More Like this

1. Crystallographic characterization of rare-earth cyanotriphenylborate complexes and the cyanoborates [NCBPh ₃ ] ¹⁻ , [NCBPh ₂ Me] ¹⁻ , and [NCBPh ₂ (μ-O)BPh ₂ ] ¹⁻

   https://doi.org/10.1107/S2056989021006861  

   Dumas, Megan T. ; White, Jessica R. ; Ziller, Joseph W. ; Evans, William J. ( August 2021 , Acta Crystallographica Section E Crystallographic Communications)

   The investigation of the coordination chemistry of rare-earth metal complexes with cyanide ligands led to the isolation and crystallographic characterization of the Ln III cyanotriphenylborate complexes dichlorido(cyanotriphenylborato-κ N )tetrakis(tetrahydrofuran-κ O )lanthanide(III), [ Ln Cl 2 (C 19 H 15 BN)(C 4 H 8 O) 4 ] [lanthanide ( Ln ) = dysprosium (Dy) and yttrium Y)] from reactions of LnCl 3 , KCN, and NaBPh 4 . Attempts to independently synthesize the tetraethylammonium salt of (NCBPh 3 ) − from BPh 3 and [NEt 4 ][CN] in THF yielded crystals of the phenyl-substituted cyclic borate, tetraethylazanium 2,2,4,6-tetraphenyl-1,3,5,2λ 4 ,4,6-trioxatriborinan-2-ide, C 8 H 20 N + ·C 24 H 20 B 3 O 3 − or [NEt 4 ][B 3 (μ-O) 3 (C 6 H 5 ) 4 ]. The mechanochemical reaction of BPh 3 and [NEt 4 ][CN] without solvent produced crystals of tetraethylazanium cyanodiphenyl-λ 4 -boranyl diphenylborinate, C 8 H 20 N + ·C 25 H 20 B 2 NO − or [NEt 4 ][NCBPh 2 (μ-O)BPh 2 ]. Reaction of BPh 3 and KCN in THF in the presence of 2.2.2-cryptand (crypt) led to a crystal of bis[(2.2.2-cryptand)potassium] 2,2,4,6-tetraphenyl-1,3,5,2λ 4 ,4,6-trioxatriborinan-2-ide cyanomethyldiphenylborate tetrahydrofuran disolvate, 2C 18 H 36more »KN 2 O 6 + ·C 24 H 20 B 3 O 3 − ·C 14 H 13 BN − ·2C 4 H 8 O or [K(crypt)] 2 [B 3 (μ-O) 3 (C 6 H 5 ) 4 ][NCBPh 2 Me]·2THF. The [NCBPh 2 (μ-O)BPh 2 ] 1− and (NCBPh 2 Me) 1− anions have not been structurally characterized previously. The structure of 1-Y was refined as a two-component twin with occupancy factors 0.513 (1) and 0.487 (1). In 4 , one solvent molecule was disordered and included using multiple components with partial site-occupancy factors.« less
2. Higher spin states in some low-energy bis(tetramethyl-1,2-diaza-3,5-diborolyl) sandwich compounds of the first row transition metals: boraza analogues of the metallocenes

   https://doi.org/10.1039/C8NJ05517C  

   Chen, Jianlin ; Feng, Hao ; Xie, Yaoming ; King, R. Bruce ; Schaefer, Henry F. ( March 2019 , New Journal of Chemistry)

   The known sandwich compound [η 5 -(CH 2 ) 3 N 2 (BPh) 2 CMe] 2 Fe in which adjacent C 2 units are replaced by isoelectronic BN units can be considered as a boraza analogues of ferrocene similar to borazine, B 3 N 3 H 6 , considered as a boraza analogue of benzene. In this connection, the related bis(1,2,3,5-tetramethyl-1,2-diaza-3,5-diborolyl) derivatives (Me 4 B 2 N 2 CH) 2 M (M = Ti, V, Cr, Mn, Fe, Co, Ni) for all of the first row transition metals have been optimized using density functional theory for comparison with the isoelectronic tetramethylcyclopentadienyl derivatives (Me 4 C 5 H) 2 M. Low-energy sandwich structures having parallel B 2 N 2 C rings in a trans orientation are found for all seven metals. The 1,2-diaza-3,5-diborolyl ligand appears to be a weaker field ligand than the isoelectronic cyclopentadienyl ligand as indicated by higher spin ground states for some (η 5 -Me 4 B 2 N 2 CH) 2 M sandwich compounds relative to the corresponding metallocenes (η 5 -Me 4 C 5 H) 2 M. Thus (η 5 -Me 4 B 2 N 2 CH) 2 Cr has a quintet ground state in contrastmore »to the triplet ground state of (η 5 -Me 4 C 5 H) 2 Cr. Similarly, the sextet ground state of (η 5 -Me 4 B 2 N 2 CH) 2 Mn lies ∼18 kcal mol −1 below the quartet state in contrast to the doublet ground state of the isoelectronic (Me 4 C 5 H) 2 Mn. These sandwich compounds are potentially accessible by reaction of 1,2-diaza-3,5-diborolide anions with metal halides analogous to the synthesis of [η 5 -(CH 2 ) 3 N 2 (BPh) 2 CMe] 2 Fe.« less
3. Reductive cleavage of N , N ′-di- tert -butylcarbodiimide generates tert -butylcyanamide ligands, (Me ₃ CNCN) ⁻ , that bind potassium both end-on and side-on in the same single crystal

   https://doi.org/10.1107/S205698902000732X  

   Chung, Amanda B. ; Ziller, Joseph W. ; Evans, William J. ( July 2020 , Acta Crystallographica Section E Crystallographic Communications)

