The kinetic inertness of copper(II) complexes of several carboxymethyl-armed cyclams and cyclens in 5 M HCl have been determined confirming that the complex derived from crossbridged cyclam (Cu-CB-TE2A) is by far the most resistant to acid decomplexation. FT-IR studies in D 2 O solution revealed its unique resistance to full carboxylate protonation and its retention of coordination by both pendant arms even in 1 M DCl. The X-ray structure of its monoprotonated form, + , also established full coordination by both

A cross-bridged cyclam ligand bearing two N-carboxymethyl pendant arms (1) has been found to form a copper(II) complex that exhibits significantly improved biological behavior in recent research towards (64)Cu-based radiopharmaceuticals. Both the kinetic inertness and resistance to reduction of Cu-1 are believed to be relevant to its enhanced performance. To explore the influence of pendant arm length on these properties, new cross-bridged cyclam and cyclen ligands with longer N-carboxyethyl pendant arms, 2 and 4, and their respective copper(II) complexes have been synthesized. Both mono- as well as di-O-protonated forms of Cu-2 have also been isolated and structurally characterized. The spectral and structural properties of Cu-2 and Cu-4, their kinetic inertness in 5 M HCl, and electrochemical behavior have been obtained and compared to those of their N-carboxymethyl-armed homologs, Cu-1 and Cu-3. Only the cyclam-based Cu-1 and Cu-2 showed unusually high kinetic inertness towards acid decomplexation. While both of these complexes also exhibited quasi-reversible Cu(II)/Cu(I) reductions, Cu-2 is easier to reduce by a substantial margin of +400 mV, bringing it within the realm of physiological reductants. Similarly, of the cyclen-based complexes, Cu-4 is also easier to reduce than Cu-3 though both reductions are irreversible. Biodistribution studies of (64)Cu-labeled 2 and 4 were performed in Sprague Dawley rats. Despite comparable acid inertness to their shorter-armed congeners, both longer-armed ligand complexes have poorer bio-clearance properties. This inferior in vivo behavior may be a consequence of their higher reduction potentials.

The synthesis of the two digermanes Bu s 3GeGePh3 and PhMe2GeGePh3, as well as the branched tetragermane PhGe(GeBu n 3)3, was achieved using the hydrogermolysis reaction. These species were fully characterized by NMR (1H, 13C) spectroscopy and elemental analysis, and the crystal structure of PhMe2GeGePh3 was determined. These three species, along with 11 other oligogermanes, were also characterized by 73Ge NMR spectroscopy. Chemical shifts of the 73Ge NMR resonances for these oligogermanes have been correlated with the substitution pattern at germanium and also with the number of germanium−germanium bonds at the individual Ge centers. Germanium centers having only one attached germanium atom result in resonances appearing in the range δ −30 to −65 ppm, while those having two or three bonded germanium atoms exhibit resonances in the respective ranges δ −100 to −120 and δ −195 to −210 ppm. Chemical shifts of resonances for germanium centers bearing phenyl substituents appear upfield from those having alkyl substituents.

Ethylene cross-bridged tetraamine macrocycles are useful chelators in coordination, catalytic, medicinal, and radiopharmaceutical chemistry. Springborg and co-workers developed trimethylene cross-bridged analogues, although their pendant-armed derivatives received little attention. We report here the synthesis of a bis-carboxymethyl pendant-armed cyclen with a trimethylene cross-bridge (C3B-DO2A) and its isomeric ethylene-cross-bridged homocyclen ligand (CB-TR2A) as well as their copper(II) complexes. The in vitro and in vivo properties of these complexes are compared with respect to their potential application as 64Cu-radiopharmaceuticals in positron emission tomography (PET imaging). The inertness of Cu-C3B-DO2A to decomplexation is remarkable, exceeding that of Cu-CB-TE2A. Electrochemical reduction of Cu-CB-TR2A is quasi-reversible, whereas that of Cu-C3B-DO2A is irreversible. The reaction conditions for preparing 64Cu-C3B-DO2A (microwaving at high temperature) are relatively harsh compared to 64Cu-CB-TR2A (basic ethanol). The in vivo behavior of the 64Cu complexes was evaluated in normal rats. Rapid and continual clearance of 64Cu-CB-TR2A through the blood, liver, and kidneys suggests relatively good in vivo stability, albeit inferior to 64Cu-CB-TE2A. Although 64Cu-C3B-DO2A clears continually, the initial uptake is high and only about half is excreted within 22 h, suggesting poor stability and transchelation of 64Cu to proteins in the blood and/or liver. These data suggest that in vitro inertness of a chelator complex may not always be a good indicator of in vivo stability.

