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

The interactions between two hydrogen bond donors and two hydrogen bond acc eptors (DD:AA) have been used to form extended linear polymers based on bis (thiosemicarbazide)nickel(II) cations and terephthalate aions. In order to investigate the influence of the other hydrogen bond donors and acceptors p resent on these structures, the bis-(thiosemicarbazide)nickel(II) complexes trans-[NiL2](2+), where L is the methyl substituted thiosemicarbazides L-2 [NHMeC(S)NHNH2], L-3 [NHMeC(S)NHNMe2] and L-4 [NH2C(S)NHNMe2], have been p repared as terephthalate (tere) salts and their crystal structures investig ated. The supramolecular structures of trans-[Ni(L-2)(2)[tere].4H(2)O 2 and trans- [Ni(L-3)(2)(OH2)(2)[tere] 3 show the expected R-2(2)(8) motif linki ng 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(L-4)(2)(OH2)(2)][ter e]. 2H(2)O 4, in contrast, shows the absence of the expected cation...anion ...cation chains. In this case, the cations and anions are linked by only o ne hydrogen bond, though interactions with the water molecules lead to an e fficient hydrogen bond structure with all potential hydrogen bond donors an d acceptors involved in hydrogen bonding interactions. These structures dem onstrate 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 ni ckel co-ordination geometry and the presence or absence of the anticipated linear hydrogen bonded chains.