The activation of small molecules by dinuclear complexes of copper and other metals

Synthesis, characterization, and structure of macrocyclic mono- and C2-symmetric, binuclear nickel calixsalen complexes

Mono- (3a,b) and binuclear (4a,b) tetradentate NiII complexes of a series of 26-membered macrocyclic salen dimers, [salen(CH2)]2, are prepared in good yield by solvent-controlled reaction with Ni(OAc)2. The mononuclear complex 3b crystallizes in the trigonal space group 3P1(#144), a = 18.2566(2) A, c = 15.9244(2) A, V = 4596.57(8) A3, and Z = 3. Refinement converged with R = 0.054 and Rw = 0.049 for 6852 reflections with I > 2.003 sigma(I). The NiII in complex 3b coordinates in an approximate square planar geometry to one of the two available tetradentate salen sites. Complex 4b crystallizes in the orthorhombic space group P2(1)2(1)2(1)(#19), a = 19.531(2) A, b = 22.891(3), c = 13.373(1) A, V = 5960(1) A3, and Z = 4. The refinement converged with R = 0.067 and Rw = 0.065 for 3752 reflections with I > 2.003 sigma(I). Complex 4b coordinates two distorted square planar, cofacially oriented NiII-salen units held 7.1 A apart by a rigid, syn-folded macrocyclic structure. The solution spectroscopic data and solid-state crystallographic data of 3b and 4b demonstrate the presence of a molecular-sized cavity which shows host-guest properties. Reaction of the flexible 32-membered disalen macrocycle [salen(OCH2CH2O)]2 with Ni(OAc)2 resulted in formation of a binuclear complex, 5. Complex 5 crystallizes in the triclinic space group P1(#1), a = 10.366(4) A, b = 12.170(3) A, c = 10.021(2) A, alpha = 106.29(2) degrees, beta = 91.69(2) degrees, gamma = 68.63(2) degrees, V = 1126.3(5) A3, and Z = 1. The refinement converged with R = 0.052 and Rw = 0.053 for 2385 reflections with I > 2.003 sigma(I). The binuclear complex 5 contains two cofacially oriented, square planar NiII-salen groups lying 3.5 A apart in an anti-folded macrocyclic structure.

Mass spectrometric characterization of Limulus polyphemus hemocyanin

Electrospray ionization-mass spectrometry of ion-exchange and reverse-phase purified hemocyanin from Limulus polyphemus revealed six predominant isoforms with molecular weights ranging from 71,730 to 72,695 Da. The heaviest of these agreed closely with the molecular weight calculated for the previously determined Edman sequence with substitution of isoleucine for valine at position 9 and inclusion of three internal disulfide bonds and one copper atom. Proposed structures for the other isoforms were made on the basis of the molecular weight measurements. Reverse-phase chromatography can be used in addition to the traditional ion-exchange step to produce hemocyanin preparations of greater purity that might be valuable for further detailed investigations of the physicochemical properties of these important proteins. The results reflect yet again the value of mass spectrometry for recognizing molecular microheterogeneity in biological macromolecules and for following protein purification.

Synthesis and Magnetic Properties of New Tetranuclear Copper(II)–Nickel(II) Complexes of Macrocyclic Oxamides

Four new oxamido-bridged [Cu3IINiII] complexes of [14]N4 and [15]N4 macrocyclic oxamides have been prepared and characterized, and the magnetic interaction between the Cu(II) and Ni(II) ions has been investigated.

Synthesis and Characterization of New Symmetrical Binucleating Ligands and Their &mgr;-Phenoxo-Bridged Bicopper(II) Complexes: Structural, Electrochemical, and Magnetic Studies

The new pentadentate binucleating ligands 2,6-Bis[N-(3,5-dimethyl-2-hydroxybenzyl)-N-methylaminomethyl]-4-chlorophenol, H(3)L(1), and 2,6-bis[N-(3,5-dichloro-2-hydroxybenzyl)-N-cyclohexylaminomethyl]-4-methylphenol, H(3)L(2), and their binuclear copper(II) complexes of the general formulas [Cu(2)L(1)(X)] (X = OMe, OH, Br (1-3)) and [Cu(2)L(2)(X)] (X = OMe, OH, Br (4-6)) have been prepared. The molecular structure of the complex [Cu(2)L(1)(OMe)].MeOH was studied by X-ray crystallography. It exists as a discrete binuclear species in which the copper atoms are in a distorted square planar environment with two oxygen bridges provided by the phenolate of the ligand and methoxy exogenous donor and the Cu.Cu distance is 3.030 Å. A cyclic voltammetric study of the complexes shows two quasireversible reduction waves at negative potentials. A cryomagnetic investigation on powdered samples of the complexes (1-6) shows moderately strong antiferromagnetic coupling (-2J in the range 120-300 cm(-)(1)). A comparison of the electrochemical and magnetic properties of the complexes prepared from both ligands is discussed. Crystal data for the complex [Cu(2)L(1)(OMe)].MeOH: molecular formula C(30)H(39)ClCu(2)N(2)O(5), monoclinic, space group P2(1)/c with a = 13.222(1) Å, b = 15.912(1) Å, c = 14.149(1) Å, beta = 91.64(1) degrees, and Z = 4.

