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1. Electronic structure of cobalt valence tautomeric molecules in different environments

   https://doi.org/10.1039/d2nr06834f  

   Mishra, Esha; Ekanayaka, Thilini K.; Panagiotakopoulos, Theodoros; Le, Duy; Rahman, Talat S.; Wang, Ping; McElveen, Kayleigh A.; Phillips, Jared P.; Zaid Zaz, M.; Yazdani, Saeed; et al (January 2022, Nanoscale)

   Future molecular microelectronics require the electronic conductivity of the device to be tunable without impairing the voltage control of the molecular electronic properties. This work reports the influence of an interface between a semiconducting polyaniline polymer or a polar poly-D-lysine molecular film and one of two valence tautomeric complexes, i.e. , [Co III (SQ)(Cat)(4-CN-py) 2 ] ↔ [Co II (SQ) 2 (4-CN-py) 2 ] and [Co III (SQ)(Cat)(3-tpp) 2 ] ↔ [Co II (SQ) 2 (3-tpp) 2 ]. The electronic transitions and orbitals are identified using X-ray photoemission, X-ray absorption, inverse photoemission, and optical absorption spectroscopy measurements that are guided by density functional theory. Except for slightly modified binding energies and shifted orbital levels, the choice of the underlying substrate layer has little effect on the electronic structure. A prominent unoccupied ligand-to-metal charge transfer state exists in [Co III (SQ)(Cat)(3-tpp) 2 ] ↔ [Co II (SQ) 2 (3-tpp) 2 ] that is virtually insensitive to the interface between the polymer and tautomeric complexes in the Co II high-spin state. 

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2. Silylene-assisted hydride transfer to CO ₂ and CS ₂ at a [P ₂ Si]Ru pincer-type complex

   https://doi.org/10.1039/C7DT03659K  

   Whited, Matthew T.; Zhang, Jia; Ma, Senjie; Nguyen, Binh D.; Janzen, Daron E. (January 2017, Dalton Transactions)

   The synthesis and characterization of base-stabilized and base-free pincer-type bis(phosphine)/silylene [P 2 Si]Ru complexes are reported. The base-free complex readily reduces CO 2 and CS 2 via silylene-assisted hydride transfer, affording structurally distinct products with silicon-to-ruthenium formate and dithioformate bridges. 

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3. Spectroelectrochemical and Theoretical Study of [Si(ttpy)2](PF6)4: A Potential Polychromatic Electrochromic Dye

   https://doi.org/10.3390/molecules27238521  

   Peloquin, Derek M.; Bimukhanov, Askhat N.; Aldongarov, Anuar A.; Merkert, Jon W.; Donovan-Merkert, Bernadette T.; Schmedake, Thomas A. (December 2022, Molecules)

   Complexes consisting of earth-abundant main group metals such as silicon with polypyridine ligands are of interest for a variety of optical and electronic applications including as electrochromic colorants. Previous spectroelectrochemical studies with tris(2,2′-bipyridyl)silicon(IV) hexafluorophosphate, [Si(bpy)3](PF6)4, demonstrated an ability to control the color saturation of the potential electrochromic dye, with the intensity of the dye’s green color increasing as the charge state sequentially reduces from 4+ to 1+. In this study, the synthesis of bis(4′-(4-tolyl)-2,2′:6′,2″-terpyridine)silicon(IV) hexafluorophosphate, [Si(ttpy)2](PF6)4, is reported along with electrochemical and spectroelectrochemical analyses. Computational modeling (density functional theory) is used to further elucidate the electrochromic properties of previously reported Si(bpy)3n+ species and the new Si(ttpy)2n+ species. While the homoleptic tris(bidentate)silicon(IV) complexes are attractive as electrochromic dyes for tunable color saturation, the bis(tridentate)silicon(IV) complexes are attractive as polychromatic electrochromic dyes. 

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4. Sensitized and Self‐Sensitized Photocatalytic Carbon Dioxide Reduction Under Visible Light with Ruthenium Catalysts Shows Enhancements with More Conjugated Pincer Ligands

   https://doi.org/10.1002/ejic.202101016  

   Das, Sanjit; Nugegoda, Dinesh; Yao, Wenzhi; Qu, Fengrui; Figgins, Matthew_T; Lamb, Robert_W; Webster, Charles_Edwin; Delcamp, Jared_H; Papish, Elizabeth_T (February 2022, European Journal of Inorganic Chemistry)

   Abstract A new method to synthesize complexes of the type [(CNC)Ru^II(NN)L]ⁿ⁺has been introduced, where CNC is a tridentate pincer composed of two (benz)imidazole derived NHC rings and a pyridyl ring, NN is a bidentate aromatic diimine ligand, L=bromide or acetonitrile, and n=1 or 2. Following this new method a series of six new complexes has been synthesized and characterized by spectroscopic, analytic, crystallographic, and computational methods. Their electrochemical properties have been studiedviacyclic voltammetry under both N₂and CO₂atmospheres. Photocatalytic reduction of CO₂to CO was performed using these complexes both in the presence (sensitized) and absence (self‐sensitized) of an external photosensitizer. This study evaluates the effect of different CNC, NN, and L ligands in sensitized and self‐sensitized photocatalysis. Catalysts bearing the benzimidazole derived CNC pincer show much better activity for both sensitized and self‐sensitized photocatalysis as compared to catalysts bearing the imidazole derived CNC pincer. Furthermore, self‐sensitized photocatalysis requires a diimine ligand for CO₂reduction with catalyst2_ACNbeing the most active catalyst in this series with TON=85 and TOF=22 h⁻¹with an electron donating 4,4′‐dimethyl‐2,2′‐bipyridyl (dmb) ligand and a benzimidazole derived CNC pincer. 

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5. Halogen Bonding Involving I2 and d8 Transition-Metal Pincer Complexes

   https://doi.org/10.3390/cryst11040373  

   Freindorf, Marek; Yannacone, Seth; Oliveira, Vytor; Verma, Niraj; Kraka, Elfi (April 2021, Crystals)

   We systematically investigated iodine–metal and iodine–iodine bonding in van Koten’s pincer complex and 19 modifications changing substituents and/or the transition metal with a PBE0–D3(BJ)/aug–cc–pVTZ/PP(M,I) model chemistry. As a novel tool for the quantitative assessment of the iodine–metal and iodine–iodine bond strength in these complexes we used the local mode analysis, originally introduced by Konkoli and Cremer, complemented with NBO and Bader’s QTAIM analyses. Our study reveals the major electronic effects in the catalytic activity of the M–I–I non-classical three-center bond of the pincer complex, which is involved in the oxidative addition of molecular iodine I2 to the metal center. According to our investigations the charge transfer from the metal to the σ* antibonding orbital of the I–I bond changes the 3c–4e character of the M–I–I three-center bond, which leads to weakening of the iodine I–I bond and strengthening of the metal–iodine M–I bond, facilitating in this way the oxidative addition of I2 to the metal. The charge transfer can be systematically modified by substitution at different places of the pincer complex and by different transition metals, changing the strength of both the M–I and the I2 bonds. We also modeled for the original pincer complex how solvents with different polarity influence the 3c–4e character of the M–I–I bond. Our results provide new guidelines for the design of pincer complexes with specific iodine–metal bond strengths and introduce the local vibrational mode analysis as an efficient tool to assess the bond strength in complexes. 

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