Charge Distribution and Structure of Complexes MeIGaCl4, MeIGa2Cl7, and KAl2Br7 (MeI = Na⊕, K⊕, Rb⊕, Cs⊕, Ga⊕). An NQR Investigation (35Cl, 69Ga, 81Br)

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Abstract35Cl and 69GaIII NQR frequencies are reported for MeGa2IIICl7 (Me = Na, K, Rb, Ga1) together with the 35Cl NQR frequencies for MeGaIIICl4 (Me = Na, K, Rb, Cs, Ga1), and the 81Br and 79Br NQR frequencies for KAl2Br7. Most of the corresponding 37Cl and 71GaIII resonances in MeGa2Cl7 are reported too. With the exception of RbGaCl4 and CsGaCl4 all NQR investigations were done as a function of the temperature.The complexes MeGa2Cl7 show seven 35Cl and two 69Ga NQR lines each. From the 35Cl NQR spectra it is concluded that the ion (Ga2Cl7)⊕ has a bridged structure analogous to the ions (Me2X7)⊕ in KAl2Br7 and Te4(Al2Cl7)2. Six of the 35Cl resonances are assigned to crystallographically inequivalent terminal Cl atoms, the seventh 35Cl resonance showing a low frequency shift is assigned to the bridging Cl atom. The charge distribution of the ion (Ga2Cl7)⊕ was estimated within the frame of the Townes‐Dailey theory. The selfconsistency of the calculations is satisfactory.For two compounds, CsCl · xGaCl3 and RbCl · yGaCl3, investigated by NQR spectroscopy, no definite structural proposals are available up to now.From the 81Br NQR spectrum of KAl2Br7 no assignment either to terminal Br atoms or to the bridging Br atom is possible. A small degree of (p → d)π character involving the terminal AlBr bonds is considered a conceivable explanation.From the 35Cl NQR spectra in KGaCl4 and GaGaCl4 polymorphism is found. The transformation to the high temperature phase in either complex is accompanied with a lowering of symmetry of the GaCl4 tetrahedra and an increase of the crystal field splitting. This finding is in qualitative agreement with a decrease in volume on changing to the high temperature phase.