Supporting coordination through hydrogen bonding in lanthanide complexes of 7-azaindole-N-oxide
Literature Information
Oskar G. Wood, Leanne Jones, Chris S. Hawes
Ligands capable of simultaneous metal coordination and hydrogen bond donation provide useful structural features to enhance cooperativity and favour specific geometries within the coordination sphere. Here we present the first structurally characterised examples of coordination compounds containing protonated 7-azaindole-N-oxide HL, bearing a neutral oxo donor capable of terminal or bridging coordination modes adjacent to a convergent hydrogen bond donor. The ligand itself shows a strong tendency for dimeric assembly in the solid state, but is easily deprotonated to give the chelate complex [CuL2] 1. In the presence of lanthanide ions, however, four new complexes [Eu(NO3)3(HL)3] 2, [Gd(NO3)3(HL)3] 3, [Eu2(μ2-HL)2(HL)4Cl6] 4 and [YbCl3(HL)3][YbCl(HL)5OH2]2Cl 5 were prepared and crystallographically characterised. All four species show strong tendencies for hydrogen bonding from the ligand to impact their overall structures, including a C3 propellor-like macrocyclic motif in 2 and 3 and a combination of intramolecular N–H⋯Cl contacts, and intermolecular tridentate anion binding in 5. Solution studies including HRMS and phosphorescence emission spectroscopy reveal persistence of the europium complex 2 in solution, despite the multiple possible binding modes of this ligand, hinting at a degree of cooperativity in these systems. These results show the utility of hydrogen bonding within the coordination sphere for influencing structural outcomes, relevant to the construction of stable higher-order crystalline assemblies.
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CrystEngComm

CrystEngComm is the forum for the design and understanding of crystalline materials. We welcome studies on the investigation of molecular behaviour within crystals, control of nucleation and crystal growth, engineering of crystal structures, and construction of crystalline materials with tuneable properties and functions. We publish hypothesis-driven research into… how crystal design affects thermodynamics, phase transitional behaviours, polymorphism, morphology control, solid state reactivity (crystal-crystal solution-crystal, and gas-crystal reactions), optoelectronics, ferroelectric materials, non-linear optics, molecular and bulk magnetism, conductivity and quantum computing, catalysis, absorption and desorption, and mechanical properties. Using Techniques and methods including… Single crystal and powder X-ray, electron, and neutron diffraction, solid-state spectroscopy, spectrometry, and microscopy, modelling and data mining, and empirical, semi-empirical and ab-initio theoretical evaluations. On crystalline and solid-state materials. We particularly welcome work on MOFs, coordination polymers, nanocrystals, host-guest and multi-component molecular materials. We also accept work on peptides and liquid crystals. All papers should involve the use or development of a design or optimisation strategy. Routine structural reports or crystal morphology descriptions, even when combined with an analysis of properties or potential applications, are generally considered to be outside the scope of the journal and are unlikely to be accepted.