[L_nIrX_aY_a]^x  Formula (1)

X and Y are, identically or differently on each occurrence, a monodentate, monoanionic ligand which is bonded to the iridium via a heteroatom;

n is on each occurrence 2 or 3;

a is 0 if n is 3 and is 1 if n is 2;

x is −1 when n is 2 and a is 1 and x is 0 when n is 3 and a is 0;

L is on each occurrence, identically or differently, a ligand of formula (2) which coordinates to Ir via both oxygen atoms

wherein

R¹ and R² are, identically or differently on each occurrence, H, CN, a straight-chain, branched or cyclic alkyl group having up to 20 C atoms, or a straight-chain, branched or cyclic alkoxy group having up to 20 C atoms, wherein one or more non-adjacent CH₂ groups of said alkyl or alkoxy groups are optionally replaced by —O—, —S—, —NR³—, —CONR³—, —CO—O—, —CR³═CR³— or —C≡C— and wherein one or more H atoms may be replaced by F, or an aromatic or heteroaromatic ring system having 4 to 14 C atoms, wherein said aromatic or heteroaromatic ring systems may be substituted by one or more non-aromatic radicals R¹; and wherein a plurality of substituents R¹ and/or R² together optionally define a monocyclic or polycyclic aliphatic ring system or a monocyclic or polycyclic aromatic ring system; and

R³ is, identically or differently on each occurrence, H or an aliphatic or aromatic hydrocarbon radical having up to 20 C atoms,

comprising the steps of

(1) reacting an iridium(III) salt starting compound with compounds containing anions of the formula (2) in a first solvent or solvent mixture,

(2) partially or fully exchanging the first solvent or solvent mixture with a second solvent or solvent mixture, which is different from the first solvent or solvent mixture, while substantially retaining the amount of the salt-like components of the reaction mixture, and

(3) completing the reaction in said second solvent or solvent mixture.