Synthesis and crystal structure of the mixed lithium sodium guanidide [Li 4Na 2{NC(NMe 2) 2} 6]: A stack of three (metal-nitrogen) 2 dimeric rings with additional intramolecular (tertiary amine) nitrogen-lithium coordinations

Abstract

The tetralithium disodium guanidide [Li 4Na 2{NC(NMe 2) 2} 6], crystallized from a 1 : 1 : 2 Bu nLi : Bu nNa : HNC(NMe 2) 2 mixture, has been studied by X-ray crystallography and found to be related to the ketimide [Li 4Na 2{NC(Ph)Bu t} 6], reported earlier as having a stacked-core of three (metal-nitrogen) 2 ring dimers with Li + and Na + cations in end rings and the central ring, respectively. However, it also displays a unique feature : intramolecular donor-acceptor interactions which connect dimethylaminonitrogen atoms project from the central ring to Li + cations in the end rings. Although these interactions are long range (average length 2.304 Å, cf. 2.139 Å for LiN core bonds), they still significantly influence the core bonding as evidenced by an analysis of bond lengths and bond angles.