Synthesis, Characterization, and Structure of Macrocyclic Mono- and C2-Symmetric, Binuclear Nickel Calixsalen Complexes

Abstract

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) A, c = 15.9244(2) A, V = 4596.57(8) A3, and Z = 3. Refinement converged with R = 0.054 and Rw = 0.049 for 6852 reflections with I > 2.003 sigma(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 P2(1)2(1)2(1)(#19), a = 19.531(2) A, b = 22.891(3), c = 13.373(1) A, V = 5960(1) A3, and Z = 4. The refinement converged with R = 0.067 and Rw = 0.065 for 3752 reflections with I > 2.003 sigma(I). Complex 4b coordinates two distorted square planar, cofacially oriented NiII-salen units held 7.1 A 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) A, b = 12.170(3) A, c = 10.021(2) A, alpha = 106.29(2) degrees, beta = 91.69(2) degrees, gamma = 68.63(2) degrees, V = 1126.3(5) A3, and Z = 1. The refinement converged with R = 0.052 and Rw = 0.053 for 2385 reflections with I > 2.003 sigma(I). The binuclear complex 5 contains two cofacially oriented, square planar NiII-salen groups lying 3.5 A apart in an anti-folded macrocyclic structure.