Preparation, crystal structure and chelate substitution reactions of [Mn4O2(O2CPh)6(dpm)2] (dpm = the anion of dipivaloylmethane)

The reaction of [N-n Bu-4][ Mn4O2(O2CPh)(9)(H2O)] with 2 equiv. of Na(dpm) (dpm(-) is the anion of dipivaloylmethane) gives [NnBu4][Mn4O2(O2CPh)(7)(dpm)(2)] (1), which undergoes chelate substitution with picolinic acid (picH) or dibenzoylmethane (dbmH) to give the corresponding pic(-) and dbm(-) complexes, 2 and 3, respectively. Reaction of I with 1 equiv. of Me3SiCl converts it to [Mn4O2(O2CPh)(6)(dpm)(2)] (4), whose crystal structure shows a butterfly-like [Mn4O2](8+) core but with two five-coordinate Mn-III ions. Compound 4 also undergoes chelate substitution with picH, dbmH, 2-(hydroxymethyl)pyridine and hexafluoroacetylacetone to give the corresponding complexes. With trans-1,2-bis(4-pyridyl)ethylene (bpe), a bridged compound [Mn4O2(O2CPh)(6)(dpm)(2)(bpe)](2) is obtained, analogous to the dbm- compound previously characterized crystallographically; Magnetic susceptibility studies of 4 in the 5.00-300 K range give J(bb)= -27.5 cm(-1), J(wb)= -0.4 cm(-1) ((H) over cap= -2J (S) over cap (i)(S) over cap (j) convention), and g = 1.87, indicating 4 to have a quintuply degenerate (n, 0, n) ground state (n = 4, 3, 2, 1, 0) as a result of the large J(bb)/J(wb) ratio. (C) 2001 Elsevier Science Ltd. All rights reserved.