Bulky countercation effects on the crystal packing of anionic dithiooxalato-containing Ni(ii), Pd(ii) and Pt(ii) complexes: spectroscopic–redox correlations†
a
Anna
Switlicka,
*b
Barbara
Machura,
b
Nicolás
Moliner,
a
Renato
Rabelo,
a
Rafael
Ruiz-García,
a
Salah-Eddine
Stiriba,
a
Joan
Cano
a
and
Miguel
Julve
*a
Abstract
Herein, we report the synthesis, X-ray structures, thermal stability, spectroscopic characterization and redox properties of compounds of formulas (BzPh3P)2[Ni(dto)2] (1), (BzPh3P)2[Pd(dto)2]·nCH2Cl2 [n = 0 (2) and 3 (2·3CH2Cl2)], (BzPh3P)2[Pt(dto)2] (3), (Ph4As)2[Ni(dto)2]·n(CH3)2CO [n = 0 (4) and 1 (4·(CH3)2CO)], (Ph4As)2[Pd(dto)2] (5) and (Ph4As)2[Pt(dto)2] (6) (dto2− = dithiooxalate, BzPh3P+ = benzyltriphenylphosphonium and Ph4As+ = tetraphenylarsonium), together with the synthesis and X-ray structure of the corresponding diphenyl dithioxalate proligand (Ph2dto). The crystal structures of 1–6 and those of the solvated compounds 2·3CH2Cl2 and 4·Me2CO have in common the presence of discrete planar [M(dto)2]2− complex anions where the divalent metal ions exhibit rectangular (M = Ni) or quasi square planar MS4 (M = Pd and Pt) environments. The M–S bond lengths are typical of nd8 MII ions [n = 3 (Ni), 4 (Pd) and 5 (Pt)] in a low-spin (LS) electronic configuration, varying in the order 2.17 (Ni) < 2.30 (Pd) ≈ 2.29 Å (Pt). The electroneutrality is achieved by bulky BzPh3P+ (1–3 and 2·3CH2Cl2) and Ph4As+ [4–6 and 4·(CH3)2CO] countercations. Segregated (1–3 and 4–6) or mixed [2·3CH2Cl2 and 4·(CH3)2CO] layers of complex anions and cations linked by electrostatic forces and Van der Waals interactions together with very weak S⋯O![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
C and C–H⋯OC type contacts occur in them. The dichloromethane and acetone molecules of crystallization occupy the interlayer space or are embedded within the mixed layers, respectively. The redox chemistry of the [M(dto)2]2− complex anions of 4–6 was investigated by cyclic voltammetry in acetonitrile solution. The one-electron metal centred irreversible oxidations were evident in the cyclic voltammograms with oxidation potentials of +0.18 (Ni), +0.72 (Pd) and +0.45 V (Pt) vs. Fc+/Fc. The UV-vis spectra of acetonitrile solutions of the square planar [M(dto)2]2− species of 4–6 are similar, and they show a broad, intense metal-to-ligand charge transfer (MLCT) transition centred at 498 (Ni), 376 (Pd) and 422 nm (Pt). A linear correlation between the values of energy of the MLCT transition and those of the formal redox potential is found along this [MII(dto)2]2− family pointing out an important contribution from a nd–nd (n = 3–5) transition.
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