Ruksanna Ahmad

Coordination Networks with Carborane Anions: Ag(i) and Nitrogen Bridging Ligands

New crystalline coordination networks based on Ag(i) and N-bridging ligands — pyrazine (pyz), 4,4′-bipyridine (bpy), and 2,3-bis-(2-pyridyl)pyrazine (bppz) — incorporating carborane monoanions (CB11H12)− or [Co(C2B9H11)2]− were isolated and characterized using single crystal X-ray diffraction, microanalysis, and infrared spectroscopy. All the complexes with the bpy and bppz ligands reveal 1D coordination infinite chains involving the Ag(i) and the ligands, and layered extended structures with rows of carborane anions between the layers of chains. Interestingly, two polymorphs of the complex [Ag(bpy)(CH3CN)][Co(C2B9H11)2] were observed. The complex [Ag(pyz)(CH3CN)2][Co(C2B9H11)2] shows a 1D coordination polymer, while the pyz complex with the smaller carborane anion {[Ag(pyz)](CB11H12)} exhibits a 3D coordination network structure with four Ag···H−B interactions between the silver centre and carborane anions.

Network structures of cyclotriveratrylene and its derivatives

The host molecule cyclotriveratrylene can be incorporated into network structures by acting as a hydrogen bond acceptor or as a chelating ligand for Group 1 metals. New CTV-based ligands with pyridyl functional groups have been synthesised for use as multifunctional ligands in coordination networks. Resultant hydrogen bonded network structures and coordination networks show a range of chain, 2-D and 3-D structures with hexagonal 63 nets predominating. Recent results are discussed including highly complex 3-D networks where the molecular hosts pack in a tetrameric back-to-back fashion.

Synthesis and Structural Studies of Cyclotriveratrylene Derivatives

Cyclotriveratrylene (CTV) derived host molecules with ethyl, propyl, allyl or propargyl functional groups have been synthesised using standard or solventless reaction methodologies. The known structural and clathrate chemistry of cyclotriveratrylene (CTV) and these analogues has been extended. Crystal structures of the hexa(ethyl), tri(ethyl), tri(propargyl) analogues have been determined, and show either intra-cavity host-guest binding or self-stacking motifs. Two new clathrates of CTV have also been structurally characterised, namely CTV.(DMSO)2.(H2O)2 with intra-cavity complexation of DMSO, and CTV.(EtOH)0.25 which has a γ-phase CTV structure.

Building cyclotriveratrylene host molecules into network structures

Cyclotriveratrylene is a rigid bowl-shaped host molecule that can be used as a 3-connecting crystal engineering tecton by virtue of its tris-dimethoxy arrangement which may act as hydrogen bond acceptors, or chelating ligand sites. Network structures of unusual topology have resulted, and a number of common structural types are emerging. The tetragonal structure of [Fe(H2O)6]{(CH3CN)(CTV)}4(H2O)4[Co(C2B9H11)2]2 has been determined and features an unusual 3,12-connected 3D hydrogen bonded network structure, with the [Fe(H2O)6]2+ complex cation disordering to achieve the required geometry for the network. The structure of [Ag(CTV)2(H2O)3(CH3CN)2](CB11H12) has been determined and likewise conforms to a key structural type, and shows novel coordination of CTV to Ag+ centres.

Propeller-shaped chain and 2D grid coordination polymers with the host molecule cyclotriveratrylene and (CB9H5Br5)−

The host molecule cyclotriveratrylene (CTV) forms coordination polymers with the Group 1 metals K+ and Rb+ and with the carbaborane (CB9H5Br5)− as the counter-anion. [K(CTV)2](CB9H5Br5)(CF3CH2OH)2 has a chain structure with an unusual propeller-shaped cross-section, while [Rb(CTV)(CB9H5Br5)(CH3CN)] has a two-dimensional grid structure of distorted hexagonal topology and is one of the few examples of a rubidium acetonitrile complex.