The kinetics and mechanism of the cesium cation complexation by 5,11,17,23-tetra-p-tert-butyl-25,26,27,28-tetramethoxycalix[4]arene (1) were studied in a 1:1 (v/v) mixture of deuterated chloroform and deuterated acetonitrile using H-1 NMR, Cs-133 NMR, and 2D-EXSY Cs-133 NMR spectroscopy. The results show the formation of 1:1 complexes with the partial cone (pc) and 1,3-alternate (alt,3) conformer of 1. In the latter case, Cs+ is bound asymmetrically to one of the two metal binding sites, composed of two phenolic oxygen and two phenyl groups. The equilibrium association constants are respectively 194 and 33 M-1 at 236 K. In the case of the pc complex Delta H = -14 +/- 1 kJ/mol and Delta S = -12 +/- 4 J/(mol K), while for the alt,3 complex Delta H = -11 +/- 1 kJ/mol and Delta S = -11 +/- 7 J/(mol K). The preferred complexation pathway of Cs+ by 1 follows the complexation by the pc conformer, which can undergo a conformational exchange to the alt,3 conformer, from which Cs+ cannot escape directly with a measurable rate. The activation parameters for the complex formation between solvated Cs+ and the pc conformer and for the exchange between the alt,3 and the pc complexes are Delta H* = 38 +/- 2 kJ/mol and Delta S* = -66 +/- 6 J/(mol K), and Delta H* = 61 +/- -5 kJ/mol and Delta S* = -9 +/- 15 J/(mol K), respectively. H-1 NMR spectroscopy shows that the exchange of Cs+ between the two binding sites of the alt,3 complex proceeds through an interconversion to the pc complex and not through an internal tunneling process of Cs+.