Platinum nuclear properties

Much of the Pt Mossbauer work performed so far has been devoted to studies of platinum metal and alloys in regard to nuclear properties (magnetic moments and lifetimes) of the excited Mossbauer states of Pt, lattice dynamics, electron density, and internal magnetic field at the nuclei of Pt atoms placed in various magnetic hosts. The observed changes in the latter two quantities, li/ (o)P and within a series of platinum alloys are particularly informative about the conduction electron delocalization and polarization. 

Table I. Nuclear Properties of the Platinum Group Metals"...

The elements will be discussed in the order of increasing atomic number in the Periodic Table, i.e. nickel, zinc, technetium, ruthenium, silver, hafnium, tantalum, tungsten, rhem um, osmium, iridium, platinum, gold, and mercury. Full numerical data of the relevant nuclear properties are summarized, as for other elements, in Appendix 1. 

Plutonium-noble metal compounds have both technological and theoretical importance. Modeling of nuclear fuel interactions with refractory containers and extension of alloy bonding theories to include actinides require accurate thermodynamic properties of these materials. Plutonium was shown to react with noble metals such as platinum, rhodium, iridium, ruthenium, and osmium to form highly stable intermetallics. 

The particular NMR properties of Pt caused an additional problem. Due to the presence of surfaces near most of the nuclei, the NMR line is very broad (approximately 4 kG wide). This means that only a small fraction of the nuclear spins can be excited by an rf pulse and thus contribute to any given NMR signal. Given these various constraints, our NMR studies of platinum catalysts required 1-gram samples containing 5-10% Pt by weight. 

Tphe application of nuclear magnetic resonance to the study of the compounds of the platinum group metals has been limited by the properties of these nuclei. Data are collected in Table I for all of the isotopes of these elements which have nonzero spins. 

Plutonium-noble metal compounds have both technological and theoretical importance. Modeling of nuclear fuel interactions with refractory containers and extension of alloy bonding theories to include actinides require accurate thermodynamic properties of these materials. Plutonium was shown to react with noble metals such as platinum, rhodium, iridium, ruthenium, and osmium to form highly stable intermetallics. Vapor pressures of phases in these systems were measured by the Knudsen effusion technique. Use of mass spectrometer-target collection apparatus to perform thermodynamic studies is discussed. The prominent sublimation reactions for these phases below 2000 K was shown to involve formation of elemental plutonium vapor. Thermodynamic properties determined in this study were correlated with corresponding values obtained from theoretical predictions and from previous measurements on analogous intermetallics. 

When the platinum nucleophilicity scale was first proposed it was implied that one np, scale was applicable to all substrates and that plots of logk2 against npt°(Y) were linear, taking the form log 10 2 = S np, (Y) + C, where S is termed the nucleophilic discrimination factor of the substrate and C its intrinsic reactivity. Discussions of mechanism based on a comparison of nucleophilic discrimination factors are frequently encountered. Nucleophiles that do not retain their positions in the nucleophilicity scale, e.g. NO2", SeCN and SC(NH2)2, were termed biphilic by Cattahni since their behaviour could be explained by their n-acceptor properties. When the Pt reaction centre had a greater n-basicity than the standard complex (for example a smaller effective nuclear charge) the substrate was more reactive than predicted and vice versa. This concept had been deduced some years earlier by Bosnich from his work with octahedral Ru complexes... 

This approach was followed concurrendy with that of steroids as part of platinum coordination complexes for which the principal target was found to be DNA. Despite many structural modifications, the results were not spectacular [104-106]. Very often these Pt hybrids or their associated SERMs provided no synergy [107], as far as new, useftil properties were concerned. On the other hand, with covalent organometallic complexes, a number of pioneering results made it possible to study their recognition for specific nuclear receptors, and to develop novel affinity markers or suicide substrates. These preferentially targeted key proteins in specific biological functions to the detriment of DNA. 

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