Rayyat Huseyn Ismayilov

Two Linear Undecanickel Mixed-Valence Complexes: Increasing the Size and the Scope of the Electronic Properties of Nickel Metal Strings**

The importance of one-dimensional (1D) transition-metal complexes stems from their ability to provide a fundamental understanding of metal–metal interactions and electron transport along an extended metal-atom chain (EMAC), and from the perspective of taking advantage of their specific properties for potential applications, such as molecular metal wires and switches. A series of string complexes of oligo-apyridylamino ligands ranging from 3 to 9 core metal atoms has been synthesized and characterized by Cotton s group and our group. Attempts to characterize such very long EMACs with high electron conductivity were hindered by the synthetic difficulties rapidly increasing with the size of the metal chain. We synthesized [Ni9(m9-peptea)4Cl2] ten years ago, but all attempts to characterize a longer chain of Ni atoms have, to date, been unsuccessful, owing to very low yields and to the instability of the target compound, probably because of the high flexibility of large pyridylamino ligands. Recently we developed a new family of ligands by substituting rigid and potentially redox active naphthyridine (na) groups for the pyridine (py) rings. Naphthyridinemodulated ligands stabilize nickel ions in a low oxidation state, giving rise to mixed-valent [Ni2(napy)4] 3+ units (napy= naphthyridine). Using this strategy, we obtained a series of stable, low-oxidation-state-nickel string complexes combining mixed-valency, a property important in the development of novel electronic materials, with an enhanced electron mobility, which is able to increase the conductance of molecular metal wires. We report a new tetranaphthyridyltriamine ligand, N-(2(1,8-naphthyridin-7-ylamino)-1,8-naphthyridin-7-yl)-N-(1,8naphthy-ridin-2-yl)-1,8-naphthyridine-2,7-diamine (H3tentra) and two undecanickel complexes of the deprotonated tentra trianion, [Ni11(tentra)4Cl2](PF6)4 (1) and [Ni11(tentra)4(NCS)2](PF6)4 (2). The ligand H3tentra was synthesized on the basis of Buchwald s palladium-catalyzed procedures by the crosscoupling of bis(2-chloro-1,8-naphthyridin-7-yl)amine and 2amino-1,8-naphthyridine. Undecametallic complex [Ni11(tentra)4Cl2](PF6)4 (1) was obtained by the reaction of anhydrous NiCl2 with the H3tentra ligand in an argon atmosphere employing naphthalene as solvent and tBuOK as a base to deprotonate the amine groups. The thiocyanate species (2) was obtained from 1 by an axial ligand exchange reaction. The crystal structures of 1 and 2 are shown in Figure 1 and the Supporting Information Figure 1S, respectively. Both 1 and 2 are tetracationic molecules associated each with four PF6 counterions. They crystallize in unusually large cells, with one dimension exceeding 50 . The Ni11 chain of 1 and 2 is linear and wrapped in a helical manner by four tentra trianions. In both complexes, the atoms of the axial ligands are collinear with the Ni11 axis; the molecular lengths are 27.7 and 32.4 for 1 and 2, respectively. These are the longest EMAC complexes reported to date. The nature of the axial ligand does not significantly affect the metal–metal bond length, and no obvious structural change is observed for compound 2 with respect to 1. Therefore, we will only analyze the structure of 1 in detail. Selected bond lengths for 1 are displayed in Figure 1c together with the corresponding values obtained from geometry optimization at the DFT/B3LYP level. Molecule 1 consists of eleven nickel atoms in a linear chain with the Ni-Ni-Ni bond angles in the range of 179–1808. The N-Ni-Ni-N torsion angles for adjacent nickel are between 13.0 and 18.78, much smaller than those in oligo-a-pyridylamino ligand EMAC complexes (ca. 22.58). Metal–metal distances usually decrease from the end to the center of the chain in both nickel and cobalt EMACs of oligo-a-pyridyl[*] Dr. R. H. Ismayilov, Dr. W.-Z. Wang, Dr. G.-H. Lee, S.-A. Hua, Prof. Dr. S.-M. Peng Department of Chemistry, National Taiwan University 1, Sec. 4, Roosevelt Road, Taipei, 106 (Taiwan, ROC) Fax: (+886)2-8369-3765 E-mail: smpeng@ntu.edu.tw

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.

