Details

Autor(en) / Beteiligte

• Brown, Michael D.
• Davis, Martin F.
• Dyke, John M.
• Ferrante, Francesco
• Levason, William
• Ogden, J. Steven
• Webster, Michael

Titel

Synthesis, Structures and DFT Calculations on Alkaline-Earth Metal Azide-Crown Ether Complexes

Ist Teil von

• Chemistry : a European journal, 2008-03, Vol.14 (8), p.2615-2624

Ort / Verlag

Weinheim: WILEY-VCH Verlag

Erscheinungsjahr

2008

Quelle

Wiley-Blackwell Full Collection

Beschreibungen/Notizen

• The first examples of azide complexes of calcium, strontium or barium with crown ethers have been prepared and fully characterised, notably [Ba([18]crown‐6)(N3)2(MeOH)], [Sr([15]crown‐5)(N3)2(H2O)], [Ca([15]crown‐5)(N3)2(H2O)] and [Sr([15]crown‐5)(N3)(NO3)]. Crystal structures reveal the presence of a variety of coordination modes for the azide groups including κ1‐, μ‐1,3‐ and linkages via H‐bonded water molecules, in addition to azide ions. The [Ba([18]crown‐6)(N3)2(MeOH)]⋅1/3 MeOH contains dinuclear cations with three μ‐1,3‐NNN bridges, the first example of this type in main group chemistry. The structures obtained have been compared with molecular structures computed by density functional theory (DFT). This has allowed the effects of the crystal lattice to be investigated. A study of the MNterminal metal–azide bond length and charge densities on the metal (M) and terminal nitrogen centre (Nterminal) in these complexes has allowed the nature of the metal–azide bond to be investigated in each case. As in our earlier work on alkali metal azide‐crown ether complexes, the bonding in the alkaline‐earth complexes is believed to be predominantly ionic or ion‐dipole in character, with the differences in geometries reflecting the balance between maximising the coordination number of the metal centre, and minimising ligand–ligand repulsions. A variety of coordination modes for the azide groups including κ1, μ‐1,3 and linkages via H‐bonded water molecules in addition to azide ions are displayed by a series of azide complexes of Ca, Sr and Ba with crown ethers. For example, [Ba([18]crown‐6)(N3)2(MeOH)]⋅1/3 MeOH contains dinuclear cations and three μ‐1,3‐NNN bridges (see picture), the first of this type in main group chemistry.