Τίτλος:
Di-2-pyridyl ketone oxime [(py)(2)CNOH] in manganese carboxylate
chemistry: mononuclear, dinuclear and tetranuclear complexes, and
partial transformation of (py)(2)CNOH to the gem-diolate(2-) derivative
of di-2-pyridyl ketone leading to the formation of NO3-
Περίληψη:
The use of di-2-pyridyl ketone oxime, (py)(2)CNOH, in manganese
carboxylate chemistry has been investigated. Using a variety of
synthetic routes complexes [Mn(O2CPh)(2) (py)(2)CNOH(2)] .
0.25H(2)O(1.0.25H(2)O), Mn-4(O2CPh)(2) (py)(2)CO2(2)
(py)(2)CNO(2)Br-2] . MeCN (2 . MeCN), [Mn-4(O2CPh)(2) (
py)(2)CO2(2) ( py)(2)CNO(2)Cl-2] . 2MeCN ( 3 . 2MeCN),
[Mn-4(O2CMe)(2) (py)(2)CO2(2) (py)(2)CNO(2)Br-2] . 2MeCN ( 4 .
2MeCN), [Mn-4(O2CMe)(2) ( py)(2)CO2(2) (py)(2)CNO(2)(NO3)(2)]
. MeCN . H2O( 5 . MeCN . H2O) and [Mn-2(O2CCF3)(2)( hfac)(2) (
py)(2)CNOH(2)] (6) have been isolated in good yields. Remarkable
features of the reactions are the in situ transformation of an amount of
( py) 2CNOH to yield the coordination dianion, (py)(2)CO22- of the
gem-diol derivative of di-2-pyridyl ketone in 2-5, the coordination of
nitrate ligands in 5 although the starting materials are nitrate-free
and the incorporation of CF3CO2- ligands in 6 which was prepared from
Mn(hfac)(2) . 3H(2)O( hfac(-) = hexa uoroacetylacetonate). Complexes 2 4
have completely analogous molecular structures. The centrosymmetric
tetranuclear molecule contains two Mn-II and two Mn-III six-coordinate
ions held together by four mu-oxygen atoms from the two 3.2211
(py)(2)CO22- ligands to give the unprecedented [Mn-II ( mu-OR) Mn-III
(mu-OR)(2)Mn-III ( mu-OR) Mn-II](6+) core consisting of a planar zig-zag
array of the four metal ions. Peripheral ligation is provided by two
2.111 (py)(2)CNO-, two 2.11 PhCO2- and two terminal Br- ligands. The
overall molecular structure of 5 is very similar to that of 2-4 except
for the X- being chelating NO3-. A tentative reaction scheme was
proposed that explains the observed oxime transformation and nitrate
generation. The CF3CO2- ligand is one of the decomposition products of
the hfac ligand. The two Mn-II ions are bridged by two neutral ( py)
2CNOH ligands which adopt the 2.0111 coordination mode. A chelating
hfac(-) ligand and a terminal CF3CO2- ion complete a distorted
octahedral geometry at each metal ion. The CV of complex 3 reveals
irreversible reduction and oxidation processes. Variable-temperature
magnetic susceptibility studies in the 2 300 K range for the
representative tetranuclear clusters 2 and 4 reveal weak
antiferromagnetic exchange interactions, leading to non-magnetic S-T = 0
ground states. Best-fit parameters obtained by means of the program
CLUMAG and applying the appropriate Hamiltonian are J(Mn(II) ...
Mn(III)) = 1.7 (2), 1.5 (4) cm(-1) and J(Mn(III) ... Mn(III)) = 3.0 (2,
4) cm(-1).
Συγγραφείς:
Milios, CJ
Kyritsis, P
Raptopoulou, CP
Terzis, A and
Vicente, R
Escuer, A
Perlepes, SP
