Bimetallic Ba(II)-Cr(III) and trimetallic Ba(II)-Ln(III)-Cr(III) (Ln(III) = Gd, Tb, Dy, Ho, Er, Yb, Y) coordination polymers formed by Cr(III)-containing building blocks with cyclopropane-1,1-dicarboxylate anions

The reaction of chromium(III) nitrate with Ba(cpdc) (H 2 cpdc = cyclopropane-1,1-dicarboxylic acid) in a ratio of 1:3 yielded a 1D coordination polymer {[Ba 2 Cr 2 (OH) 2 (cpdc) 4 (H 2 O) 8 ] & sdot; 5H 2 O} n ( 1 ) formed by binuclear units [Cr 2 (OH) 2 (cpdc) 4 ] 4- and a 3D polymer [Ba 2 Cr(cpdc) 3 (NO 3 )(H 2 O) 6 ] n ( 2 ) constructed from tris-chelate blocks [Cr (cpdc) 3 ] 3- . The addition of rare-earth metal nitrates (Cr:Ln = 1:2) in this reaction led to the formation of a series of trimetallic 3D coordination polymers {[Ba 3 Ln 2 Cr 4 (cpdc) 12 (H 2 O) 24 ] & sdot; 8H 2 O} n ( 3 Ln , Ln = Gd, Tb, Dy, Ho, Er, Yb, Y), in whose structures tris-chelate fragments [Cr(cpdc) 3 ] 3- are bound in layers by Ln 3+ ions and, further, in a framework due to the coordination of Ba 2+ ions. The crystal structures of 1 , 2 , and 3 Gd were determined by single -crystal X-ray diffraction (XRD), and isostructurality of all the compounds in the series 3 Ln was proved by powder X-ray diffraction (PXRD). DC -magnetic susceptibility measurements revealed weak ferromagnetic exchange interactions between Cr 3+ ions in compound 1 ( J = +0.74 cm -1 ). According to ac -magnetic susceptibility measurements, complexes 3 Er and 3 Y exhibit field -induced slow relaxation of magnetization. According to the data of simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC) performed under Ar atmosphere, dehydration of the compounds obtained takes place in one (for 1 and 3 Gd ) or three stages (for 2 ). The initial temperature of the organic part degradation process decreases when moving from compound 1 containing dimerized bis-chelate fragments [Cr 2 (OH) 2 (cpdc) 4 ] 4- (330 degrees C) to compounds 2 (276 degrees C) and 3 Gd (261 degrees C) based on tris-chelate units [Cr(cpdc) 3 ] 3- .