The clathrate structures of the host 1,l '-binaphthyl-2,2'-dicarboxylic acid (1 ) with dimethylformamide, (2), dimethyl sulphoxide, (3), and bromobenzene, (4) as guest molecules have been studied. X-Ray structure analyses show that the capacity for inclusion is primarily dependent on the proton donoracceptor (co-ordinating) ability of the host. Nevertheless, the structures are very different. In (2) [crystal data: a = 14.91 6(13), b = 9.882(10), c = 17.1 28(13) A, p = 90.45(7)", space group P2,/c, Z = 4, R, = 0.066 for 2 550 observations] the guest molecules can act both as proton donor and acceptor in hydrogen bonding with the host, in ( 3 ) [a = 12.912(5), b = 17.979(15), c = 9.702(7) A, p = 1 1 0.79(7)", P2,/n, Z = 4, R, = 0.080 for 1 932 reflexions] the guest molecule acts as proton acceptor only, and in (4) [a = 9.955(2), b = 10.426(3), c = 12.005(3) A, cc = 77.34(2), p = 93.02(2), y = 104.59(2)", P i , 2 = 2, R, = 0.074 for 1 555 observations] a 'true' clathrate structure is established, with bromobenzene being incorporated in a hydrogen-bonded host matrix of (1). The decrease in coordinating bond strength between host and guest is also manifested in the gradual increase of disorder observed for these guest species. Conclusions concerning the clathrate formation selectivity of (1 ) are derived from the structural observations. Clathrate compounds and related lattice-controlled host-guest systems t are becoming objects of considerable a t t e n t i ~n . ~. ~
