Hydrogen bond directed crystal engineering of nickel complexes: the effect of ligand methyl substituents on supramolecular structure

Abstract

The interactions between two hydrogen bond donors and two hydrogen bond acceptors (DD∶AA) have been used to form extended linear polymers based on bis(thiosemicarbazide)nickel(II) cations and terephthalate anions. In order to investigate the influence of the other hydrogen bond donors and acceptors present on these structures, the bis(thiosemicarbazide)nickel(II) complexes trans-[NiL2]2+, where L is the methyl substituted thiosemicarbazides L2 [NHMeC(S)NHNH2], L3 [NHMeC(S)NHNMe2] and L4 [NH2C(S)NHNMe2], have been prepared as terephthalate (tere) salts and their crystal structures investigated. The supramolecular structures of trans-[Ni(L2)2][tere]·4H2O 2 and trans-[Ni(L3)2(OH2)2][tere] 3 show the expected R22(8) motif linking the cations and anions into chains which are, in turn, cross-linked into sheets via amino N–H· · ·O hydrogen bonds in 2 and aqua O–H· · ·O hydrogen bonds in 3. The supramolecular structure of trans-[Ni(L4)2(OH2)2][tere]·2H2O 4, in contrast, shows the absence of the expected cation· · ·anion· · ·cation chains. In this case, the cations and anions are linked by only one hydrogen bond, though interactions with the water molecules lead to an efficient hydrogen bonded structure with all potential hydrogen bond donors and acceptors involved in hydrogen bonding interactions. These structures demonstrate that the presence or absence of NH groups that are not involved in cation· · ·anion· · ·cation chain formation has a marked effect on both the nickel co-ordination geometry and the presence or absence of the anticipated linear hydrogen bonded chains.