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Abstract We present an interesting relationship between the orthogonality catastrophe (OC) and the quantum speed limit (QSL) for a spin chain with uniform nearest neighbour couplings perturbed by an impurity spin. We thoroughly study the catastrophic QSL that specifies a bound on the evolution time between the initial and final states and in this respect, link it to the emerging OC effect. It is found that the speed of state evolution subtle but fundamental, and the bound characterized by QSL shows the same behaviours as the OC effect in the thermodynamic limit. It allows us to reveal some universal properties, in particular finite temperature effects. Significantly, the threshold of temperature and system size is clearly demonstrated for the QSL under finite temperature.

In the molecule of the title compound, C22H22ClN3O2, the three fused rings of the benzofuro[3,2-d]pyrimidine system are almost coplanar. This ring system is oriented with respect to the substituted benzene ring at a dihedral angle of 79.05 (3)°. Intramolecular C—H...N hydrogen bonding results in the formation of a six-membered ring. In the crystal structure, π–π stacking interactions involving the furan, pyrimidinone and benzene rings are present [centroid-to-centroid distances in the range 3.258 (1)–3.870 (1) Å].

The asymmetric unit of the title compound, C22H16ClN3O5, consists of two crystallographically independent molecules. The fused rings of the imidazo[1,2-a]benzo[4,5]furo[3,2-d]pyrimidine system are nearly coplanar and the chlorophenyl rings are twisted with respect to the two pyrimidinone ring systems by 71.00 (2) and 62.59 (2)°. The C atoms of the ethyl side chain are disordered and were refined using a split model. In the crystal structure, the molecules are connected via weak intra- and intermolecular C—H...O interactions are present. The ethyl group in one molecule is disordered over two positions, with site occupancy factors 0.55 and 0.45; in the other molecule only the methyl group is disordered over two positions, with site occupancy factors 0.6 and 0.4.