Bonding Scheme, Hydride Character, and Magnetic Paths of (HPO₃)^2– Versus (SeO₃)^2– Building Units in Solids

Abstract

The abilities of the (HPO 3 ) 2− and (SeO 3 ) 2− anions as structure building units and as spin exchange paths between magnetic ions were investigated by preparing and analyzing the isostructural Fe 2 (SeO 3 ) 3 and Fe 2 (HPO 3 ) 3 . In both compounds, the face-sharing Fe 2 O 9 dimers are interconnected into chains by the (HPO 3 ) 2− and (SeO 3 ) 2− anions. The (HPO 3 ) 2− is the structural counterpart of the Se electron lone pair of (SeO 3 ) 2− due to the weak hydride character of the terminal hydrogen. However, they differ considerably as spin exchange paths between magnetic cations. Both compounds exhibit an effective magnetic dimer behavior, unexpectedly arising from the interdimer FeO•••OFe exchange along the chain, but weaker in Fe 2 (HPO 3 ) 3 by a factor of ∼3. It is consistent with the general tendencies of the phosphite anions to act as a weak magnetic mediator, which is caused by the through-bond effect of the P 3+ ion in the FeO•••P 3+ •••OFe exchange path, much weaker than in the selenite phase in absence of P 3+ d contribution. Reasons for stronger exchanges through phosphates or sulfates are also discussed.

Metamagnetic Transitions versus Magnetocrystalline Anisotropy in Two Cobalt Arsenates with 1D Co2+ Chains

“…This accounts only for about 50% and 18% of the expected Smag = 2Rln(4) for a spin 3/2 system for compound (1) and (2) respectively. The rest of the entropy is spread at higher temperatures, typical for low-dimensional antiferromagnets 25 but one should also note for (2) the poor accuracy on the sample weight dealing with crystals deposited one by one on the sample holder and that the crystals were not aligned when deposited.…”

The first lead cobalt phosphite, PbCo2(HPO3)3

“…The observed values are similar to those found in other related compounds containing the phosphite ion. 6,28 2.5 UV/vis spectroscopy The UV/vis absorbance spectrum was collected at room temperature with a PerkinElmer Lambda 650 spectrophotometer in the 250-800 nm range using an integration sphere designed for the characterization of solids. The spectrum is given in Fig.…”

“…14 In Fe 2 (HPO 3 ) 3 with face-sharing Fe dimers similar to those in the title compound, i.e., three μ 2 -η 1 bridging modes (which mean three M-O-M paths with one single oxygen bridging two metal atoms in each) that the intra-dimer exchanges are ten times weaker than the inter-dimer exchanges. 6 It mostly leads to extended Curie-Weiss (CW) thermal regimes down to low temperature in the absence of long-range magnetic ordering above 10 K. For instance, the behaviors reported for A I [M III (HPO 3 ) 2 ] (A = K, NH 4 , Rb; M = V, Fe) 28 show smooth deviation from the CW law, and Néel temperatures occur only for Fe 3+ (S = 5/2) phases below T N = 9 K at maximum.…”

“…Thus, it plays a role analogous to that of the lone electron pair E in specific oxoanions such as ESe 4+ O 3 , as demonstrated by the recent report on Fe 2 (SeO 3 ) 3 versus Fe 2 (HPO 3 ) 3 . 6 The co-presence of asymmetric anionic groups and stereochemically active lone electron pairs of cations (e.g. Sn 2+ , Pb 2+ , Sb 3+ , Bi 3+ ) in solids appears as a promising route to non-centrosymmetric polar crystal structures, [7][8][9][10] very attractive in terms of their possible applications in optics, asymmetric catalysis and enantioselective separation processes.…”

“…13 Moreover, the Co-containing materials based on HPO 3 anionic groups may exhibit particular magnetic 14,15 or photosensitive properties. 16,17 Particularly, due to the weak aptitude of phosphite as magnetic transmitters, 6,14 they can form ideal diamagnetic spacers. Despite the report of about twenty different hybrid organic/inorganic cobalt phosphite phases, the structural chemistry of inorganic cobalt phosphites remains poorly explored.…”