Challenging the HSAB principle on molecular machines' precursors

The Hard-and-Soft-Acids-and-Bases (HSAB) principle has been challenged for the first time on molecular machines' precursors, while studying on calixarene-based rotaxane complexes containing tris(N-phenylureido)-calix[6]arene as wheel and a 4,4'-bipyridinium dication's units as axle; The results clearly indicate the invariance of genuine vs. hard and soft acidic - bonding complex with the interlocked molecular system is present in terms of maintaining the chemical reactivity combined pattern of charge exchange, charge tunneling, opening and stabilizing reactivity tendency as provided within the orthogonal chemical space of chemical global indicators - in first (electronegativity and chemical hardness) and second (chemical power and electrophilicity) generations and of their principles, respectively. Moreover, we asses for the first time the molecular machine precursor system with the 3D total charge density isosuface confinement within two ends of 3D electrostatic potentials branches of the optimized interlocked rotaxane system. Further investigations are thus called for best generalizing the present findings.