Mono- (3a,b) and binuclear (4a,b) tetradentate Ni-II complexes of a series of 26-membered macrocyclic salen dimers, [salen(CH2)](2), are prepared in good yield by solvent-controlled reaction with Ni(OAc)(2). The mononuclear complex 3b crystallizes in the trigonal space group 3P(1)(#144), a = 18.2566(2) Angstrom, c = 15.9244(2) Angstrom, V = 4596.57(8) Angstrom(3), and Z = 3. Refinement converged with R = 0.054 and R-w = 0.049 for 6852 reflections with I > 2.003 sigma(I). The Ni-II in complex 3b coordinates in an approximate square planar geometry to one of the two available tetradentate salen sites. Complex 4b crystallizes in the orthorhombic space group P2(1)2(1)2(1)(#19), n = 19.531(2) Angstrom, b = 22.891(3), c = 13.373(1) Angstrom, V = 5960(1) Angstrom(3), and Z = 4. The refinement converged with R = 0.067 and R-w = 0.065 for 3752 reflections with I > 2.003 sigma(I). Complex 4b coordinates two distorted square planar, cofacially oriented Ni-II-salen units held 7.1 Angstrom apart by a rigid, syn-folded macrocyclic structure. The solution spectroscopic data and solid-state crystallographic data of 3b and 4b demonstrate the presence of a molecular-sized cavity which shows host-guest properties. Reaction of the flexible 32-membered disalen macrocycle [salen(OCH2CH2O)](2) with Ni(OAc)(2) resulted in formation of a binuclear complex, 5. Complex 5 crystallizes in the triclinic space group P1(#1), a = 10.366(4) Angstrom, b = 12.170(3) Angstrom, c = 10.021(2) Angstrom, alpha = 106.29(2)degrees, beta = 91.69(2)degrees, gamma = 68.63(2)degrees, V = 1126.3(5) Angstrom(3), and Z = 1. The refinement converged with R = 0.052 and R-w = 0.053 for 2385 reflections with I > 2.003 sigma(1). The binuclear complex 5 contains two cofacially oriented, square planar Ni-II-salen groups lying 3.5 Angstrom apart in an anti-folded macrocyclic structure.