Synthesis, Redox, and Magnetic Properties of a Neutral, Mixed-Valent Heptanuclear Manganese Wheel withS= 27/2 High-Spin Ground State^,

Abstract

Reaction of lithium tetrachloromanganate(II) with N-n-butyldiethanolamine H2L3 (3) in the presence of LiH leads to the formation of wheel-shaped, mixed-valent heptanuclear, neutral complex {MnII subset[MnII2MnIII4Cl6(L3)6]} (4). The manganese wheel crystallizes in the triclinic space group P as 4.2CHCl3 or 4.3THF when either diethyl ether or n-pentane was allowed to diffuse into solutions of 4 in chloroform or tetrahydrofuran. The oxidation states of each manganese ion in 4.2CHCl3 or 4.3THF were assigned on the basis of detailed symmetry, bond length, and charge considerations, as well as by the Jahn-Teller axial elongation observed for the manganese(III) ions, and were further supported by cyclic voltammetry. The analysis of the SQUID magnetic susceptibility data for complex 4.2CHCl3 showed that the intramolecular magnetic coupling of the manganese(II,III) ions is dominated by ferromagnetic exchange interactions. This results in an S = 27/2 ground-state multiplet at low magnetic field. At fields higher than 0.68 T, the energetically lowest state is given by the mS = 31/2 component of the S = 31/2 multiplet due to the Zeeman effect. The ligand-field-splitting parameters were determined by anisotropy SQUID measurements on single crystalline samples along the crystallographic x, y, and z axes (D = -0.055 K, E = 6.6 mK) and by high-frequency electron spin resonance measurements on a polycrystalline powder of 4.2CHCl3 (D = -0.068 K, E = 9.7 mK). The resulting barrier height for magnetization reversal amounts to U approximately 10 K. Finally, 2DEG Hall magnetization measurements revealed that 4.2CHCl3 shows single-molecule magnet behavior up to the blocking temperature of about 0.6 K with closely spaced steps in the hysteresis because of the quantum tunneling of the magnetization.

Supramolecular Coordination Chemistry: The Synergistic Effect of Serendipity and Rational Design

“…[9a, [52][53][54][55][56] The CV of 79 displayed three quasi-reversible oxidation processes, which are attributed to the consecutive one-electron oxidations of the three peripheral Mn II ions to Mn III . Again, oxidation of the central Mn II ion is not observed (Figure 47).…”

“…In contrast, starting from N-n-butyldiethanolamine H 2 L 1 , lithium hydride, and dilithium tetrachloromanganate(II), the neutral, metal-centered, homonuclear, mixed-valent, six-membered manganese wheel [Mn II &{Mn II 2 Mn III 4 Cl 6 (L 1 ) 6 }] (78) was generated in a one-pot reaction (Scheme 32). [52] However, upon reaction of N-substituted diethanolamines H 2 L 2 with cesium carbonate and bis(tetraethylammonium)tetrachloromanganate(II), the metal-centered, mixed-valent manganese wheels Et 4 N-[Mn II &{Mn II 3 Mn III 3 Cl 6 (L 2 ) 6 }] (79) with an anionic core were generated (Scheme 32). [53] In the solid state, the {Mn&Mn 6 } core [45d,m, 54] of 78·2 CHCl 3 possesses idealized S 6 symmetry.…”

Five Disk‐Shaped {MII7} (M = Mn, Fe, Co, Cu, Zn) Clusters and One Capsule‐Like {CuII6NaI2} Cluster Assembled from the Same Schiff Base Ligand

“…A growing number of {M 7 } clusters with disk‐shaped configurations have been discovered. In our literature survey, we found 41 {M 7 } compounds with disk‐shaped cores . Table listed the formulas, supporting ligands, M II ··· M II distances, and magnetic properties of these clusters.…”

Supramolekulare Koordinationschemie – Synergie von Zufallsentdeckung und rationalem Design

“…In den Abschnitten 9.2 und 10.1 wurden die nichtbesetzten, neutralen, homovalenten, sechskernigen Eisenräder 62 sowie die sechskernigen Kupferräder 71 und 72 vorgestellt. Bei der Umsetzung von N ‐ n ‐Butyldiethanolamin H 2 L 1 , Lithiumhydrid und Dilithiumtetrachloromanganat(II) in einer Eintopf‐Reaktion erhält man nun das neutrale, metallzentrierte, homonucleare, gemischtvalente, sechsgliedrige Manganrad [Mn II ⊂{Mn II 2 Mn III 4 Cl 6 (L 1 ) 6 }] ( 78 ) (Schema ) 52. Andererseits entstehen bei der Reaktion von N‐substituierten Diethanolaminen H 2 L 2 mit Caesiumcarbonat und Bis(tetraethylammonium)tetrachloromanganat(II) die metallzentrierten, gemischtvalenten Manganräder Et 4 N[Mn II ⊂{Mn II 3 Mn III 3 Cl 6 (L 2 ) 6 }] ( 79 ) mit anionischem Gerüst (Schema ) 53…”

“…Wie bekannt, unterbleibt innerhalb des angewendeten Potentialbereichs eine Oxidation des zentralen Mn II ‐Ions 9a. 52–56 Im CV von 79 erkennt man drei quasi‐reversible Redoxwellen, die den aufeinanderfolgenden Einelektronenoxidationen der drei peripheren Mn II ‐Ionen zu Mn III entsprechen. Das zentrale Mn II ‐Ion wird auch hier nicht oxidiert (Abbildung 47).…”