N-[2-(4-methoxyphenyltelluro)ethyl]phthalimide (L1) synthesized by reacting ArTe- (generated in situ) with N-(2-bromoethyl)phthalimide, has been characterized structurally. The Te-C(alkyl) (2.147(5) Å) is somewhat longer than Te-C(aryl) (2.111(4) Å). The L1 on reaction with RuCl3·xH2O results in a novel heterocycle, Te-chloro,Te-anisyl-1a-aza-4-oxa-3-tellura-1H,2H,4aH-9-fluorenone (1), which is characterized structurally and is a unique example of a tellura heterocycle containing oxygen as well as nitrogen in the same ring. The oxidation state of Te changes to +IV in the formation of 1. The Te-Cl and Te-O bond lengths in 1 are 2.604(2) and 2.038(4) Å, respectively. The reaction of L1 with [RuCl2(p-cymene)]2 gives [RuCl2(p-cymene)·L1] (2) which is characterized structurally. The Ru-C (av), Ru-Cl and Ru-Te bond lengths are 2.192(1), 2.417(1)-2.434(1) and 2.651(5) Å, respectively. The difference in Te-C(alkyl) and Te-C(aryl) bond lengths is not affected on the ligation of L1 with ruthenium(II). © 2000 Elsevier Science S.A.