Chang Neng Chen

Efficient photo-driven hydrogen evolution by binuclear nickel catalysts of different coordination in noble-metal-free systems.

Exploration of the complex Ni2(MBD)4 (MBD = 2-mercaptobenzimidazole) (C1) having different coordinated Ni atoms as a photocatalyst for hydrogen evolution is made. For comparison, the bimetallic Ni2(MBT)4 (MBT = 2-mercaptobenthiazole) (C2) complex with the same coordinated Ni atoms was synthesized. Both of the complexes have been successfully constructed for photo-induced hydrogen production using organic dyes as photosensitizers and triethanolamine (TEOA) as the effective electron donor by visible light (>400 nm) in acetonitrile-water solution. The time-dependence of H2 generation and DFT computational studies demonstrate that the complex C1 is more active than C2 for H2 evolution. The mechanisms of photocatalytic hydrogen generation for C1 and C2 involve different protonation sites resulting from the differences between the two structures.

Syntheses, structures, and magnetic properties of a family of tetra-, hexa-, and nonanuclear Mn/Ni heterometallic clusters

A family of Mn(III)/Ni(II) heterometallic clusters, [Mn(III)(4)Ni(II)(5)(OH)(4)(hmcH)(4)(pao)(8)Cl(2)]·5DMF (1·5DMF), [Mn(III)(3)Ni(II)(6)(N(3))(2)(pao)(10)(hmcH)(2)(OH)(4)]Br·2MeOH·9H(2)O (2·2MeOH·9H(2)O), [Mn(III)Ni(II)(5)(N(3))(4)(pao)(6)(paoH)(2)(OH)(2)](ClO(4))·MeOH·3H(2)O (3·MeOH·3H(2)O), and [Mn(III)(2)Ni(II)(2)(hmcH)(2)(pao)(4)(OMe)(2)(MeOH)(2)]·2H(2)O·6MeOH (4·2H(2)O·6MeOH) [paoH = pyridine-2-aldoxime, hmcH(3) = 2, 6-Bis(hydroxymethyl)-p-cresol], has been prepared by reactions of Mn(II) salts with [Ni(paoH)(2)Cl(2)], hmcH(3), and NEt(3) in the presence or absence of NaN(3) and characterized. Complex 1 has a Mn(III)(4)Ni(II)(5) topology which can be described as two corner-sharing [Mn(2)Ni(2)O(2)] butterfly units bridged to an outer Mn atom and a Ni atom through alkoxide groups. Complex 2 has a Mn(III)(3)Ni(II)(6) topology that is similar to that of 1 but with two corner-sharing [Mn(2)Ni(2)O(2)] units of 1 replaced with [Mn(3)NiO(2)] and [MnNi(3)O(2)] units as well as the outer Mn atom of 1 substituted by a Ni atom. 1 and 2 represent the largest 3d heterometal/oxime clusters and the biggest Mn(III)Ni(II) clusters discovered to date. Complex 3 possesses a [MnNi(5)(μ-N(3))(2)(μ-OH)(2)](9+) core, whose topology is observed for the first time in a discrete molecule. Careful examination of the structures of 1-3 indicates that the Mn/Ni ratios of the complexes are likely associated with the presence of the different coligands hmcH(2-) and/or N(3)(-). Complex 4 has a Mn(III)(2)Ni(II)(2) defective double-cubane topology. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1-4. Fitting of the obtained M/(Nμ(B)) vs H/T data gave S = 5, g = 1.94, and D = -0.38 cm(-1) for 1 and S = 3, g = 2.05, and D = -0.86 cm(-1) for 3. The ground state for 2 was determined from ac data, which indicated an S = 5 ground state. For 4, the pairwise exchange interactions were determined by fitting the susceptibility data vs T based on a 3-J model. Complex 1 exhibits out-of-phase ac susceptibility signals, indicating it may be a SMM.

Octanuclear MnIII6MnIILn (Ln = Gd, Dy and Er) clusters with a novel core topology: syntheses, structures, and magnetic properties

Reactions of [Mn6O2(piv)10(py)2.5(piv)1.5], Ln(NO3)3·6H2O and N-mdeaH2 in MeCN in the presence of Me3SiCl generated a family of octanuclear Mn/Ln complexes [Mn6(III)Mn(II)Ln(N-mdea)3(N-mdeaH)(piv)8O2(OH)3(NO3)(H2O)]·xCH3CN·xH2O [Ln = Gd (1), Dy (2), Er (3), pivH = pivalic acid, N-mdeaH2 = N-methyl diethanolamine]. Each complex possesses a [Mn6(III)Mn(II)Ln(μ3-O)2(μ3-OH)3](16+) core containing two butterfly-like subunits of [Mn3Ln(μ3-OH)2] and [Mn4(μ3-O)2] sharing a common vertex, and an outer Mn atom ligated to one of the subunits through a μ3-OH(-) ligand. The core topology represents a new Mn/Ln core type. The magnetic susceptibility study of 1-3 indicates the presence of dominant antiferromagnetic interactions within the complexes. For complex 1, which contains an isotropic Gd(III) atom, fitting of the obtained M/(NμB) vs. H/T data gave S = 4, g = 1.90, and D = -0.31 cm(-1). The results were further supported by ac data. Complex exhibits out-of-phase ac susceptibility signals, indicating it may be a SMM.

