The mercuraindacycles bis(mu-1,8-naphthalenediyl)mercury(II)(bis(tetrahydrofuran)chloroindium(II I)) (5) and bis(mu-1,5-naphthalenediyl)mercury(II)(bis(tetrahydrofuran)bromoindium(III )) (7) are the products of the reaction of indium(I) halides with. 1,8-naphthalenediylbis(mercury(II) halides). Their formation involves a partial transmetalation followed by a spontaneous ring closure. Compounds 5 and 9 have been characterized by H-1, C-13, and Hg-199 NMR spectroscopy. The X-ray crystal structures of 5.(InCl3(THF)(3)) and 7 have been determined. Compound 5 crystallizes as an InCl3(THF)(3) adduct in the monoclinic space group P2(1)/c with a = 17.529(2) Angstrom, b = 8.954(1) Angstrom, c = 27.704(1): Angstrom, beta = 107.02(1)degrees, V = 4157.8(7) Angstrom(3), and Z = 4. Compound 7 crystallizes in the orthorhombic space group PZ(1)2(1)2(1) with a = 8.368(1) Angstrom, b = 15.357(1) Angstrom, c = 19.446(1) Angstrom, V = 2499.0(4) Angstrom(3), and Z = 4. In both structures, the eight-membered dimetallacycles adopt a twisted conformation with conspicuously short In Hg transannular distances. Finally, the X-ray crystal structure of the diindacycle bis(mu-1,8-naphthalenediyl)bis-(bis(tetrahydrofuran) chloroindium(III)) (8) is reported. This compound is isolated as a low-yield side product in the synthesis of 5. Compound 8 crystallizes in the tetragonal space group P4/n with a 19.492(1) Angstrom, c = 10.432 Angstrom, V = 3963.5(5) Angstrom(3), and Z = 4.