Anion Recognition of Chloride and Bromide by a Rigid Dicobalt(II) Cryptate

The crystal structures of [Co2L(Cl)](ClO4)3 (1), [Co2L(Br)](ClO4)3 (2), [Co2L(OH)(OH2)]I3 (3), and [Co2L1(Cl)](ClO4)3 (4), the density functional theory calculations, as well as the binding constants of [Co2L]4+ toward Cl− and Br− and of [Co2L1]4+ toward Cl−, are reported in this paper (L = N[(CH2)2NHCH2(C6H4-p)CH2NH(CH2)2]3N, L1 = N[(CH2)2NHCH2(C6H4-m)CH2NH(CH2)2]3N). The rigid dicobalt(II) cryptate [Co2L]4+ shows the recognition of Cl− and Br− but not of F− and I−, because of the size matching to its rigid cavity. We also found that the relative rigid tripodal skeleton of L than that of L1 results in the higher affinity of [Co2L]4+ toward Cl−. Magnetic susceptibility measurements of 1 and 2 indicate that the two Co(II) atoms in the cryptates are antiferromagnetically coupled through the Cl−/Br− bridge, with g = 2.19, J = −13.7 cm−1 for 1, and g = 2.22, J = −17.1 cm−1 for 2.