The synthesis, X-ray structure and variable-temperature magnetic study of new compounds of formula PPh4[Cr(dmbipy)(ox)2] ·5H2O (1), AsPh4[Cr(dmbipy)(ox)2] ·5H2O (2), Ba(H2O)2[Cr(dmbipy)(ox)2]2n·17/2nH2O (3) and Ag(H2O)[Cr(dmbipy)(ox)2]n·3nH2O (4) (PPh4+= tetraphenylphosphonium cation; AsPh4+= tetraphenylarsonium cation; dmbipy = 4,4′-dimethyl-2,2′-bipyridine; ox2-= oxalate dianion) are reported herein. The isomorphous compounds 1 and 2 are made up of discrete [Cr(dmbipy)(ox)2]-anions, XPh4+cations [X = P (1) and As (2)] and uncoordinated water molecules. The chromium environment in 1 and 2 is distorted octahedral with Cr-O and Cr-N bond distances varying in the ranges 1.950(2)-1.9782(12) and 2.047(3)-2.0567(14), respectively. The angles subtended at the chromium atom by the two bidentate oxalate ligands cover the range 82.58(10)-83.11(5)°, and they are somewhat greater than those concerning the chelating dmbipy [79.04(10) (1) and 79.24(5)° (2)]. The [Cr(dmbipy)(ox)2]-unit of 1 and 2 also occurs in 3 and 4 but it adopts different coordination modes. It acts as a chelating ligand through its two oxalate groups towards the divalent barium cations in 3 affording neutral chains with diamond-shaped units sharing the barium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The barium atom in 3 is coordinated by eight oxygen atoms from four oxalate groups and two aqua ligands. The structure of 4 consists of neutral bimetallic layers where the [Cr(dmbipy)(ox)2]-unit acts as a ligand towards the univalent silver(I) cation through its two oxalate groups, one of them being bidentate and the other bidentate/monodentate (outer). Each silver atom is six-coordinated with a water molecule and five oxygen atoms from three oxalate groups building a highly distorted octahedral environment. Magnetic susceptibility measurements for 1-4 in the temperature range 1.9-300 K show the occurrence of weak ferro- (1 and 2) and antiferromagnetic (3 and 4) interactions which are mediated by π-π stacking between dmbipy ligands through the spin polarization mechanism. A comparative study of the potentiality of the [Cr(AA)(ox)2]-unit (AA = bidentate nitrogen donor) as a building block for designing heterometallic species is carried out in the light of the available structural information. © The Royal Society of Chemistry.
[Cr(dmbipy)(ox)2]-: a new bis-oxalato building block for metal assembling.Crystal structures and magnetic properties of XPh4[Cr(dmbipy)(ox)2].5H2O(X = P and As), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n.17/2nH2O and {Ag(H2O)[Cr(dmbipy)(ox)2]}n.3nH2O
Marino, Nadia;
2009-01-01
Abstract
The synthesis, X-ray structure and variable-temperature magnetic study of new compounds of formula PPh4[Cr(dmbipy)(ox)2] ·5H2O (1), AsPh4[Cr(dmbipy)(ox)2] ·5H2O (2), Ba(H2O)2[Cr(dmbipy)(ox)2]2n·17/2nH2O (3) and Ag(H2O)[Cr(dmbipy)(ox)2]n·3nH2O (4) (PPh4+= tetraphenylphosphonium cation; AsPh4+= tetraphenylarsonium cation; dmbipy = 4,4′-dimethyl-2,2′-bipyridine; ox2-= oxalate dianion) are reported herein. The isomorphous compounds 1 and 2 are made up of discrete [Cr(dmbipy)(ox)2]-anions, XPh4+cations [X = P (1) and As (2)] and uncoordinated water molecules. The chromium environment in 1 and 2 is distorted octahedral with Cr-O and Cr-N bond distances varying in the ranges 1.950(2)-1.9782(12) and 2.047(3)-2.0567(14), respectively. The angles subtended at the chromium atom by the two bidentate oxalate ligands cover the range 82.58(10)-83.11(5)°, and they are somewhat greater than those concerning the chelating dmbipy [79.04(10) (1) and 79.24(5)° (2)]. The [Cr(dmbipy)(ox)2]-unit of 1 and 2 also occurs in 3 and 4 but it adopts different coordination modes. It acts as a chelating ligand through its two oxalate groups towards the divalent barium cations in 3 affording neutral chains with diamond-shaped units sharing the barium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The barium atom in 3 is coordinated by eight oxygen atoms from four oxalate groups and two aqua ligands. The structure of 4 consists of neutral bimetallic layers where the [Cr(dmbipy)(ox)2]-unit acts as a ligand towards the univalent silver(I) cation through its two oxalate groups, one of them being bidentate and the other bidentate/monodentate (outer). Each silver atom is six-coordinated with a water molecule and five oxygen atoms from three oxalate groups building a highly distorted octahedral environment. Magnetic susceptibility measurements for 1-4 in the temperature range 1.9-300 K show the occurrence of weak ferro- (1 and 2) and antiferromagnetic (3 and 4) interactions which are mediated by π-π stacking between dmbipy ligands through the spin polarization mechanism. A comparative study of the potentiality of the [Cr(AA)(ox)2]-unit (AA = bidentate nitrogen donor) as a building block for designing heterometallic species is carried out in the light of the available structural information. © The Royal Society of Chemistry.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
