[15]crown-5: An unsymmetrical bifacial hydrogen-bond acceptor in crystal engineering

Reaction of [15]crown-5 with erbium nitrate and a range of nickel salts res ults in the formation of the hydrogen-bonded chain species [Er(NO3)(3)(H2O) (3)]. [15]crown-5 .H2O (3), [Ni(H2O)(6)]Br-2. [15]crown-5 . 2H(2)O (4), [Ni (H2O)(6)](ClO4)(2). [15]crown-5 . 2H(2)O (5), [Ni(H2O)(6)](NO3)(2). [15]cro wn-5 . 2H(2)O (6) and [{Ni(H2O)(4)}(2)(mu -Cl)(2)]Cl-2. [15]crown-5 (7). Co mplexes 3-5 exhibit low symmetry structures with 2-4 unique crown ether mol ecules, whereas 6 and 7 are more symmetrical. The factors contributing to t his behaviour are discussed within the wider context of [15]crown-5 structu res in the Cambridge Structural Database.