Figure 13.11c shows the solid state structure of the [Al(BH₄)₄]‾ ion, present in [Ph₃MeP][Al(BH₄)₄]. In the light of these structural data, account for the following observations, recorded for the compound in solution. 

(a) At 298 K, the ¹H NMR spectrum of [Ph₃MeP][Al₉BH₄)₄] shows one broad signal in addition to signals assigned to the cation; this pattern of signals is retained at 203 K. 

(b) In the 11B NMR spectrum (298 K) of the same compound, a quintet is observed. 

(c) In the IR spectrum of [Ph₃MeP][Al(BH₄)₄], absorptions due to bridging Al—H—B and terminal B—H interactions are both observed.

Figure 13.11c.

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(c)