   N , N ′-Di- tert -butylcarbodiimide, Me 3 CN=C=NCMe 3 , undergoes reductive cleavage in the presence of the Gd II complex, [K(18-crown-6) 2 ][Gd II (N R 2 ) 3 ] ( R = SiMe 3 ), to form a new type of ligand, the tert -butylcyanamide anion, (Me 3 CNCN) − . This new ligand can bind metals with one or two donor atoms as demonstrated by the isolation of a single crystal containing potassium salts of both end-on and side-on bound tert -butylcyanamide anions, (Me 3 CNCN) − . The crystal contains [K(18-crown-6)(H 2 O)][NCNCMe 3 - kN ], in which one ( t BuNCN) − anion is coordinated end-on to potassium ligated by 18-crown-6 and water, as well as [K(18-crown-6)][η 2 -NCNCMe 3 ], in which an 18-crown-6 potassium is coordinated side-on to the terminal N—C linkage. This single crystal also contains one equivalent of 1,3-di- tert -butyl urea, (C 9 H 20 N 2 O), which is involved in hydrogen bonding that may stabilize the whole assembly, namely, aqua( tert -butylcyanamidato)(1,4,7,10,13,16-hexaoxacyclooctadecane)potassium(I)–( tert -butylcyanamidato)(1,4,7,10,13,16-hexaoxacyclooctadecane)potassium(I)– N , N ′-di- tert -butylcarbodiimide (1/1/1) [K(C 5 H 9 N 2 )(C 12 H 24 O 6 )]·[K(C 5 Hmore »9 N 2 )(C 12 H 24 O 6 )(H 2 O)]·C 9 H 20 N 2 .« less
4. Impact of molecular structure on singlet and triplet exciton diffusion in phenanthroline derivatives

   https://doi.org/10.1039/D0TC00716A  

   Rai, Deepesh ; Bangsund, John S. ; Barriocanal, Javier Garcia ; Holmes, Russell J. ( May 2020 , Journal of Materials Chemistry C)

   We demonstrate the impact of subtle changes in molecular structure on the singlet and triplet exciton diffusion lengths ( L D ) for derivatives of the archetypical electron-transport material 4,7-diphenyl-1,10-phenanthroline (BPhen). Specifically, this work offers a systematic characterization of singlet and triplet exciton transport in identically prepared thin films, highlighting the differing dependence on molecular photophysics and intermolecular spacing. For luminescent singlet excitons, photoluminescence quenching measurements yield an L D from <1 nm for BPhen, increasing to (5.4 ± 1.2) nm for 2,9-dichloro-4,7-diphenyl-1,10-phenanthroline (BPhen-Cl 2 ) and (3.9 ± 1.1) nm for 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The diffusion of dark triplet excitons is probed using a phosphorescent sensitizer-based method where triplets are selectively injected into the material of interest, with those migrating through the material detected via energy transfer to an adjacent, phosphorescent sensitizer. Interestingly, the triplet exciton L D decreases from (15.4 ± 0.4) nm for BPhen to (8.0 ± 0.7) nm for BPhen-Cl 2 and (4.0 ± 0.5) nm for BCP. The stark difference in behavior observed for singlets and triplets with functionalization is explicitly understood using long-range Förster and short-range Dexter energy transfer mechanisms, respectively.
5. Work function and temperature dependence of electron tunneling through an N-type perylene diimide molecular junction with isocyanide surface linkers

   https://doi.org/10.1039/C7NR06461F  

   Smith, Christopher E. ; Xie, Zuoti ; Bâldea, Ioan ; Frisbie, C. Daniel ( January 2018 , Nanoscale)

   Conducting probe atomic force microscopy (CP-AFM) was employed to examine electron tunneling in self-assembled monolayer (SAM) junctions. A 2.3 nm long perylene tetracarboxylic acid diimide (PDI) acceptor molecule equipped with isocyanide linker groups was synthesized, adsorbed onto Ag, Au and Pt substrates, and the current–voltage ( I – V ) properties were measured by CP-AFM. The dependence of the low-bias resistance ( R ) on contact work function indicates that transport is LUMO-assisted (‘n-type behavior’). A single-level tunneling model combined with transition voltage spectroscopy (TVS) was employed to analyze the experimental I – V curves and to extract the effective LUMO position ε l = E LUMO − E F and the effective electronic coupling ( Γ ) between the PDI redox core and the contacts. This analysis revealed a strong Fermi level ( E F ) pinning effect in all the junctions, likely due to interface dipoles that significantly increased with increasing contact work function, as revealed by scanning Kelvin probe microscopy (SKPM). Furthermore, the temperature ( T ) dependence of R was found to be substantial. For Pt/Pt junctions, R varied more than two orders of magnitude in the range 248 K < T < 338 K. Importantly,more »the R ( T ) data are consistent with a single step electron tunneling mechanism and allow independent determination of ε l , giving values compatible with estimates of ε l based on analysis of the full I – V data. Theoretical analysis revealed a general criterion to unambiguously rule out a two-step transport mechanism: namely, if measured resistance data exhibit a pronounced Arrhenius-type temperature dependence, a two-step electron transfer scenario should be excluded in cases where the activation energy depends on contact metallurgy. Overall, our results indicate (1) the generality of the Fermi level pinning phenomenon in molecular junctions, (2) the utility of employing the single level tunneling model for determining essential electronic structure parameters ( ε l and Γ ), and (3) the importance of changing the nature of the contacts to verify transport mechanisms.« less