title: Coordination chemistry of a new cofacial binucleating macropolycycle derived from 1,4,7-triazacyclononane.
abstract: We have prepared and characterized a new phenol-based compartmental ligand (H(2)L) incorporating 1,4,7-triazacyclononane ([9]aneN(3)), and we have investigated its coordination behavior with Cu(II), Zn(II), Cd(II), and Pb(II). The protonation constants of the ligand and the thermodynamic stabilities of the 1:1 and 2:1 (metal/ligand) complexes with these metal ions have been investigated by means of potentiometric measurements in aqueous solutions. The mononuclear [M(L)] complexes show remarkably high stability suggesting that, along with the large number of nitrogen donors available for metal binding, deprotonated phenolic functions are also involved in binding the metal ion. The mononuclear complexes [M(L)] show a marked tendency to add a second metal ion to afford binuclear species. The formation of complexes [M(2)(H(2)L)](4+) occurs at neutral or slightly acidic pH and is generally followed by metal-assisted deprotonation of the phenolic groups to give [M(2)(HL)](3+) and [M(2)(L)](2+) in weakly basic solutions. The complexation properties of H(2)L have also been investigated in the solid state. Crystals suitable for X-ray structural analysis were obtained for the binuclear complexes [Cu(2)(L)](BF(4))(2).(1)/(2)MeCN (1), [Zn(2)(HL)](ClO(4))(3).(1)/(2)MeCN (2), and [Pb(2)(L)](ClO(4))(2).2MeCN (4). In 1 and 2, the phenolate O-donors do not bridge the two metal centers, which are, therefore, segregated each within an N(5)O-donor compartment. However, in the case of the binuclear complex [Pb(2)(L)](ClO(4))(2).2MeCN (4), the two Pb(II) centers are bridged by the phenolate oxygen atoms with each metal ion sited within an N(5)O(2)-donor compartment of L(2)(-), with a Pb.Pb distance of 3.9427(5) A.
authors.affiliation: Dipartimento di Chimica Inorganica ed Analitica, Università degli Studi di Cagliari, Complesso Universitario di Monserrato, S.S. 554 Bivio per Sestu, 09042 Monserrato (CA), Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Tei
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Arca
authors.forename: M Carla
authors.initials: MC
authors.lastname: Aragoni
authors.forename: Andrea
authors.initials: A
authors.lastname: Bencini
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Blake
authors.forename: Claudia
authors.initials: C
authors.lastname: Caltagirone
authors.forename: Francesco A
authors.initials: FA
authors.lastname: Devillanova
authors.forename: Patrizia
authors.initials: P
authors.lastname: Fornasari
authors.forename: Alessandra
authors.initials: A
authors.lastname: Garau
authors.forename: Francesco
authors.initials: F
authors.lastname: Isaia
authors.forename: Vito
authors.initials: V
authors.lastname: Lippolis
authors.forename: Martin
authors.initials: M
authors.lastname: Schröder
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Teat
authors.forename: Barbara
authors.initials: B
authors.lastname: Valtancoli