Synthesis and characterization of homo- and heterovalent tetra- hexa- hepta- and decanuclear manganese clusters using pyridyl functionalized β-diketone, carboxylate and triethanolamine ligands

Abstract

The syntheses and characterizations are reported for six new homo- and heterovalent manganese clusters, utilizing pyridyl functionalized β-diketones ligands. The reaction of the trinuclear complex [Mn3O(O2CPh)6(H2O)(Py)2] with 1,3-di(pyridine-2-yl)propane-1,3-dione (dppdH) in CH2Cl2 resulted in a mixed-valence Mn3IIMn6IIIMnIV decanuclear cluster of formula [Mn10O7(dppd)3(O2CPh)11]·4CH2Cl2 (1). The structure of the core of 1 is based upon a centred tricapped trigonal prism. Reacting Mn(BF4)2·xH2O with dppdH and triethylamine (NEt3) in CH2Cl2–MeOH gave a rare, homoleptic hexanuclear cluster of formula [MnII6(dppd)8][BF4]4 (2) which has a triangular based core. Reaction of Mn(Y)2·xH2O, Y = NO3− or BF4−, with dppdH or 1-phenyl-3-(2-pyridyl)propane-1,3-dione (pppdH) in the presence of triethanolamine (teaH3) and NEt3 gave a heptanuclear ‘disc’ like manganese core of general formula [MnII7(X)6(tea)(OH)3][Y]2·solv (3) X = pppd− or dppd− and Y = NO3− or BF4−. The addition of N-(2-pyridinyl)acetoacetamide (paaH) to Mn(Y)2·4H2O Y = NO3− or ClO4− in MeOH gave a second divalent heptanuclear cluster with a ‘disc’-like core of general formula [Mn7(paa)6(OMe)6][X]2·solv (4) (X = NO3− or ClO4−), whilst the addition of paaH to a mixture of Mn(NO3)2·4H2O, teaH3 and NEt3 in CH2Cl2–MeOH resulted in the formation of a mixed-valence Mn2IIMn2III tetranuclear ‘butterfly’ complex of formula [Mn4(paa)4(teaH)2][NO3]2·2MeOH·2CH2Cl2 (5). Compound 5 displays the rare MnII/III oxidation state distribution of the body positions being MnII while the wing tips are MnIII. The in situ formation of the tetranuclear [Mn4(teaH)2(teaH2)2(O2C(CH3)3)2][O2C(CH3)3]2‘butterfly’ complex followed by the addition of Mn(O2CMe)2·4H2O resulted in a mixed-valence Mn4IIMnIIIMnIV hexanuclear species of formula [Mn6O2(teaH2)4(O2CMe)4][NO3]2[O2CMe]·CH2Cl2·MeOH·2H2O (6). The core of 6 displays a face sharing dicubane topology. Compounds 1 and 6 both display novel trapped-valence metal cores containing three different oxidation states on the manganese ion. Compounds 1, 2 and 3 are the first manganese based dppd clusters, while 4 and 5 are the first with the pyridylamino-substituted β-diketone ligand (paaH). The magnetic data for 1, 2, 3, 4, and 6 are dominated by antiferromagnetic interactions within the clusters, leading to small ground spin values of S = 1 for 1, S = 3 for 2, S = 5/2 for 3, S = 5/2 for 4 and S = 1/2 for 6. Compound 5, however, displays overall ferromagnetic interactions with the data indicating an S = 6 ground state. 5 also exhibits probable single molecule magnet behaviour as indicated by frequency dependent out-of-phase χM′′ peaks in the AC susceptibility measurements. Show more