This construct A = {{IdentityMatrix[n], a, 0},{-IdentityMatrix[n], 0, b}} can not be transposed because it is not rectangular. Even the transformation behaviour of the elements in one super-row, i.e. {matrix, vector, scalar} does not fit. All this does not fit into the framework of multi-linear algebra. If A is intended as block matrix, then the vector a and the scalar 0 must be replaced by matrix blocks.
