The preparation and magnetic properties are reported for [Cu2(tren)2(bridge)](004)4, where the bridge is either pyrazine (pyz) or l,4-diazabicyclo[2.2.2]octane (Dabco), and [Cu2(tren)2(bridge)](BPh4)4, where the bridge is either 4,4'bipyridine (4,4'-bpy) or 1,2-bis(4-pyridyl)ethylene (BPE). Only the pyrazine complex shows signs of an antiferromagnetic exchange interaction in magnetic susceptibility data taken down to 4.2 K. In this complex, the interaction is weak with J = -3.2 cm-1, in spite of the fact that the two Cu(tren)2+ units have their dz2 orbitals in which the unpaired electrons reside pointing directly into the nitrogen lone-pair orbitals of the pyrazine. The Cu-tren-BPE complex does show evidence of a very weak (0.02 cm""1 < ]T| < ~0.5 cm-1) exchange interaction with the appearance of a seven-line copper hyperfine pattern in its Qband EPR spectrum. The magnetic susceptibility vs. temperature curve for the potentially polymeric compound [Cu(pyz)2]-(C104)2 shows a maximum at 12.1 K. The complex [VO(hfac)2]2B with B = Dabco does not show any signs of an exchange interaction in magnetism data taken to 4.2 K, but when B is either pyz, 2-Me-pyz, or 2,5-Me2-pyz, there is a maximum in the susceptibility vs. temperature curves at 31.5, 12.1, and 7.0 K, respectively. The data for these last three binuclear vanadyl complexes were fit to give J = -19, -6.7, and -4.0 cm""1. It is suggested that the pyrazine bridges in these vanadyl complexes are bridging between equatorial sites. From the work on the copper(II) and vanadyl complexes, it is concluded that pyrazine (or Dabco) is not a very good bridge for propagating an exchange interaction between two metal ions with ground states, or, for that matter, between two metal ions with tt ground states. The formation constants K\ and K2 for binding to pyrazine one or two VO(hfac)2 complexes to form VO(hfac)-pyz or [VO(hfac)]2-pyz were determined to be K\ =* 1.5 X 106 M-1 and A2 =* 2.0 X 103 M-1, respectively.

is that L~(~-B U O )~A I H~, Li(t-BuO),AIH, and LiA1H4 are in slow equilibrium according to eq 2. Confirmation of this suggestion was sought by approaching the equilibrium from the opposite direction. If this equilibrium is present, one should be able to start with a solution of Li(t-BuO),AIH and add LiA1H4 to reestablish the equilibrium. Spectrum G in Figures 2-4 was obtained in just such a manner. To a solution of Li(t-BuO),AIH (spectrum E in Figures 2, 4, and 5) was added a solution of LiA1H4 so that the new molar ratio was 1.7. Note that in the 27Al spectrum ( Figure 2) the broad singlet -21.9 ppm from LiAIH4 is gone and that in the I3C spectrum ( Figure 4) the singlet for Li(t-BuO),AIH is nearly gone while the singlet for L~(~-B U O )~A I H~ has reappeared.From the ratio of the integrated areas of the methyl singlets in the I3C spectrum one can obtain the ratio Rc:The 27Al spectra of solutions containing tert-butyl alcohol/LiA1H4 molar ratios between 0.5 and 2.0 consist of a broad singlet due to L~(~-B U O )~A I H~ and Li(t-BuO),AIH with a quintet from LiAIH4 imposed upon it. Using the instruments computer, one may subtract the LiAIH4 quintet from the spectra to obtain just the broad singlet whose area is proportional to the concentration of Li(t-BuO),A1H2 plus Li(t-BuO),AIH; the resulting broad singlets are shown in Figure 3. In this way one may determine the ratio RAI: [LiAIH,] [ L~(~-B U O )~A I H~] + [ Li(t-BuO),AIH] = RAl (4) Together, these ratios allow the calculation of the equilibrium constant [Li( t-BuO),AIH] 2[LiA1H4] [Li( ~-B U O )~A I H~] K , = (5) K , = ( 3 / 2 R~)~R~1 ( 3 / 2 & -I-1) Combining eq 3-5 one can obtain ( 6 )The data in Table I indicate an equilibrium constant of 2.2 X lo-'. Con c 1 us i o n sWe find that for molar ratios for tert-butyl alcohol/LiAIH, up to 2 the major tert-butoxyaluminate in solution is Li(t-B U O )~A I H~ and that it is in a slow equilibrium with LiA1H4 and Li(t-BuO),AIH. If Li(t-BuO)AIH, is present, its concentration must be low compared to the Li(t-BuO)2A1H2 concentration.Clearly the tert-butoxyaluminate system is not as simple a system as some have thought it to be.Acknowledgments. The support of the Department of Chemistry at The University of Toledo is gratefully acknowledged. We thank Professors J. Fry and J. Gano for helpful discussion.Abstract: In this article the equilibrium constant and enthalpy for formation of the dioxygen adduct of the bis(sa1icyliden-iminato-3-propyl)methylaminocobalt(II) complex (CoSMDPT) are reported in methylene chloride solution (-9.8 kcal mol-'). When small amounts of 2,2,2-trifluoroethanoI (TFE) are added, extra stabilization of the dioxygen adduct is found. The measured enthalpy for adduct formation increases to -1 1.8 kcal mol-'. Infrared frequency shift studies of the 0-H stretching vibration indicate that TFE undergoes a hydrogen-bonding interaction with the coordinated dioxygen. An enthalpy-frequency shift, AuOH, relation provides an estimate of a 6.6 kcal mol-' hydrogen bond strength. This is one of the few instances i...

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Die Cu‐Komplexe (I) werden durch die Umsetzung entsprechender Cu(II)‐Salze mit dem Tripodliganden und den NN‐Liganden dargestellt.

Die Gleichgewichtskonstante und die Bildungsenthalpie des Disauerstoffadduktes des Co‐Komplexes (I) mit dem linearen fünfzähnigen Schiffbasenliganden werden in Methylen‐ Chlorid mitgeteilt.