<SUP>1</SUP>H NMR studies on strongly antiferromagnetically coupled dicopper(II) systems

The 1H NMR spectra of three well-characterized &#956; -phenoxo and &#956; -hydroxo spin coupled dicopper(II) complexes 1, 2, and 3 which are strongly antiferromagnetically coupled in the solid state have been studied in solution. The complexes studied were [(Cu2(DAP)2IPA)(OH)(H2O)](ClO4)2&#183;H2O (1) (DAP = 1,3-diaminopropane; IPA = 2-hydroxy-5-methylisophthalaldehyde), [(Cu2(DMDAP)2IPA)(OH)(H2O)](ClO4)2 (2) (DMDAP = N,N-dimethyl-1,3-diaminopropane), and [(Cu2(AEP)2IPA)(OH)(H2O)](ClO4)2 (3) (AEP = 2-(2-aminoethyl)pyridine). All three complexes exhibit relatively sharp hyperfine shifted NMR signals. Signal assignments were based on intensity and T1 values. An analysis of the relaxation data shows that, for these binuclear copper(II) systems, the reorientational correlation time (&#964;c) is dominated probably by a combination of electronic relaxation &#964;s and rotational correlation time (&#964;r) due to an exchange-modulated dipolar mechanism. The temperature dependence of the isotropic shifts has been interpreted in terms of the contact hyperfine interaction constant (A) and exchange coupling constant (-2J). The fitting of these shifts represents a good method for the evaluation of -2J in solution, which is compared to the solid state -2J value obtained by the SQUID method. The results indicate that the structures and magnetic properties of all three complexes (1-3) support a general correlation with the antiferromagnetic coupling constants as evidenced by both solid and solution studies. Our results show that 1H NMR spectroscopy is an excellent tool to probe the solution structures of magnetically coupled binuclear Cu(II) centers in model complexes as well as biological systems. One of these complexes was crystallized from aqueous solution. The crystal and molecular structure of [(Cu2(DMDAP)2IPA)(OH)(H2O)](ClO4)2 (2) has been determined. This crystallizes in the monoclinic system, space group Cc with formula weight = 692.48, a = 12.472(2) &#197;, b = 19.554(2) &#197;, c = 12.185(12) &#197;, &#946; = 107.48 (9)&#176;, Z = 4. The two Cu atoms in this copper(II) complex are bridged by the oxygen atoms of the phenolate and hydroxy groups. The axial position at one Cu atom is occupied by a water molecule, while another Cu has weak interaction with a perchlorate group. The coordination geometries around the two Cu atoms are distorted square pyramidal and square planar

Synthesis, structure, magnetic properties, and <SUP>1</SUP>H NMR studies of a moderately antiferromagnetically coupled binuclear copper(II) complex

A binuclear Cu(II) complex of [(Cu2(HAP)2IPA)(OH)(H2O)](ClO4)2&#183;H2 O (HAP = 3-amino-1-propanol; IPA = 2-hydroxy-5-methylisophthalaldehyde) has been synthesized and characterized by X-ray crystallography, by solid state magnetic susceptibility, and in solution by 1H NMR studies. The binuclear copper(II) complex crystallizes in the orthorhombic system, space group Pbcn, a = 27.9972(9) &#197;, b = 8.8713(3) &#197;, c = 19.5939(6) &#197;, and Z = 8. The two copper(II) atoms in this binuclear Cu(II) complex are bridged by the oxygen atoms of the phenolate and hydroxy groups. The axial position at one Cu atom is occupied by a water molecule while another Cu has weak interaction with a perchlorate group. The coordination geometries around the two Cu atoms are distorted square pyramid and square planar. The solid state magnetic susceptibility measurement reveals a moderate antiferromagnetic exchange interaction between the two Cu atoms with a -2J value of 113 &#177; 9 cm-1. The variable-temperature 1H NMR studies in CD3CN solution show that the observed relatively sharp hyperfine shifted signals follow a Curie behavior. The exchange coupling constant (-2J) obtained in solution by using chemical shift as a function of temperature also reveals a moderate antiferromagnetic exchange interaction between two Cu(II) ions. An analysis of the relaxation data shows that the reorientational correlation time (&#964;c) is dominated probably by a combination of electronic relaxation time &#964;sand rotational correlation time (&#964;r) due to an exchange-modulated dipolar mechanism for this moderately antiferromagnetically coupled binuclear copper(II) system

Presence of Jahn-Teller distortions in a novel six-coordinate Ag(II) complex: temperature dependent EPR, optical and magnetic susceptibility measurements

Single-crystal variable temperature EPR, optical and polycrystalline magnetic susceptibility studies have been made on a novel six-coordinate Ag(II) complex. Temperature dependent EPR studies on pure single crystals of this compound reveal that dynamic Jahn-Teller distortion operates above 230 K, between 230 K and 120K static Jahn-Teller distortion sets in and below 110 K there is evidence of exchange interaction. Crystal g values were obtained by least-squares fitting with the data obtained from the orientation dependent EPR spectra of the undiluted single crystal of this complex at 300 K and 77 K. From an optical study the Jahn-Teller stabilization energy is found to be &#8764; 2250cm⁻¹. Comparison of Absmax values for other silver(II) compounds enables us to conclude that the formal geometry of this complex is a tetragonally distorted octahedral. Infrared spectra of this complex were also recorded over a wide range of temperature. Magnetic susceptibility measurements over a wide range of temperature on the powder sample of this compound reveal that the complex is antiferromagnetically coupled in the temperature range 5–40 K with 2J = 0.906cm⁻¹, and above 40K it is ferromagnetically coupled with 2J = +7.4cm⁻¹. The effective magnetic moment (μeff) of this complex has been compared with that of a series of other silver(II) complexes available in the literature. Finally, the spectral and magnetic data of this complex have been compared with those of a corresponding isostructural and isomorphous copper(II) complex

