Synthesis and Characterization of [MnIII6(N-formylsalicylhydrazidate)6(MeOH)6]: A New Type of Macrocyclic Hexanuclear Manganese Cluster

Abstract

The macrocyclic hexanuclear metal cluster, [Mn-6(III)(fshz)(6)S-6], 1 (S = MeOH), was prepared using a trianionic pentadentate ligand, N-formylsalicylhydrazidate (fshz(3-)). Due to the meridional coordination of the ligand to the metal ion, the ligand is not only bridging the ring metal ions using a hydrazide N-N group but also enforcing the stereochemistry of the metal ions as a propeller configuration. The alternations of the chiralities of the metal centers expand the cyclic ring system of complex 1 to the 24-membered ring system. The neutral hexanuclear manganese complex with noncrystallographic pseudo-C-3i symmetry is in the crystallographic inversion center. The disc-shaped hexanuclear cluster is 1.8 nm in diameter and 0.8 nm in thickness and has a vacant cavity in the center of the cluster. Three solvent molecules coordinated at the metal centers with Lambda configuration are in one face of the cluster, and the remaining three solvent molecules coordinated at the other metal centers with Delta configuration are in the other face of the cluster. The two faces of the cluster have opposite chiralities to each other. The crystal packing structure of complex I shows that the disc-shaped hexanuclear clusters are aligned approximately along the crystallographic a axis. The cavities of the clusters in the crystal structure are also aligned, and one-dimensional channels are formed. The solution integrity of the cluster was addressed using solution mass spectrometry, paramagnetically shifted H-1 NMR spectroscopy, and UV-visible spectroscopy. Crystallographic data for 1: triclinic, P (1) over bar, a = 10.0237(9) Angstrom, b = 15.096(1) Angstrom, c = 15.617(1) Angstrom, alpha = 112.142(5)degrees, beta = 106.615(5)degrees, gamma = 99.958(7)degrees, V= 1989.8(3) Angstrom(3), Z = 2, D-calcd = 1.510 g cm(-1), R1 = 0.0502 and wR2 = 0.1424 for 4249 reflections with I > 2 sigma(I), GOF = 1.065.