Toward the next generation fuel cell systems, the development of a novel electrocatalyst for the polymer electrolyte fuel cell (PEFC) is crucial to overcome the drawbacks of the present electrocatalyst. As a conductive supporting material for the catalyst, carbon nanotubes (CNTs) have emerged as a promising candidate, and many attempts have been carried out to introduce CNT, in place of carbon black. On the other hand, as a polymer electrolyte, polybenzimidazoles (PBIs) have been recognized as a powerful candidate due to the high proton conductivity above 100 °C under non-humid conditions. In 2008, we found that these two materials have a strong physical interaction and form a stable hybrid material, in which the PBIs uniformly wrap the surfaces of the CNTs. Furthermore, PBIs serve as effective binding sites for the formation of platinum (Pt) nanoparticles to fabricate a ternary composite (CNT/PBIs/Pt). In this review article, we summarize the fundamental properties of the CNT/PBIs/Pt and discuss their potential as a new electrocatalyst for the PEFC in comparison with the conventional ones. Furthermore, potential applications of CNT/PBIs including use of the materials for oxygen reduction catalysts and reinforcement of PBI films are summarized.

Fuel cell electrocatalyst using polybenzimidazole-modified carbon nanotubes as support materials.

Fascinating variability in the chemistry and properties of 2,6-bis-(benzimidazol-2-yl)-pyridine and 2,6-bis-(benzthiazol-2-yl)-pyridine and their complexes

Recently, we introduced a new force field (FF) to simulate transport properties of imidazolium-based room-temperature ionic liquids (RTILs) using a solid physical background. In the present work, we apply this FF to derive thermodynamic, structure, and transport properties of the mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], and acetonitrile (ACN) over the whole composition range. Three approaches to derive a force field are formulated based on different treatments of the ion–ion and ion–molecule Coulomb interactions: unit-charge, scaled-charge and floating-charge approaches. The simulation results are justified with the help of experimental data on specific density and shear viscosity for these mixtures. We find that a phenomenological account (particularly, a simple scaled-charge model) of electronic polarization leads to the best-performing model. Remarkably, its validity does not depend on the molar fraction of [BMIM][BF4] in the mixture. The derived FF is so far the first molecular model which is able to simulate all transport properties of the mixtures, comprising RTIL and ACN, fully realistically.

A new force field model of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and acetonitrile mixtures.

A donor-site engineering approach facilitates the formation of heteroleptic [Pd2 L2 L'2 ]4+ cage structures through a favored cis-'in2 /out2 ' spatial configuration of the methyl groups of 5- and 3-substituted bis-monodentate picolyl ligands with flat acridone and bent phenothiazine backbones. The heteroleptic cages were confirmed by ESI-MS and 2D NMR experiments as well as DFT calculations, which pointed toward a cis-configuration being energetically favored. This was further supported by the synthesis and X-ray structure of a previously unreported cis-[Pd(2-picoline)4 ]2+ complex. The formation of homoleptic structures, however, was met with considerable steric hindrance at the PdII centers, as observed by the formation of [Pd2 L3 (solvent)2 ]4+ and [Pd2 L2 (solvent)4 ]4+ species when only one type of acridone-based ligand was offered. In contrast, bent phenothiazine ligands with outside-pointing methyl groups showed the ability to form interpenetrated double-cages, as revealed by X-ray crystallography. The general route presented herein enables the assembly of uniform cis-[Pd2 L2 L'2 ]4+ coordination cages, thus furthering the possibility to increase structural and functional complexity in supramolecular systems.

https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10.1002/chem.201802188

Donor-Site-Directed Rational Assembly of Heteroleptic cis-[Pd2L2L′2] Coordination Cages from Picolyl Ligands

Spherical assemblies of the type [Pdn L2n ]2n+ can be obtained from PdII salts and curved N-donor ligands, L. It is well established that the bent angle, α, of the ligand is a decisive factor in the self-assembly process, with larger angles leading to complexes with a higher nuclearity, n. Herein, we report heteroleptic coordination cages of the type [Pdn Ln L'n ]2n+ , for which a similar correlation between the ligand bent angle and the nuclearity is observed. Tetranuclear cages were obtained by combining [Pd(CH3 CN)4 ](BF4 )2 with 1,3-di(pyridin-3-yl)benzene and ligands featuring a bent angle of α=120°. The use of a dipyridyl ligand with α=149° led to the formation of a hexanuclear complex with a trigonal prismatic geometry; for linear ligands, octanuclear assemblies of the type [Pd8 L8 L'8 ]16+ were obtained. The predictable formation of heteroleptic PdII cages from 1,3-di(pyridin-3-yl)benzene and different dipyridyl ligands is evidence that there are entire classes of heteroleptic cage structures that are privileged from a thermodynamic point of view.

