Anion recognition of chloride and bromide by a rigid dicobalt(II) cryptate

The crystal structures Of [Co2L(CI)](CIO4)(3) (1), [Co2L(Br)](CIO4)(3) (2), [Co2L(OH)(OH2)I-3 (3), and [Co2L1(CI)](CIO4)(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 = NI(CH2)(2)NHCH2(C6H4-P)CH2NH(CH2)(2)](3)N, L-1 = N[(CH2)(2)NHCH2(C6H4-M)CH2NH(CH2)(2)](3)N). 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 L-1 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.