Synthetic, spectroscopic, and solution studies of imidazolate-bridged dicopper(II) complexes

Abstract

The synthesis and spectroscopic characterization of discrete, water soluble, imidazolate-bridged copper(I1) complexes are reported. Binuclear imidazolate-bridged complexes were crystallized from basic aqueous or methanolic solutions of Cu(pip)2+, pip = 24 (2-(2-pyridyl)ethylimino)methyl]pyridine, or CU(PMDT)~+, PMDT = 1,1,4,7,7-pentamethyldiethylenetriamine, and various substituted imidazoles. The condensation of imidazole-4,5-dicarboxaldehyde with (2-(2-aminoethyl)-pyridine)copper(II) afforded the Cu2bpim3+ cation, where bpim is 4,5-bis[(2-(2-pyridyl)ethylimino)methyl]imidazolate. Addition of imidazole and sodium hydroxide to aqueous solutions of this cation yielded the tetranuclear complex [C~~bpim(im)]~(N0~)~4H~O (im = imidazolate). Potentiometric titrations and solution electron spin resonance spectroscopic studies showed that the integrity of the imidazolate bridge in the Cu2bpim3+ cation is maintained in the range 3.5 < pH < 11.5. Similar studies of the [Cu(pip)12im3+ complex revealed that the bridge is broken both by protonation of the imidazolate group at low pH and by competition with hydroxide ions at high pH. Four protons are reversibly titrated in solutions of [Cu2bpim(im)]:+ corresponding to protonation of the imidazolate rings that link the two Cu2bpim3+ units in this complex to form 2 equiv of imidazolium ion. IntroductionThe imidazolate (im) anion, the deprotonated form of im-

Electrochemical studies of a dinuclear copper complex with imidazole derivative ligand H3bphenim

“…2(b)) due to a partial structural change when the complex is dissolved. This behavior coincides with that of many reported models where the imidazolate bridge is broken in solution or remains only in a narrow range of pH [20,24,25].…”

Stereochemistry of imidazolate-bridged copper(II) complexes: [Cu2bpim(im)]2(NO3)4.3H2O, C44H50Cu4N20O15, [Cu(pip)]2(im)(NO3)3.2.5H2O, C29H34Cu2N11O11.5,[Cu(pmdt)]2(2-Meim)(ClO4)3, C22H51Cl3Cu2N8O12, and [Cu(pmdt)]2(Bzim)(ClO4)3.H2O, C25H53Cl3Cu2N8O13

“…Atoms C(2), C(3), C(5), C(6) and C(7) were refined isotropically in two positions (A and B) while all other atoms were refined anisotropically. Although chemical analyses of several subsequent batches of crystals consistently indicated that compound (2) is a tetrahydrate (Kolks, Frihart, Coughlin & Lippard, 1981), only three water molecules were located crystallographically. Two of these, O(W1) and O(WI*), are coordinated to the Cu while the third, O(W2), is lattice water.…”

Magnetic Interactions through Imidazolate-Bridges: Synthesis, Spectroscopy, Crystal Structure and Magnetic Properties of μ-Imidazolato-Bridged Copper(II) Complexes

“…The magnetic exchange coupling constant J for µ-imidazolato bridged dicopper(II) complexes reported so far varies in the range Ϫ10 to Ϫ180 cm Ϫ1 [7Ϫ14, 16,17,21]. Several magneto-structural correlations between the exchange coupling constant J and structural parameters have been proposed [18Ϫ22].…”