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1 Introduction In order to try to get multi-layer systems [1,2], the inclusion of superconducting chains has been tested in the metallic diselenides {MSe 2 with M = (Nb, Ta, V)}. However the outcome derivatives are the result of the dissolution of small amount of intermetallic A15 compounds {A 3 B with A = (Nb, V) and B = (Al, Ga, Ge, Sb, Sn)} in the host matrix 2H-NbSe 2 , 2H-TaSe 2 and 1T-VSe 2 . In the case of the two superconductors 2H-NbSe 2 and 2H-TaSe 2 , electronic instabilities lead only to an incommensurate charge density waves distortion (ICDW) whereas in 1T-VSe 2 they lead to an ICDW followed by commensurate charge density waves (CCDW). Moreover 1T-VSe 2 is always non-stoichiometric and its formula is V 1+x Se 2 with x ≈ 0.005.After a very precise study of the Nb 3 Sn/NbSe 2 system [3,4], the chemical process of the synthesis can be understood in order to study new systems. In all cases the chemical formula of the new obtained phases can be written as following B(M/A) 5 Se 9 were B can be Al, Ga, Ge, Sb, Sn, A is Nb or V, and M stands for Nb, Ta, V. In addition, and to further explore the incidence of the MSe 2 network as that of the metal B of the starting A 3 B (A15), the Nb 3 Sn/VSe 2 , V 3 Ga/NbSe 2, V 3 Ga/TaSe 2 systems are studied, and completed through the B (or B' ≠ B) metals used in front of the A15 phases. Some of the new phases are superconductors, the others being ferromagnets.The

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International audienceSyntheses performed in the A3B/MSe2 systems lead to the formation of (B/B')(M/A)5Se9 phases (ferromagnets or superconductors) {A=M= (Nb, V, Ta); B=B'= (Al, Ge, Ga, Sn, Sb)}. The magnetic studies on GaV5Se9,, GaV0.15Ta4.85Se9 and Sn0.94Ga0.05V0.30Nb4.70Se9, compared to that of SnNb5Se9, GaNb5Se9 show that the presence of V modifies the superconducting exchanges and allows ferromagnetic couplings. Through Point-Contact Spectroscopy on SnNb5Se9, it is shown that nanoclusters of the pristine NbSe2 and Nb3Sn exist, so the properties result from a synergy between them and the matrix, and it could be a mesoscopic superconductor. The superconductors' s Tc values vary from 17.5(2) K for SnNb5Se9 to 6.0(2) K for SbNb5Se9, and the ferromagnetic state transition from 22K for GaV5Se9, to 35 K for Sn0.94Ga0.05V0.30Nb4.70Se9. The 119Sn and 121Sb Mössbauer studies of Sn0.94Ga0.05V0.30Nb4.70Se9 and SbNb5Se9 are compared to that obtained for SnNb5Se9 itself; for this last one, 3 types of sites corresponding to 2 species of Sn were observed with a reversible dynamic process between the 2 SnII Sn-Se sites correlated to a modification of the Sn-Nb site(1). SbNb5Se9, at 5 K, shows just a singlet, attributed to Sb surrounded by Se ; from 298 K to 5 K, Sn0.94Ga0.05V0.30Nb4.70Se9, presents one asymmetrical Sn-Se site without any transferred field on Sn and an increased asymmetry when T decreases. Sn0.94Ga0.05V0.30Nb4.70Se9 is a weak and complicated ferromagnet. In both cases, GaV5Se9, and Sn0.94Ga0.05V0.30Nb4.70Se9, the ESR spectrum observed at 300 K can be fitted with 2 lorentzian distributions: for the first case, with axial symmetries, for the second only one remains with an axial symmetry, belonging to the V sites. its vanadium sites are thus less symmetrical than in the first case