Dynamic and static Jahn-Teller distortions in a CuN₆ cage complex

EPR studies of pure and doped (in an isostructural diamagnetic zinc lattice) polycrystalline [Cu(di(amH)sar)](NO3)4 over a wide range of temperature (7–280 K) show that both undergo a transition from dynamic to static Jahn-Teller distortions. The spectra were simulated to get the g- and A-tensors. The transition temperature for the pure polycrystalline sample is ⩽120 K and for the doped one it is above room temperature. There is evidence for the existence of cooperative and localized Jahn-Teller distortions respectively in pure and doped crystals. From the g-tensors of the pure polycrystalline sample there is evidence, supported by single-crystal results, of rapid electronic exchange between two inequivalent Cu(II) sites

Studies on nitrosyl hemes in Ni(II)–Fe(II) hybrid hemoglobins

Subunit heterogeneity within a particular subunit in hemoglobin A have been explored with electron paramagnetic resonance spectroscopy using the nitrosyl hemes in Ni–Fe hybrid Hb under various solution conditions. Our previous studies on the crystal structure of NiHb demonstrated the presence of subunit heterogeneity within α-subunit. To further cross check this hypothesis, we made a hybrid Hb in which either the α- or β-subunit contains iron, which alone can bind to NO. By this way dynamic exchange between penta- and hexa-coordinated forms within a subunit was confirmed. Upon the addition of inositol hexa phosphate (IHP) to these hybrids, R to T state transition is observed for [α2(Fe–NO)β2(Ni)] but such a direct transformation is less marked in [α2(Ni)β2(Fe–NO)]. Hence the bond between Nε and Fe is fundamental to the structure–function relation in Hb, as the motion of this nitrogen triggers the vast transformation, which occurs in the whole molecule on attachment of NO

Structure, characterisation and dynamics of copper(I) complexes of 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine

Two mononuclear copper(I) complexes of a tripodal ligand, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L), have been prepared, [CuL(ClO4)]·CH2Cl21 and [CuL(PPh3)]ClO42. A new route to L is also proposed. The crystal structures of both complexes have been determined. In 1 the perchlorate is bonded through one of its oxygens with a distance of 2.426(3)Å. In 2 the perchlorate ion is thermally disordered. A variable-temperature NMR study of both complexes revealed that the methylene carbon of 2 is chiral at low temperatures. Carbon monoxide formed a terminal adduct with 1

Metal-ion coordination in copper and nickel reconstituted hemoglobins

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A novel polymer of a binuclear nickel(II) complex bridged by 1,3-diaminopropane: structure and magnetism

A novel polymer of a binuclear nickel(II) complex of [Ni2L(&#956; -H2N-(CH2)3-NH2)2&#183;(H2O)2]n&#183;(ClO4)n&#183;(H2O)n (where L = [2 + 2] condensation of 2,6-diformyl-4-methylphenol with 1,3-diaminopropane) has been synthesized and characterized. The crystal structure of the compound has been solved. The compound crystallizes in the monoclinic system, space group P21/a, with formula weight = 901.004, a = 13.918(2) &#197;, b = 18.111(3)&#197; , c = 16.079(2) &#197;, &#946; = 103.46(3)&#176;, and Z = 4. The interesting feature of this compound is the bridging behavior of 1,3-diaminopropane in an end-to-end fashion. Nickel atoms are placed in a distorted octahedral environment. The magnetic properties of the compound have been studied by means of susceptibility measurement vs temperature, which reveals a moderately strong intramolecular antiferromagnetic coupling (J) of -30 &#177; 4 cm-1 and a weak intermolecular ferromagnetic coupling (zJ') of 2 &#177; 1 cm-1

Synthesis and characterization of a stable paramagnetic hexacoordinated oxochromium(IV) complex with dianionic tetradentate schiff base ligand salen

A paramagnetic octahedral oxochromium(IV) complex with dianionic tetradentate ligand salen (where H2salen is N,N'-bis(salicylidene)-1,2-ethylenediamine) has been synthesized. This compound [CrO(OH2)(salen)] (1) is characterized by elemental analysis, magnetic moment measurement, IR, UV-Vis and EPR spectroscopic studies. Measured room temperature (RT) magnetic moment value is 2.96 BM for 1 indicates a d2 system with a triplet ground state. The magnetic moment value rules out a large spin-orbit coupling. The RT and LNT powder EPR spectra of 1 in X-band clearly shows two lines, one around g = 1.965 and the other with larger intensity at g = 4.26 &#177; 0.10. The first line at g = 1.965 corresponds to the |0&gt; &#8596; |&#177; 1&gt; transition from the Kramers doublet |&#177; 1&gt;, while the broad and intense line at low field with the g-value of 4.26 &#177; 0.10 is due to the forbidden transition |-1&gt; &#8596; |+1&gt;. Compound 1 displays two successive reductions at -0.76 and -1.63 V (versus Ag/AgCl), respectively, while it undergoes only one irreversible oxidation as evident from the well-defined anodic wave at +1.48 V in its cyclic voltammogram