On Bonding, Structure, and Stability of Ternary Hydrides A2MH2 (A = Li, Na; M = Pd, Pt)

Stabilization of Electron-Dense Palladium−Hydrido Complexes in Solid-State Hydrides

“…Our new assignment on Na 2 PdH 2 is also consistent with the one recently proposed by Liao et al Here, however, we should note that their calculations on a A 2 PdH 2 unit in a crystal field are not supported by our experimental results. They expect very similar symmetric stretching frequencies under exchange of Na for Li.…”

“…Increasing counterion interaction with the molecular entities is underlined by the increasing band broadening in the vibrational spectra in the order K 2 PdH 4 → Na 2 PdH 2 → Li 2 PdH 2 → NaBaPdH 3 → Ba 2 PdH 4 . A strong counterion influence was also suggested by Liao et al in their recent theoretical investigation of the molecular units Li 2 PdH 2 and Na 2 PdH 2 . When the effect of the crystal field was included, they observed an increase of the Pd−H distance of ca.…”

“…Synthesis and Structure Determinations. K 2 PdH 4 , Li 2 PdH 2 , Na 2 PdH 2 , NaBaPdH 3 and Ba 2 PdH 4 were all synthesized by direct reaction between hydrogen and the nominal compositions of the alkaline and/or alkaline earth metal hydrides and palladium under conditions described previously. − , All samples are air and moisture sensitive and were therefore handled and stored under argon atmosphere. The structures have already been determined using single-crystal X-ray diffraction or powder X-ray diffraction of the hydrides combined with neutron powder diffraction on the corresponding deuterides to locate the hydrogen atoms. − , Phase analysis on all samples in this investigation was performed by powder X-ray diffraction using a focusing Guiner-Hägg camera and the samples were found to be single phased.…”

“…Two 14-electron and possibly a 17-electron complex have also been proposed. , Some of the hydrides have in addition to the TM−hydrido complexes, hydrogen bound in interstitial sites coordinated by the s-elements forming structural building blocks similar to the structures of the binary alkali and alkaline earth hydrides. The puzzling variety of compositions, transition metal coordinations, and geometries have generated a number of theoretical studies. − Very recently two rather contradictory concepts were presented in this journal trying to rationalize mainly the coordination geometries and electron counts in the new hydrido complexes. Firman and Landis propose a Valence Bond (VB) model with sd n hybridized transition metal orbitals leading to hypervalently bonded hydrido complexes for systems with more than 12 valence electrons .…”

Theoretical Studies in Palladium and Platinum Molecular Chemistry

“…It is shown that the crystal field strongly shifts the MH 6 2- → MH 4 2- + H 2 and MCl 6 2- → MCl 4 2- + Cl 2 disproportionation equilibria to the right except for PdCl 6 2- and PtCl 6 2- , thus in agreement with the known stability of these systems in the crystal. A similar study has also been performed on the ternary hydrides A 2 MH 2 (A = Li, Na; M = Pd, Pt) . Finally, we briefly quotesince it is at the borderline of the scope of this reviewa careful analysis of the change of the CO stretching frequency in the Pt−CO complex due to the interaction of Pt with zeolite protons …”