FeII/III and MnII complexes based on 2,4,6-tris(2-pyridyl)-triazine: synthesis, structures, magnetic and biological properties.

Reaction of the polypyridyl ligand 2,4,6-tris(2-pyridyl)-s-triazine (tpt) with mono- and polynuclear Fe(iii) or Mn(ii) precursors, specifically tri- or hexanuclear Fe(iii) pivalates (piv-), [Mn6O2(piv)10(Hpiv)4] and Mn(ii) isobutyrate (ib-), in various solvents and under various reaction conditions showcase the ligand's surprising coordination characteristics. The reactions result in mononuclear [FeIII(tpt)(tptH)][FeIIICl4]4·2(thf)·0.23(H2O) (1), [FeIII(piv)(tpt)Cl2] (2), [FeII(tpt)Cl2]·2(H2O) (3a), dinuclear [FeIII 2O(tpt)2Cl4] (3), and heptanuclear [FeIII 7O4(piv)12(tpt-O)]·A [A = MeCN (4a) or 4(dioxane) (4b)] and [FeIII 7O4(piv)11(tpt-O)(i-PrO)(i-PrOH)]·0.75(i-PrOH) (5), as well as the mononuclear compounds [MnII(tpt)(NO3)(H2O)2](NO3) (6) and [MnII(tpt)(ib)(Cl)(MeOH)]·MeOH (7). Single-crystal X-ray diffraction analyses identify tpt as a tridentate NNN donor ligand that forms two five-membered metallocycles in 1-3, 6 and 7, whereas in 4 and 5 five tpt N atoms form coordinative bonds accompanied by an unusual metal-induced oxidation of one of the carbon atoms of the central triazine core. Magnetic properties of Fe(iii)-tpt (2-5), Fe(ii)-tpt (3a), and Mn(ii)-tpt (7) compounds show dominant antiferromagnetic coupling for polynuclear coordination cluster compounds. The Mn(ii)-tpt complexes 6 and 7 exhibit efficient catalytic properties in the production of enzymes by microorganisms, which concerns the synthesis of exocellular proteases in Fusarium gibbosum CNMN FD 12 or Trichoderma koningii Oudemans CNMN FD 15 fungi strains. Thus, compounds 6 and 7 can be used for producing proteolytic enzymes with wide applications including in the food, detergents and pharmaceutical industries.

Iron(III) carboxylate/aminoalcohol coordination clusters with propeller-shaped Fe8 cores: approaching reasonable exchange energies.

A series of new octanuclear propeller-like aminoalcohol-supported Fe(III) oxocarboxylate coordination clusters, [Fe8O3(O2CCHMe2)9(tea)(teaH)3]·MeCN·2(H2O) (1), [Fe8O3(O2CCHMe2)6(N3)3(tea)(teaH)3] (2), [Fe8O3(O2CCMe3)6(N3)3(tea)(teaH)3]·0.5(EtOH) (3), and [Fe8O3(O2CCHMe2)6(N3)3(mdea)3(MeO)3] (4) (where teaH3 = triethanolamine; mdeaH2 = N-methyldiethanolamine) has been isolated and magnetochemically analyzed combining the programs wxJFinder and CONDON in an approach to avoid overparameterization issues that are common to larger spin polytopes. Dominant antiferromagnetic exchange interactions exist in all clusters along the edges of the propellers, while moderate ferromagnetic interactions are found along the propeller axes in their {Fe8O3} metallic cores.

A one-dimensional coordination polymer based on Cu3-oximato metallacrowns bridged by benzene-1,4-dicarboxylato ligands: structure and magnetic properties.

A one-dimensional linear coordination polymer {[Cu3(µ3-OH)(2-pyao)3(bdc)]·6(H2O)}n () composed of trinuclear [Cu3(µ3-OH)(2-pyao)3](2+) metallacrown cores bridged by bis-carboxylato linkers has been obtained by treatment of copper(ii) fluoride with pyridine-2-aldoxime (2-pyaoH) ligand and benzene-1,4-dicarboxylic acid (H2bdc). Magnetic susceptibility measurements show strong antiferromagnetic interactions between Cu(ii) centers within the trinuclear metallacrown core with J = -430 cm(-1).

Avoiding magnetochemical overparametrization, exemplified by one-dimensional chains of hexanuclear iron(III) pivalate clusters.

