Addition of lithium hexamethyldisilazide to an equimolar amount of calcium bis(hexamethyldisilazide) in toluene gave 'solvent-free', [Li{μ-N(SiMe 3 ) 2 } 2 Ca{N(SiMe 3 ) 2 }] (1). An X-ray study reveals a dinuclear arrangement based on a planar LiNCaN four-membered ring: both metals engage in additional H 3 C...M (where M=Li, Ca) interactions with the μ-N(SiMe 3 ) 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{μ-N(SiMe 3 ) 2 } 2 Mg{N(SiMe 3 ) 2 }], where only the lithium centre engages in such intramolecular agostic H 3 C...Li interactions.