Synthesis, structure and magnetic properties of cobalt(II) and copper(II) coordination polymers assembled by phthalate and 4-methylimidazole

New coordination polymers [M(Pht)(4-MeIm)2(H2O)]n (M=Co (1), Cu (2); Pht2−=dianion of o-phthalic acid; 4-MeIm=4-methylimidazole) have been synthesized and characterized by IR spectroscopy, X-ray crystallography, thermogravimetric analysis and magnetic measurements. The crystal structures of 1 and 2 are isostructural and consist of [M(4-MeIm)2(H2O)] building units linked in infinite 1D helical chains by 1,6-bridging phthalate ions which also act as chelating ligands through two O atoms from one carboxylate group in the case of 1. In complex 1, each Co(II) atom adopts a distorted octahedral N2O4 geometry being coordinated by two N atoms from two 4-MeIm, three O atoms of two phthalate residues and one O atom of a water molecule, whereas the square-pyramidal N2O3 coordination of the Cu(II) atom in 2 includes two N atoms of N-containing ligands, two O atoms of two carboxylate groups from different Pht, and a water molecule. An additional strong O–H⋯O hydrogen bond between a carboxylate group of the phthalate ligand and a coordinated water molecule join the 1D helical chains to form a 2D network in both compounds. The thermal dependences of the magnetic susceptibilities of the polymeric helical Co(II) chain compound 1 were simulated within the temperature range 20–300 K as a single ion case, whereas for the Cu(II) compound 2, the simulations between 25 and 300 K, were made for a linear chain using the Bonner–Fisher approximation. Modelling the experimental data of compound 1 with MAGPACK resulted in: g=2.6, |D|=62 cm−1. Calculations using the Bonner–Fisher approximation gave the following result for compound 2: g=2.18, J=–0.4 cm−1

Multi-temperature X-ray diffraction, Mössbauer spectroscopy and magnetic susceptibility studies of a solvated mixed-valence trinuclear iron formate, [Fe3O(HCO2)6(NC5H4CH3)3)]·1.3(NC5H4CH3)

Structural analysis of the solvated mixed-valence (MV) trinuclear iron carboxylate, [Fe3O(HCO2)(6)(gamma- pic)(3)].x(gamma-pic), 1, (gamma-pic = 4-methylpyridine; x approximate to 1.3), has been performed from X-ray diffraction data at four temperatures. Analysis of the X-ray diffraction and variable temperature Mossbauer data for 1 clearly shows the presence of localised valence states for iron atoms at and below 100 K. Both physical methods agree that compound 1 exhibits a continuously growing degree of electron transfer (ET) between the three iron sites with increasing temperature; however, the extent of ET is significantly larger for one of the iron(III) sites. All three terminal gamma-pic groups remain ordered at and below room temperature, whereas the gamma-pic solvent molecules have a temperature dependent disorder over a number of positions. The distribution of the solvent over disorder positions is suggested to influence the degree of ET between the metal sites. From the molecular geometry in the Fe3O-core, an estimate of 260 cm(-1) in energy difference between the two vibronic states corresponding to electronic localisation on either of the two iron atoms involved in ET is obtained. This value is close to an estimate for the energy difference assessed by using a Blume-Emery-Griffith Hamiltonian to describe the localised-delocalised transition in mixed valence molecular compounds

Multi-temperature crystallographic studies of mixed-valence polynuclear complexes; valence trapping process in the trinuclear oxo-bridged iron compound, [Fe3O(O2CC(CH3)3)6(C5H5N)3]

Single-crystal X-ray diffraction data have been collected on five different crystals at 12 different temperatures (10, 28, 35, 60, 85, 100, 118, 135, 160, 200, 240, 295 K) on a trinuclear, oxo-bridged, mixed-valence iron complex, Fe3O(O2CC(CH3)3)6(C5H5N)3, using both synchrotron and conventional radiation sources. The present study for the first time provides structural information for an oxo-bridged trinuclear compound below the boiling point of nitrogen (77 K). The use of very low-temperature crystallographic data is crucial for understanding the physical properties of the complex. No change of space group is observed in the whole temperature range, although a reversible broadening of the Bragg peaks is observed around 85 K. The structure has ordering processes involving the tert-butyl groups, and above 85 K, four tert-butyl groups become disordered. Around 150 K, a fifth tert-butyl becomes disordered, whereas the last tert-butyl is ordered at all temperatures. Very significant temperature-dependent changes in the Fe-ligand bond lengths are observed which are interpreted as being due to dynamic disorder caused by intramolecular electron transfer (ET) between the metal sites. The ET process is significantly affected by changes in the molecular potential energy surface (PES) caused by the dynamic behavior of the tert-butyls. The dynamic disorder of the Fe3O core resulting from the ET process is examined through analysis of the atomic displacement parameters. The ET process involves only two of the three iron sites, with the third site appearing to be valence-trapped at all temperatures. The trapping of this iron site at all temperatures appears to be related to the asymmetry caused by the different dynamic behaviors of the tert-butyls. At very low temperatures (<10 K), the system becomes valence-trapped and consists of a single configuration without disorder. Boltzmann population models are used to estimate the energy difference between the two lowest-lying minima on the PES (ΔE < 100 cm-1) and between two disordered configurations of each of the tert-butyls (ΔE = 217, 212, 255, 359, and 345 cm-1)

Nickel(II)-, cobalt(II)-, copper(II)-, and zinc(II)-phthalate and 1-methylimidazole coordination compounds: synthesis, crystal structures and magnetic properties

Three new coordination polymers [M(Pht)(1-MeIm)2]n (where M=Cu (1), Zn (2), Co (3); Pht2−=dianion of o-phthalic acid; 1-MeIm=1-methylimidazole) and two compounds [M(1-MeIm)6](HPht)2 · 2H2O (M=Co (4), Ni (5)) have been synthesized and characterized by X-ray crystallography. The structures of 1–3 (2 is isostructural to 3) consist of [M(1-MeIm)2] building units connected by 1,6-bridging phthalate ions to form infinite chains. In complex 1, each copper(II) center adopts a square coordination mode of N2O2 type by two O atoms from different phthalate ions and two N atoms of 1-MeIm, whereas in 3 two independent metal atoms are tetrahedrally (N2O2) coordinated to a pair of Pht ligands and a pair of 1-MeIm molecules. There are only van der Waals interactions between the chains in 1, while the three-dimensional network in 3 is assembled by C–H⋯O contacts. In contrast to polymers 1–3 the structures of 4 and 5 (complexes are also isostructural) are made up of the [M(1-MeIm)6]2+ cation, two hydrogen phthalate anions (HPht−) and two H2O solvate molecules. The coordination around each metal(II) atom is octahedral with six nitrogen atoms of 1-MeIm. Extended hydrogen bonding networks embracing the solvate water molecules and a phthalate residue as well as the weak C–H⋯O interactions stabilize the three-dimensional structures. Magnetic studies clearly show that the magnetic ions do not interact with each other. Furthermore, in compound 4 we have another example of a highly anisotropic Co2+ ion with a rhombic g-tensor and large zero-field-splitting. The complexes were also characterized by IR and 1H NMR spectroscopy, thermogravimetric analysis, and all data are discussed in the terms of known structures