Structural dynamics and functional tuning of large host cavity created by cyclic metal arrangement

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This study was initiated with the aim of creating new gigantic large-macrocyclic ligands and their metal complexes. The methodology employed in this work is based on the metal-templated Schiff-base macrocyclization technique that exploits equimolar of diamine and dialdehyde precursors. 2,6-diformyl-4-methylphenol (dfmp) and three diamine spacers, i. e., 1,11-diamino- 3,6,9-trimethyl-3, 6, 9-triazaundecane (N5-diamine), 1, 14-diamino-3, 6, 9, 12,-trimethyl- 3, 6, 9, 12-tetraazatetradecane (N6-diamine) and 1,14-diamino-3,12,-dimethyl-3,12- diaaza-6,9-dioxotetradecane (NOON-diamine), were used as the dialdehyde and diamine precursors, respectively. The three diamine precursors were synthesized and fully characterized in this study.The reaction of N5-diamine, dfmp, Zn(CH_3COO)_2, and excess of NaClO_4 afforded the tetranuclear complex [Zn_4(H_2L_<N5>^<2+2>)(CH_3COO)_4](ClO_4)_4・1.5CH_3CN as yellow crystalline powder. The elemental analysis and IR spectroscopy indicated that this complex ha … More s a discrete tetranuclear core characterized with the dimer of [Zn_2(μ-phenoxo)(μ-acetato)_2] dimmers, where H_2L_<N5>^<2+2> is the tetranucleating ligand obtained by the [2+2] Schiff-base macrocyclization.The reaction of dfmp, N6-diamine and Cu(ClO_4)_2 in 1:1:2 molar ratio produced deep blue crystals [Cu_2L_<N6>^<1+1>(μ-OH)](ClO_4)_2・H_2O (complex 1), whose structure was fully characterized by X-ray crystallography. On contrary that H_2L_<N5>^<2+2> obtained from N5-diamine is the [2+2] macrocyclization product, (L_<N6>^<1+1>)^<2-> is the [1+1] product and functions as a dinucleating ligand. Cryomagnetic measurement of complex 1 showed that significant antiferromagnetic interaction operates between two copper atoms from the dinuclear species (J=-112 cm^<-1>).The similar reaction using Co(CH_3COO)_2, followed by the addition of excess amount of NaClO_4, gave the dark brown crystals [Co^<II>Co^<III>L_<N6>^<1+1>(μ-CH_3COO)(μ-OH)](ClO_4)_2 (complex 2). X-ray crystallography and spectroscopy (IR, UV-vis) clearly indicated that complex 2 has a dinuclear core in a mixed valent form of Co(II)-Co(III) being bridged by the phenoxo from the macricycle (L_<N6>^<1+1>)^<2->, hydroxo, and acetato oxygens. Cyclic voltammogram of complex 2 in CH_3CN showed that the Co(II)Co(III) mixed valence state is significantly stabilized (proportionation constant K=2.5×10^<12>). Less