MS-86-1 Microsymposium Acta Cryst. (2021), A77, C547 Designing Composite Spin Chain Structures Built up of Dimeric and Trimeric Polyhedral Units: The oxides A1+y[(Mn1-xCox)1-z◊z]O3 (A = Ca, Sr; x = 3/8) O. Pérez 1 , V. Caignaert 1 , B. Raveau 1 , V. Hardy 1 , N. Sakly 1 , Md. Motin Seikh 2 1 Laboratoire CRISMAT, UMR 6508 CNRS-ENSICAEN, University of Caen, Bd du Maréchal Juin, 14050 Caen Cedex, France 2 Department of Chemistry, Visva-Bharati University, Santiniketan 731235, West Bengal, India olivier.perez@ensicaen.fr Spin chain oxides containing cobalt and manganese whose structure is closely related to the 2H hexagonal perovskite [1-5] offer a very attractive field for the investigation of magnetic and multiferroic properties. The structure of the prototypic one-dimensional manganate and cobaltate Sr4Mn2CoO9 consists of chains of face-sharing MnO6 octahedra and trigonal CoO6 prisms. According to the very important study performed by Perez-Mato et al [2], these spin chain oxides can be described as a composite 2H hexagonal perovskite family A1+x(Mn1-Cox)O3. Recently the possibility of extra oxygen incorporation during synthesis has been evidenced leading to a large family aperiodic chain structures [6] expressed by the simple formal formula Sr1+x(Mn1-xCox)O3+δ; it induces a decrease of the proportion of the number of trigonal prismatic sites (NP) with respect to the octahedral sites (NO) within the chains as δ increases and concomitantly the formation of cobalt vacancies on the trigonal prismatic sites. Therefore the structural formula of these oxides must be expressed as Sr1+y[(Mn1-xCox)1-z◊z]O3.] The air-synthesized oxide x = 3/8-Sr1+x(Mn1-xCox)O3+δ is of great interest, since by decreasing the oxygen over stoichiometry to δ=0, one should obtain the oxide “Sr11Mn5Co3O24”(x = y, z = 0) expected to be built up of trimeric and dimeric polyhedral units according to the sequence [Sr4Mn2CoO9]2.[Sr3CoMnO6]. Such an oxide containing exclusively strontium was never synthesized in air due to the partial oxidation of Co 2+ into Co 3+ , imposing δ>0. We then have investigated the substitution of calcium for strontium in the pure Sr- phase x = 3/8 (δ~0.09). The objective was to design composite structures built up of trimeric and dimeric units by decreasing δ down to zero through Ca for Sr substitution in order to finally obtain the stoichiometric oxide A11Mn5Co3O24 (A = Sr,Ca). We report herein on a series of A11/8(Mn5/8Co3/8)O3+δ oxides with composite structures, commensurate or incommensurate, built up of trimeric M3O9 and dimeric M2O6 units (M = Mn, Co, O) with cationic vacancies on the trigonal prismatic sites. We also show the possibility to synthesize the quasi commensurate stoichiometric composite Sr4.2Ca6.8[Mn2CoO9]2.[MnCoO6] (δ = 0.002). [1] J. Darriet, M.A. Subramanian, J. Mater. Chem. 5 (1995) 543-552. [2] J.M. Perez-Mato, M. Zakhour-Nakhl, F. Weill, J. Darriet, J. Mater. Chem. 9 (1999) 2795-2807. [3] K. Boulahya, M. Parras, J.M. Gonzalez-Calbet, J. Solid State Chem. 145 (1999) 116-127. [4] K.E. Stitzer, J. Darriet, H.-C. zur Loye, Curr. Opin. Solid State Mater. Sci. 5 (2001) 535-544. [5] H.-C. zur Loye, Q. Zhao, D.E. Bugaris, W.M. Chance, Cryst. Eng. Commun. 14 (2012) 23-39. [6] Caignaert V, Perez O, Boullay P, Seikh MM, Sakly N, Hardy V, Raveau B, J. of Mater Chem. C 8 (2020) 14559-14569 Keywords: Composite, aperiodicity, non stoichiometry