Chen-Yu Yeh

Extended Metal-Atom Chains with an Inert Second Row Transition Metal : [Ru5(μ5-tpda)4X2] (tpda2-= tripyridyldiamido dianion, X = Cl and NCS)

EMACs (extended metal-atom chains) offer a unique platform for the exploration of metal-metal interactions. There has been significant advances on the synthesis of EMACs, such as lengthening the chains up to 11 metal atoms thus far, integrating naphthyridine moieties for tuning the charge carried at metal centers, and manipulation of metal-metal interactions. However, the metal centers in EMACs hitherto are limited to first row transition metals which are more labile than those relatively inert ones with electrons filled in the 4d and 5d shells. In this Communication, the synthesis, crystallographic, magnetic, and electrical conducting studies of [Ru5(mu5-tpda)4Cl2] and [Ru5(mu5-tpda)4(NCS)2], the first pentanuclear EMACs of second-row transition metal, are reported.

Four quadruple metal-metal bonds lined up: linear nonachromium(II) metal string complexes.

Through a new pyrazine-modulated penta-pyridyl-tetraamine ligand, H(4)N(9)-mpz, linear nonachromium(II) complexes with four quadruple metal-metal bonds were successfully obtained, and their structure, magnetic and electrochemistry properties were studied.

Weak antiferromagnetic coupling for novel linear hexanuclear nickel(II) string complexes (Ni612+) and partial metal–metal bonds in their one-electron reduction products (Ni611+)

The preparation, crystal structures, magnetic properties and electrochemistry of novel linear hexanuclear nickel string complexes (Ni6(12+)) and their corresponding 1-e(-) reduction products (Ni6(11+)) are reported. In these complexes, the hexanickel chain is in a symmetrical arrangement (approximately D(4) symmetry) and is helically supported by four bpyany(2-) ligands [bpyany(2-) = the dianion of 2,7-bis(alpha-pyridylamino)-1,8-naphthyridine]. The Ni6(12+) complexes show that the two terminal nickel ions have high-spin states (S = 1) and the four inner ones have low-spin states (S = 0). The two terminal nickel ions exhibit weak antiferromagnetic coupling of ca.-5 cm(-1). All of Ni6(12+) complexes display three reversible redox couples at about -0.70, -0.20 and +1.10 V (vs. Ag/AgCl). The first reduction wave at about -0.20 V suggests facility of 1-e(-) reduction for the Ni(6)(12+) compounds. The reaction of Ni(6)(12+) complexes with hydrazine afforded the 1-e(-) reduction products (Ni6(11+)). As far as we are aware, the shortest bond distance of 2.202 A with a partial metal-metal bond was observed in Ni6(11+) compounds. The magnetic results of these Ni6(11+) compounds are in agreement with a localized model, in which the two terminal nickel ions are in a spin state of S = 1 whereas the central Ni3-Ni4 pair in a spin state of S = 1/2. The N6(11+) compounds show relatively strong antiferromagnetic coupling of about 60 cm(-1) between the terminal and the central dinickel ions.

Linear pentacobalt complexes: synthesis, structures, and physical properties of neutral and one-electron oxidation compounds

A series of linear pentanuclear cobalt complexes, including both neutral and one-electron oxidized forms, have been synthesized. The one-electron oxidation products were prepared either by reaction with silver salts or by bulk electrolysis. In all of these complexes, the pentacobalt chain adopts a symmetrical arrangement and is helically wrapped by four tpda [the dianion of N,N′-bis(α-pyridyl)-2,6-diaminopyridine] ligands. Two sets of Co–Co bond distances are observed, in which the average internal (inner) bond is about 0.06 A shorter than the external (outer) one. After one-electron oxidation, the average Co–Co and Co–N bond distances are not significantly different from those of the neutral analogues, whereas the Co–X (X = axial ligand) bond lengths exhibit a slight decrease in length. All of these complexes show two reversible redox couples at about +0.35 and +0.85 V (vs. Ag/AgCl). The first oxidation is a metal-centered reaction and the product has been structurally characterized. The second oxidation product is stable on the time scale of spectroelectrochemistry, but undergoes reduction to form the corresponding one-electron oxidation product under the crystallization conditions. The NMR results are consistent with the paramagnetism of both the neutral and oxidized complexes. The magnetic measurements indicate that the neutral and one-electron oxidized molecules have spin states of S = 1/2 and 1, respectively.

