Di-2-pyridyl ketone oxime [(py)_2CNOH] in manganese carboxylate chemistry:mononuclear,dinuclear and tetranuclear complexes,and partial transformation of (py)_2CNOH to the gem-diolate(2-) derivative of di-2-pyridyl ketone leading to the formation of N

摘要

The use of di-2-pyridyl ketone oxime,(py)_2CNOH,in manganese carboxylate chemistry has been investigated.Using a variety of synthetic routes complexes [Mn(O_2CPh)_2{(py)_2CNOH}_2]centre dot0.25H_2O (1centre dot0.25H_2O),Mn_4(O_2CPh)_2{(py)_2-CO_2}_2{(py)_2CNO}_2Br_2]centre dotMeCN (2centre dotMeCN),[Mn_4(O_2CPh)_2{(py)_2CO_2}_2{(py)_2CNO}_2Cl_2]centre dot2MeCN (3centre dot2MeCN),[Mn_4(O_2CMe)_2{(py)_2CO_2}_2{(py)_2CNO}_2Br_2]centre dot2MeCN(4centre dot2MeCN),[Mn_4(O_2CMe)_2{(py)_2CO_2}_2{(Py)_2CNO}_2(NO_3)_2].MeCNcentre dotH_2O (5centre dotMeCNcentre dotH_2O) and [Mn_2(O_2CCF_3)_2(hfac)_2{(py)_2CNOH}_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)_2CO_2~(2-),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 CF_3CO_2~- ligands in 6 which was prepared from Mn(hfac)_2centre dot3H_2O (hfac~-=hexafluoroacetylacetonate).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)_2CO_2~(2-) ligands to give the unprecedented [Mn~(II)(mu-OR)Mn~(III)(mu-OR)_2Mn~(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)_2CNO~-,two 2.11 PhCO_2~- 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 NO_3~-.A tentative reaction scheme was proposed that explains the observed oxime transformation and nitrate generation.The CF_3CO_2~- 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 CF_3CO_2~- 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).