Abstract: Tridentate mono-anionic ligands have the structureX-A-Y-Q-Zwhere each of X and Y is independently P, As or N,Z is phenol, thiophenol or thiol, andA and Q are hydrocarbon linking groups.The ligands from cationic complexes with Technetium-99m, e.g. [Tc.sup.III K.sub.2 ].sup.+ where K is the ligand, having useful imaging properties.

Abstract: The invention concerns cationic complexes of Technetium-99m with bidentate ligands (L), including complexes having the formulae [Tc(NO) X L.sub.2 ].sup.+ and [Tc L.sub.3 ].sup.+, which are of interest as heart imaging agents. The ligands are characterized by having the formula Y.sub.2 QZQY.sub.2, where each Q is phosphorus or arsenic, Z is a 2 or 3 carbon atom linking group, and at least one of the groups Y and Z includes at least one --COC--ether group.

Abstract: A composition for use in the preparation of a bone-scanning agent comprises a mixture of a bis-phosphonic acid of formula (I), wherein R.sup.1 and R.sup.3 may be the same or different group selected from H, --SO.sub.3 H and a lower aliphatic group which may optionally contain one or more hetero atoms and which contains at least one --SO.sub.3 H group; R.sup.2 is a group selected from H, --OH, --NH.sub.2, --NHMe, --NMe.sub.2 and lower alkyl optionally substituted by one or more polar groups; R.sup.4 is a group selected from H, --OH, --NH.sub.2 --NHMe, --NMe.sub.2, --SO.sub.3 H and a lower alkyl optionally substituted by one or more polar groups; and n is 0 or 1; with the proviso that when n is 0, R.sup.1 is not H and that when n is 1, R.sup.1 and R.sup.3 cannot both be H; or a non-toxic salt thereof, together with a reducing agent for pertechnetate ions. Technetium-99m, as an aqueous solution of pertechnetate ions, is added to the composition to form a complex of Tc-99m, and the bisphosphonate.