Photoelectron spectra of potassium salts of hydrotris(pyrazol-1-yl)borates: electronic structure of the electron withdrawing scorpionates Tp(CF3)2, Tp*Cl and comparison to Tp* and Tp

Bis(acetylacetonato)bis(pyrazolato)ruthenate(iii) as a redox-active scorpionate ligand

The potential of a new anionic octahedral metal complex [Ru(III)(acac)2(pz)2](-) ((-)) (pzH = pyrazole) as a ligand with a scorpionate coordination behaviour like tris(pyrazolyl)borate (tp) and reversible redox activity is presented. Trinuclear metal complexes, [Ru(III)2Zn(II)(acac)4(pz)4] () and [Ru(II)Ru(III)2(acac)4(pz)4] (), were each synthesized by the reaction of ZnCl2 or Ru3(CO)12 with [Ru(III)(acac)2(pz)(pzH)] (H) that is in situ deprotonated and acts as a precursor of (-). Single-crystal X-ray diffraction studies clarified that (-) acts as a scorpionate ligand; two (-) units in and one unit in function as bidentate ligands with two pyrazolates as pincers, while another (-) unit in functions as a tridentate ligand with one oxygen atom as a tail in addition to the two pyrazolate pincers. Moreover, and showed reversible multi-stage redox behaviours based on the Ru(II)/Ru(III) and Ru(III)/Ru(IV) couples of the (-) units in the cyclic voltammetry (CV) measurements. Based on the X-ray, IR, and CV measurements and the comparison with other Ru(ii) complexes with tp derivatives, the (-) unit was found to act as a redox-active scorpionate with electron withdrawing properties compared to the tp.

Spectroscopic mapping and selective electronic tuning of molecular orbitals in phosphorescent organometallic complexes - a new strategy for OLED materials

The improvement of molecular electronic devices such as organic light-emitting diodes requires fundamental knowledge about the structural and electronic properties of the employed molecules as well as their interactions with neighboring molecules or interfaces. We show that highly resolved scanning tunneling microscopy (STM) and spectroscopy (STS) are powerful tools to correlate the electronic properties of phosphorescent complexes (i.e., triplet emitters) with their molecular structure as well as the local environment around a single molecule. We used spectroscopic mapping to visualize several occupied and unoccupied molecular frontier orbitals of Pt(II) complexes adsorbed on Au(111). The analysis showed that the molecules exhibit a peculiar localized strong hybridization that leads to partial depopulation of a dz² orbital, while the ligand orbitals are almost unchanged. We further found that substitution of functional groups at well-defined positions can alter specific molecular orbitals without influencing the others. The results open a path toward the tailored design of electronic and optical properties of triplet emitters by smart ligand substitution, which may improve the performance of future OLED devices.

Thallium(I) complexes of fluorinated bis- and tris(pyrazolyl)borate ligands: [H2B{3,5-(CF3)2pz}2]Tl and [HB{3,5-(CF3)2pz}3]Tl

X-ray crystal structural data at 100 (2) K for the thallium(I) complex of a fluorinated bis(pyrazolyl)borate, {bis[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl-κN2]borato}thallium(I), [Tl(C10H4BF12N4)], abbreviated as [H2B{3,5-(CF3)2pz}2]Tl, and the related tris(pyrazolyl)borate, {tris[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl-κN2]borato}thallium(I), [Tl(C15H4BF18N6)], abbreviated as [HB{3,5-(CF3)2pz}3]Tl, are reported. [H2B{3,5-(CF3)2pz}2]Tl features a two-coordinate TlIatom with a bent geometry and a boat-shaped bis(pyrazolyl)borate ligand. It also has several additional inter- and intramolecular Tl...H and Tl...F contacts in the solid state. The tris(pyrazolyl)borate analogue [HB{3,5-(CF3)2pz}3]Tl has a trigonal–pyramidal thallium centre and features inter- and intramolecular Tl...F contacts.

Sandwich Compounds of Cyanotrispyrazolylborates: Complexation-Induced Ligand Isomerization

Reaction of the new cyanoscorpionate ligand, hydrotris(4-cyano-3-phenyl)pyrazolylborate (Tp(Ph),(4CN)) with Co(II), Mn(II), and Fe(II) unexpectedly results in the isolation only of crystals containing sandwich complexes in which the ligands have been isomerized to produce the heterocyanoscorpionate hydrobis(4-cyano-3-phenylpyrazolyl)(4-cyano-5-phenylpyrazolyl)borate (Tp(Ph),(4CN*)). The three complexes have been characterized crystallographically and are isostructural, with each ligand acting in a tridentate manner toward the metal. The isomerization of the ligand appears to be more facile than that of the analogous non-cyano ligand, Tp(Ph), with which crystals of the unisomerized sandwich compound have been isolated for Mn(II) and Fe(II).

Electronic structure of four-coordinate C3v nickel(II) scorpionate complexes: investigation by high-frequency and -field electron paramagnetic resonance and electronic absorption spectroscopies

A series of complexes of formula TpNiX, where Tp*- = hydrotris(3,5-dimethylpyrazole)borate and X = Cl, Br, I, has been characterized by electronic absorption spectroscopy in the visible and near-infrared (NIR) region and by high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy. The crystal structure of TpNiCl has been previously reported; that for TpNiBr is given here: space group = Pmc2(1), a = 13.209(2) A, b = 8.082(2) A, c = 17.639(4) A, alpha = beta = gamma = 90 degrees , Z = 4. TpNiX contains a four-coordinate nickel(II) ion (3d8) with approximate C3v point group symmetry about the metal and a resulting S = 1 high-spin ground state. As a consequence of sizable zero-field splitting (zfs), TpNiX complexes are "EPR silent" with use of conventional EPR; however, HFEPR allows observation of multiple transitions. Analysis of the resonance field versus the frequency dependence of these transitions allows extraction of the full set of spin Hamiltonian parameters. The axial zfs parameter for TpNiX displays pronounced halogen contributions down the series: D = +3.93(2), -11.43(3), -22.81(1) cm(-1), for X = Cl, Br, I, respectively. The magnitude and change in sign of D observed for TpNiX reflects the increasing bromine and iodine spin-orbit contributions facilitated by strong covalent interactions with nickel(II). These spin Hamiltonian parameters are combined with estimates of 3d energy levels based on the visible-NIR spectra to yield ligand-field parameters for these complexes following the angular overlap model (AOM). This description of electronic structure and bonding in a pseudotetrahedral nickel(II) complex can enhance the understanding of similar sites in metalloproteins, both native nickel enzymes and nickel-substituted zinc enzymes.