Abstract: Compounds of formula (I) are usefully employed in pharmaceutical compositions either in a mixture or in association with a pharmaceutically acceptable carrier or diluent; ##STR1## wherein M is a diamagnetic metal atom or a diamagnetic metal compound of silicon or a compound of silicon or is 2H; one H being bonded to each of the two nitrogen atoms depicted as being bonded to M (positions 29 and 31 shown); R.sub.1 to R.sub.25 are the same or different and are independently selected from C.sub.1 -C.sub.20 alkyl, C.sub.2 -C.sub.20 alkenyl, X--O--Y, (a), X.sup.2 COOX.sup.1, X.sup.2 CONR.sup.1 R.sup.11 and H; wherein X and X.sup.2 are independently selected from a chemical bond, --(CH.sub.2).sub.n -- where n is an integer from 1 to 20 and --(CH.sub.2).sub.a CH.dbd.CH(CH.sub.2).sub.b where a and b are independently selected from integers 0-20 and a+b totals from 0 to 20; X.sup.1 is independently selected from C.sub.1-20 alkyl, C.sub.2-20 alkenyl and H, R.sup.1 and R.sup.11 are independently selected from H, C.sub.

Abstract: A method of applying a stable intermetallic diffusion barrier layer to a metallic article is described. In many instances, protective coatings are incompatible with the material of the substrate to which they are applied. Such incompatibility is overcome in the invention through in situ formation of an intermediate stable diffusion barrier layer by sequential deposition and subsequent reaction of suitable metals to form a continuous intermetallic layer. A conventional overlay coating may then be applied to the intermetallic layer without risk to the underlying substrate. The invention also contemplates creation of unitary diffusion barriers from multi-layer deposits; deposition of plural diffusion barriers, and formation of complete protective systems comprising substrate, diffusion barrier(s) and overlay coating prior to heat treatment in situ.