Maria Luisa Calatayud

Syntheses, crystal structures and magnetic properties of chromato-, sulfato-, and oxalato-bridged dinuclear copper(II) complexes

Abstract Four dinuclear copper(II) complexes of formula [Cu2(bpca)2(H2O)3(CrO4)]·H2O (1), [Cu2(bpca)2(H2O)3(SO4)]·H2O (2), [Cu2(bpca)2(H2O)2(C2O4)]·2H2O (3), and [Cu2(bpca)2(C2O4)] (4) [bpca=bis(2-pyridylcarbonyl)amide anion] have been synthesized and their magnetic behavior has been investigated as a function of temperature. The structures of 1–3 have been determined by single-crystal X-ray diffraction, whereas the structure of 4 was already known. The structures of this family of complexes are made up of neutral chromateO1,O1′ (1), sulfateO1,O1′ (2) and oxalateO1,O2:O1′,O2′-bridged (3 and 4) dinuclear copper(II) units. The two copper atoms within the dinuclear unit of the isomorphous compounds 1 and 2 show different surroundings: they exhibit distorted square pyramidal (Cu(2)) and octahedral (Cu(1)) surroundings with the three bpca-nitrogen atoms and either a chromate (1)/sulfate (2)oxygen atom (Cu(2)) or a wateroxygen atom (Cu(1)) defining the equatorial positions, whereas the axial sites are occupied by a water molecule (Cu(2) and Cu(1)) and a chromate (1)/sulfate (2)oxygen atom (Cu(1)). Each copper atom of the centrosymmetric compound 3 is six-coordinated with the three bpca-nitrogen atoms and an oxalateoxygen forming the equatorial plane, whereas the axial positions are occupied by the other oxalateoxygen and a water molecule. Complex 4 is also centrosymmetric, each copper atom exhibiting a distorted square pyramidal surrounding. The equatorial plane is the same as in 3, and an oxalateoxygen occupies the axial position. The intramolecular coppercopper distances are 3.660(1) A (1), 3.747(1) A (2) and 5.631(1) A (3) (5.442(1) A in 4). The magnetic study of 1–4 reveals the occurrence of weak intramolecular antiferro- (1 and 2) and ferromagnetic (3 and 4) interactions. The magnitude and nature of the magnetic coupling through these extended bridges are analyzed and discussed in the light of the available structural data.

Crystal structures and magnetic properties of the squarate-O1,On-bridged dinuclear copper(II) complexes [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (n=2) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (n=3)

Abstract Two dinuclear copper(II) complexes of the formula [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (1) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (2) [phen=1,10-phenanthroline, bipy=2,2′-bipyridine and C4O4 2−=dianion of 3,4-dihydroxy-3-cyclobuten-1,2-dione (squaric acid)] have been synthesized and characterized by single-crystal X-ray diffraction. Their structures consist of [Cu2(phen)4(C4O4)]2+ (1) and [Cu2(bipy)4(C4O4)]2+ (2) dinuclear copper(II) cations, uncoordinated CF3SO3 − anions and crystallization water molecules. The copper is in a distorted square pyramidal environment: one squarate-oxygen atom and three phen- (1) or bipy- (2) nitrogen atoms of two phen (1) or bipy (2) terminal ligands form a distorted square plane around the copper whereas the axial position is occupied by the remaining phen- (1) or bipy- (2) nitrogen atom. The squarate adopts the μ-1,2- (1) and μ-1,3- (2) bis(monodentate) coordination modes, the intradimer copper–copper separation being 4.912(2) (1) and 7.310(1) (2) A, respectively. Variable temperature magnetic susceptibility measurements reveal the occurrence of significant intramolecular antiferromagnetic coupling, the relevant parameters being J=−26.4 cm−1 and g=2.14 for 1 and J=−8.6 cm−1 and g=2.07 for 2 (J being the exchange parameter in the isotropic spin Hamiltonian Ĥ=−JŜA · ŜB). The influence of both the symmetry of the copper(II) centered magnetic orbitals and the coordination modes of the bridging squarate on the magnitude of antiferromagnetic coupling in related squarate-bridged copper(II) complexes is analyzed and discussed.

Syntheses, crystal structures and magnetic properties of di- and trinuclear croconato-bridged copper(II) complexes

The new croconato-bridged copper(II) compounds [Cu2(terpy)2(H2O)2(C5O5)](NO3)2·H2O (1) and [Cu3(phen)5(C5O5)2](CF3SO3)2 (2) (C5O52− = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione; terpy = 2,2′:6′,2″-terpyridine; phen = 1,10-phenanthroline) have been prepared, and their crystal structures and variable temperature magnetic susceptibilities determined. The structure of complex 1 consists of croconato-bridged dinuclear [Cu2(terpy)2(H2O)2(C5O5)]2+ complex ions, nitrate counter ions and water of hydration. The croconato ligand exhibits an asymmetrical bis-bidentate coordination mode through four of its five oxygen atoms. The two crystallographically independent copper atoms have similar coordination geometries: elongated, distorted octahedral with three terpyridyl nitrogen atoms and one croconate oxygen atom in the equatorial plane, and a second croconate oxygen atom and a water molecule in the axial positions, the stronger axial interaction in each case being to the water molecule. The intramolecular copper–copper separation across the croconate bridge is 6.852(1) A. The structure of complex 2 is built of croconato-bridged trinuclear [Cu3(phen)5(C5O5)2]2+ complex ions and triflate counter ions. The terminal copper atoms [Cu(1) and Cu(1a)] have, to the first approximation, a square pyramidal coordination geometry with one croconate oxygen and three phen nitrogen atoms in equatorial positions, and a fourth phen nitrogen atom in the apical position. A second semi-coordinated croconate oxygen atom is located in the remaining axial position. The central copper atom [Cu(2)] is elongated octahedral with two croconate oxygen and two phen nitrogen atoms in equatorial positions, and two oxygen atoms, one from each croconate group, in axial positions. The croconate ligands in 2 adopt an unusual asymmetrical bis-bidentate bridging mode involving three adjacent oxygen atoms, the copper–copper separation across this bridge being 4.177(1) A. Variable temperature magnetic susceptibility measurements show the occurrence of weak [J = −2.94 cm−1 (1)] and intermediate [J = −47.1 cm−1 (2)] intramolecular antiferromagnetic interactions across the bridging croconato. These values are analyzed in the light of their structures and compared with those previously reported for the parent compounds.