‘Counting ions’ in Alfred Werner’s coordination chemistry using electrical conductivity measurements

AbstractFrom 1888 till 1892 Alfred Werner, the founder of coordination chemistry, developed together with his friend Arturo Miolati electrical conductivity of ionic complexes as an auxilliary analytical tool for structural elucidations of complexes. The used electrical conductivity device was based on a design of Wilhelm Ostwald consisting of a generator for alternating current (induction apparatus with Wagner hammer), a measuring cell with platinated electrodes and a rheostatic part including a buzzer for balancing resistivity conditions. Electrical conductivities were examined in the ion-isomeric series of Pt(II)(NH3)nCl2 (n = 0 - 4), Pt(IV)(NH3)nCl4 (n = 0 - 6) and Co(III)(NH3)nCl3 (n = 0 - 6) complexes producing approximately V-shaped curves in dependence of the stoichiometry factor n. Replacing in the coordination spheres neutral Lewis base type ligands by ‘anionic residues’ generated charged complexes, which by conductivity measurements laid grounds for Alfred Werner’s coordination theory [primary (from ‘anionic residues’) and secondary valencies (from Lewis bases)] and the Nobel Prize in 1913. From 1893 on seven PhD theses were prepared in Alfred Werner’s group, which dealt with conductivity measurements establishing identification processes of complexes by ‘ion counting’. In 1902 Alfred Werner ceased to apply electrical conductivity in his group switching to meanwhile more timely coordination chemistry fields.Resumen (‘Contando iones’ en la química de coordinación de alfred werner con el uso de mediciones de conductividad)Desde 1888 hasta 1892 Alfred Werner, el fundador de la química de coordinación, desarrrolló junto con su amigo Arturo Miolati la medición de conductividad eléctrica de iones complejos como una herramienta analítica auxiliar para la elucidación de la estructura de complejos. El aparato utilizado para la conductividad eléctrica estaba basado en un diseño de Wilhelm Ostwald, que consistía de un generador de corriente alterna (aparato de inducción con martillo de Wagner), una celda de medición con electrodos platinados y un componente reostático que incluía un timbre para balancear las condiciones de resistividad. Las conductividades eléctricas fueron examinadas en una serie de iones isoméricos complejos de Pt(II)(NH3)nCl2 (n = 0 - 4), Pt(IV)(NH3)nCl4 (n = 0 - 6) y de Co(III)(NH3)nCl3 (n = 0 - 6), que produjeron curvas en forma de V con dependencia en el factor estequiométrico, n. Al reemplazar en la esfera de coordinación ligantes neutros tipo base de Lewis por ‘residuos aniónicos’ se generaron complejos cargados, que por mediciones de la conductividad condujeron a Alfred Werner a la teoría de la coordinación [valencia primaria (proveniente de los ‘residuos aniónicos’) y secundaria (de las bases de Lewis)]. A partir de 1893, siete tesis doctorales fueron elaboradas por miembros del grupo de Werner en las que con mediciones de la conductividad establecieron el proceso de identificacion de complejos por ‘conteo de iones’. A partir de 1902, Alfred Werner cerró la aplicación de la conductividad eléctrica en su grupo cambiando a otros temas más avanzados de la química de coordinación

1,3-Bis(pyridin-2-yl)-1H-benzimidazol-3-ium tetra­fluoridoborate

The asymmetric unit of the title compound, C17H13N4 +·BF4 −, contains one half of the benzimidazolium cation and one half of the tetra­fluoridoborate anion, with crystallographic mirror planes bis­ecting the mol­ecules. One F atom of the tetra­fluoridoborate is equally disordered about a crystallographic mirror plane. In the crystal, C—H⋯F inter­actions link the cations and anions into layers parallel to (100). The crystal packing is further stabilized by F⋯π contacts involving the tetra­fluoridoborate anions and the five-membered rings [F⋯centroid = 2.811 (2) Å]

Dinitrosyl rhenium complexes for ring-opening metathesis polymerization (ROMP)

