ABSTRACT
The divalent heteroleptic lanthanoid fluoride complex, [Yb(C5Ph4H)(µ-F)(thf)2]2, as well as [Yb(C5Ph4H)2(thf)] and [Yb(C5Ph4H)(C6F5)(thf)2] were obtained from reactions of ytterbium metal with Hg(C6F5)2 and tetraphenylcyclopentadiene under different conditions, and C-F activation of C6F5H by Yb metal was observed.
ABSTRACT
Reaction of [15]crown-5 with erbium nitrate and a range of nickel salts results in the formation of the hydrogen-bonded chain species [Er(NO3)3(H2O)3]. [15]crown-5 H2O (3), [Ni(H2O)6]Br2 [15]crown-5 2H2O (4), [Ni(H2O)6](ClO4)2 x [15]crown-5 2H2O (5), [Ni(H2O)6](NO3)2 [15]crown-5 2H2O (6) and [[Ni(H2O)4]2(muCl)2]Cl2 [15]crown-5 (7). Complexes 3-5 exhibit low symmetry structures with 2-4 unique crown ether molecules, whereas 6 and 7 are more symmetrical. The factors contributing to this behaviour are discussed within the wider context of [15]crown-5 structures in the Cambridge Structural Database.
ABSTRACT
Hydroxo- and methoxo-bridged tetranuclear copper(II) complexes of the tetramacrocyclic ligand 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene (Ldur), have been prepared from [Cu4Ldur(H2O)8](ClO4)8.9H2O (1). Addition of base to an aqueous solution of 1 gave [Cu4Ldur(mu2-OH)4](ClO4)4 (2). Diffusion of MeOH into a DMF solution of 2 produces [Cu4Ldur(mu2-OMe)4](ClO4)4.HClO4.2/3MeOH (3), a complex which hydrolyzes on exposure to moisture regenerating 2. The structurally related azido-bridged complex, [Cu4Ldur(mu2-N3)4](PF6)4.4H2O.6CH3CN (4), was produced by reaction of Ldur with 4 molar equiv of Cu(OAc)2.H2O and NaN3 in the presence of excess KPF6. Compounds 2-4 crystallize in the triclinic space group P1 (No. 2) with a = 10.248(1) A, b = 12.130(2) A, c = 14.353(2) A, alpha = 82.23(1) degrees, beta = 80.79(1) degrees, gamma = 65.71(1) degrees, and Z = 1 for 2, a = 10.2985(4) A, b = 12.1182(4) A, c = 13.9705(3) A, alpha = 89.978(2) degrees, beta = 82.038(2) degrees, gamma = 65.095(2) degrees, and Z = 1 for 3, and a = 12.059(2) A, b = 12.554(2) A, c = 14.051(2) A, alpha = 91.85(1) degrees, beta = 98.22(1) degrees, gamma = 105.62(1) degrees, and Z = 1 for 4. The complexes feature pairs of isolated dibridged copper(II) dimers with "roof-shaped" Cu2(mu2-X)2 cores (X = OH-, OMe-, N3-), as indicated by the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 degrees for 3, and 153 degrees for 4). This leads to Cu.Cu distances of 2.940(4) A for 2, 2.962(1) A for 3, and 3.006(5) A for 4. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -27 cm(-1)) for the hydroxo-bridged copper(II) centers in 2 and very strong antiferromagnetic coupling (J = -269 cm(-1)) for the methoxo-bridged copper(II) centers in 3. Pairs of copper(II) centers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) reported thus far for bis(mu2-1,1-azido)-bridged dicopper units. Spectral measurements on a neat powdered sample of 4 at 33.9 GHz or 90 Ghz confirm the spin-triplet ground state for the azido-bridged copper(II) pairs.
ABSTRACT
The pKa values associated with protonation of the one-electron reduced forms of series of [L'2Ru(II)L]2+ complexes [L' = bidentate polypyridyl ligand; L = bidentate polypyridyl ligand with additional uncoordinated N atoms in the aromatic ring system: e.g., dpp = 2,3-bis(2-pyridyl)pyrazine, bpz = 2,2'-bipyrazine] were assessed using pulse radiolysis techniques by the measurement of spectral variations as a function of pH. A linear correlation was observed between pKa and E (RuL'2L2+/+) for complexes in which the protonatable ligand was at the same time the site of reduction. In complexes where one or more of the nonprotonatable ligands (L') had very low pi* energy levels [e.g. (CF3)4bpy], reduction occurs on a nonprotonatable ligand and a dramatic decrease in the pKa values was observed for the reduced species. In complexes where the energies of the protonatable and nonprotonatable ligands were comparable, the protonation behavior was consistent with some orbital mixing/ delocalization of the electronic charge.
