In the solution state, an equimolar mixture of syn- and anti-conformations is present for the ligand N,N′-bis(4-pyridylformyl)piperazine, L. Combining L with cis-Pd(en)(NO3)2 resulted in the formation of metallomacrocycle cis-[Pd2(en)2(L) 2](NO3)4, 1, quantitatively. Coordinated L in complex 1 was found to exist exclusively in the syn-conformation. The equimolar mixture of syn- and anti-conformations was re-established by ethylenediamine induced demetallation of 1. © 2014 the Partner Organisations.

Dillip Kumar Chand

Department Of Chemistry

Venkatachalam Ramkumar

Conformations

Coordination reactions

Mixtures

ANTI-CONFORMATIONS

Complex 1

Demetallation

Equimolar mixtures

Ethylene diamine

METALLOMACROCYCLES

SYN-ISOMERS

Palladium compounds

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RSC Advances

A rare variety of coordination rings having the M<inf>3</inf>L<inf>6</inf> composition are prepared by the combination of Pd(NO<inf>3</inf>)<inf>2</inf> with an imidazolyl or benzimidazolyl appended bidentate non-chelating ligand (i.e.L1 or L2). The variable concentration 1H NMR spectra of the trinuclear complexes [Pd<inf>3</inf>(L1)<inf>6</inf>](NO<inf>3</inf>)<inf>6</inf>, 1a and [Pd<inf>3</inf>(L2)<inf>6</inf>](NO<inf>3</inf>)<inf>6</inf>, 2a in DMSO-d<inf>6</inf> provided valuable information on the self-assembly phenomenon of the already self-assembled complexes. Interestingly, the signals of 2a are broadened upon increasing the concentration. The solution of 2a in DMSO formed a supramolecular metallogel above a certain concentration (i.e. 2% w/v), however, complex 1a could not form any gel. This phenomenon is attributed to the presence of an auxiliary π-surface in the benzimidazole moiety in L2, in contrast to the imidazole moiety of L1. The influence of anions in gel formation was studied by preparing several samples using a variety of palladium(ii) salts and L2 in DMSO. It was found that oxoanions like nitrate, perchlorate, triflate and tosylate are amicable for gel formation, probably due to their capabilities of forming H-bonds. The counter anions like tetrafluoroborate, hexafluorophosphate, or hexafluoroantimonate could not assist in the formation of gel. The stimuli-responsive nature of the gel and the reversible gel-sol conversion were demonstrated by dis-assembly and re-assembly processes of 2a as controlled by a pair of stimuli such as halide-nitrate, DMAP-HNO<inf>3</inf>, and ethylenediamine-Pd(NO<inf>3</inf>)<inf>2</inf>. No gel could be prepared by the combination of Ni(NO<inf>3</inf>)<inf>2</inf> or Pt(NO<inf>3</inf>)<inf>2</inf> with ligand L2. Thus, a subtle change in the ligand design, metal ion and counter anion is demonstrated as the responsible parameter for the construction of the three component multi-stimuli-responsive supramolecular gel. © The Royal Society of Chemistry 2015.

Dalton Transactions

Nanoscale metallogel via self-assembly of self-assembled trinuclear coordination rings: Multi-stimuli-responsive soft materials

Palladium(II) has four coordination sites and forms square planar complexes. Discrete self-assemblies are generated by the combination of a variety of palladium(II) components and ligands ranging from bi- to polydentate. The Pd(II) components used are generally of two varieties: cis-protected Pd(II) and unprotected Pd(II). Most common cis-protecting units (X-X) such as ethylenediamine, 2,2'-bipyridine and 1,3-bis(diphenylphosphino)propane and a few other related chelating systems have been exploited for the complexation reactions. The self-assemblies formed are generally represented as [{cis-Pd(X-X)} x(L) y](monoanion) 2x and [Pd m(L) n](monoanion) 2m when generated from the complexation of a suitable ligand (L) with cis-protected Pd(II) and simple Pd(II) units, respectively. When Pd(solvent) 2Cl 2 is complexed with ligands, the solvent molecules are replaced with the incoming ligands, leading to complexes in which the trans positions are occupied by the chloride anions. © 2012 Elsevier B.V.

Coordination Chemistry Reviews

Self-assembled coordination complexes from various palladium(II) components and bidentate or polydentate ligands

Inorganica Chimica Acta

Divalent metal homophthalate coordination polymers with long-spanning dipyridyl ligands containing piperazine moieties

Dual coordination in ditopic azabipyridines and azaterpyridines as a key for reversible switching

Chemical Science

Metal ion responsive adhesion of vesicles by conformational switching of a non-covalent linker

Topological diversity in copper aromatic meta-dicarboxylate coordination polymers with bis(pyridylformyl)piperazine coligands

Palladium(ii) induced complete conformational enrichment of the syn isomer of N,N′-bis(4-pyridylformyl)piperazine

Journal	Data powered by TypesetRSC Advances
Publisher	Data powered by TypesetRoyal Society of Chemistry
ISSN	20462069
Open Access	No