RESUMEN
The employment of di-2-pyridyl ketone, (py)2CO, in manganese(II) acetate chemistry is reported. The syntheses, crystal structures and magnetochemical characterisation are described for [MnII4(O2CMe)4{(py)2C(OH)O}4] () and [MnII10MnIII4O4(O2CMe)20{(py)2C(OH)O}4] (), where (py)2C(OH)O- is the monoanion of the gem-diol form of the ligand. The reaction of Mn(O2CMe)(2).4H2O with one equivalent of (py)2CO in Me2CO gives . Complex was obtained from the 1:1 reaction, in EtOH, between Mn(O2CMe)(2).4H2O and (py)2CO in the presence of NEt3. The tetranuclear molecule has a cubane topology with the MnII and the deprotonated oxygen atoms from the eta1:eta3:eta1:micro3 ligands occupying alternate vertices of the cube. The core of consists of two mixed valence cubane {MnII2MnIII2(micro3-O)2(micro3-OR'')2}4+ subunits that are linked through an unusual {MnII6(eta1:eta2:micro-O2CMe)6(eta2:eta2:micro3-O2CMe)2}4+ moiety via twelve eta1:eta1:micro MeCO2- groups. Some suggestions have been made concerning the possible assembly of from . The magnetic properties of in the 300-5 K range have been modelled with two J values, which reveal weak antiferromagnetic interactions within the molecule. Complex has a low spin ground state. This work demonstrates the flexibility, versatility and synthetic potential of combining (py)2CO with carboxylate ligands.
RESUMEN
The cluster [Ni6(H2L)2(HL1)2(N3)8].2C2H5OH.2H2O [1.2C2H5OH.2H2O], featuring four fused defective cubanes, has been obtained via azido-bridge-driven dimerization of two phenolate-centered trinuclear Ni3 fragments.
RESUMEN
X-ray absorption spectroscopy has been employed to assess the degree of similarity between the oxygen-evolving complex (OEC) in photosystem II (PS II) and a family of synthetic manganese complexes containing the distorted cubane [Mn(4)O(3)X] core (X = benzoate, acetate, methoxide, hydroxide, azide, fluoride, chloride, or bromide). These [Mn(4)(&mgr;(3)-O)(3)(&mgr;(3)-X)] cubanes possess C(3)(v)() symmetry except for the X = benzoate species, which is slightly more distorted with only C(s)() symmetry. In addition, Mn(4)O(3)Cl complexes containing three or six terminal Cl ligands at three of the Mn were included in this study. The Mn K-edge X-ray absorption near edge structure (XANES) from the oxygen-ligated complexes begin to resemble general features of the PS II (S(1) state) spectrum, although the second derivatives are distinct from those in PS II. The extended X-ray absorption fine structure (EXAFS) of these Mn compounds also displays superficial resemblance to that of PS II, but major differences emerge on closer examination of the phases and amplitudes. The most obvious distinction is the smaller magnitude of the Fourier transform (FT) of the PS II EXAFS compared to the FTs from the distorted cubanes. Curve fitting of the Mn EXAFS spectra verifies the known core structures of the Mn cubanes, and shows that the number of the crucial 2.7 and 3.3 Å Mn-Mn distances differs from that observed in the OEC. The EXAFS method detects small changes in the core structures as X is varied in this series, and serves to exclude the distorted cubane of C(3)(v)() symmetry as a topological model for the Mn catalytic cluster of the OEC. Instead, the method shows that even more distortion of the cubane framework, altering the ratio of the Mn-Mn distances, is required to resemble the Mn cluster in PS II.