Combining photosensitizers: The case of [Cl2Pt(bpym)Re(CO)3Cl] and its dithiolate analogs

The bimetallic complex [Cl2Pt(bpym)Re(CO)(3)Cl] (4) (where bpym denotes 2,2’-bipyrimidine) has been prepared along with the corresponding monometallic precursors and the dithiolate derivatives with bdt(2-) (1,2-benzene-dithiolate) and mnt(2-) (1,2-maleonitrile-dithiolate). The compounds have been characterized using elemental analysis, NMR, FTIR, UV-Vis and cyclic voltammetry methods. DFT and TD-DFT calculations on all the complexes under study allow us to correlate geometries and electronic structures. The theoretical studies of the dithiolate bimetallic complexes assigned the main band in the UV-Vis spectrum as a mixed metal ligand to ligand charge transfer transition (MML’CT), analogous to [M(diimine)(dithiolate)] complexes, with the former red shifted due to the presence of the Re(CO)(3)Cl moiety. Moreover coordination of the dithiolate ligand to the bimetallic complex 4 influences not only the energy, but also the nature of HOMO orbital altering it from Re(CO)(3)Cl to Pt/bdt character. (C) 2012 Elsevier Ltd. All rights reserved

Isolation, Characterization, and Computational Studies of the Novel [Mo-3(mu(3)-Br)(2)(mu-Br)(3)Br-6](2-) Cluster Anion

The novel trimolybdenum cluster [Mo-3(mu(3)-Br)(2)(mu-Br)(3)Br-6](2-) (1, Mo-3(9+), 9 d-electrons) has been isolated from the reaction of [Mo(CO)(6)] with 1,2-C2H4Br2 in refluxing PhCl. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (n-Bu)(4)N+ (1), Et4N+, Et(3)BzN(+)), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (n-Bu)(4)N+ salt crystallizes in the monoclinic space group C2/c, a = 20.077(2) angstrom, b = 11.8638(11) angstrom, c = 22.521(2) angstrom, alpha = 90 deg, beta = 109.348(4) deg, gamma = 90 deg, V = 5061.3(9) angstrom(3), Z = 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (mu(eff), 1.55 mu(B), r.t.) is lower than the spin-only value (1.73 mu(B)) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm(-1)). The antiferromagnetic character is delocalized over three magnetic orbitals populated by three electrons. The assignment of the infrared spectra is also provided

Isolation, Characterization, and Computational Studies of the Novel [Mo₃(μ₃-Br)₂(μ-Br)₃Br ₆]²⁻ Cluster Anion

The novel trimolybdenum cluster [Mo3(μ 3-Br)2(μ -Br)3Br6]2- (1, {Mo3}9+, 9 d-electrons) has been isolated from the reaction of [Mo(CO)6] with 1,2-C2H4Br2 in refluxing PhCl. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (n-Bu)4N+ (1), Et4N+, Et3BzN+), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (n-Bu)4N+ salt crystallizes in the monoclinic space group C2/c, a = 20.077(2) Å, b = 11.8638(11) Å, c = 22.521(2) Å, α = 90 deg, β = 109.348(4) deg, γ = 90 deg, V = 5061.3(9) Å3, Z = 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (μ eff, 1.55 μ B, r.t.) is lower than the spin-only value (1.73 μ B) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm-1). The antiferromagnetic character is delocalized over three magnetic orbitals populated by three electrons. The assignment of the infrared spectra is also provided

Role of the Acceptor in Tuning the Properties of Metal [M(II) = Ni, Pd, Pt] Dithiolato/Dithione (Donor/Acceptor) Second-Order Nonlinear Chromophores: Combined Experimental and Theoretical Studies

The mixed-ligand complexes [M­(II)­(Et₂dazdt)­(mnt)] (M = Ni, <b>1</b>; Pd, <b>2</b>; Pt, <b>3</b>) [Et₂dazdt = <i>N</i>,<i>N</i>′-diethyl-perhydrodiazepine-2,3-dithione; mnt = maleonitrile-2,3-dithiolate] have been prepared and fully characterized. X-ray diffractometric studies on <b>1</b>–<b>3</b> (the structure of <b>1</b> was already known) show that the crystals are isostructural (triclinic, <i>P</i>–1), and two independent molecular entities are present in the unit cell. These entities differ in the orientation of the ethyl substituents with respect to the epta-atomic ring. In the C₂S₂MS₂C₂ dithiolene core the four sulfur atoms define a square-planar coordination environment of the metal where the M–S bond distances involving the two ligands are similar, while the C–S bond distances in the C₂S₂ units exhibit a significant difference in Et₂dazdt (dithione) and mnt (dithiolato) ligands. <b>1</b>–<b>3</b> show in the visible region one or two moderately strong absorption peaks, having ligand-to-ligand charge-transfer (CT) character with some contribution of the metal, and show negative solvatochromism and molecular quadratic optical nonlinearity, which was determined by the EFISH (electric-field-induced second-harmonic generation) technique. These complexes are redox active and show two reversible reduction waves and one irreversible oxidation wave. Theoretical calculations based on DFT and TD-DFT calculations on complexes <b>1</b>–<b>3</b> as well as on [Pt­(Bz₂pipdt)­(mnt)] (<b>4</b>) and [Pt­(Bz₂pipdt)­(dmit)] (<b>5</b>) highlight the factors which affect the optical properties of these second-order redox-active NLO chromophores. Actually, the torsion angle of the dithione system (δ₂) inversely correlates either with the oscillator strengths of the main transition of the complexes or with their beta values. The high beta value of <b>5</b> can be attributed both to its lowest torsion angles and to the extent of the π system of its dithiolate ligand, dmit