Inorg. Chem. 1987, 26, 681-684
681
Contribution from the Department of Chemistry, University of Florence, Via Maragliano 75/77, 1-50144 Firenze, Italy, ’ and Inorganic Chemistry Department, Facultad d e Ciencias Quimicas, University of Valencia, Valencia, Spain
Solution Chemistry of Macrocycles. 5.’ Synthesis and Ligational Behavior toward Hydrogen and Copper(I1) Ions of the Large Polyazacycloalkane 1,4,7,10,13,16,19,22,25-Nonaazacycloheptacosane ([27]aneN9) Antonio Bianchi,2a Enrique Garcia-Espafia,2bMauro Giusti,2aMauro Micheloni,*2a Andrea and Piero Paoletti*2a Received July 17, 1986 The synthesis and characterization of the new large aza macrocycle 1,4,7,10,13,16,19,22,25-nonaazacycloheptacosane ( [27]aneN9) are described. The basicity constants of the macrocycle and the stability constants of the copper(I1) complexes were determined by potentiometry at 25 OC in 0.15 mol dm-’ NaCIO.,. The formation enthalpy of the species [Cu2LI4+was determined by batch microcalorimetry. Only binuclear species are formed. The binuclear species [CuZLl4+is very stable (log k = 36.03), and its formation is exothermic (AHo = -179.1 kJ mol-’). The thermodynamic quantities AGO and AHo as well as the electronic spectral feature of the [CuZLl4+species indicate that all nitrogen atoms are coordinated to the copper(I1) atoms. The macrocycle shows a great tendency to form protonated and hydroxo species: [CuZLHl5+,[Cu2LH2I6+,[Cu2LH3]’+, and [Cu2LOH]’+ are the species present at equilibrium.
Introduction The adjective “large” has been used t o describe polyazacycloalkanes having more than six nitrogen donor atoms.3 Large polyazacycloalkanes are interesting ligands for the following main reasons: (i) owing to the great number of donor atoms, they can form polynuclear metal complexes in which metal-metal interactions can be ~ t u d i e d ; (ii) ~ , ~these macrocycles are polybases with highly charged protonated species in solution in the neutral pH range. For this reason large polyazacycloalkanes are suitable for “anion-coordination” studies and “supercomplexes” format i ~ n . ~The , ~ largest polyazacycloalkane so far investigated contained eight nitrogen donor atoms and two copper(I1) ions.3 We have
now
synthesized
the
large
polyazacycloalkane
1,4,7,10,13,16,19,22,25-nonaazacycloheptacosanecontaining nine donor atoms ( [27]aneN9; hereafter abbreviated as L) and studied its ligational behavior toward hydrogen (basicity) and copper(I1) ions. n
