Spin Density Maps for the Ferrimagnetic Chain Compound MnCu(pba)(H₂O)₃·2H₂O (pba = 1,2-Propylenebis(oxamato)):  Polarized Neutron Diffraction and Theoretical Studies

Abstract

This paper is devoted to the determination of the spin density in the ferrimagnetic ground state of the bimetallic chain compound MnCu(pba)(H2O)3·2H2O, with pba = 1,3-propylenebis(oxamato). The crystal structure, previously determined at room temperature through X-ray diffraction, was redetermined at 10 K through unpolarized neutron diffraction (orthorhombic system, space group Pnma, a = 12.727(11) Å, b = 21.352(19) Å, c = 5.153(3) Å, Z = 4). The experimental spin density has been deduced from polarized neutron diffraction data recorded at 10 K under 50 kOe. Positive spin densities were observed on the manganese side and negative spin densities on the copper side. The delocalization of the spin density from the metal centers toward the oxamato bridging ligand was found to be more pronounced on the copper side than on the manganese side, so that the nodal surface (of zero spin density) is closer to manganese than to copper. The experimental spin distribution has been compared to the theoretical distributions deduced from density functional theory (DFT) calculations, using both DGauss and DMol programs. The experimental results for the title chain compound have also been compared to the spin distribution for the binuclear compound [Mn(Me6-[14]ane-N4)Cu(oxpn)](CF3SO3)2 with Me6-[14]ane-N4 = (±)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, and oxpn = N,N‘-bis(3-aminopropyl)oxamido, recently reported. The most striking difference between pair and chain compounds concerns the positive P + and negative P - spin populations carried by the manganese and copper sides, respectively. For the pair compound P + was found as 4.67(8) μB, and P - as −0.67(8) μB while for the chain compound these values are 5.05(7) μB and −1.05(10) μB, respectively. The spin distribution for the ferrimagnetic chain compound is very close to a Neel state (P + = 5 μB and P - = −1 μB).

Pyridine‐2‐sulfonates as Versatile Ligands for the Synthesis of Novel Coordinative and Hydrogen‐Bonded Supramolecules

“…The peaks due to the pyridine ring are relatively strong versus those due to the methyl group. The sulfonate group RSO 3 Ϫ shows strong bands due to ν(SϪO) vibrations generally found in the region 1300Ϫ1055 cm…”

“…The hydrogen bonding in compound 8 containing the pySO 3 Ϫ ligand forms a two-dimensional network parallel The hydrogen-bonded network of compound 7 containing the 5-mpSO 3 Ϫ ligand is also similar to that of 8. (7) when viewed along the b axis, geometry as shown in Figure 10 stacking interaction in compound 6 (ca.…”

“…The geometry around the vanadium() center is distorted octahedral. The equatorial plane of the vanadyl is occupied by the O atom of the water molecule, N atom of 3-mpSO 3 Ϫ and two O atoms of acac. One oxygen atom of 3-mpSO 3 occupies a position trans to the VϭO group.…”

“…The bond angles and lengths show trends similar to those of compounds 3Ϫ10; the VϭO bond as expected, is the shortest bond [V(1)ϪO(6) ϭ 1.588(2) Å ]. The acac Ϫ ion forms bonds stronger than those formed by the oxygen atom of 3-mpSO 3 Ϫ or it may be the trans effect of VϭO bond which lengthens V(1)ϪO(1) bond vis-à-vis V(1)ϪO(4), O(5) bonds which are short.…”

“…It may be mentioned here that only the limited coordination chemistry of pyridine-2-sulfonates is known. [15,16] The aerobic oxidation of sulfur in 2,2Ј-bis(3-methylpyridine) disulfide in the presence of copper() bromide in methanol generated 3-methylpyridine-2-sulfonic acid, which subsequently formed an infinite one-dimensional polymer, [Cu(3-mpSO 3 ) 2 ] n . A direct reaction of 3-methylpyridine-2-sulfonic acid (3-mpSO 3 H) with Zn II bromide also formed a two-dimensional hydrogen-bonded polymer, .…”