We present the results of magnetic-susceptibility, heat-capacity, electrical-resistivity, and thermoelectric-power measurements on La2Cu04 -. The crystallographic, magnetic, and electronic transport properties are found to be extremely sensitive to the oxygen-defect concentration y. Coupled with x-ray and neutron-difI'raction data presented in a companion paper, we find that long-range antiferromagnetic order develops with increasing y out of a nonmagnetic ground state at y=0 into a state with a maximum Neel temperature of 290 K at y=0.03.La2Cu04y is the parent compound of the doped high-temperature (T, (40 K) superconductors La2 (Sr, Ba)"Cu04~with x = 0.2. ' lt has a roomtemperature structure which is an orthorhombic distortion of the tetragonal K2NiF4 structure.The latter structure is regained upon heating above a transition temperature Tp of 506-536 K; the variation in Tp is thought to arise from differences in y between different samples, but a quantitative correlation has not before been established. The low-temperature structure and the temperature dependence of the orthorhombic distortion parameter have recently been studied using neutron diffraction. The electrical resistivity p and thermoelectric power S of sintered samples are nearly independent of temperature from 100-1100 K, ' but the carriers appear to localize at lower temperature T. ' ' A large scatter of unknown origin is present in the reported room-temperature S values (100-500 pV/K). Measurements of the magnetic susceptibility Z(T) have revealed peaks between 220 and 280 K in some samples of La2Cu04 -[Refs. 7(a), 10, 13-16] but not in others, ' which is another discrepancy of unknown origin. The X peak has variously been deduced to arise from a smooth vanishing of localized magnetic moments with decreasing T (Ref. 10) or from the occurrence of an antiferromagnetic (AF) or spin-densitywave transition; ' ' the T at which the anomaly occurs depends on the details of sample preparation and handling.We have carried out a series of experiments to clarify the physical properties of pure La2Cu04y as a starting point to understand and differentiate between various microscopic mechanisms for the occurrence of high-T superconductivity in the Srand Ba-doped compounds. Herein, we report the results of Z(T), heat-capacity, p(T), and S(T) measurements which establish that the crystallographic, magnetic, and electronic transport properties are extremely sensitive to the concentration of oxygen defects y in La2Cu04 -.' This sensitivity provides one explanation for the discrepancies noted above. Perhaps our most interesting results are that, in conjunction with companion x-ray and neutron-diffraction results, the X peak above is indeed due to long-range AF order, and that this order develops with increasing y out of a nonmagnetic ground state for y =0 into a state with a maximum Neel tempera-

Data on the preparation, structure, and magnetism of the new complex [Cr 4 S(O 2 CCH 3 ) 8 (H 2 O) 4 ](BF 4 ) 2 ⋅H 2 O are presented. The metal-sulfur M 4 S core structure is similar to that found in M 4 S[S 2 As(CH 3 ) 2 ] 6 (where M is cobalt or zinc) compounds and in beryllium basic acetate. However, the six-coordinate metal ions in the new Cr 4 S system distinguish it from these structures. The tetranuclear chromium complex is the first example of a new structural type. Its magnetic spin S = 6 ground state, a striking example of intramolecular ferromagnetic coupling, was determined by variable-temperature magnetic susceptibility measurements. Long-range antiferromagnetic intercluster ordering was found below 170 millikelvin.