Alkali-metal guanidinates: solid-state structural diversity in solvent-free derivatives

Reaction of 1,3-dicyclohexylcarbodiimide with alkali-metal amides, MN(SiMe3 )(2) (M = Li, Na or K), in non-co-ordinating solvents yielded the guanidina te salts {M[CyNC(N(SiMe3)(2))NCy]}(x) (M = Li, x = 2; Na, x = 3; K, x = 2) in high yield. All three species were characterized by X-ray crystallograph y and found to be free from interaction with the solvent. These compounds r epresent the first base-free examples of alkali-metal guanidinate or amidin ate species to be examined by X-ray crystallography. Although the structure s of the lithium and potassium salts have precedent in amidinate and diazaa llyl chemistry, the sodium salt represents a new mode of aggregation for sp ecies containing an anionic N-C-N linkage.