Thermochemistry of some platinum and palladium compounds

Abstract

Enthalpies of reaction, at 298 K in the liquid phase have been measured using isoperibol reaction calorimetry, and some enthalpies of isomerisation have been measured using differential scanning calorimetry.
The enthalpy of formation of crystalline ammonium tetrachloro- palladite has been obtained from measurement of its enthalpy of decomposition by ethylene in water.
The value AH° [(NH^PdCl^ (c) = -(841.0 ± 1.7) kJ mol“1 has been used as a datum in determining the enthalpies of formation, AH°[(SEt2)2PdCl2](c) = -(563.1 ± 2.1) kJ mol"1
AH°[(SeEt2)2PdCl2l(c) = -(528.9 ± 3.8) kJ mol“1 AH°((TeEt2)2PdCl2](c) - -(587.6 ± 20.5) kJ mol"1 from which relative mean bond dissociation energies have been established as follows:
<D(Pd-Se) > - < D(Pd-S) > - (9 ± 9) kJ mol”1 <D(Pd-Te) x - < D(Pd-Se) > = (28 ± 13) kJ mol"1
The enthalpies of reaction of the complex bis(triphenylphosphine)- (ethylene)platinum(o) with tetracyanoethylene and with diphenyl- acetylene have also been studied:
(PPh3)2Pt(C2H4)(c) + (CN)2C=C(CN)2(c) -? (PPh3)2Pt{(CN)2C«C(CN)2}(c) +
C2H4(g)
(PPh,)2Pt(C2H4)(c) + PhCECPh(c) -? (PPh3)2Pt(PhCECPh)(c) + CjH^g) the values obtained lend support to a bonding model in complexes of this type.
The enthalpy of reaction of bis(triphenylphosphine)(diphenyl- acetylene)platinum(O) with hydrogen chloride has been measured: (PPh3)2Pt(PhC=CPh) (c) + HCl(g) -*¦ (PPh3)2Pt(Cl)(PhC=CHPh)(c) (PPh3)2Pt(Cl)(PhC=CHPh)(c) + HC1 (g) -*• (PPh3) 2PtCl2 (c) + trans-
PhHC=CHPh(c)
The results have been used to estimate the values, D(Pt-diphenylacetylene) = 398 ± 23 kJ mol ^
D(Pt-vinylstyrene) = 215 ± 23 kJ mol *
The two complexes, bis(triphenylphosphine)(tetrachloroethylene)- platinum(O) and bis(triphenylphosphine)(vinylstyrene)platinum(O), have been subjected to differential scanning calorimetry, and enthalpies of isomerisation reactions have been measured.