[Cr(III)8M(II)6](12+) Coordination Cubes (M(II)=Cu, Co).

[Cr(III)8M(II)6](12+) (M(II) =Cu, Co) coordination cubes were constructed from a simple [Cr(III) L3 ] metalloligand and a "naked" M(II) salt. The flexibility in the design proffers the potential to tune the physical properties, as all the constituent parts of the cage can be changed without structural alteration. Computational techniques (known in theoretical nuclear physics as statistical spectroscopy) in tandem with EPR spectroscopy are used to interpret the magnetic behavior.

Computationally inexpensive interpretation of magnetic data for finite spin clusters.

We show that high-temperature expansion of the partition function is a computationally convenient tool to interpretation of magnetic properties of spin clusters wherein the spin centers are interacting via an isotropic Heisenberg exchange operator. High-temperature expansions up to order 12 are used to reproduce temperature dependent magnetic susceptibilities of a Cr(III) tetramer, a decanuclear Fe(III) wheel, a 3x3 grid arrangement of nine Mn(II) ions, and a dodecanuclear Ni(II) wheel. Excellent agreement with experiments as well as with results from computationally more elaborate methods is achieved.

Three overcrowded zinc(II) complexes with potentially hexadentate polypyridyl ligands.

In each of [N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine-kappa(6)N]zinc(II) bis(perchlorate) 0.67-hydrate, [Zn(C(26)H(28)N(6))](ClO(4))(2) x 0.67 H(2)O, (I), [N,N,N'-tris(2-pyridylmethyl)-N'-(2-quinolylmethyl)ethane-1,2-diamine-kappa(6)N]zinc(II) bis(perchlorate), [Zn(C(30)H(30)N(6))](ClO(4))(2), (II), and [N,N'-bis(2-pyridylmethyl)-N,N'-bis(2-quinolylmethyl)ethane-1,2-diamine-kappa(6)N]zinc(II) bis(perchlorate) monohydrate, [Zn(C(34)H(32)N(6))](ClO(4))(2) x H(2)O, (III), the Zn atom is coordinated to all six N atoms of the ligand. Compound (I) has one complex cation in a general position and one on a twofold axis. The coordination environments are intermediate between a regular octahedron and a pentagonal bipyramid which lacks one equatorial bond; complexes (II) and (III) are shown to be closer to the latter description. The quinolyl groups are in equatorial positions and the deviation from octahedral geometry increases with the number of these groups. This study demonstrates the systematic changes in the geometry at the central Zn atom as the overlap between the ligands increases.

First aminoacetone chelate: [Co(tren){NH2CH2C(O)CH3}]3+-a substrate binding and activation model for zinc(II)-dependent 5-aminolaevulinic acid dehydratase.

The complex p-[Co(tren){NH(2)CH(2)C(O)CH(3)}](ClO(4))(3).H(2)O was produced stereoselectively from [Co(tren)(O(3)SCF(3))(2)]O(3)SCF(3) () and 2-(aminomethyl)-2-methyl-1,3-dioxolane. The structure of was determined by X-ray crystallography. The complex is the first aminoacetone chelate to be reported and the first structurally characterized example of a non-conjugated ketone moiety coordinated to cobalt(iii). The robust complex was stable to aquation in strong acid and behaved as an acid with pK(a) = 4.99(1) indicative of a strong activation of the aminoacetone ligand towards deprotonation. The complex constitutes a structural model for a proposed substrate binding mode relevant for substrate activation of the zinc(ii)-dependent enzyme 5-aminolaevulinic acid dehydratase.

Facile cobalt(III) template synthesis of novel branched hexadentate polyamine monocarboxylates.

New hexadentate polyamine monocarboxylate ligands, 11-amino-9-(2-aminoethyl)-3,6,9-triazaundecanoate (tren-engly-), 12-amino-10-(2-aminoethyl)-3,7,10-triazadodecanoate (tren-tngly-) and 13-amino-11-(2-aminoethyl)-3,8,11-triazatridecanoate (tren-bngly-), were synthesized by intramolecular coupling of tetradentate tris(2-aminoethyl)amine (tren) and didentate N-([small omega]-formylalkyl)glycinates, OCH(CH2)nNHCH2CO2-, in easily and stereoselectively assembled cobalt(III) templates, p-[Co(tren){(RO)2CH(CH2)nNHCH2CO2}](O3SCF3)2, n = 1-3 (R = Me or Et). The reaction sequences comprised assembly of the template from [Co(tren)(O3SCF3)2]O3SCF3 (1) and (RO)2CH(CH2)nNHCH2CO2Et, deprotection of the pendant acetal in acid, intramolecular condensation of the resulting aldehyde with a coordinated primary amine at intermediate pH to form the imine and reduction of this by NaBH4. For n= 1, imine formation occurred exclusively at the primary amine trans to the carboxylate producing the hexadentate 11-amino-9-(2-aminoethyl)-3,6,9-triazaundeca-5-enoato (tren-enimgly-) complex, i-[Co(tren-enimgly)]Cl2.3.5H2O. In all instances, subsequent imine reduction gave the s isomer complex, exclusively. Complexes p-[Co(tren){(MeO)2CHCH2gly}](O3SCF3)2 (3), i-[Co(tren-enimgly)]ZnCl4.H2O (5), s-[Co(tren-engly)]ZnCl(4)(s-6), s-[Co(tren-tngly)]ZnCl4.H2O (s-7) and s-[Co(tren-bngly)ZnCl3]2ZnCl4 (s-8) were structurally characterized by X-ray crystallography. Charcoal-catalyzed equilibration of s-[Co(tren-engly)]Cl(2).2H(2)O dissolved in water produced the s- (s-6), p- (p-6) and t-[Co(tren-engly)]2+ (t-6) isomers in comparable amounts. p-6 and t-6 were also structurally characterized as their tetrachlorozincate and chloride salts, respectively. In base-catalyzed reactions, s-6 and t-6 each also formed p-6. Reduction of s-[Co(tren-engly)]Cl2.2H2O with (NH4)2S and acidification liberated the pentaamino carboxylic acid ligand which was isolated as the hydrochloride salt.