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Molecular structure of 3 a (hydrogen atoms omitted for clarity (top), ellipsoids set at 50 % probability; selected bond length of 3 a in Å: O1‐B1 1.376, B1‐N1 1.420, N1‐B2 1.444, B2‐N2 1.422, N2‐C1 1.468, C1‐O1 1.430; packing of 3 a (bottom). [20]
