ABSTRACT
The first example of a triple formato/hydroxido/sulfato (FHS) bridge for any metal is reported in compound [Cu2(bpym)(OH)(HCO2)(SO4)(H2O)2]·3H2O (1). Its structure shows the presence of alternating triple FHS bridges and 2,2'-bipyrimidine (bpym) ones. Although in the initial synthesis the sulfate anions were introduced accidentally, here we report the rational synthesis and the magnetic properties of this compound. The magnetic properties show that 1 is an alternating ferro/antiferromagnetic (F/AF) chain compound with predominant antiferromagnetic interactions and were fit to an alternating F/AF S = (1)/2 chain with g = 2.103, JAF = -139 cm(-1), and JF = 116 cm(-1) (α = JF/|JAF| = 0.83). The JAF value found corresponds very well to those previously reported for Cu-bpym-Cu bridges (average value of ca. -150 cm(-1)). The JF value is also very close to the estimated one (ca. 100 cm(-1)) from magneto-structural correlations in triply Cu-Cu bridged compounds with both hydroxido and carboxylato bridges in equatorial positions.
ABSTRACT
This paper reports the synthesis, structure solution, and magnetic characterization of four new DIMMAL-containing compounds (H2DIMMAL = 2-di1H-2-imidazolylmethylmalonic acid), H2DIMMAL x H2O (1), Na2(DIMMAL) x 5H2O (2), [Cu(HDIMMAL)2] (3), and [Cu2(DIMMAL)2(H2O)2] x 2H2O (4). Compound 1, containing two carboxylates and two protonated imidazole rings, adopts the dizwitterion configuration. These monohydrate MBBs pack together into a 3D array driven, as in the other three cases herein reported, by a combination of multiple-path H-bonds and aromatic-aromatic interactions. Compound 2 consists of centrosymmetric Na+ tetramers in which four NaO6 distorted octahedra are interconnected by carboxylate and water bridges. Compound 3 consists of mononuclear [Cu(HDIMMAL)2] units in which HDIMMAL- acts as a tridentate ligand through two imidazole N atoms and the deprotonated O from a carboxylate. Compound 4 consists of centrosymmetric cyclic dinuclear [Cu2(DIMMAL)2(H2O)2] x 2H2O units involving propionate-arm bridges. The building-block units described above, in each case, are interconnected into 3D networks by multiple H-bonding paths and aromatic-aromatic interactions. The EPR spectra are indicative of an essentially d(x2-y2) ground state for the copper(II) ions in 3 and 4 (CuN4O2 and CuN2O2O' chromophores, respectively). Magnetic susceptibility measurements in the range of 1.8-200 K for compound 4 show weak antiferromagnetic exchange between the copper(II) ions (2J = -1.6(1) cm(-1)). The effectiveness of the propionate-arm bridges, involving C-C sigma bonds, in propagating magnetic exchange between the copper(II) ions is discussed.
ABSTRACT
A novel mu-pyrazolato-mu-hydroxo-dibridged copper(II) complex has been synthesized and structurally characterized: [(Cu(mepirizole)Br)2(mu-OH)(mu-pz)] (mepirizole=4-methoxy-2-(5-methoxy-3-methyl-1H-pyrazol-1-yl)-6-methylpyrimidine; pz=pyrazolate). The title compound crystallizes in the monoclinic system, space group P2(1)/c, with a=15.618(2) A, b=15.369(3) A, c=16.071(3) A, and beta=112.250(1) degrees. The structure is built up of dinuclear [(Cu(mepirizole)Br)2(mu-OH)(mu-pz)] units with five-coordinated copper(II) ions (CuBrN3O chromophores) linked by mu2-OH and mu2-pyrazolato bridges that are well separated from each others. The intramolecular copper-copper distance is 3.378(3) A. Magnetic susceptibility data show that the copper atoms are strongly antiferromagnetically coupled with J=-770 cm(-1). The obtained triplet-singlet energy gap is compared with those reported for a series of related dimers. The strong antiferromagnetic coupling arising from the complementarity of the hydroxo and pyrazolato bridges has been discussed on the basis of DFT calculations.
