Schiff base ligand: the product of condensation of 3-nitro-salicylaldehyde and tris(hydroxymethyl)aminomethane. 

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Context 1

... last few decades polynuclear complexes have been in focus of intense interest due to their relevance to the active sites of metaloenzimes, and their potential applications as magnetic materials. Thus development of synthetic approaches that could lead to new polynuclear compounds or improve their yields is quite important. Our research group is interested in employment of so-called "direct synthesis" (DS), a serendipitous self-assembling approach based on utilization of metal powders as starting materials to construct coordination compounds both homo- and heterometallic ones. Recently we have shown its ability to produce Co/Fe complexes with Schiff base ligand (Chygorin et al. , 2012; Nesterov et al. , 2012). It should be noted that outcome of DS is not highly predictable and sometimes we can isolated homometallic or mononuclear complexes only. Such a case was observed in the investigated system: Cu 0 –FeCl 2. 4H 2 O–H 4 L–Et 3 N–dmf, where H 4 L is 2-hydroxymethyl-2{[(2-hydroxy-3-nitrophenyl)methylene]amino}propane-1,3-diol (Fig. 1). The Schiff base ligand, that is obtained by condencation of the salicylaldehyde derivative and tris(hydroxymethyl)aminomethane is typical hydroxy-rich ligand, which can coordinate to several metal centers and accepts various coordination modes, and thus it is an attractive ligand system for serendipitous self-assembling. Despite of this fact this Schiff base ligand has recived little attention to date [only 35 hits were found by searching via CSD ( bin/catreq.cgi?)]. Herein we report the synthesis of a new tetranuclear cubane complex starting from potentially polydentate hydroxyl-rich ligand. The reaction of copper powder with iron(II) chloride in dmf solution of the tetrapodal Schiff base ligand, formed in situ , in basic medium with free access of air leads to the isolation of the homometallic cuban complex [Cu 4 (C 11 H 12 O 6 N 2 ) 4 ]. The Schiff base ligand H 4 L was obtained by condensation of 3-nitro-salicylaldehyde and tris(hydroxymethyl)aminomethane (Fig. 1). The molar ratio of starting materials (Cu 0 : FeCl 2 : Schiff base ligand) was taken 1:1:2. The reaction was carried out in air with heating and stirring till total dissolution of metal powder was observed. Tetranuclear molecular complex (Fig. 2) consists of the discrete [Cu 4 (H 2 L) 4 ] moiety with a {Cu 4 O 4 } cubane-like core. Eight alternately arranged netal centers and oxygen atoms from methoxy groups form a distorted {Cu 4 O 4 } cube with local S 4 -symmetry. Each of four ligands coordinates in a tridentate mode as an (H 2 L) 2- dianion, with the phenoxyl and one of the alkoxyl groups deprotonated. The NO 2 donor set from one ligand molecule together with O-atom from methoxy arm of another ligand forms distorted square coordination polyhedra around each metal center (with RMS deviation of atoms from square plane of 0.135 Å). Coordination lengths vary in the range of 1.892 - 1.955 Å, and X —Cu—Y angles vary in the range of 84.8 - 94.9° that is comparable with the known literature data. The oxygen atom of the methoxy group of the third ligand molecule coordinates on this metal atom with Cu—O length of 2.524 Å, so that can be threated as additional coordination. In crystal, weak C4—H4B···O2′ hydrogen bonds (1.25 - y , x - 0.25, z - 0.25; H···O′ 2.51 Å, C—H···O′ 153°) form three-dimensional-connected network with channels along (111) crystallographic direction. Minimal ...

Context 2

... last few decades polynuclear complexes have been in focus of intense interest due to their relevance to the active sites of metaloenzimes, and their potential applications as magnetic materials. Thus development of synthetic approaches that could lead to new polynuclear compounds or improve their yields is quite important. Our research group is interested in employment of so-called "direct synthesis" (DS), a serendipitous self-assembling approach based on utilization of metal powders as starting materials to construct coordination compounds both homo- and heterometallic ones. Recently we have shown its ability to produce Co/Fe complexes with Schiff base ligand (Chygorin et al. , 2012; Nesterov et al. , 2012). It should be noted that outcome of DS is not highly predictable and sometimes we can isolated homometallic or mononuclear complexes only. Such a case was observed in the investigated system: Cu 0 –FeCl 2. 4H 2 O–H 4 L–Et 3 N–dmf, where H 4 L is 2-hydroxymethyl-2{[(2-hydroxy-3-nitrophenyl)methylene]amino}propane-1,3-diol (Fig. 1). The Schiff base ligand, that is obtained by condencation of the salicylaldehyde derivative and tris(hydroxymethyl)aminomethane is typical hydroxy-rich ligand, which can coordinate to several metal centers and accepts various coordination modes, and thus it is an attractive ligand system for serendipitous self-assembling. Despite of this fact this Schiff base ligand has recived little attention to date [only 35 hits were found by searching via CSD ( bin/catreq.cgi?)]. Herein we report the synthesis of a new tetranuclear cubane complex starting from potentially polydentate hydroxyl-rich ligand. The reaction of copper powder with iron(II) chloride in dmf solution of the tetrapodal Schiff base ligand, formed in situ , in basic medium with free access of air leads to the isolation of the homometallic cuban complex [Cu 4 (C 11 H 12 O 6 N 2 ) 4 ]. The Schiff base ligand H 4 L was obtained by condensation of 3-nitro-salicylaldehyde and tris(hydroxymethyl)aminomethane (Fig. 1). The molar ratio of starting materials (Cu 0 : FeCl 2 : Schiff base ligand) was taken 1:1:2. The reaction was carried out in air with heating and stirring till total dissolution of metal powder was observed. Tetranuclear molecular complex (Fig. 2) consists of the discrete [Cu 4 (H 2 L) 4 ] moiety with a {Cu 4 O 4 } cubane-like core. Eight alternately arranged netal centers and oxygen atoms from methoxy groups form a distorted {Cu 4 O 4 } cube with local S 4 -symmetry. Each of four ligands coordinates in a tridentate mode as an (H 2 L) 2- dianion, with the phenoxyl and one of the alkoxyl groups deprotonated. The NO 2 donor set from one ligand molecule together with O-atom from methoxy arm of another ligand forms distorted square coordination polyhedra around each metal center (with RMS deviation of atoms from square plane of 0.135 Å). Coordination lengths vary in the range of 1.892 - 1.955 Å, and X —Cu—Y angles vary in the range of 84.8 - 94.9° that is comparable with the known literature data. The oxygen atom of the methoxy group of the third ligand molecule coordinates on this metal atom with Cu—O length of 2.524 Å, so that can be threated as additional coordination. In crystal, weak C4—H4B···O2′ hydrogen bonds (1.25 - y , x - 0.25, z - 0.25; H···O′ 2.51 Å, C—H···O′ 153°) form three-dimensional-connected network with channels along (111) crystallographic direction. Minimal ...