The invention comprises metal complexes <FORM:0956242/C2/1> (B) where M represents ruthenium or osmium in the valency states II or III or Bis a bidentate ligand provided by 1,10-phenanthroline, substituted 1,10-phenanthroline and 2,21-bipyridine; X ligand groups (at least one being different from B) occupying the four remaining co-ordination positions associated with the metal the ligand groups being uni-, bi-, tri- or quadri-dentate or mixtures of unibi-and tridentate ligands, in the case where B is 1,10-phenanthroline and two of the remaining co-ordination positions of X are filled with 1,10-phenanthroline, the further two remaining co-ordinating positions are filled with substituted 1,10-phenanthroline or substituted 2,21-bi-pyridine or bidentate ligands which reduce the positive electrical charge m on the complex; m is the electrical charge on the complex, m being +2, +1, 0, -1 or -2, Y a cation for negative values of m and an anion for positive values of m; p is a number determined by the value of m and the valency of Y; Fe (III) is ferric iron; B1 a bidentate ligand provided by a substituted 1,10-phenanthroline or substituted 2,21-bipyridine; Z is an anion of an inorganic or organic acid and q is a number determined by the valency of Z; the substituted 1,10-phenanthrolines B and B1 being substituted by one to six alkyl, phenyl, tolyl, or xylyl groups in the 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-positions and the substituted 2,21-bipyridine by one to four alkyl, phenyl, tolyl or xylyl groups in the 4-, 5-, 6-, 41-, 51 or 61-positions, there being alkyl groups in one to six of the specified positions of the substituted 1,10-phenanthroline and phenyl, tolyl and xylyl groups in one or two of the positions, such alkyl substituents totalling one to fourteen carbon atoms and where di-substitution involves the 3-, 4- and 7-, 8-positions either pairs of carbon atoms may form part of 5-membered or 6-membered cycloalkane ring system and such phenyl, tolyl and xylyl mono- and di-substitutents totalling from six to sixteen carbon atoms and there being alkyl groups in one to four of the specified positions of the 2,21-bipyridine and mono- and di-substitution in the 5- and 51 positions with phenyl, tolyl and xylyl groups, the alkyl groups totalling from one to ten carbon atoms and phenyl, tolyl and xylyl groups from six to sixteen carbon atoms, avoiding steric hindrance in the case where the 1,10-phenanthroline is substituted in the 2- and 9-positions and the 2,21-bipyridine in the 6-and 61-positions; the preparation of compounds (A) by reacting together in a liquid medium under conditions in which reduction may occur to produce A, a complex (MBL4) (C) where L is a halogen atom or mixtures of halogen atoms and unidentate ligands, halogen atoms and a bidentate ligand, a halogen atoms and a tridentate ligand with an amount of substituting ligand or ligands to introduce the desired ligand group X by replacement of groups L or by heating, under conditions that will produce the desired complex, a complex BH+ (MBL14) (D) where L1 is a halogen atom to introduce the ligand B into the complex (1) by replacement of two of the groups L1 and the preparation of compounds (B) by reacting together in an acid medium a ferric salt with a base B1. Unidentate biligands X may be any organic or inorganic group capable of coordinating to the metal M such as organic compounds containing nitrogen or sulphur, including heterocyclics, thioethers, mercaptans thioureas and nitriles; inorganic and organic ions including hydroxyl, halide, thiocyanate, and acetate; neutral inorganic groups which donate electrons to form co-ordinate bonds including water and ammonia. Bidentate ligands are aliphatic compounds, substituted and unsubstituted aromatic and heterocyclic compounds and may be neutral groups, including diamines, dithiols, mercapto alkanols, substituted or unsubstituted 2,21-bipyridine or 1,10-phenanthroline; groups capable of losing one or more protons, causing reduction in the charge on the complex ion, including, diketones, glycine and b -hydroxy-quinoline and its derivatives; ions such as oxalate and tartrate. Tridentate ligands may be neutral groups including triamines, and 2,21,211-terpyridine; or charge reducing groups including a ,b -diaminopropionic acid. Quadridentate are organic groups and may be neutral groups including tetra-amines and charge reducing groups including 1,8-diamino-3, 6-dithiooctane, and ethylenediamine bis(acetylacetone). 5-Methyl-1, 10-phenanthroline and K2 (OS (IV)Cl6) react to give K(C13H11N2)(OS (IV)Cl6) which on pyrolysis forms the starting material (OS (IV) (C13H10N2)Cl4), tetrachloro (5-methyl -1,10-phenanthroline) osmium (IV). 1,10-Phenanthroline and K(Ru(III)Cl5H2O) may be reacted together to give the salt Phen H+ (Ru(III)PhenCl4) ('Phen' represents 1,10-phenanthroline) which on oxidation with chlorine gives (Ru(IV)PhCl4) and this on reduction and treatment with ammonium chloride gives NH4 (Ru (III) Phen Cl4). Therapeutic compositions comprise a metal complex of the invention and a carrier.  The compositions are presented in forms suitable for the treatment of bacterial infections in humans, e.g. saline solutions, creams, lotions eye or nose drops, pessaries, suppositories, tablets and lozenges; for veterinary treatments, e.g. in a carrier such as paraffin and wax base or in anthelmintic preparations as a drench, preferably as an aqueous solution or suspension; or as plant fungicides or virocides as aqueous solutions or dispersible powders.