title: Magnetic property studies of manganese-phosphate complexes.
abstract: Phosphoric acid forms two distinct coordination compounds with manganese salts in aqueous media, a two-dimensional layered structure, [Mn(HPO4).(H2O)3], 1, under ambient conditions, and a three-dimensional synthetic mineral, [Mn5(mu-OH2)2(HPO4)2(PO4)2(H2O)2], 2, under hydrothermal procedures, at 120 degrees C. In compound 1, the oxygen atom of the doubly deprotonated phosphoric acid interconnects the metal centers to form a layered structure. The neutral hydrophilic layers of 1 are separated by 5.5 A and may potentially intercalate hydrophilic organic guest molecules. The metal centers in 2 are octahedral and bridged by PO4(3-), HPO4(2-), and OH2 groups to form a complex three-dimensional network. XPS analysis on 1 and 2 confirms that manganese exists in the +2 oxidation state. Compound 2 is a poor ion exchanger, but some improvement is observed on partial dehydration. The magnetic properties of both 1 and 2 were studied in detail to examine the amplitude of the magnetic interactions through phosphate ligand bridges. While 1 reveals dominant antiferromagnetic interactions between the spin carriers, a complete investigation of the magnetic properties of 2 revealed its true nature to be a glassy magnet.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, Texas 77842-3012, USA.
authors.forename: C V
authors.initials: CV
authors.lastname: Krishnamohan Sharma
authors.forename: Charles C
authors.initials: CC
authors.lastname: Chusuei
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Clérac
authors.forename: Teresia
authors.initials: T
authors.lastname: Möller
authors.forename: Kim R
authors.initials: KR
authors.lastname: Dunbar
authors.forename: Abraham
authors.initials: A
authors.lastname: Clearfield