Synthesis, Characterization, and Structure of Macrocyclic Mono- and <i>C</i>₂-Symmetric, Binuclear Nickel Calixsalen Complexes

Mono- (3a,b) and binuclear (4a,b) tetradentate NiII 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 3P1(#144), a = 18.2566(2) Å, c = 15.9244(2) Å, V = 4596.57(8) Å3, and Z = 3. Refinement converged with R = 0.054 and Rw = 0.049 for 6852 reflections with I > 2.003σ(I). The NiII 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 P212121(#19), a = 19.531(2) Å, b = 22.891(3), c = 13.373(1) Å, V = 5960(1) Å3, and Z = 4. The refinement converged with R = 0.067 and Rw = 0.065 for 3752 reflections with I > 2.003σ(I). Complex 4b coordinates two distorted square planar, cofacially oriented NiII−salen units held 7.1 Å 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) Å, b = 12.170(3) Å, c = 10.021(2) Å, α = 106.29(2)° , β = 91.69(2)°, γ = 68.63(2)°, V = 1126.3(5) Å3, and Z = 1. The refinement converged with R = 0.052 and Rw = 0.053 for 2385 reflections with I > 2.003σ(I). The binuclear complex 5 contains two cofacially oriented, square planar NiII−salen groups lying 3.5 Å apart in an anti-folded macrocyclic structure.