Migratory Transmetalation in Diphenoxo-Bridged Cu(II)M(II) Complexes of a Dinucleating Macrocycle with N(amine)(2)O(2) and N(imine)(2)O(2) Metal-Binding Sites

A phenol-based heterodinucleating macrocycle (H(2)L), comprised of two 2-((methylamino)methyl)-6-(iminomethyl)-4-bromophenolate entities bridged by the -(CH(2))(2)- groups between amine nitrogens and by the -(CH(2))(3)- groups between imine nitrogens, displays dissimilar N(amine)(2)O(2) and N(imine)(2)O(2) metal-binding sites sharing the phenolic oxygens and is prepared as a Cu(II)Pb(II) complex [CuPb(L)](ClO(4))(2). An analogous complex [CuPb(L)(BzO)(dmf)]ClO(4) crystallizes in the triclinic space group P&onemacr;, (No. 2), with a = 13.998(2) Å, b = 15.568(2) Å, c = 8.699(2) Å, alpha = 95.32(1) degrees, beta = 92.23(1) degrees, gamma = 82.81(1) degrees, V = 1871.9(5) Å(3), and Z = 2. Refinements based on 3788 reflections with I > 3.00sigma(I) converged with R = 0.058 and R(w) = 0.069. The Cu(II) resides at the N(imine)(2)O(2) site and assumes a planar geometry. The Pb(II) resides at the N(amine)(2)O(2) site and assumes a seven-coordinate geometry by further addition of a dmf molecule and a bidentate benzoate group. The Cu--Pb separation, doubly bridged by the phenolic oxygens, is 3.466(2) Å. The reaction of [CuPb(L)](ClO(4))(2) with metal(II) sulfate salts provides Cu(II)M(II) complexes [CuM(L)](ClO(4))(2).nH(2)O (M = Mn (n = 2), Co (n = 2), Ni (n = 0), Cu (n = 0), Zn (n = 1)). The CuZn complex, [CuZn(L)(AcO)]ClO(4), crystallizes in the triclinic space group P&onemacr;, (No. 2), with a = 12.290(3) Å, b = 13.402(4) Å, c = 11.501(2) Å, alpha = 95.10(2) degrees, beta = 116.68(2) degrees, gamma = 112.00(2) degrees, V = 1491.8(9) Å(3), and Z = 2. Refinements based on 2497 reflections with I > 3.00sigma(I) converge with R = 0.046 and R(w) = 0.034. The Cu(II) is bound at the N(amine)(2)O(2) site and the Zn(II) is bound at the N(imine)(2)O(2) site with a Cu--Zn separation of 2.942(2) Å. Further, the acetate group bridges the two metal ions providing a five-coordinate geometry about both metal ions. The CuM complexes except for the CuZn complex show significant antiferromagnetic spin-exchange within each dinuclear unit. The CuNi complex shows the ESR spectrum of the spin-doublet ground state which demonstrates the delocalization of the unpaired electron over the CuNi core.

Modeling of End-On (&mgr;-Peroxo)dicopper(II) Complexes

A force field for (&mgr;-peroxo)dicopper(II) complexes was developed, based on a well-established parameter set for copper(II) complexes, the structural and spectroscopic data of a (&mgr;-peroxo)dicopper(II) complex with tris(2-pyridylmethylamine) donors and a series of (&mgr;-peroxo)dicobalt(III) compounds. This force field is shown to well reproduce the structural properties of the available structures of (&mgr;-peroxo)dicopper(II) and (&mgr;-peroxo)dicobalt(III) complexes, and it was used to compute a series of (&mgr;-peroxo)dicopper(II) compounds with two tris(2-pyridylmethylamin) units linked by different organic spacers at a 5-pyridyl position at each tetradentate moiety. The computed structures and strain energies indicate that (i) in the compound with an ethyl spacer group the ligand induces a considerable strain and distortion in the &mgr;-peroxo product, and these effects compensate the favorable entropy effects due to the ligand preorganization, in agreement with the published experimental results; (ii) the (&mgr;-peroxo)dicopper(II) compound with the propyl-linked ligand is relatively unstrained and structurally very similar to the parent compound; and (iii) larger spacer groups lead to rather distorted (&mgr;-peroxo)dicopper(II) products.