The tridentate ligand N-(2-hydroxypropyl)aminopropionic acid (H2hap) and the tripod ligand nitrilodi(propionic acid) acetic acid (H3ndpa) have been synthesised and found to interact with Cu(II) to produce tetranuclear compounds. In the cyclic complex [Cu(Hhap)(NO3)]4 (1), the four Cu(II) centres form a slightly buckled square linked via syn–anti carboxylate bridges. In [Cu4(ndpa)2(H2O)8(NO3)2]·2H2O (2), and [Cu4(ndpa)2(H2O)10]SO4·6H2O (3), two Cu(II) centres are each chelated by a ndpa3− ligand which in turn are linked by coordination of the outer carboxylate oxygens on the longer propionate arms of the ligands to two further {Cu(H2O)3}2+ units resulting in a rhomboid array of Cu(II) centres. In the closely related complexes [Cu4(ndpa)2(H2O)6Cl2]·4H2O (4), and [Cu4(ndpa)2(H2O)6Br2]·4H2O (5), replacement of one aqua ligand by an outer carboxylate oxygen from the shorter acetate arm of an adjacent complex results in the formation of infinite sheets of linked tetranuclear units. Magnetic studies performed between 1.8 and 300 K on these complexes indicate that ferromagnetic or antiferromagnetic coupling between Cu(II) ions can be observed depending on the geometry of the carboxylate bridging mode. Compound 1 shows a paramagnetic behaviour with a ferromagnetic interaction (J/kB=+3.9 K, S=2 ground state) between adjacent Cu(II) ions through equatorial–equatorial syn–anti carboxylate bridges. In compound 2, within the rhombus motif ferromagnetic (J1/kB=+12.1 K) and antiferromagnetic (J2/kB=−0.4 K) interactions through syn–anti bridges but in equatorial–equatorial and equatorial–axial modes, respectively, are present. Finally, in the 2-D 4 and 5 the linkage of the rhombus motif, which is isolated in 2, by equatorial–axial anti–anti carboxylate bridges, leads to dominating ferromagnetic interactions (J′=+0.2 K) between the ferromagnetically interacting Cu(II) dimers (J1=+8.8 K).

Reactions of [MoO2 (acetylacetonate)(2)] with the proligands (N-hydroxyimino)diacetic acid (H(3)hidpa), R, R-2,2'-(N-hydroxyimino)dipropionic acid (R,R-H(3)hidpa) or R,S-2,2'-(N-hydroxyimino) dibutyric acid (R,S-H(3)hidba) yielded the compounds [PPh4][Delta,Lambda -Mo(hida)(2)]. CH2Cl2 1, [H5O2][Delta -Mo(R,R-hidpa)(2)] 2, [PPh4][Mo(R,S-hidba)(2)]. 2H(2)O 3a and Na[Delta,Lambda -Mo(R,S-hidba)(2)]. 1/4 Pr-i(2) O 3b, respectively. Reactions of H(3)hida with a methanolic solution of [PPh4][MoOCl4 (H2O)] in the presence of NaOH (ca. pH 8) provided an alternative synthesis for 1. The complex of 1 when transferred into CH2Cl2 using [PPh4]Br yielded brown block-like crystals from a CH2Cl2-EtOH solution, however, 2 and 3b were crystallised from H2O and MeCN solutions with [H5O2](+) and [Na](+) counter cations, respectively. X-Ray crystallography confirmed the same distinctive eight-co-ordinate geometry of the complex anions of 1, 2 and 3b as identified for Amavadin, the form in which vanadium(IV) is bound in Amanita muscaria mushrooms. EPR and UV/vis spectra recorded for 1, 2 and 3a are consistent with the presence of molybdenum(V). Cyclic voltammetric studies using a glassy carbon working electrode in CH2Cl2 for 1 exhibited a reversible Mo-VI/Mo-V and a quasi-reversible Mo-V/Mo-IV redox couple at E-1/2 = +0.96 and -0.99 V (vs. a saturated calomel electrode), respectively. Complex 3a also displayed a reversible Mo-VI/Mo-V redox couple at E-1/2 = +0.77 V, whereas the Mo-V/Mo-IV couple was irreversible (E-pc = -1.28 V). Additional electrochemical studies with 2 recorded a reversible Mo-VI/Mo-V redox couple in Me2SO (E-1/2 = +0.77 V), however in H2O this one-electron oxidation process is irreversible.

Getrennte Bereiche unterschiedlicher Polarität in der Struktur einer anorganischen Clusterverbindung werden durch die Einführung eines organischen Liganden an der Peripherie des Aggregats begünstigt. Dies wurde anhand der Synthese von Verbindungen, die das Titelanion enthalten, demonstriert (Beispiel siehe Bild).

Chelating ligands based on the iminodiacetic acid moiety can be used to control the solvolysis reactions of paramagnetic transition metal ions and allow various cluster-based magnetic materials to be isolated and characterised. This paper discusses the strategies that can be used to favour certain types of supramolecular interaction with the ultimate goal of engineering arrays of ‘single molecule magnets’. Ten different systems, which have been crystallographically characterised, are presented to illustrate the approach.

Separate areas of differing polarity in the structure of an inorganic cluster compound are favored by the introduction of organic ligands on the periphery of the aggregate. This has been demonstrated by the synthesis of compounds containing the title anion (see picture for an example).

Transition metal centres, clusters and aggregates are common in biological systems and fulfil a variety of functions. Nature has the ability to tailor the properties of such species by controlling the molecular and supramolecular environment of the metal centres through the influence of additional structure-directing chemical species. We have been inspired by this to develop synthetic methods which explore the effects of such templating species on the structure and properties of coordination compound aggregates. We have found that chelating ligands can be used to manipulate the hydrolysis of transition metal ions and direct structure and properties both at the molecular and supramolecular levels. Results for a series of iron(III) compounds formed with ligands based around the iminodiacetate moiety are presented.