Transition metal and organometallic anion complexation agents

A di-palladium urea complex as a molecular receptor for anions

A new di-nuclear palladium complex containing thiol-urea ligands has been prepared, structurally characterized and its interaction with anionic species studied in solution.

Readily Prepared Metallo-Supramolecular Triple Helicates Designed to Exhibit Spin-Crossover Behaviour

New dinuclear supramolecular cylinders have been designed to exhibit spin-crossover behaviour, a form of molecular bistability. This has been achieved within the framework of our imine-based approach to supramolecular architecture by switching from pyridylimine systems to imidazolimines. Spin-crossover behaviour is achieved while retaining the simplicity and ease-of-synthesis of our molecular design. The imidazole groups used also introduce additional NH groups that engage in hydrogen-bonding to anions and solvents. In the case of the iron(II) tetrafluoroborate complex this hydrogen bonding links supramolecular cylinders into an extended two-dimensional array. Consistent with this, a sharper spin-crossover transition is observed for this compound than for the corresponding hexafluorophosphate salt. More subtle anion effects are indicated in the perchlorate salt which gives a two-step spin conversion, thereby displaying tristability.

A new fluoride selective electrochemical and fluorescent chemosensor based on a ferrocene–naphthalene dyad

A new difunctionalized receptor based on an aza-ferrocenophane structure shows electrochemical and fluorescent responses to fluoride anion.

Electrochemical anion recognition with ferrocene functionalised macrocycles

The syntheses and characterization of two new redox active cyclam ligands ferrocenylmethyl-(6-methyl-1,4,8,11-tetraazacyclotetradec-6-yl)-amine (L3) and 1,1'-ferrocenylmethyl-bis(6-methyl-1,4,8,11-tetraazacyclotetradec-6-yl)-amine (L4) are reported. The compounds each possess a ferrocenyl group bearing one (L3) or two (L4) appended macrocycles linked by their exocyclic amino groups and the crystal structures of both compounds have been determined. Anion binding of L3 and L4 was investigated by electrochemical titrations where H-bonding to each macrocycle causing a shift in the Fc+/0 redox potential was used as a reporter of guest binding. The Zn(II) complex of L3 has also been isolated and characterized structurally. These compounds were analysed for their capacity to electrochemically recognize anions in both aqueous and non-aqueous solution. We have found that L3, L4 and [ZnL3]2+ sense Cl- and AcO- anions in MeCN-CH2Cl2, a function that is lost in aqueous solution.

New Ligands for Enantioselective Recognition of Chiral Carboxylates Based on 1,1'-Binaphthalene-2,2'-diamine

Simple bis(arylureido)binaphthalenes and (arylamido)binaphthalenes have been synthesized in both racemic as well as optically active forms. One of these compounds has been found to complex chiral anions with modest enantioselectivity.

Statistical mechanical approach to competitive binding of metal ions to multi-center receptors

A microscopic site binding model to treat binding of several metal ions to multi-center receptors is proposed. The model introduces the appropriate parameterization in terms of microscopic complexation constants and metal-metal pair interaction energies. The model is solved with statistical mechanical techniques, including direct enumeration or transfer matrices. We obtain microscopic and macroscopic complexation constants, microstate probabilities, and binding isotherms for chain-like receptors, including the long-chain limit. Various examples to illustrate the usefulness of the model are given.

Redox sensing of anions in pure aqueous environment by ferrocene-containing 4,4′-bipyridinium-based receptors and polymer films

Selective voltammetric sensing of ATP(2-) anions in water was achieved using ferrocene-viologen based redox active receptors and related polymer films.

2,6-Di(pyrimidin-4-yl)pyridine Ligands with Nitrogen-Containing Auxiliaries: The Formation of Functionalized Molecular Clefts upon Metal Coordination

A series of ligands (1-4) based on a 2,6-di(pyrimidin-4-yl)pyridine scaffold have been synthesized, and their abilities to form complexes with Zn(II) and Cu(II) have been determined using UV/vis spectroscopy in buffered aqueous solution (0.01 M N-[2-hydroxyethyl]piperazine-N'-[3-ethanesulfonic acid] (HEPES) at pH = 6.8). The Zn(II) complex of 1 was determined to have a formation constant of 8.4 x 10(3) M(-)(1) while the formation constant of the Cu(II) complex was found to be 1 x 10(6) M(-)(1). The presence of auxiliary amines in 2 increased the stability of the Zn(II) complex relative to that of 1 by a factor of over 40, suggesting possible coordination of the auxiliaries to the Zn(II) center. The guanidinium and 2-amino-4,5-dihydro-imidazolinium groups of 3 and 4 considerably diminished the stability of the Zn(II) and Cu(II) complexes relative to those of 1. X-ray crystal structures of 1-Zn, 3-Zn, 4, and 4-Zn were obtained and are discussed. A significant increase in the stability of 3-Zn, but not in the stability 1-Zn, was observed upon the addition of 1 equiv of sodium phosphate, implicating a stabilizing interaction of the guanidinium groups of 3-Zn and the phosphate anion.