Manipulation of electronic structure via supporting ligands: a charge disproportionate model within the linear metal framework of asymmetric nickel string [Ni7(phdptrany)4Cl](PF6)

This paper describes the synthesis and physical properties of an uniquely asymmetric heptanickel string complex exhibiting a charge disproportionate model along the linear nickel framework.

Synthesis, structures, magnetism and electrochemical properties of triruthenium–acetylide complexes

A series of triruthenium complexes with arylacetylide axial ligands Ru(3)(dpa)(4)(C(2)X)(2)(BF(4))(y)(dpa = dipyridylamido; X = Fc, y= 0 (1); X = Ph, y= 0 (2); X = PhOCH(3), y= 1 (3); X = PhC(5)H(11), y= 1 (4); X = PhCN, y= 0 (5); X = PhNO(2), y= 0 (6)) have been synthesized. The crystal structures show that the Ru-Ru bond lengths (2.3304(9)-2.3572(5)A) of these compounds are longer than those of Ru(3)(dpa)(4)Cl(2)(Ru-Ru=2.2537(1)A). This is ascribed to the formation of the stronger pi-backbonding from metal to axial ligand which weakens the Ru-Ru interactions and the bond order is reduced in the triruthenium unit. Cyclic voltammetry and differential pulse voltammetry show that compound exhibits electronic coupling between the two ferrocenyl units with DeltaE(1/2) close to 100 mV. Compounds 2-6 display three triruthenium-based reversible one-electron redox couples, two oxidations and one reduction, and the electrode potentials shift upon varying the substituents. A linear relationship is observed when the Hammett constants are plotted against the redox potentials.

Synthesis, structure, magnetism, and electrochemical properties of a linear pentanuclear Ni5 compound derived from an oligo-α-pyridylamino ligand: Ni5(μ-dmpdda)4(NCS)2

The synthesis, crystal structures, electrochemical, and magnetic properties of a linear pentanuclear Ni5 compound derived from an oligo-α-pyridylamino ligand, [Ni5(μ-dmpdda)4(NCS)2] [dmpdda-H2 = N,N′-di(4-methylpyridin-2-yl)pyridine-2,6-diamine], are reported. Ni5(μ-dmpdda)4(NCS)2 involve a Ni5 linear chain unit with all of the Ni–Ni–Ni angles being nearly 180°, terminated by two axial ligands. The pentanuclear linear metal chain is helically wrapped by four syn–syn–syn–syn type dmpdda2− ligands. There are two types of Ni–Ni distances in this complex. Terminal Ni–Ni distances bonded with the axial ligand are longer (2.377 Å); the inner Ni–Ni distances are short at 2.2968 Å. Terminal Ni(II) ions bonded with the axial ligands are square-pyramidal (NiN4NCS) with long Ni–N bonds (2.092 Å), consistent with a high-spin Ni(II) configuration. The inner three Ni(II) ions have short Ni–N (1.901–1.925 Å) bond distances, consistent with a square planar (NiN4), diamagnetic arrangement of a low-spin Ni(II) configuration. This compound exhibits magnetic behavior similar to [Ni5(μ-tpda)4(NCS)2], indicating an antiferromagnetic interaction of two terminal high-spin Ni(II) ions.

Supramolecular assembly of linear trinickel complexes incorporating metalloporphyrins: a novel one-dimensional polymer and oligomer

One-dimensional polymeric or oligomeric chains, in which various linear trinickel complexes linked to the axial sites of metalloporphyrins by the combination of self-assembly and coordination chemistry, have been constructed. A carboxylate group of carboxylpyridine was attached to the end of linear trinickel complexes to produce the linear building blocks, Ni3(dpa)4X2 [X = 4-PyCOO− (1) or 3-PyCOO− (2)], which was then reacted with metalloporphyrins to form stable polymers or oligomers. The new self-assembled oligomeric chain, [Ni3(dpa)4(4-PyCOO)2][ZnTPP]2 (3), and two novel self-assembled one-dimensional polymeric chains, {[Ni3(dpa)4(4-PyCOO)2][MnTPP]}n(ClO4)n (4), and {[Ni3(dpa)4(3-PyCOO)2][MnTPP]}n(ClO4)n (5), [dpa− = di(α-pyridyl)amido anion; TPP = meso-tetraphenylporphyrinato dianion], have been synthesized and their structures were determined by X-ray diffraction. The UV/vis spectra indicate the absence of any noticeable interactions between the linear trinickel units and metalloporphyrins in these chains. The magnetic susceptibility measurements in the solid state show that both polymers 4 and 5 have a very weak ferromagnetic interaction.

