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On Bonding, Structure, and Stability of Ternary Hydrides A 2 MH 2 (A = Li, Na; M = Pd, Pt)
Author(s) -
Liao MengSheng,
Zhang QianEr,
Schwarz W. H. Eugen
Publication year - 1998
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/(sici)1521-3749(199809)624:9<1419::aid-zaac1419>3.0.co;2-i
Subject(s) - disproportionation , crystallography , bond length , chemistry , bond dissociation energy , alkali metal , ternary operation , crystal structure , bond energy , dissociation (chemistry) , ion , lattice energy , bond order , density functional theory , metal , molecule , computational chemistry , catalysis , biochemistry , organic chemistry , computer science , programming language
Bonding, structure, and stability of solid A 2 MH 2 with A = Li, Na; M = Pd, Pt were investigated with a relativistically corrected density‐functional approach, which reliably describes the trends among these four compounds. In order to examine the influence of the ligands (A) and of the crystalline environment, calculations were also made for free A 2 MH 2 molecules and MH 2 2– ions. The free MH 2 2– complex is held together by strong bonds between formally closed shell atomic units because of strong M‐d,s hybridization. The M–H bonds are further stabilized by the alkali metal ion ligands and by the crystal surrounding. The crystal field expands the H–A distance and enhances the H–A polarity. Relativistic effects contribute to M–H bonding in the solid state. The experimentally determined bond lengths and their trends are in accordance with theory. Due to relativistic and lanthanide effects, the Pt–H bond length becomes nearly as short as the Pd–H one. The small Li ion causes a distortion of the Li 2 PtH 2 crystal resulting in an even shorter Pt–H bond length. In the gas‐phase, A 2 PtH 2 is more stable against dissociation than A 2 PdH 2 . The stability of the solid compounds is strongly influenced by the cohesive energy of the metal M, and also by the nature of the alkali metal. The evaluated enthalpies of formation favor increasing stability of solid A 2 MH 2 against disproportionation into M and AH from Pt to Pd and from Li to Na. This is in agreement with experimental findings. The assignment of the experimental vibrational excitations should be reconsidered.