Metalla-macro-tricyclic cryptands: anion encapsulation and selective separation of sulfate via in situ crystallization

A conformationally flexible bis-pyridyl-bis-amide ligand, namely N,N'-bis-(3-pyridyl)-isophthalamide (L1), has been exploited to synthesize metalla-macro-tricyclic cryptands by reacting it with various Cu(II) salts having different counteranions. Out of the five coordination compounds, namely [{Cu(mu-L1)(2)(H2O)(2)}center dot SO4 center dot 2H(2)O center dot X] (1a), [{Cu(mu-L1)(H2O)(4)}center dot SO4 center dot 3H(2)O](proportional to) (1b), [{Cu(mu-L1)(2)(H2O)(2)}center dot SiF6 center dot CH3OH center dot 4H(2)O](proportional to) (2), [{Cu(mu-L1)(2)(mu-Cl)}center dot ClO4](proportional to) (3) and [{Cu(mu-L1)(2)(H2O)}center dot(NO3)(2)center dot 2H(2)O center dot X](proportional to) (4a) (X = disordered solvents), compounds such as 1a,2 and 3 are metallacryptands, of which 3 is the first example of a polymeric metalla-macro-tricyclic cryptand. The effect of the conformation-dependent ligating topology and hydrogen bonding backbone of ligand L1, and counteranions on the formation of metallacryptands is discussed. Interestingly, an important anion, namely SO42-, has been separated by concomitantly crystallizing 1a and 1b from a complex mixture of anions, such as SO42-, NO3- and ClO4-, by following an in situ crystallization technique. Magnetic interactions in 3 have been investigated as a typical example. Weak antiferromagnetic coupling is observed in 3, as expected given the topology of the networks.