A compound of formula (I-A'): wherein R 1 to R 4 are each independently an optionally substituted aryl, R 5, R 6, R 8 and R 9 are each independently selected in the group consisting of H, halogen, optionally substituted C 1 -C 6 alkyl, optionally substituted C 2 -C 6 alkenyl, optionally substituted C 2 -C 6 alkynyl, optionally substituted carbocycle, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heterocycle, CN, NO 2, COR 19, OR 20 and NR 21 R 22, R 19 is selected in the group consisting of H, optionally substituted C 1 -C 6 alkyl, OR 27 and NR 28 R 29, R 20, R 21, R 22, R 27, R 28 and R 29 are each independently selected in the group consisting of H, optionally substituted C 1 -C 6 alkyl and optionally substituted CO-C 1 -C 6 alkyl, O -- Y -- O is a bidentate ligand, selected in the group consisting of: in which R 30, R 31 and R 32 each independently represent one or several substituent(s) independently selected in the group consisting of H, halogen, optionally substituted C 1 -C 6 alkyl, CN, NO 2, COR 33, OR 34 and NR 35 R 36, R 33 is H, halogen, optionally substituted C 1 -C 6 alkyl, OR 37 or NR 38 R 39, R 34 to R 39 are each independently selected in the group consisting of H, optionally substituted C 1 -C 6 alkyl and optionally substituted CO-C 1 -C 6 alkyl, X - is a pharmaceutically acceptable anion, preferably selected in the group consisting of PF 6 -, Cl -, Br -, BF 4 -, (C 1 -C 6 alkyl)-C O -, (C 1 -C 6 haloalkyl)-C O -, (C 1 -C 6 alkyl)-SO 3 - and (C 1 -C 6 haloalkyl)-SO 3 -, m is equal to 0 when O -- Y -- O is A and m is equal to +1 when O -- Y -- O is B or C, or a pharmaceutically acceptable salt and/or solvate thereof. R 1 to R 4 are each independently an optionally substituted aryl, R 5, R 6, R 8 and R 9 are each independently selected in the group consisting of H, halogen, optionally substituted C 1 -C 6 alkyl, optionally substituted C 2 -C 6 alkenyl, optionally substituted C 2 -C 6 alkynyl, optionally substituted carbocycle, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heterocycle, CN, NO 2, COR 19, OR 20 and NR 21 R 22, R 19 is selected in the group consisting of H, optionally substituted C 1 -C 6 alkyl, OR 27 and NR 28 R 29, R 20, R 21, R 22, R 27, R 28 and R 29 are each independently selected in the group consisting of H, optionally substituted C 1 -C 6 alkyl and optionally substituted CO-C 1 -C 6 alkyl, O -- Y -- O is a bidentate ligand, selected in the group consisting of: in which R 30, R 31 and R 32 each independently represent one or several substituent(s) independently selected in the group consisting of H, halogen, optionally substituted C 1 -C 6 alkyl, CN, NO 2, COR 33, OR 34 and NR 35 R 36, R 33 is H, halogen, optionally substituted C 1 -C 6 alkyl, OR 37 or NR 38 R 39, R 34 to R 39 are each independently selected in the group consisting of H, optionally substituted C 1 -C 6 alkyl and optionally substituted CO-C 1 -C 6 alkyl, X - is a pharmaceutically acceptable anion, preferably selected in the group consisting of PF 6 -, Cl -, Br -, BF 4 -, (C 1 -C 6 alkyl)-C O -, (C 1 -C 6 haloalkyl)-C O -, (C 1 -C 6 alkyl)-SO 3 - and (C 1 -C 6 haloalkyl)-SO 3 -, m is equal to 0 when O -- Y -- O is A and m is equal to +1 when O -- Y -- O is B or C, or a pharmaceutically acceptable salt and/or solvate thereof.