Synthesis and electrocatalytic reactivity for water oxidation of two cerium complexes

<p>Two cerium complexes with and without manganese ion, [MnCe₄(dipic)₆(H₂O)₂₀][Ce(dipic)₃]₂·7H₂O (dipic = dipicolinate) (<b>1</b>) and [Ce₂(H₂O)₄(O₂CMe)₆][Ce(H₂O)₄(NO₃)₂(O₂CMe)]₂·2H₂O·2MeOH (<b>2</b>), have been prepared, and their electrocatalytic reactivity for water oxidation has been investigated. Compound <b>1</b> is a heterometallic 3d-4f compound which possesses four Ce(IV) ions, two Ce(III) ions, and one Mn(II). Compound <b>2</b> is composed of three neutral parts, one of which is a dinuclear cerium molecule lying on an inversion center, and the other two are symmetric monomer units; the four cerium ions in <b>2</b> are all Ce(III). Electrochemical studies of <b>1</b> and <b>2</b> show that <b>1</b> can catalyze water oxidation at the potential ~1.5 V with an overpotential of <i>ca.</i> 900 mV <i>versus</i> NHE. Control potential electrolysis (CPE) experiments at 1.50 V of <b>1</b> displayed a stable current density of 2.5 mA/cm², and the calculated Faradaic efficiency is 60%. However, no electrocatalytic reactivity was observed for <b>2</b>. By comparison experiments, it was found that the electrocatalysis of <b>1</b> may result from the cooperative catalytic effect of the 4f cerium ion and 3d transition metal manganese ion.</p

Multistate Photochromism in a Ruthenium Complex with Dithienylethene–Acetylide

The preparation, characterization, and photochromic properties of the ruthenium­(II) vinylidene complex <b>1o</b> and the ruthenium­(II) acetylide complex <b>2o</b> and its oxidized species <b>2o</b>⁺ with one dithienylethene (DTE) unit are described. Complexes <b>1o</b> and <b>2o</b> can be mutually transformed upon the addition of base or acid due to the interconversion RuCCH–DTE ⇆ Ru–CC–DTE. <b>2o</b> and its oxidized species <b>2o</b>⁺ can be interconverted through a reversible redox process. It is found that the ring-closing absorption band of DTE shows a progressive red shift in the order 628 nm (<b>1c</b>) → 641 nm (<b>2c</b>⁺) → 692 nm (<b>2c</b>). The photocyclization/cycloreversion quantum yields are in the order <b>1</b> (Φ_o→c = 0.0066, Φ_c→o = 0.001) < <b>2</b>⁺ (Φ_o→c = 0.35, Φ_c→o = 0.012) < <b>2</b> (Φ_o→c = 0.58, Φ_c→o = 0.019), implying that the photochemical reactivity exhibits the order <b>1</b> < <b>2</b>⁺ < <b>2</b>, coinciding well with the progressively increased electronic density at the reactive carbon atoms. The interconversion among six states is clearly demonstrated by NMR, UV–vis–near-IR, and IR spectral, electrochemical, and computational studies