The nano-scale molecule with the longest delocalized metal–metal bonds: linear heptacobalt(II) metal string complexes [Co7(µ7-L)4X2]

A new type of pyrazine-modulated oligo-alpha-pyridylamino ligands, N2-(pyrazin-2-yl)-N6-(6-(pyrazin-2-ylamino)pyridin-2-yl)pyridine-2,6-diamine (H3pzpz) and N2-(pyrazin-2-yl)-N6-(6-(pyridin-2-ylamino)pyridin-2-yl)pyridine-2,6-diamine (H3tpz), were synthesized and characterized by IR, 1H NMR and MS(FAB). Using and , the linear heptacobalt(II) metal string complexes [Co7(micro7-L)4X2] (L=pzpz3-, X=Cl-, NCS-; L=tpz3-, X=Cl-, X=NCS-) were synthesized and structurally characterized. The structures showed the shortest Co-Co distance (2.194 A) and the longest Co chain (13.5 A) obtained to date with direct Co-Co bonds. The Co-Co distances are in the range 2.194-2.309 A. Electrochemical studies showed two reversible oxidations and one reversible reduction, while all the redox reactions of H3pzpz complexes, and , occurred at higher potentials than H3tpz complexes, and . The complexes are fairly stable to oxidation. Temperature-dependent magnetic research on revealed anomalous magnetic behavior with intermediate magnetic moment values between quartet and doublet states, and deviation from the Curie-Weiss law.

Transition metal complexes of a super rigid anthyridine ligand: structural, magnetic and DFT studies

Transition metal complexes of iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) with a plane, super rigid ligand, 1,13,14-triaza-dibenz[a,j]anthracene (L), [M2L4](ClO4)4 (M = Fe, Co, Ni, Cu, Zn), were synthesized and their magnetic properties were studied. All complexes are dinuclear, tetracationic complexes bridged by four tridentate ligands. In a complex each L coordinates to two metal atoms with two nitrogen atoms chelating to one metal and the third nitrogen atom mono-coordinating to another metal. Crystal structure analysis indicated that the molecular structures of the five complexes are essentially the same despite significant distortion from the Jahn–Teller effect of the copper complex. The Cu–Cu distance is 2.907(1) A, and all other M–M distances are ca. 3.3 A. Antiferromagnetic couplings were observed for the Fe, Co, Ni and Cu complexes. The exchange parameters were J = −6 and −129 cm−1 for Ni and Cu complexes, respectively. The mechanism was discussed by spin-polarization, superexchange coupling and DFT calculations. The J value obtained from the density functional B3LYP calculations is in good agreement with the experimentally determined value.

Fine tuning of pentachromium(II) metal string complexes through elaborate design of ligand

New pentachromoium metal string complexes [Cr5(μ5-L)4X2] (X = Cl−, L = dppzda2− (1), dpzpda2− (2); X = NCS−, L = dppzda2− (3), dpzpda2− (4)) were designed and synthesized through pyrazine-modulation of tripyridyldiamine ligand. X-Ray crystallographic studies revealed a linear metal chain structure consisting of two quadruple Cr–Cr bonds and a separated high spin Cr(II) at an end in crystallized form. A quintet ground state was observed for all pentachromium(II) molecules by magnetic study with g values of 2.04–2.18. While the electronic structure remained unchanged after the modification of ligands, electrochemistry showed a significant change in the molecular orbital energy levels of metal string molecules. Observation of the first oxidation peak of 1 at +0.57 V and of 2 at +0.73 V revealed that these complexes are quite resistant to oxidation. Single molecular conductance measurements showed that the complex exhibited good electronic conductance.

Bis(morpholin-4-ium) tetra-chlorido-cobalt(II).

The title compound, (C4H10NO)2[CoCl4], is an ionic compound consisting of two protonated tetrahydro-1,4-oxazine (morpholine) cations and a [CoCl4]2− dianion. The CoII ion is in a tetrahedral coordination geometry. The cations exhibit chair-shaped conformations. A three-dimensional supramolecular architecture is formed through N—H⋯Cl and C—H⋯Cl hydrogen bonds between the dianions and the cations.

CCDC 1470917: Experimental Crystal Structure Determination

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A coordination polymer consisting of two different one-dimensional copper(II) chains

The title compound, catena-poly[[[diaqua(methanol-κO)copper(II)]-μ-N-(4-methylpyrimidin-2-yl-κN(1))pyrazin-2-amine-κ(2)N(1):N(4)] [[aqua(aqua/methanol-κO)(perchlorato-κO)copper(II)]-μ-N-(4-methylpyrimidin-2-yl-κN(1))pyrazin-2-amine-κ(2)N(1):N(4)] tris(perchlorate) methanol monosolvate 1.419-hydrate], {[Cu(C9H9N5)(CH3OH)(H2O)2][Cu(C9H9N5)(ClO4)(CH3OH)0.581(H2O)1.419](ClO4)3·CH3OH·1.419H2O}n, is a one-dimensional straight-chain polymer of N-(4-methylpyrimidin-2-yl)pyrazin-2-amine (L) with Cu(ClO4)2. The complex consists of two crystallographically independent one-dimensional chains in which the Cu(II) atoms exhibit two different octahedral coordination geometries. The L ligand coordinates to two Cu(II) centres in a tridentate manner, with the pyrazine ring acting as a bridge linking the Cu(II) coordination units and building an infinite one-dimensional chain. Extensive hydrogen bonding among perchlorate anions, water molecules and L ligands results in three-dimensional networks.