Porphyrin Dimers Bridged by an Electrochemically Switchable Unit

In the past decade much effort has been devoted to the synthesis and studies of molecular systems comprising porphyrin units bridged by well-defined p-conjugated spacers at the mesoor b-positions. These conjugated oligoporphyrin systems are expected to have potential applications in molecular wires and electronic devices due to their unique optical, physical, and chemical properties. Photophysical studies on electron transfer of a series of ferrocene–oligoporphyrin–fullerene triads show that a meso–meso butadiyne-bridged oligoporphyrin acts as an efficient molecular wire for long-range charge transfer over 65 &. More recently, the conductivity measurements on butadiyne-bridged porphyrin polymers indicate that the formation of doublestrand 4,4’-bipyridyl ladder complex by addition of bipyridine to the single-strand porphyrin polymer leads to an increase in conductivity by an order of magnitude. EPR studies performed by Therien and co-workers on meso– meso ethyne-linked porphyrin oligomers show that this type of conjugated molecules is able to mediate charge migration over a distance of about 75 &. The synthesis of meso– meso, b–b, b–b triply-linked porphyrin tapes reported by Osuka represents a milestone in the area of porphyrin molecular wires. The fully conjugated porphyrin tapes exhibit remarkable properties including very low optical HOMO– LUMO gap, low oxidation potential and rigid structure, and they may find use in a variety of molecular electronics. Despite extensive studies on the conjugated porphyrin arrays, oligoporphyrin molecular wires that show switchable conductance states by chemical or electrochemical means are rare. One example is the porphyrin arrays in which the individual macrocyles are laterally-linked by a quinonoid unit at the b,b’-positions of the porphyrin rings. In this system, the electronic communication between porphyrin units can be modulated by quinonoid/benzenoid conversion using chemical or electrochemical means. Another example of switchable porphyrin wires is the systems where proquinoidal units bridge two porphyrins. It is well known that the reversible conversion between quinone and hydroquinone can be achieved by chemical or electrochemical methods. Incorporation of a quinone unit into the central part of a porphyrin dimer via acetylene linkers would allow the interporphyrin interaction to be switched off and on in a controllable fashion and this type of molecules may have the potential for the application in switchable molecular wires. Therefore, we set out to design and synthesize a series of porphyrin dimers Ni22, Ni23, and Ni24 to explore their potential as redox-controllable switching molecules. The synthetic routes to porphyrin dimers Ni22, Ni23, and Ni24 were outlined in Scheme 1. [11] The coupling reaction of porphyrin Ni1 with the diiodide gave porphyrin dimer Ni22. [12] Demethylation of Ni22 to give Ni23 employing excess BBr3 was unsuccessful. However, the demethylation can be achieved by the reaction of excess BBr3 with the free base of the zinc analogue Zn22, obtained by a procedure similar to that for Ni22. [13] Subsequent nickel insertion afforded porphyrin dimer Ni23. The oxidation reaction of dimer Ni23 with PbO2 gave porphyrin Ni24. [14] For comparison purposes, porphyrin Ni5 was synthesized by employing a procedure similar to that for Ni22. The molecular structures of these porphyrins were confirmed by various spectroscopic methods such as NMR, UV/Vis, IR spectroscopy, and mass spectrometry. Figure 1 shows the crystal structure of compound Ni5. The bond lengths and angles fall in the normal range. The porphyrin ring adopts an essentially planar conformation [a] C.-L. Mai, Y.-L. Huang, Prof. C.-Y. Yeh Department of Chemistry National Chung Hsing University Taichung 402 (Taiwan) Fax: (+886) 4-2286-2547 E-mail : cyyeh@dragon.nchu.edu.tw [b] Dr. G.-H. Lee, Prof. S.-M. Peng Department of Chemistry National Taiwan University Taipei 106 (Taiwan) Supporting information for this article is available on the WWW under http://www.chemistry.org or from the author.

CCDC 1470917: Experimental Crystal Structure Determination

Related Article: Wen-Zhen Wang, Shu-Bo Geng, Shuang Liu, Dan Zhao, Xin-Gang Jia, Hai-Long Wei, Rayyat H. Ismayilov, Chen-Yu Yeh, Gene-Hsiang Lee, Shie-Ming Peng|2017|J.Mol.Struct.|1138|222|doi:10.1016/j.molstruc.2017.02.090