Dinuclear cobalt and manganese squarate complexes with bidentate N-donor ligand: syntheses, crystal structures, spectroscopic, thermal and voltammetric studies

Abstract

The crystal structures of [M 2 (phen) 4 (H 2 O) 2 (C 4 O 4 )]AE C 4 O 4 AE 8H 2 O [M = Co 2+ (1), Mn 2+ (2); phen: 1,10-phenanthroline] complexes have been prepared and characterized by IR spectroscopy, thermal analysis and single X-ray diffraction techniques. Their structures consist of [Co 2 (phen) 4 (H 2 O) 2 (C 4 O 4 )] 2+ (1) and [Mn 2 (phen) 4 (H 2 O) 2 (C 4 O 4 )] 2+ (2) dinuclear cobalt(II) and manganese(II) cations, uncoordinated C 4 O 4 2) (SQ 2) ) dianion and crystalization water molecules. In both complexes the metal ions have distorted octahedral geometry. The squarate adopts the l-1,3 (1) and (2) bis(monodentate) coordination modes, the intradimer M-M separation being 8.053(7) Å (1) and 8.175(4) Å (2), respectively, while the other squarate acts as a counter anion. The voltammetric behaviour of complexes (1) and(2) was investigated in DMSO (dimethylsulfoxide) solution by cyclic voltammetry using n-Bu 4 NClO 4 as supporting electrolyte. The complexes exhibit both metal and ligand centred electroactivity in the potential ±1.75 V versus Ag/ AgCl reference electrode. The dianion SQ 2) is oxidized in two consecutive steps to the corresponding radical monoanion and neutral form.

Polynuclear and polymeric squarato-bridged coordination compounds

“…The μ 2 -bridged-squarato bonding mode is the most common among all squarato compounds, where two coordination modes exist, namely the μ 1,3 (I, trans) and μ 1,2 (II, cis) (Scheme 2). A number of dinuclear μ 1,3 -bridged-squarato metalIJII) complexes were structurally characterized (1-17): 10,18,[24][25][26][27][29][30][31][32][33][34][35][36] [Cu 2 IJL) 2 IJμ 1,3 -C 4 O 4 )IJH 2 O) y ] n+ , where L = bdmpzpy, y = 2, n = 2; 10 terpy, y = 2, n = 2; 18 bpy, y = 4, n = 2; 27 TPA, y = 0, n = 2; 29 Me 3 TPA, y = 0, n = 2; 33 MeDPA, y = 2, n = 2; 29 bpcam, y = 2, n = 2; 30 pmedien, y = 2, n = 2; 32 bpca, y = 2, n = 0; 34 29 [Cu 2 IJ2,2′-bpy…”

“…In the presence of organic coligands the metallic salt is mixed with the ligand in MeOH, EtOH, DMSO or DMF and the preformed metal( ii )–ligand is then treated with an aqueous solution of sodium squarate. 10,11,14–36 In most cases, heating the reaction mixture on a steam bath is required depending on the nature of the metal ion. Some of the squarato metal complexes were also synthesized by hydrothermal reactions (160–200 °C) in aqueous solutions containing equimolar amounts of M( ii ) halide, organic co-ligand and sodium squarate or squaric acid.…”

“…[20][21][22][23] Following the above discussion, the squarate dianion has been employed as a bridging ligand for assembling divalent metal ions and hence for the construction of polynuclear metal complexes with different nuclearity and coordination polymers with different dimensionality (1D, 2D, 3D). Thus, in addition to metalIJII) complexes where the squarate is acting as a counterion [24][25][26][27] and mononuclear aqua-metalIJII) species (Mn, Zn, Cd) where the squarate is acting as a simple monodentate ligand, 28 enormous numbers of bridged-squarato coordination compounds were isolated and structurally characterized. The diverse polydentate nature of the squarate dianion led to a variety of bonding modes that range from μ 2 -bis-to μ 8 -octakisIJmonodentate).…”

μ-Squarato-κ2O1:O2-bis{[2-(2-aminoethyl)pyridine-κ2N,N′]aquanickel(II)} squarate 0.25-hydrate

“…and their structures have been reported [Uçar et al, 2006;Uçar et al 2007;]. In these compounds, squaric acid behaves as a monodentate ligand [Bulut et al, 2004] or acts as both a monodentate and bidentate ligand, or has a µ-1,3 coordination, while in this study, it has µ-1,2 bis(monodentate) coordination between the metal ions.…”

“…For general background, see: Bernardinelli et al (1989); Bulut et al (2004); Castro et al (1995Castro et al ( , 1997; Crispini et al (2000); Kirchmaier et al (2003); Lee et al (1996); Milet et al (2003); Solans et al (1990); Spek (2003); Trombe et al (2002); Uçar (2008); Uçar et al (2006Uçar et al ( , 2007; Yang et al (2003). (2) 172(3) N4-H4BÁ Á ÁO2 ii 0.88 (2) 2.52 (2) 3.078 2122.6 (18) N4-H4BÁ Á ÁO6 0.88 (2) 2.52 33.350 (2) 158(2) N4-H4AÁ Á ÁO4 iii 0.86 (2) 2.27 (2) 3.091 (2) 161 (2) N2-H2BÁ Á ÁO3 iv 0.83 (2) 2.14 (3) 2.963 (2) 169 (2) Symmetry codes: (i) x; Ày þ 2; z þ 1 2 ; (ii) x; y À 1; z; (iii) x; Ày þ 1; z þ 1 2 ; (iv) Àx þ 1 2 ; y À 1 2 ; Àz þ 1 2 .…”