  The dynamics of spin-lattice relaxation (slr) of metal-organic Pt(II)
compounds is studied. Often, such systems are characterized by pronounced
zero-field splittings (zfs) of the lowest-lying triplets. Previous expressions
for the Orbach slr process do not allow to treat such splitting patterns
properly. We discuss the behavior of a modified Orbach expression for a model
system and present results of a fit of the temperature dependence of the
spin-lattice relaxation rate of Pt(2-thpy)$_2$ based on the modified
expression.