Luminescent square-planar platinum(II) complexes with tridentate 3-bis(2-pyridylimino)isoindoline and monodentate N-heterocyclic ligands

A series of platinum(II) complexes with 1,3-bis(2-pyridylimino)isoindoline (BPI) derivatives were prepared by substitution of the coordinated Cl in the precursor complex Pt(BPI)Cl with a N-heterocyclic ligand such as pyridine, phthalazine or phenanthridine. These complexes display orange to red luminescence in fluid dichloromethane solutions and in the solid states at room temperature. The photophysical properties were tuned by introducing electron-withdrawing -NO(2) or electron-donating -NH(2) to the BPI ligand. The DFT computational studies suggest that the emission in the N-heterocyclic ligand substituted platinum(II) complexes originates mainly from the (3)[π→π*(BPI)] (3)IL triplet excited state, mixed with some (3)[dπ(Pt)→π*(BPI)] (3)MLCT character. Compared with the precursor Pt(BPI)Cl, both the low-energy absorption and the emission in the N-heterocyclic ligand substituted platinum(II) complexes exhibits a distinct blue-shift due to an obviously enhanced contribution from the (3)IL state and a reduced (3)MLCT character.

Efficient photocatalytic hydrogen evolution with end-group-functionalized cobaloxime catalysts in combination with graphite-like C3N4

Three comparable hybrid photocatalytic systems, comprising semiconductor g-C3N4, end-group-functionalized cobaloxime complexes (carboxy-functionalized cobaloxime, C1; pyrene-functionalized cobaloxime, C2; and non-functionalized cobaloxime, C3), and triethanolamine (TEOA), are active for visible-light-driven hydrogen production in CH3CN–H2O (9/1, v/v) solution. Upon irradiation for 12 h, the turnover numbers of hydrogen evolution are 234, 281 and 195 for the hybrid systems C1/g-C3N4, C2/g-C3N4 and C3/g-C3N4, respectively. The highest hydrogen evolution efficiency of the C2/g-C3N4 system can be attributed to the strongest π–π interactions between the pyrene moiety and g-C3N4. Based on electrochemical properties, steady-state photoluminescence spectra and theoretical analyses, the visible light absorption of g-C3N4, the catalytic H2-evolving ability of cobaloxime as well as the efficient charge separation of the excited g-C3N4 in the presence of both TEOA and cobaloxime, are responsible for the high activity of these hybrid systems.

Photoswitchable electrochemical behaviour of a [FeFe] hydrogenase model with a dithienylethene derivative

A diiron dithiolate complex 1o with a dithienylethene (DTE) phosphine ligand has been elaborately designed and fully investigated by spectroscopic and DFT computational studies. Upon irradiation with UV light, the DTE moiety in complex 1o undergoes an excellent photocyclization reaction to attain ring-closed state 1c in high yield (>95%), accompanied by a colour change from orange to deep blue. On the other hand, upon irradiation with visible light (>460 nm), ring-closed form 1c in CH(3)CN solution reverts perfectly into ring-open form 1o. Both 1o and 1c were characterised by IR, (1)H, (31)P, (19)F NMR and electrochemical spectroscopy. The electrochemical behaviours of both the open and closed forms were investigated by cyclic voltammetry. Upon photocyclization reaction, a 290 mV (from -2.29 V to -2.00 V) positive shift is induced in the potential of electrochemical catalytic proton reduction, due to the electron-withdrawing effect of the ring-closed DTE moiety. Consequently, complex 1 can reversibly photoswitch the potential of proton reduction on the [FeFe] moiety.

Synthesis, structures and electrochemistry studies of 2Fe2S–Fe(II)(S–2N)2 models for H-cluster of [FeFe]-hydrogenase

A series of model complexes [(μ-pdt)Fe(2)(CO)(5)](2)M(sip)(2) (M = Fe, Ni) were synthesized as H-cluster analogues of [FeFe]-hydrogenase. Their electrochemical behaviours were investigated and it is proposed that the bridging metal bis(tris-chelate) groups act as electron transfer sites in theses mimics.

A triclinic polymorph of bis­(μ2-ethane­thiol­ato)-1:2κ2S:S;3:4κ2S:S-(μ4-disulfido-1:2:3:4κ4S:S:S′:S′)tetra­kis­[tricarbonyl­iron(II)](2 Fe—Fe)

Next to the monoclinic polymorph [Cheng et al. (2005 ▶). Acta Cryst. E61, m892–m894], the triclinic title compound, [Fe4(C2H5S)2(S2)(CO)12], is the second known form of this composition. The structure is composed of an [Fe2(C2H5S)(S)(CO)6] subcluster, which is linked to its counterpart by an inversion centre located at the mid-point of the central disulfide bond. The Fe2S2 core of each subcluster exhibits a butterfly-like shape, with two S atoms bridging two Fe atoms. In the subcluster, each Fe atom is coordinated in a distorted octahedral coordination by three terminal carbonyl C atoms, two S atoms and one Fe atom. The crystal packing is accomplished through van der Waals interactions.

Phosphine-participated formation and crystal structures of nickel complexes with 2-sulfanylphenol and phosphine ligands

Neutral tri- and mono-nuclear complexes [Ni3(OC6H4S)2(HOC6H4S)2(PBu3n)2]·2EtOH 1 and [Ni(OC6H4S)-(PMe2Ph)2]2 of 2-sulfanylphenol were obtained in the presence of a phosphine in EtOH solutions, and their crystal structures determined. Complex 1 is made up of three nickel ions chelated and bridged by two OC6H4S2– dianions in ObSt fashion and two HOC6H4S– monoanions in HOtSb fashion, where the central nickel(II) atom has an elongated octahedral geometry whereas the two at the sides have square-planar surroundings. In 2 the nickel(II) atom is located in a square-planar environment, chelated by a OC6H4S2– dianion in OtSt mode. Complex 1 is paramagnetic and its magnetic behaviour is explained by single-ion anisotropy.