The two tetraazamacrocycle-N.N',N",N"'-tetraacetic acids H,dota and H,teta form with Ni2+, Cu2+, and Zn2+ (M") mononuclear complexes MLH, and M'[ML], M' being an alkaline earth ion. The structures of Ni(H2dota) and Cu(H,dota) have been solved by X-ray structure analysis. The metal ions are in a distorted octahedral geometry coordinated by four amino N-atoms and two carboxylates. In the case of Cu2+, the distortions are more pronounced than for Ni2+ indicating that the Juhn-Teffer effect is operating. Starting from these two structures, the coordination geometry of the other complexes is discussed using VIS and IR spectra.

With a view to radiopharmaceutical application, four In3+ complexes of mono-and bi-functional carboxymethylated tetra-azamacrocyclic ligands were prepared, the structures of two of them were solved by X-ray diffraction and their stability was determined by measuring the exchange to transferrin in blood serum.t "'In decays by electron capture, it emits 2 y rays with energies of 173 keV and 247 keV with a half-life of 68 h.All ligands had satisfactory elemental analysis, n.m.r. and mass spectra.

Pyracylene (cyclopent[fg\ acenaphthylene, 1) is available in two steps from pyrene and, contrary to previous experience, can be crystallized, stored as a solid, and even sublimed without decomposition. The X-ray structure of 1 exhibits a pronounced alternation of bond lengths along the 12-ir periphery. The absorption spectrum (with transition moment directions) and the photoelectron spectrum of 1 are reported and analyzed. Pyracylene is quite stable to irradiation both as a solid and in solution. Radiationless deactivation of the lowest excited singlet state is very rapid; fluorescence and intersystem crossing yields were below our limits of detection (F < 3 X 10"4, 0T < 2 X 10"2). The lowest triplet state, observed by flash photolysis with a sensitizer (Xmx = 360 nm, e > 104 M"1 cm"1; = 520 nm, t = 7500 M"1 cm"1), is also rather short-lived (r = 4.6 ms). The triplet energy of 1 is bracketed in the range of 103 ± 20 kj mol"1 on the basis of energy-transfer experiments. A major component of flame soots, which had been tentatively attributed to 1 by GC-MS analysis, is shown not to be identical with 1. The heat of formation of 1 is calculated as AfH = 410 kj mol"1 with the MMP2 force field.The literature on pyracylene (cyclopent \fg] acenaphthylene, 1) displays a remarkable dichotomy. On the one hand, 1 is held to be very unstable, a prototype "antiaromatic" molecule with a •This work is part of the Ph. D. thesis of B.F.

The three ligands H,dotd, H4teta, and H,heta give bmuclear complexes with Cu2+ and Ni", the spectral properties of which have been studied. The structures of Cu2(dota). 5H20 and Cu,(teta). 6H20 have been established by X-ray diffraction analysis.

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