The Mn(II)-2,2′-dipyridylamine-pseudohalide system: Synthesis, crystal structure and luminescence behaviour of [Mn(dpa) 2(X) 2] · H 2O and [Mn(dpa) 2(X)(OH 2)]ClO 4 (dpa = 2,2′-dipyridylamine; [formula omitted], NCO −)

Abstract

Four complexes of the type [Mn(dpa) 2(X) 2] · H 2O (dpa = 2,2′-dipyridylamine; X = N 3 - , 1 ; X = NCO −, 2) and [Mn(dpa) 2(X)(OH 2)]ClO 4 ( X = N 3 - , 3 ; X = NCO −, 4) have been synthesized using single-pot reactions of manganese(II) salt, dpa and X in 1:2:2 and 1:2:1 molar ratios, respectively. The compounds have been characterized by microanalytical, physicochemical, spectroscopic and magnetic results. Room temperature magnetic moments ( μ eff) are in the range 5.88–5.97 BM and are typical of high-spin manganese(II) complexes ( t 2 g 5 idealized, S = 5/2). The complexes display a Mn(III)–Mn(II) couple at ∼0.6 V versus SCE in DMF solutions. X-ray structure determinations show that in 1– 4 the manganese(II) centres are in a distorted octahedral environment. Compounds 1 and 2 contain the MnN 6 chromophore, completed by two bidentate dpa units and two terminal azido groups in 1 or N-coordinated cyanato ligands in 2, along with a water of crystallization. In 3 and 4, one water molecule acts as a coordinating ligand replacing one of the terminal pseudohalides in 1 and 2, respectively, resulting in a MnN 5O chromophore. The amine H, terminal azido N or cyanato O, O and H’s of the water molecule are engaged in extensive hydrogen bonding of the type N–H⋯N, O–H⋯N and N–H⋯O in 1 and 2. Additionally O–H⋯O bonding is observed in 3 and 4. Supramolecular 2D sheet structures are obtained arising from such weak intermolecular forces. All the complexes display high-energy intraligand 1(π–π*) fluroscence and intraligand 3(π–π*) phosphorescence in glassy solutions (DMF at 77 K).