Aggregation of tetranuclear Mn building blocks with alkali ion. Syntheses, crystal structures and chemical behaviors of monomer, dimer and polymer containing [Mn4(mu3-O)2]8+ units

Aggregation of tetranuclear Mn(4)O(2) building blocks with alkali ion was studied. Several Mn(iii) complexes containing Mn(4)O(2)(AcO)(7)(pyz)(2)](-) (pyz = pyrazinate) anion(s) were obtained from an assembly system containing Mn(ii), MnO(4)(-), HOAc and Hpyz (Napyz or Kpyz). These Mn(4)O(2)](8+) complexes have monomeric (1 and 2), dimeric (4 and 5) and one-dimensional chain () structures of which alkali metal ion connects the Mn ions of adjacent Mn(4)O(2)](8+) units through mu(1,1)- and mu(1,3)-carboxylate bridges. Complexes 2 or 3 were converted into Mn(12)O(12)(AcO)(16)(H(2)O)(4)] in EtOH solution in the presence of HOAc. However, in MeOH solution, a coordination polymer Mn(2)(HCOO)(4)(H(2)O)(4)](n) was obtained accompanying the oxidation of MeOH to become HCHO and HCOOH. Tracing the (1)H NMR spectra of 2 or 3 in CD(3)OD, the disappearance of the resonance signals in 3 h indicated the decomposition of the Mn(4)O(2)](8+) cores. Complex 2 exhibits its proton NMR signals in CDCl(3) which are similar to those of its pic analogue but accompany downfield shift to various extents for all the corresponding signals. Variable-temperature magnetic susceptibilities of complexes 2-5 in the range 5-300 K were recorded and were fitted for an Mn(4)O(2) butterfly core, giving the fitting parameters J(bb) = -2.67 to -3.76 cm(-1) and J(wb) = -1.16 to -3.14 cm(-1). Small J values indicate weak antiferromagnetic coupling interactions of the Mn(iii) sites and the spin ground states are considered as S(T) = 0 based on the J(bb)/J(wb) ratio approximately 1 for these complexes. The ESR spectra were recorded for complex 2 in dual-mode at liquid-helium temperatures and no obvious signal could be found. The addition of p-cresol gives rise to the reduction of the Mn(4)O(2)](8+), resulting in observable signals.