Influence of copper valence states on antiferromagnetic Behavior: A Comparative study of three Copper-based polyoxomolybdate hybrid compounds

Three Cu-based polyoxomolybdate coordination polymers, [Cu I x Cu II 1-x (mbpy)(H 2 O)][Cu II (mbpy)(H 2 O) 2 ][Na(HPO 4 )(H x PO 4 )-Mo 5 O 15 ]·5·.5H 2 O ( 1 ), Cu(mbpy)Mo 2 O 7 ( 2 ) and [(Cu II (mbpy))(Cu I y Cu II 1-y (mbpy))(H 2 O)(H y PO 4 )] 2 [H 3 PMo VI 10 Mo V 2 O 40 ]·H 2 O ( 3 ) (mbpy = 4,4′-dimethyl-2,2′-dipyridyl, 0 <  x  < 1, 0 <  y  < 1), have been hydrothermally synthesized. Single crystal X-ray diffraction analysis of compounds 1 – 3 indicates that three different types of polyoxomolybdate unit, namely Strandberg-type {P 2 Mo 5 }, dimeric {Mo 2 } and Keggin-type {PMo 12 }, are included, respectively. Compound 1 is constructed by Strandberg-type {P 2 Mo 5 } and Cu(mbpy) to form a dimeric unit. Compound 2 has a 1D nanorod-like structure connected by the simplest {Mo 2 } unit. Compound 3 is an isolated structure consisting of a Keggin-type {PMo 12 } and a {Cu 4 } unit. BVS and XPS studies demonstrate that both Cu + and Cu 2+ coexist in compounds 1 and 3 , and magnetic measurement indicates the existence of anti-ferromagnetic interactions in compounds 1 – 3 . We proposed three possible magnetic modes, namely {Cu 4 }, linear {Cu 2 } and {Cu 4 -Mo 2 }, to explain the complex magnetic behavior and try to use both magnetic study and the structure analysis to probe the Cu(I) centers in the compounds.