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Synthesis, Structures and DFT Calculations on Alkaline‐Earth Metal Azide‐Crown Ether Complexes
Author(s) -
Brown Michael D.,
Davis Martin F.,
Dyke John M.,
Ferrante Francesco,
Levason William,
Ogden J. Steven,
Webster Michael
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701502
Subject(s) - azide , chemistry , crown ether , crystallography , ligand (biochemistry) , metal , alkaline earth metal , density functional theory , ionic bonding , molecule , inorganic chemistry , crystal structure , alkali metal , ion , computational chemistry , organic chemistry , biochemistry , receptor
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)(N 3 ) 2 (MeOH)], [Sr([15]crown‐5)(N 3 ) 2 (H 2 O)], [Ca([15]crown‐5)(N 3 ) 2 (H 2 O)] and [Sr([15]crown‐5)(N 3 )(NO 3 )]. Crystal structures reveal the presence of a variety of coordination modes for the azide groups including κ 1 ‐, μ‐1,3‐ and linkages via H‐bonded water molecules, in addition to azide ions. The [Ba([18]crown‐6)(N 3 ) 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 MN terminal metal–azide bond length and charge densities on the metal (M) and terminal nitrogen centre (N terminal ) 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.