A Mn4 single-molecule magnet displays asymmetric Berry-phase interference patterns in the transverse-field (HT ) dependence of the magnetization tunneling probability when a longitudinal field (HL) is present, contrary to symmetric patterns observed for HL = 0. Reversal of HL results in a reflection of the transverse-field asymmetry about HT = 0, as expected on the basis of the time-reversal invariance of the spin-orbit Hamiltonian which is responsible for the tunneling oscillations. A fascinating motion of Berry-phase minima within the transverse field magnitude-direction phase space results from a competition between non-collinear magneto-anisotropy tensors at the two distinct Mn sites.

The synthesis of [Mn(4)(anca)(4)(Hmdea)(2)(mdea)(2)].2CHCl(3) (1) is reported along with room temperature fluorescence, UV-vis, and NMR spectra. Direct current magnetization versus field data reveal a S = 8 ground state. Quantized steps in temperature- and field-dependent magnetization versus field hysteresis loops confirm single-molecule magnet behavior.

Two heterometallic [Dy III 6 Mn III 12 ] clusters comprising of the same [Mn III 8 O 13 ] fragment, four isolated Mn III ions and two linear [Dy III 3 ] units have been synthesised. Except for the same composition, the main difference of these two cores lies in the coordination environment and the orientations of the linear [Dy III 3 ] units. This difference leads to an alternation in the symmetry of the two cores that significantly modulates their magnetic properties including ground spin state and slow relaxation behavior.

The syntheses, structures, and magnetic properties of two new single-stranded hexadecanuclear manganese wheels [Mn16(CH3COO)8(CH3CH2CH2COO)8(teaH)12] x 10 MeCN (1 x 10 MeCN) and [Mn16((CH3)2CHCOO)16(teaH)12] x 4 CHCl3 (2 x 4 CHCl3), where teaH(2-) is the dianion of triethanolamine, are reported. 1 crystallizes in the tetragonal I4(1)/a space group [a = b = 33.519(4) A and c = 16.659(2) A]. 2 crystallizes in the monoclinic C2/c space group [a = 21.473(5), b = 26.819(6), c = 35.186(7), and beta = 93.447(5) degrees]. Both complexes consist of 8 Mn(II) and 8 Mn(III) ions alternating in a wheel-shaped topology with 12 monoprotonated triethanolamine ligands. Variable-temperature direct current (DC) magnetic susceptibility data were collected in 1 T, 0.1 and 0.01 T fields, and in the 1.8-300 K temperature range for 1 and 2. Variable-temperature variable-field DC magnetic susceptibility data were obtained in the 1.8-10 K and 0.1-5 T ranges and least-squares fitting of these reduced magnetization versus H/T data indicates a S = 13 ground-state for 1 and 2. Single-crystal magnetization hysteresis measurements were performed in a 0.04-1 K temperature range for complex 2. Hysteresis loops were observed that showed a temperature dependence, which indicates that 2 exhibits magnetization relaxation and is a SMM. Both 1 and 2 show frequency-dependent out-of-phase signals in the AC susceptibility measurements, collected in a temperature range of 1.8-5 K and in the frequency range of 50-10,000 Hz. Extrapolation of the in-phase component of the AC susceptibility data to 0 K indicates an S = 12 ground state for 1 and an S = 11 ground-state for 2. Complex 1 has the highest-spin ground state reported to date for a single-stranded manganese wheel and is likely to be an SMM based on a frequency-dependent out-of-phase signal in the AC susceptibility. The AC susceptibility as well as magnetization hysteresis data for 2 confirm that this species is an SMM.