Tetranuclear Manganese Complexes with Dimer-of-Dimer and Ladder Structures from the Use of a Bis-Bipyridyl Ligand

Abstract

The reaction of the bis-chelating ligand 1,2-bis(2,2'-bipyridine-6-yl)ethane (L) with the trinuclear species of formula [Mn(3)O(O(2)CR)(6)(py)(3)](ClO(4)) (R = Me (1); R = Et (2); R = Ph (3)) has afforded the new tetranuclear mixed-valent complexes [Mn(4)O(2)(O(2)CR)(4)L(2)](ClO(4))(2) (R = Me (4); R = Et (5); R = Ph (6)) and [Mn(4)O(2)(OMe)(3)(O(2)CR)(2)L(2)(MeOH)](ClO(4))(2) (R = Me (7); R = Et (8); R = Ph (9)). Complexes 4-6 were obtained in yields of 20%, 44%, and 37%, respectively. They are mixed-valent, with an average Mn oxidation state of +2.5. Complexes 7-9 were obtained in yields of 57%, 65%, and 70%, respectively. They are also mixed-valent, but with an average Mn oxidation state of +2.75. Complexes 4 x 2THF and 9 x 3MeOH x H(2)O crystallize in the triclinic space group P1 macro and contain [Mn(4)(mu(3)-O)(2)](6+) and [Mn(4)(mu(3)-O)(2)(mu-OMe)(2)](5+) cores, respectively, the latter being a new structural type in the family of Mn(4) complexes. Reactivity studies of 4-9 have shown that 4-6 can be converted into 7-9, respectively, and vice versa. The magnetic properties of 5 and 9 have been studied by dc and ac magnetic susceptibility techniques. Complex 5 displays antiferromagnetic coupling between its Mn ions resulting in a spin ground state of S = 0. Complex 9 also displays antiferromagnetic coupling, but the resulting ground state is S = (7)/(2), as confirmed by fitting magnetization versus field data collected for 9 at low temperatures, which gave S = (7)/(2), D = -0.77 cm(-1), and g = 1.79. Complex 9 exhibits a frequency-dependent out-of-phase ac susceptibility peak, indicative of the slow magnetization relaxation that is diagnostic of single-molecule magnetism behavior.

Role of oxido incorporation and ligand lability in expanding redox accessibility of structurally related Mn4 clusters

“…The other manganese centers in the base have similar Mn-alkoxide and Mn-pyridine distances to 1 , and are thus assigned as Mn II ions. The Mn 4 (μ 4 -O)(μ 2 -O) structural motif has not been previously described, although Mn 4 O 2 complexes of butterfly 34 , planar 35 , fused-cubane 52 , and ladder-like 53 shapes have been reported, for example.…”

Structural diversity in manganese, iron and cobalt complexes of the ditopic 1,2-bis(2,2′-bipyridyl-6-yl)ethyne ligand and observation of epoxidation and catalase activity of manganese compounds

“…Complex 3 has a dimer of dimers structure of the tetranuclear Mn core that resembles, with some important differences (see below), a similar complex prepared in an analogous way by using a 1,2-bis(2,2¢-bipyridyl-6-yl)ethane ligand. 12 Complex 3 crystallized in the triclinic space group P 1. The asymmetric unit in the crystal structure of 3 consists of a binuclear [Mn 2 O(OAc) 2 L] + fragment and a PF 6 anion.…”

Synthesis, Crystal Structures, and Magnetic Properties of Mixed-Valent Tetranuclear Complexes with Y-Shaped MnII2MnIII2 Core

“…Specifically, tetranuclear manganese complexes have received considerable interest because the unique tetranuclear manganese cluster structure with calcium ion was found in the PS-II in green plants [9][10][11][12]. Many kinds of tetranuclear Mn II 2 Mn III 2 complexes have appeared in the literature, and butterfly-shaped tetranuclear Mn II 2 Mn III 2 complexes have remarkable magnetic properties with ferromagnetic couplings and SMM behavior [13][14][15]. Based on this background, we have focused on the synthesis of manganese complexes with multidentate organic ligands [16][17][18][19][20][21][22][23][24][25][26][27][28].…”