Synthesis, structure, reactivity, and theor. studies of a new type of Ni triple-decker complexes are reported. A prominent feature of its mol. structure is the (h3:h3)-bis(enyl) coordination of two [(h5-Me4EtC5)Ni] fragments to the central arene ring of the polycondensed p-perimeter decacyclene. The central arene ring of decacyclene displays a distinct chair conformation with significant tilt angles of 25.5 and 26.1 Deg. The three naphthalene units are twisted in a propeller-like fashion with torsion angles of 16 Deg, 16.6 Deg, and 19 Deg, which is twice the twisting obsd. for the free decacyclene ligand. According to Extended Huckel MO (EHMO) calcns., a qual. measure for arene lability in the title compd. and a no. of related arene-bridged metal complexes can be attributed to a subsequent filling of metal-arene antibonding orbitals. The exptl. obsd. reactivities of p-arene exchange in these complexes are reproduced nicely by the EHMO calcns. The title compd. offers access to a no. of organonickel chalcogenolato complexes under mild conditions by cleavage of the S-S, Se-Se, or Te-Te bonds of diorganyl dichalcogenides R-E-E-R. The title compd. is also capable of Csp2-H activation of azobenzene and [(dimethylamino)methyl]ferrocene resulting in orthometalated complexes contg. five-membered metallacycles. PES and semi-empirical ZINDO/S calcns. were used to study the product of the orthometalation of the title compd. with azobenzene. These studies reveal that the HOMO of the metallacycle (IE = 6.45 eV) has dominant Ni-Cp and Ni-Caryl p-antibonding character.