–X··Cu bridging interactions. Cyclic voltammetry in dichloroethane showed chemically reversible multiferrocenyl oxidation signals with evidence for product electro-crystallization. The oxidation products were isolated by electrodeposition onto a Pt disc electrode and investigated by scanning electron microscopy which confirmed the spontaneous formation of crystalline oxidation products with distinctive morphologies. Energy dispersive X-ray elemental analysis shows the presence of hexafluorophosphate (counterion) with the P:Fe ratio of 1:1, 0.5:1, and 1:1 for the electrocrystallized products <b>3</b>, <b>4</b>, and <b>5</b>, respectively, suggesting the formulas [<b>3</b>]⁴⁺(PF₆^–)₄, [<b>4</b>]²⁺(PF₆^–)₂, and [<b>5</b>]⁴⁺(PF₆^–)₄ for the electro-crystallized products

Long-Range Intramolecular Electronic Communication in Bis(ferrocenylethynyl) Complexes Incorporating Conjugated Heterocyclic Spacers: Synthesis, Crystallography, and Electrochemistry

A new series of bis­(ferrocenylethynyl) complexes, <b>3</b>–<b>7</b>, and a mono­(ferrocenylethynyl) complex, <b>8</b>, have been synthesized incorporating conjugated heterocyclic spacer groups, with the ethynyl group facilitating an effective long-range intramolecular interaction. The complexes were characterized by NMR, IR, and UV–vis spectroscopy as well as X-ray crystallography. The redox properties of these complexes were investigated using cyclic voltammetry and spectroelectrochemistry. Although there is a large separation of ∼14 Å between the two redox centers, Δ<i>E</i>_1/2 values in this series of complexes ranged from 50 to 110 mV. The appearance of intervalance charge-transfer bands in the UV–vis–near-IR region for the monocationic complexes further confirmed effective intramolecular electronic communication. Computational studies are presented that show the degree of delocalization across the Fc–CC–CC–Fc (Fc = C₅H₅FeC₅H₄) highest occupied molecular orbital