6533b7d5fe1ef96bd1263b9b

RESEARCH PRODUCT

Iron(III), chromium(III) and cobalt(II) complexes with squarate: Synthesis, crystal structure and magnetic properties

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The preparation and variable temperature-magnetic investigation of three squarate-containing complexes of formula [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 1 ) [Cr 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ]·2H 2 O ( 2 ) and [Co(C 4 O 4 )(H 2 O) 4 ] n ( 3 ) [H 2 C 4 O 4  = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe 2 (OH) 2 (C 4 O 4 ) 2 (H 2 O) 4 ] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environment at each iron atom in 1 . The iron–iron distance with the dinuclear unit is 3.0722(6) A and the angle at the hydroxo bridge is 99.99(7)°, values which compare well with the corresponding ones in the isostructural compound 2 (2.998 A and 99.47°) whose structure was reported previously. The crystal structure of 3 contains neutral chains of squarato- O 1 , O 3 -bridged cobalt(II) ions where four coordinated water molecules complete the six-coordination at each cobalt atom. The cobalt–cobalt separation across the squarate bridge is 8.0595(4) A. A relatively important intramolecular antiferromagnetic coupling occurs in 1 whereas it is very weak in 2 , the exchange pathway being the same [ J  = −14.4 ( 1 ) and −0.07 cm −1 ( 2 ), the spin Hamiltonian being defined as H ^ = - J S ^ 1 · S ^ 2 ]. A weak intrachain antiferromagnetic interaction between the high-spin cobalt(II) ions occurs in 3 ( J  = −0.30 cm −1 ). The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures and they are compared with those reported for related systems.