Synthesis, X‐ray Powder Structure, and Magnetic Properties of Layered Ni^II Methylphosphonate, [Ni(CH₃PO₃)(H₂O)], and Ni^II Octadecylphosphonate, [Ni{CH₃‐(CH₂)₁₇‐PO₃}(H₂O)]

Abstract

[Ni(CH(3)PO(3))(H(2)O)] (1) and [Ni(CH(3)-(CH(2))(17)-PO(3))(H(2)O)] (2) were synthesised by reaction of NiCl(2).6 H(2)O and the relevant phosphonic acid in water in presence of urea. The compounds were characterised by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy, and their magnetic properties were studied by using a SQUID magnetometer. The crystal structure of 1 was determined "ab initio" from X-ray powder diffraction data and refined by the Rietveld method. The crystals of 1 are orthorhombic, space group Pmn2(1), with a=5.587(1), b=8.698(1), c=4.731(1) A. The compound has a hybrid, layered structure made up of alternating inorganic and organic layers along the b direction of the unit-cell. The inorganic layers consist of Ni(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one oxygen atom from the water molecule. These layers are separated by bilayers of methyl groups and van der Waals contacts are established between them. A preliminary structure characterisation of compound 2 suggests the crystallisation in the orthorhombic system with the following unit-cell parameters: a=5.478(7), b=42.31(4), c=4.725(3) A. The oxidation state of the Ni ion in both compounds is +2, and the electronic configuration is d(8) (S=1), as determined from static magnetic susceptibility measurements above 50 K. Compound 1 obeys the Curie-Weiss law at temperatures above 50 K; the Curie (C) and Weiss (theta) constants were found to be 1.15 cm(3) K mol(-1) and -32 K, respectively. The negative value of theta indicates an antiferromagnetic exchange coupling between near-neighbouring Ni(II) ions. No sign of 3D antiferromagnetic long-range order is observed down to T=5 K, the lowest measured temperature. Compound 2 is paramagnetic above T=50 K, and the values of C and theta were found to be 1.25 cm(3) K mol(-1) and -24 K, respectively. Below 50 K the magnetic behavior of 2 is different from that of 1. Zero-field cooled (zfc) and field-cooled (fc) magnetisation plots do not overlap below T=21 K. The irreversible magnetisation, DeltaM(fc-zfc), obtained as a difference from fc and zfc plots starts to increase at T=20 K, on lowering the temperature, and it becomes steady at T=5 K. The presence of spontaneous magnetisation below T=20 K indicates a transition to a weak-ferromagnetic state for compound 2.

Studies on Cage‐Type Tetranuclear Metal Clusters with Ferrocenylphosphonate Ligands

“…Most studies to date have been carried out on phenylphosphonic and alkylphosphonic acids. [23][24][25] Phosphonic acids with other organic functional groups such as azacrown ethers, [26][27][28] amines, [29][30][31] sulfonate/sulfonic acid [32,33] and carboxylate/carboxylic acid groups [34][35][36][37] have been found to be better ligands that can form many complexes with novel structures and properties. Motivated by the current work on functional coordinate materials bearing ferrocene (Fc) groups, we have synthesized a ferrocenylphosphonic acid, and subsequently used it for coordination with metal salts, thus yielding materials displaying both ferrocene and metal-phosphonate properties in conjunction with robust inorganic backbones.…”

Three-, Two-, and One-Dimensional Metal Phosphonates Based on [Hydroxy(4-pyridyl)methyl]phosphonate: M{(4-C5H4N)CH(OH)PO3}(H2O) (M = Ni, Cd) and Gd{(4-C5H4N)CH(OH)P(OH)O2}3·6H2O

“…Each {CPO 3 } tetrahedron is corner-shared with three {NiO 5 N} octahedra through three phosphonate oxygens and vice versa, thus forming an inorganic layer containing 12-membered rings of {−Ni−O−P−O−} 3 (Figure ). The layer is reminiscent of that in compound Cu 2 (H 2 O) 2 {O 3 PCH 2 N(C 2 H 4 ) 2 NCH 2 PO 3 }, although it is remarkably different from those observed in other monophosphonate compounds such as Ni(CH 3 PO 3 )(H 2 O) . The coordinated water molecules point toward the middle of the cavities.…”

Synthesis, Structures, and Magnetic Properties of End-to-End Azide-Bridged Manganese(III) Chains: Elucidation of Direct Magnetostructural Correlation

“…Thus, the apparent upturn in χ m T supports the onset of spin canting in the antiferromagnetic homospin system. This characteristic feature is associated with operative single-ion anisotropy of the Mn(III) ion. , Such spin-canted behavior has also been observed in diverse coordination polymers involving Mn(III), Co(II), and Ni(II) spin centers connected by different bridging groups. − …”