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(MDABCO(+))(C60(·-))(TPC) (1), in which MDABCO(+) is N-methyldiazabicyclooctanium, TPC is triptycene, and both have threefold symmetry, is a rare example of a fullerene-based quasi-2D metal and contains closely packed hexagonal fullerene layers with interfullerene center-to-center distances of 10.07 Å at 300 K. Evidence for the metallic nature of 1 was obtained by optical and microwave conductivity measurements on single crystals. The metal is characterized by a nontypical Drude response and relatively large optical mass (m*/m0 =6.7). The latter indicates a narrow-band nature, which is consistent with the calculated bandwidth of 0.10-0.15 eV. The coexistence of metallic and antiferromagnetic nonmetallic 2D layers was observed in 1 above 200-230 K. It was assumed that the nonmetallic layers undergo a transition to the metallic state below 200 K due to ordering of the fullerene and cationic sublattices. New layered complex (MQ(+))(C60(·-))(TPC) (2) with a hexagonal arrangement of C60(·-) was obtained by increasing the interfullerene distance with the bulkier N-methylquinuclidinium cations (MQ(+)) having threefold symmetry. The structure of 2 is characterized by increased interfullerene center-to-center distances in the layers (10.124, 10.155, and 10.177 Å at 250 K). Unit-cell doubling parallel to the 2D layer (along the b axis) was observed at low temperatures. In contrast to metallic 1, 2 exhibits a nonmetallic spin-frustrated state with an antiferromagnetic interaction of spins (the Weiss temperature is -27 K) and no magnetic ordering down to 1.9 K. It was supposed that the expanded interfullerene distances in the triangular arrangement decrease the bandwidth and suppress metallic conductivity in 2, and thus a Mott-Hubbard insulating state with antiferromagnetically frustrated spins results.

Oxidation of {cryptand(Na + )}(C 60 *-) and {cryptand(Na + )} 2 (C 60 2 À ), which display integer À 1 and À 2 charges on the fullerene unit, by iron(II) octaethyltetrapyrazinoporphyrazine allowed the crystallization of complexes with noninteger average charges on C 60 . The complex {cryptand(Na + )}(C 60 ) 3 -·2C 6 H 4 Cl 2 (1), with a partial charge of -0.33 on C 60 , exhibits a closely-packed 3D structure formed by fragments of hexagonal fullerene layers. Complex 1 shows high conductivity in the 295-120 K range: conductivities of 50-60 and 100-250 S·cm À 1 were measured using four-probe and microwave techniques, respectively. Metallic behavior of 1 is observed down to 150-120 K. Metallic conductivity is still observed in 1 after one month of exposure to air. The complexes {cryptand(Na + )}(C 60 ) 2 À (2) and {cryptand (Na + )} 8 (C 60 ) 6 8 À (3), which display average charges of À 0.5 and À 1.33, respectively, on C 60 , do not show metallic conductivity. This can be explained by charge disproportionation and the formation of neutral and À 1-charged C 60 in 2, and À 1-and À 2-charged C 60 in 3. Despite the close packing of the fullerene molecules in crystal structures, no dimerization of C 60 is observed in 1 and 2. On the contrary, diamagnetic, singly-bonded (C 60 À ) 2 dimers are formed in {cryptand(Li + )} 2 (C 60 À ) 2 ·C 6 H 4 Cl 2 ·C 6 H 14 (4), which contains fullerene molecules bearing a full À 1 charge.[a] Dr.

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YBa 2 Cu 3 O 7 epitaxial film quality has reached a stage where rf applications at T⩽80 K are carried through. Higher-operating temperatures or better power handling are very much desired. Tl2Ba2CaCu2O8 (TBCCO) is an excellent candidate with its higher-transition temperature Tc≈100–105 K. We study the rf field dependence of surface impedance Zs of epitaxial TBCCO films using dielectric resonators with TE011-modes at 8.5 and 15.3 GHz at 4.2 K<T<100 K and at 0.01 mT⩽Hrf⩽10 mT in the frequency and time domain. High-quality films show surface resistances at low fields Rs(77 K) superior to YBCO and promising power handling with a nonlinearity onset above turn-up field μ0H*⩾3 mT. Defective TBCCO films show anomalous nonlinear behavior δRs(Hrf)∝√Hrf for μ0Hrf⩽μ0H*∼0.3–1 mT, extremely pronounced at T<40 K, indicating the presence of very weak links yielding flux flow, followed at higher fields μ0Hrf≳0.5 mT by hysteresis losses with a linear field dependence δRs(Hrf)∝Hrf. Better quality TBCCO films show δRs(Hrf)∝Hrf2 up to fields of about 5–10 mT. The δRs(Hrf)∝Hrfn (n=1,2) dependencies together with ratios r(T)=δXs/δRs∼1–10 hint to hysteresis losses of Josephson fluxons enhanced by slits or holes in the films.