Crystallographic coincidence of two bridging species in a dinuclear CoIII ethynyl­benzene complex

In the title compound, trans,trans-[μ-(m-phenyl­ene)bis­(ethyne-1,2-di­yl)]bis­[chlorido(1,4,8,11-tetra­aza­cyclo­tetra­deca­ne)cobalt(III)]–trans,trans-[μ-(5-bromo-m-phenyl­ene)bis­(ethyne-1,2-di­yl)]bis­[chlorido(1,4,8,11-tetra­aza­cyclo­tetra­deca­ne)cobalt(III)]–tetra­phenyl­borate–acetone (0.88/0.12/2/4), [Co2(C12H4)Cl2(C10H24N4)2]0.88[Co2(C10H3Br)Cl2(C10H24N4)2]0.12(C24H20B)2·4C3H6O, with the exception of the acetyl­ene and bromine groups, all atomic postitions are the same in the two compounds and are modeled at full occupancy. The CoIII ions are six-coordinate with acetyl­ide and chloride ligands bound to the axial sites and the N atoms from the cyclam rings coordinated at the equatorial positions. N—H⋯O and N—H⋯Cl hydrogen-bonding interactions help to consolidate the crystal packing

Synthesis and characterization of low-dimensional paramagnetic acetylide complexes

2011 Spring.Includes bibliographical references.To view the abstract, please see the full text of the document

Crystal structures of two cross-bridged chromium(III) tetraazamacrocycles

The crystal structure of dichlorido(4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane)chromium(III) hexafluoridophosphate, [CrCl2(C12H26N4)]PF6, (I), has monoclinic symmetry (space group P21/n) at 150 K. The structure of the related dichlorido(4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane)chromium(III) hexafluoridophosphate, [CrCl2(C14H30N4)]PF6, (II), also displays monoclinic symmetry (space group P21/c) at 150 K. In each case, the CrIII ion is hexacoordinate with two cis chloride ions and two non-adjacent N atoms bound cis equatorially and the other two non-adjacent N atoms bound trans axially in a cis-V conformation of the macrocycle. The extent of the distortion from the preferred octahedral coordination geometry of the CrIII ion is determined by the parent macrocycle ring size, with the larger cross-bridged cyclam ring in (II) better able to accommodate this preference and the smaller cross-bridged cyclen ring in (I) requiring more distortion away from octahedral geometry

Synthesis and characterization of the chromium(III) complexes of ethylene cross-bridged cyclam and cyclen ligands

Dichloro(4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2] tetradecane) chromium(III) chloride, Dichloro(4,10-dibenzyl-1,4,7,10-tetraazabicyclo[ 5.5.2] tetradecane) chromium(III) chloride, and Dichloro(4,11-dimethyl- 1,4,8,11-tetraazabicyclo[6.6.2] hexadecane) chromium)(III) chloride have been prepared by the reaction of anhydrous chromium(III) chloride with the appropriate cross-bridged tetra-azamacrocycle. Aquation of these complexes proved difficult, but Chlorohydroxo(4,11-dimethyl- 1,4,8,11tetraazabicyclo[6.6.2] hexadecane) chromium)(III) chloride was synthesized directly from chromium(II) chloride complexation followed by exposure or the reaction to air in the presence of water. The four complexes were characterized by X-ray crystal structure determination. All contain the chromium(III) ion in a distorted octahedral geometry and the macrocycle in the cis-V configuration, as dictated by the ethylene cross-bridge. Further characterization of the hydroxo complex reveals a magnetic moment of mu(eff) = 3.95 B.M. and electronic absorbtions in acetonitrile at lambda(max) = 583 nm (epsilon = 65.8 L/cm mol), 431 nm (epsilon = 34.8 L/cm mol) and 369 nm (epsilon = 17 L/cm mol). (C) 2008 Elsevier B.V. All rights reserved

Two Pathways for Electrocatalytic Oxidation of Hydrogen by a Nickel Bis(diphosphine) Complex with Pendant Amines in the Second Coordination Sphere

A nickel bis­(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni­(P^Cy₂N^{<i>t‑</i>Bu}₂)₂]­(BF₄)₂ (P^Cy₂N^{<i>t‑</i>Bu}₂ = 1,5-di­(<i>tert</i>-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the Ni^II complex gives three isomers of the doubly protonated Ni⁰ complex [Ni­(P^Cy₂N^{<i>t‑</i>Bu}₂H)₂]­(BF₄)₂. Using the p<i>K</i>_a values and Ni^II/I and Ni^I/0 redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni­(P^Cy₂N^{<i>t</i>‑Bu}₂)₂]²⁺ was determined to be −7.9 kcal mol^–1. The catalytic rate observed in dry acetonitrile for the oxidation of H₂ depends on base size, with larger bases (NEt₃, <i>t</i>-BuNH₂) resulting in much slower catalysis than <i>n</i>-BuNH₂. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt₃ and <i>t</i>-BuNH₂. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H₂ using <i>n</i>-BuNH₂ as a base and with added water, a turnover frequency of 58 s^–1 is observed at 23 °C

Two Pathways for Electrocatalytic Oxidation of Hydrogen by a Nickel Bis(diphosphine) Complex with Pendant Amines in the Second Coordination Sphere

A nickel bis­(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni­(P^Cy₂N^{<i>t‑</i>Bu}₂)₂]­(BF₄)₂ (P^Cy₂N^{<i>t‑</i>Bu}₂ = 1,5-di­(<i>tert</i>-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the Ni^II complex gives three isomers of the doubly protonated Ni⁰ complex [Ni­(P^Cy₂N^{<i>t‑</i>Bu}₂H)₂]­(BF₄)₂. Using the p<i>K</i>_a values and Ni^II/I and Ni^I/0 redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni­(P^Cy₂N^{<i>t</i>‑Bu}₂)₂]²⁺ was determined to be −7.9 kcal mol^–1. The catalytic rate observed in dry acetonitrile for the oxidation of H₂ depends on base size, with larger bases (NEt₃, <i>t</i>-BuNH₂) resulting in much slower catalysis than <i>n</i>-BuNH₂. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt₃ and <i>t</i>-BuNH₂. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H₂ using <i>n</i>-BuNH₂ as a base and with added water, a turnover frequency of 58 s^–1 is observed at 23 °C

Two Pathways for Electrocatalytic Oxidation of Hydrogen by a Nickel Bis(diphosphine) Complex with Pendant Amines in the Second Coordination Sphere

A nickel bis­(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni­(P^Cy₂N^{<i>t‑</i>Bu}₂)₂]­(BF₄)₂ (P^Cy₂N^{<i>t‑</i>Bu}₂ = 1,5-di­(<i>tert</i>-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the Ni^II complex gives three isomers of the doubly protonated Ni⁰ complex [Ni­(P^Cy₂N^{<i>t‑</i>Bu}₂H)₂]­(BF₄)₂. Using the p<i>K</i>_a values and Ni^II/I and Ni^I/0 redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni­(P^Cy₂N^{<i>t</i>‑Bu}₂)₂]²⁺ was determined to be −7.9 kcal mol^–1. The catalytic rate observed in dry acetonitrile for the oxidation of H₂ depends on base size, with larger bases (NEt₃, <i>t</i>-BuNH₂) resulting in much slower catalysis than <i>n</i>-BuNH₂. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt₃ and <i>t</i>-BuNH₂. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H₂ using <i>n</i>-BuNH₂ as a base and with added water, a turnover frequency of 58 s^–1 is observed at 23 °C