The treatment of benzene solutions of the cations [Re(NO)2(PR3)2][BArF4] (R = Cy and R = iPr; [BArF4] = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) with phenyldiazomethane afforded the moderately stable cationic rhenium(I) benzylidene dinitrosyl bis(trialkyl) phosphine complexes as [BArF4]- salts in good yields. The cationic rhenium dinitrosyl bisphosphine complexes catalyze the ring-opening metathesis polymerization (ROMP) of highly strained nonfunctionalized cyclic olefins to give polymers with relatively high polydispersity indices, high molecular weights, and Z configurations of the double bonds in the polymer chain backbones of over 80 %. The benzylidene derivatives are almost inactive in ROMP catalysis with norbornene and in olefin metathesis. NMR experiments gave first hints for the initial formation of carbene complexes when [Re(NO)2(PR3)2][BArF4] was treated with norbornene. The carbene formation is initiated by an unique reaction sequence where the cleavage of the strained olefinic bond starts with phosphine migration forming a cyclic ylid carbene complex. The [2+2] addition of a norbornene molecule to the Re=C bond leads to the rhenacyclobutane complex, which is expected to be converted into an iminate complex by attack of the ylid function onto one of the NNO atoms followed by Wittig-type phosphine oxide elimination. The formation of phosphine oxide was confirmed by NMR spectroscopy. This species is thought to drive the ROMP metathesis with alternating rhenacyclobutane formations and cycloreversions. The proposed mechanism is supported by density functional theory (DFT) calculation

Chemistry of chromium bis-acetylide complexes

Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)2Cr(dmpe)2] n+ (R=Ph, SiMe3, SiEt3, C≡C-SiMe3 n=0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies. Graphical Abstrac

Bis[1,3-bis­(2,4,6-trimethyl­phen­yl)-2,3-dihydro-1H-imidazol-2-yl­idene]dichloridodinitro­syltungsten(II) tetra­hydro­furan-d 8 monosolvate

The mol­ecular structure of the title compound, [WCl2(NO)2(C21H24N2)2]·C4D8O, displays a distorted octa­hedral arrangement around the W atom with two trans 1,3-bis­(2,4,6-trimethyl­phen­yl)imidazol-2-yl­idene (IMes) carbene ligands in axial positions. The four equatorial positions are occupied by nitrosyl and chloride ligands, which are trans to each other. The Ccarbene—W—Ccarbene bond angle of 173.44 (18)° and the Cl—W—Nnitros­yl bond angles of 171.34 (11) and 171.32 (13)° deviate only slightly from linearity. The distortion comes from the nitrosyl and chloride ligands which are not fully coplanar since the two N atoms deviate from the WCl2 plane by −0.279 (4) and 0.272 (4) Å, respectively. An inter­molecular C—H⋯O inter­action connects the organometallic mol­ecule and the tetra­hydro­furan-d 8 solvent mol­ecule

In the footsteps of Alfred Werner: The institute of Inorganic Chemistry at the University of Zurich

Inorganic chemistry has a long-standing tradition at the University of Zurich starting with Carl Jacob Lowig, the first professor of chemistry. The influence of Nobel Prize winner Alfred Werner in coordination, organometallic, and bioinorganic chemistry extends right up to the present day as can be seen in many of the research fields of the current professors and young research scientists. With all due respect for the long tradition in inorganic chemistry the Institute of Inorganic Chemistry is also looking forwards to define its role to meet the challenges of the future

Field-induced Conductance Switching by Charge-state Alternation in Organometallic Single-Molecule Junctions

Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These molecular intrinsic properties are usually addressed by varying the molecules electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high to low current ratios exceeding 1000 at voltage stimuli of less than 1.0 V. DFT calculations identify a localized, redox active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarised ground state unique to the Mo centre. This situation opens an additional slow and incoherent hopping channel for transport, triggering a transient charging effect of the entire molecule and a strong hysteresis with unprecedented high low-to-high current ratios.Comment: 9 pages, 4 figure

Synthetic and mechanistic studies of metal-free transfer hydrogenations applying polarized olefins as hydrogen acceptors and amine borane adducts as hydrogen donors

Metal-free transfer hydrogenation of polarized olefins (RR'C=CEE': R, R' = H or organyl, E, E' = CN or CO(2)Me) using amine borane adducts RR'NH-BH(3) (R = R' = H, AB; R = Me, R' = H, MAB; R = (t)Bu, R' = H, tBAB; R = R' = Me, DMAB) as hydrogen donors, were studied by means of in situ NMR spectroscopy. Deuterium kinetic isotope effects and the traced hydroboration intermediate revealed that the double H transfer process occurred regio-specifically in two steps with hydride before proton transfer characteristics. Studies on substituent effects and Hammett correlation indicated that the rate determining step of the H(N) transfer is in agreement with a concerted transition state. The very reactive intermediate NH(2)=BH(2)] generated from AB was trapped by addition of cyclohexene into the reaction mixture forming Cy(2)BNH(2). The final product borazine (BHNH)(3) is assumed to be formed by dehydrocoupling of NH(2)=BH(2)] or its solvent stabilized derivative NH(2)=BH(2)]-(solvent), rather than by dehydrogenation of cyclotriborazane (BH(2)NH(2))(3) which is the trimerization product of NH(2)=BH(2)]