One-dimensional chain coordination polymers based on hexanuclear iron(III) pivalate building blocks and 1,4-dioxane (diox) or 4,4'-bipyridine (4,4'-bpy) bridging ligands, [Fe6O2(O2CH2)(O2CCMe3)12(diox)]n (1) and [Fe6O2(O2CH2)(O2CCMe3)12(4,4'-bpy)]n (2), showcase the utility of the angular overlap model, implemented in the program wxJFinder, in the predictive identification of the relative role of intra- and intercluster coupling.

An octanuclear iron(III) isobutyrate wheel.

The reaction of the µ(3)-oxido-centred trinuclear isobutyrate cluster [Fe(3)O(O(2)CCHMe(2))(6)(H(2)O)(3)](+) with an excess of phenol (PhOH) in chloroform produces a novel octanuclear Fe(III) cluster, cyclo-tetra-µ(2)-hydroxido-dodeca-µ(2)-isobutyrato-κ(24)O:O'-octa-µ(2)-phenolato-κ(16)O:O'-octairon(III) phenol hexasolvate monohydrate, [Fe(8)(C(4)H(7)O(2))(12)(C(6)H(5)O)(8)(OH)(4)]·6C(6)H(5)OH·H(2)O. The neutral cluster is located about a centre of inversion and consists of a planar ring of eight Fe(III) centres with two types of bridges between adjacent Fe atoms: each Fe atom is bridged to one of its neighbours by a µ-hydroxide and two 1,3-bridging carboxylates, or by two phenolate and one 1,3-bridging isobutyrate ligand. The cavity within the {Fe(8)} wheel is occupied by a disordered water molecule. Intermolecular O-H···O hydrogen bonds and C-H···π interactions connect the clusters and the phenol solvent molecules to form a three-dimensional network.

{Fe6O2}-Based Assembly of a Tetradecanuclear Iron Nanocluster.

The tetradecanuclear FeIII pivalate nanocluster [Fe14O10(OH)4(Piv)18], comprising a new type of metal oxide framework, has been solvothermally synthesized from a hexanuclear iron pivalate precursor in dichlormethane/acetonitrile solution. Magnetic measurements indicate the presence of very strong antiferromagnetic interactions in the cluster core.

One-dimensional manganese coordination polymers composed of polynuclear cluster blocks and polypyridyl linkers: structures and properties.

The synthesis, crystal structures and magnetic properties of five new manganese compounds are reported. These include a linear trinuclear cluster [Mn(II)(3)(O(2)CCHMe(2))(6)(dpa)(2)].2MeCN (1) (dpa = 2,2'-dipyridylamine), a tetranuclear cluster [Mn(II)(2)Mn(III)(2)O(2)(O(2)CCMe(3))(6)(bpy)(2)] (3) (bpy = 2,2'-bipyridine), and chain coordination polymers composed of cluster blocks such as Mn(3), Mn(3)O, and Mn(4)O(2) bridged by 2,2'-bipyrimidine (bpm) or hexamethylentetramine (hmta) ligands to give ([Mn(II)(3)(O(2)CCHMe(2))(6)(bpm)].2EtOH)(n) (2), [Mn(II)(2)Mn(III)(2)O(2)(O(2)CCHMe(2))(6)(bpm)(EtOH)(4)](n) (4), and (([Mn(II)Mn(III)(2)O(O(2)CCHMe(2))(6)(hmta)(2)].EtOH)(n) (5). The magnetic analysis of the compounds was achieved using a combination of vector coupling and full-matrix diagonalization methods. Susceptibility data for compound 1 was fitted using a vector coupling model to give g = 2.02(1) and 2J/k(B) = -5.38(2) K. To model the trimer chain, we used vector coupling for initial values of J(1) and then diagonalization techniques to estimate J(2) to give g = 1.98(1), 2J(1)/k(B) = -3.3(1) K and 2J(2)/k(B) = -1.0(1) K by approximating the system to a dimer of trimers. The analysis of 3 was made difficult by the mixture of polymorphs and the difficulties of a three-J model, while for 4 an analysis was not possible because of the size of the computation and the relative magnitudes of the three couplings. Compound 5 was modeled using the same techniques as 2 to give g = 1.99(1), 2J(1)/k(B) = +32.5(2) K, 2J(2)/k(B) = -16.8(1) K, and 2J(3)/k(B) = +0.4(1) K. The combination of techniques has worked well for compounds 2 and 5 and thus opens up a method of modeling complex chains.

