The synthesis and characterization of the pendant-armed ligand N , N′ -bis(2′-pyridylmethyl)-1,7-dithia-4,11-diazacyclotetradecane (L 4 ) and crystal structures of L 4 and the copper(II) complex [Cu(L 4 )](ClO 4 ) 2 — Crystal structure of the nickel(II) complex of N -(2′-pyridylmethyl)-1,4,7-trithia-11-azacyclotetradecane (L 2 ), [Ni(L 2 )(CH