Synthesis and structural characterisation of 'solvent-free' lithium-calcium hexamethyldisilazide, [Li{mu-N(SiMe3)(2)}(2)Ca{N(SiMe3)(2)}], exhibiting a double ration of agostic H3C center dot center dot center dot Li and H3C center dot center dot center dot Ca intramolecular interactions

Addition of lithium hexamethyldisilazide to an equimolar amount of calcium bis(hexamethyldisilazide) in toluene gave 'solvent-free'. [Li{mu-N(SiMc(3))(2)}(2)Ca{N(SiMe3)(2)] (1). An X-ray study reveals a dinuclear arrangement based on a planar LiNCaN four-membered ring: both metals engage in additional H3C...M (where M = Lt. Ca) interactions with the mu-N(SiMe3)(2) substituents resulting in a distorted tetrahedral geometry at lithium and a distorted trigonal-bipyramidal geometry at calcium. This contrasts with the previously reported mixed Li-Mg analogue, [Li{mu-N(SiMe3)(2)}(2)Mg{N(SiMe3)(2)}], where only the lithium centre engages in such intramolecular agostic H3C...Li interactions.