[Os(bipy)(CN)4]2- and its relatives as components of polynuclear assemblies: structural and photophysical properties.

A series of diimine-tetracyanoosmate anions [Os(diimine)(CN)4]2- [diimine=2,2'-bipyridine (bipy), 2,2'-bipyrimidine (bpym), 1,10-phenanthroline (phen), and 4,4'-tBu2-2,2'-bipyridine (tBu2bpy)] were prepared and isolated as their Na+ salts (water soluble) or PPN+ salts (soluble in organic solvents). Several examples were crystallographically characterized; the Na+ salts form a range of 1D, 2D, or 3D infinite coordination polymers via coordination of the cyanide groups to Na+ cations in either an end-on or a side-on manner. The [Os(diimine)(CN)4]2- anions are solvatochromic, showing three MLCT absorptions, which are considerably blue-shifted in water compared to organic solvents, in the same way as is well-known for the analogous [Ru(diimine)(CN)4]2- anions. Luminescence in the red region of the spectrum is very weak but (following the expected solvatochromic behavior) is higher energy and more intense in water. However, by exploiting the effect of metallochromism (ref 4), the emission from [Os(tBu2bpy)(CN)4]2- in MeCN can be very substantially boosted in energy, intensity, and lifetime in the presence of Lewis-acidic metal cations (Na+, Ba2+, Zn2+), which, in a relatively noncompetitive solvent, coordinate to the cyanide groups of [Os(tBu2bpy)(CN)4]2-. This has an effect similar in principle to hydrogen bonding of the cyanides to delta+ protons of water, but very much stronger, such that in the presence of Zn2+ ions in MeCN the 1MLCT and 3MLCT absorptions are blue-shifted by ca. 7000 cm(-1), and the luminescence moves from 970 nm (vanishingly weak) to 610 nm with a lifetime of 120 ns (dominant component). Thus, the binding of metal cations to the cyanides provides a mechanism to incorporate [Os(diimine)(CN)4]2- complexes into polynuclear assemblies and simultaneously increases their 3MLCT energy and lifetime to an extent that makes them comparable to much-stronger luminophores such as Ru(II)-polypyridines.

Three-component coordination networks based on [Ru(phen)(CN)4(2-) anions, near-infrared luminescent lanthanide(III) cations, and ancillary oligopyridine ligands: structures and photophysical properties.

A series of cyanide-bridged coordination networks has been prepared which contain [Ru(phen)(CN)4](2-) anions, Ln(III) cations, and additional oligopyridine ligands (1,10-phenanthroline, 2,2':6',2'''-terpyridine or 2,2'-bipyrimidine) which coordinate to the Ln(III) centres. Five structural types have been identified and examples of each type of structure are described: these are hexanuclear Ru4Ln2 clusters; two-dimensional Ru-Ln sheets with a honeycomb pattern of edge-linked Ru6Ln6 hexagons; one-dimensional chains consisting of two parallel cross-linked strands in a ladder-like arrangement; simple single-stranded chains of alternating Ru/Ln components; and a one-dimensional 'chain of squares' in which Ru2Ln2 squares are linked by bipyrimidine bridging ligands which connect to the Ln(III) corners of adjacent squares in the sequence. The 3MLCT luminescence characteristic of the [Ru(phen)(CN)4](2-) units is quenched in those networks containing Ln(III) which have low-lying near-infrared luminescent f-f states [Pr(III), Nd(III), Er(III), Yb(III)], with sensitised Ln(III)-based near-IR luminescence generated by d --> f energy-transfer. The rate of d --> f energy-transfer, and hence the degree of quenching of the 3MLCT luminescence from the [Ru(phen)(CN)4](2-) units, depends on the availability of f-f levels of an appropriate energy on the Ln(III) centre, with Nd(III) (with a high density of low-lying f-f states) being the most effective energy-acceptor and Yb(III) (with a single low-lying f-f state) being the least effective. Rates of d --> f energy-transfer to different Ln(III) centres could be determined from both the residual (partially quenched) lifetimes of the 3MLCT luminescence, and--in the case of the Yb(III) networks--by a rise-time for the sensitised near-IR luminescence. The presence of the 'blocking' polypyridyl ligands, which reduced the number of cyanide and water ligands that would otherwise coordinate to the Ln(III) centres, resulted in increases in the Ln(III)-based emission lifetimes compared to networks where these blocking ligands were not used.