Fluoride-bridged {GdIII3MIII2} (M=Cr, Fe, Ga) molecular magnetic refrigerants

et al.The reaction of fac-[MIIIF3(Me3tacn)] ×x H2O with Gd(NO3)3×5H 2O affords a series of fluoride-bridged, trigonal bipyramidal {GdIII 3MIII 2} (M=Cr (1), Fe (2), Ga (3)) complexes without signs of concomitant GdF3 formation, thereby demonstrating the applicability even of labile fluoride-complexes as precursors for 3d-4f systems. Molecular geometry enforces weak exchange interactions, which is rationalized computationally. This, in conjunction with a lightweight ligand sphere, gives rise to large magnetic entropy changes of 38.3 J kg-1 K-1 (1) and 33.1 J kg-1 K-1 (2) for the field change 7 T→0 T. Interestingly, the entropy change, and the magnetocaloric effect, are smaller in 2 than in 1 despite the larger spin ground state of the former secured by intramolecular Fe-Gd ferromagnetic interactions. This observation underlines the necessity of controlling not only the ground state but also close-lying excited states for successful design of molecular refrigerants.K.S.P. and S.P. thank the Danish Ministry of Science Innovation and Higher Education for an EliteForsk travel grant and a Sapere Aude Fellowship (10-081659), respectively. G.L., J.J.M., and M.E. acknowledge financial support by the Spanish MINECO through grant MAT2012-38318-C03-01. G.L. is also grateful to the EC for a Marie Curie-IEF (PIEF-GA-2011-299356). G.R. would like to thank DST, India (SR/S1/IC-41/2010; SR/NM/NS-1119/2011) for funding and IITB for HPC resources. S.K.S. thanks CSIR for a SRF fellowship.Peer Reviewe

Fluoride-Bridged {Gd-III M-3(III) (2)} ( M= Cr, Fe, Ga) Molecular Magnetic Refrigerants**

The reaction of fac-[(MF3)-F-III(Me(3)tacn)]xH(2)O with Gd(NO3)(3)5H(2)O affords a series of fluoride-bridged, trigonal bipyramidal {(Gd3M2III)-M-III} (M=Cr (1), Fe (2), Ga (3)) complexes without signs of concomitant GdF3 formation, thereby demonstrating the applicability even of labile fluoride-complexes as precursors for 3d-4f systems. Molecular geometry enforces weak exchange interactions, which is rationalized computationally. This, in conjunction with a lightweight ligand sphere, gives rise to large magnetic entropy changes of 38.3Jkg(-1)K(-1) (1) and 33.1Jkg(-1)K(-1) (2) for the field change 7T0T. Interestingly, the entropy change, and the magnetocaloric effect, are smaller in 2 than in 1 despite the larger spin ground state of the former secured by intramolecular Fe-Gd ferromagnetic interactions. This observation underlines the necessity of controlling not only the ground state but also close-lying excited states for successful design of molecular refrigerants