Tuning the Size and Geometry of Heteroleptic Coordination Cages by Varying the Ligand Bent Angle.

Zinc complexes of the formulae ZnX2L·nH2O [X = Cl or Br, n = 2, X = I, n = 1, L = L1, 1,3‐bis(benzimidazol‐2‐yl)benzene; X = Cl, Br or I, n = 0, L = L2, 1,3‐bis(1‐methylbenzimidazol‐2‐yl)benzene] and Zn(L)2(ClO4)2·2H2O (L = L1 and L2) were obtained by the reactions of zinc halides/perchlorate with N‐heterocycles in ethanol. The complexes have been characterized based on elemental analyses, molar conductance measurements, IR, 1H and 13C NMR spectral studies and thermal analysis.

Reactions of Zinc Salts with bis(Benzimidazolyl) Derivatives

Hydrogenation of Olefins Catalyzed by Polymer-Supported Palladium-Imidazole

[Pd(cod)(cotl)]ClO4 (cod = 1,5-cyclooctadiene, cotl = cyclooctenyl, C8H13
−) undergoes substitutions with multidentate N-heterocycles: 1,3-bis(benzimidazolyl)benzene (L1), 1,3-bis(1-methylbenzimidazol-2-yl)benzene (L2), 2,6-bis(benzimidazolyl)pyridine (L3) and 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (L4) to yield mono/binuclear complexes: [Pd(cotl)(L1)(OClO3)], [Pd(cotl)(L)]ClO4 (L = L2 or L3) and [Pd(cotl)2(L4)](ClO4)2. Dihalobridged binuclear complexes [PdX(cotl)]2 (X = Cl or Br) undergo halogen bridge cleavages with the multidentate N-heterocycles to form binuclear complexes of the type [PdX(cotl)2L] (X = Cl or Br; L = L1, L2, L3 or L4). The complexes were characterized by elemental analyses, 1H-, 13C-n.m.r., i.r., far-i.r. and FAB-mass spectral studies.

Cyclooctenyl complexes of palladium(II) with multidentate N-heterocycles

Palladium dihalides/perchlorate react with the multidentate N-heterocycles (I), 1,3-bis(benzimidazol-2-yl)benzene (L 1 ) 1,3-bis(1-methylbenzimidazol-2-yl)benzene (L 2 ), 2,6-bis(benzimidazol-2-yl)pyridine (L 3 ) and 2,6-bis(1-methyl-benzimidazol-2-yl) pyridine (L 4 ) in ethanol/tetrahydrofuran in presence of hydrohalic acid to yield complexes of the compositions, [PdX 2 L.nH 2 O] (X = Cl, L = L 1 or L 2 , n = 1; X = Cl, L = L 3 or L 4 , n = 0; X = Br, L = L 1 or L 3 n = 0; X = Br, L = L 2 , n = 3; X = Br, L = L 4 , n = 2), PdL 2 (ClO 4 ) 2 .nH 2 O (L = L 1 , n = 2; L = L 2 , n = 1) and [Pd 2 L 3 (CIO 4 ) 4 .nH 2 O] (L = L 3 , n = 2; L = L 4 , n = 0). The complexes were characterised by elemental analysis, molar conductance measurements, IR, electronic, 1 H, 1 3 C NMR and FAB-mass spectral studies.

Studies on palladium(II) complexes containing multidentate N-heterocycles

The reactions of copper(II) halides with 1,3‐bis(benzimidazol‐2‐yl)benzene and its N‐methylated derivative afforded binuclear and mononuclear complexes, respectively. Mononuclear perchlorate complexes have also been synthesized by the reactions of the aforesaid ligands with hydrated copper perchlorate. The complexes have been characterized by elemental analyses, conductivity and magnetic measurements, TGA studies, IR, electronic, and ESR spectral studies.

Shivakumaraiah

Papers

Reactions of Zinc Salts with bis(Benzimidazolyl) Derivatives

Hydrogenation of Olefins Catalyzed by Polymer-Supported Palladium-Imidazole

Cyclooctenyl complexes of palladium(II) with multidentate N-heterocycles

Studies on palladium(II) complexes containing multidentate N-heterocycles

Synthesis and Properties of Mononuclear and Binuclear Copper(II) Complexes Stabilized by bis‐Benzimidazolyl Ligands