Fluoride bridges as structure-directing motifs in 3d-4f cluster chemistry

TY - JOUR

T1 - Fluoride bridges as structure-directing motifs in 3d-4f cluster chemistry

AU - Birk, Torben

AU - Pedersen, Kasper Steen

AU - Thuesen, Christian Aagaard

AU - Weyhermüller, Thomas

AU - Schau-Magnussen, Magnus

AU - Piligkos, Stergios

AU - Weihe, Høgni

AU - Mossin, Susanne L.

AU - Evangelisti, Marco

AU - Bendix, Jesper

PY - 2012/5/7

Y1 - 2012/5/7

N2 - The use of kinetically robust chromium(III) fluorido complexes as synthons for mixed 3d-4f clusters is reported. The tendency toward linear {Cr III-F-Ln III} units dictates the cluster topology. Specifically, we show that reaction of cis-[Cr IIIF 2(NN) 2]NO 3 (NN = 1,10-phenanthroline ("phen") or 2,2′-bipyridine ("bpy")) with Ln(NO 3) 3•xH 2O produces isostructural series of molecular {Ln 2Cr 2} squares (1-9) with linear fluoride bridges. In a parallel fashion, fac-[Cr IIIF 3L], where L = N,N′,N″-trimethyl-1,4,7-triazacyclononane ("Me 3tacn"), reacts with Nd(NO 3) 3•6H 2O to form a fluoride-centered penta-nuclear complex and fac-[Cr IIIF 3L′], with L′ = 1,1,1-tris-((methylamino) methylethane) ("Me 3tame"), reacts with [Ln(hfac) 3(H 2O) 2] (hfacH = 1,1,1,5,5,5- hexafluoroacetylacetone) to yield an isostructural series of {Ln 3Cr 2} (10-14) trigonal bipyramids with no central ligand. The formation of the latter is accompanied by a partial solvolysis of the Cr(III) precursor but without formation of insoluble LnF 3. The magnetic properties of the gadolinium containing clusters allow quantification of fluoride-mediated, antiferromagnetic Gd-Cr exchange interactions of magnitude between 0.14 cm -1 and 0.71 cm -1 (Ĥ = J 12Ŝ 1•Ŝ 2 formalism) and vanishingly small J Gd-Gd of 0.06(0) cm -1. The large spin and small anisotropy together with weak exchange interactions in the {Gd 3Cr 2} (11) cluster give rise to a very large magneto-caloric effect of -ΔS m = 28.7 J kg -1 K -1 (μ 0H = 90 to 0 kOe).

AB - The use of kinetically robust chromium(III) fluorido complexes as synthons for mixed 3d-4f clusters is reported. The tendency toward linear {Cr III-F-Ln III} units dictates the cluster topology. Specifically, we show that reaction of cis-[Cr IIIF 2(NN) 2]NO 3 (NN = 1,10-phenanthroline ("phen") or 2,2′-bipyridine ("bpy")) with Ln(NO 3) 3•xH 2O produces isostructural series of molecular {Ln 2Cr 2} squares (1-9) with linear fluoride bridges. In a parallel fashion, fac-[Cr IIIF 3L], where L = N,N′,N″-trimethyl-1,4,7-triazacyclononane ("Me 3tacn"), reacts with Nd(NO 3) 3•6H 2O to form a fluoride-centered penta-nuclear complex and fac-[Cr IIIF 3L′], with L′ = 1,1,1-tris-((methylamino) methylethane) ("Me 3tame"), reacts with [Ln(hfac) 3(H 2O) 2] (hfacH = 1,1,1,5,5,5- hexafluoroacetylacetone) to yield an isostructural series of {Ln 3Cr 2} (10-14) trigonal bipyramids with no central ligand. The formation of the latter is accompanied by a partial solvolysis of the Cr(III) precursor but without formation of insoluble LnF 3. The magnetic properties of the gadolinium containing clusters allow quantification of fluoride-mediated, antiferromagnetic Gd-Cr exchange interactions of magnitude between 0.14 cm -1 and 0.71 cm -1 (Ĥ = J 12Ŝ 1•Ŝ 2 formalism) and vanishingly small J Gd-Gd of 0.06(0) cm -1. The large spin and small anisotropy together with weak exchange interactions in the {Gd 3Cr 2} (11) cluster give rise to a very large magneto-caloric effect of -ΔS m = 28.7 J kg -1 K -1 (μ 0H = 90 to 0 kOe).

KW - Chromium

KW - Fluorides

KW - Kinetics

KW - Lanthanoid Series Elements

KW - Magnetic Phenomena

KW - Models, Molecular

KW - Molecular Conformation

KW - Organometallic Compounds

KW - Temperature

U2 - 10.1021/ic300421x

DO - 10.1021/ic300421x

M3 - Journal article

C2 - 22497590

SN - 0020-1669

VL - 51

SP - 5435

EP - 5443

JO - Inorganic Chemistry

JF - Inorganic Chemistry

IS - 9

ER -