The chemical structures of reactants and reaction path are shown in Figure 2. All three materials used for synthesis of the supramolecular complex were purchased from commercially: C-Methylcalix[4]resorcinarene (CMCR, Sigma-Aldrich, purity > 90.0%), 4,4'-Bipyridine (BPY, Tokyo Chemical Industry, purity > 98.0%), Benzophenone (BZP, purity > 99.0%, Tokyo Chemical Industry). Measured melting point of these compounds are as follows: BZP = 48˚C, BPY = 111˚C, CMCR > 300˚C (unmeasurable caused by decomposition and/or sublimation above 300˚C). The values of the melting points are important in this manuscript.

Before the synthesis of the supramolecular complex, the three reactant substances, CMCR, BPY, BZP, were ground separately using a mortar and pestle in order for the increase of reaction surface in the next step of the experiment. The ground reactants were weighed (CMCR:BPY:BZP = 1:2:1 in molar ratio) and mixed gently to avoid reaction caused by friction. Then the physical mixtures of the powder was set on a heating device and the

synthesis experiments were started by increase the temperature up to 120˚C. During the temperature increase, state of the powder samples were observed using an optical microscope. After the experiments, structures of the resulting powder samples were analyzed.

Heating device used is a melting point measuring instrument (Type ATM-01), AS ONE Co.). Structure of the product crystals were characterized by XRD (RINT-2000, Rigaku,: CuKα), FT-IR (4200-type A, JASCO), TOF- SIMS (ULVAC Inc.).

By heating (from room temperature to 120˚C) the physical mixtures of CMCR/BPY/BZP powders, some changes were recognized as shown in Figure 3. Initially, CMCR/BPY/BZP were homogeneously mixed in 1:2:1 molar ratio (Figure 3(a)). With an increase of the temperature, some part of the powders were changed as shown by red circle in Figure 3(b). Melting of BPY and BZP with lower melting point must occur partially. Further increase of the temperature, the melted areas were developed as shown in Figure 3(c) and new solid phase was appeared as shown by yellow circle in Figure 3(d).

In order to identify the structure of the resultant samples, powder XRD were measured (Figure 4). Though the experiment was started using physical mixtures of CMCR/BPY/BZP, the resulting XRD pattern (red line) is much different from these reactants (black patterns CMCR, BPY, BZP from the bottom). Rather the red line is good agreement with the theoretical pattern of CMCR・2BPY・BZP calculated using the single crystal structure data [3] . FT-IR measurements of the product showed shift of stretching vibration bands of hydroxyl groups from 3245 cm⁻¹ (for pure CMCR) to 3316 cm⁻¹, suggesting formation of hydrogen bonds between CMCR and BPY ligands. In addition TOF-SIMS measurements also showed the physical mixtures were changed to homogeneously mixed new compound. From these comparison results, it may be concluded that CMCR・2BPY・BZP must be synthesized just by heating the physical mixture of the three reactants.

Here we want to point out another interesting point found in Figure 3. The reaction temperature in Figure 3 was

up to 120˚C which is much lower than melting point of CMCR (>300˚C). However, the reaction occurred. We are very interested in the reaction mechanism in such a “heterogeneous system”. DidBPY/BPZ (melt) diffuse into the solid CMCR? To confirm this, additional experiment was performed. As shown in Figure 5(a), single crystal of CMCR (indicated by blue arrow) was prepared and powder mixture of BPY/BZP (shown by red arrow) was put onto it. With the elevation of temperature, BPY/BZP was started to melt at 40˚C as indicated by yellow arrow in Figure 5(b) and morphology of the CMCR crystal was slightly changed (Figure 5(c) and Figure 5(d)). In Figure 5(e), outline of the CMCR crystal became unclear and crystalline state was changed drastically later (Figure 5(f) to Figure 5(i)). After the time shown by Figure 5(j), the melt disappeared while new solid phase appeared as shown by black arrow in Figure 5(l). From this experiment, disappearance of the CMCR is evident, suggesting the dissolution of CMCR into the BZP/BPY melt. For further confirmation of dissolution of the CMCR crystal into BPY/BZP melt, additional experiment was performed (Figure 6). In Figure 6, CMCR crys-

tal was set directly into BPY/BZP melt. As can be seen in Figure 6, CMCR crystal dissolved into the melt. From these results, our proposed method, solventless synthesis just by giving a slight heat, may be applied for even for heterogeneous system in which one of reactants is high melting point compound.

Although many cases of organic supramolecular complex synthesized by mechanochemical method are reported [1] , our method proposed in this study must be the most simple. Only a slight heat is essential point for occurrence of complex formation without solvent. For mechanochemical synthesis, heat generated by friction may cause the partial melting result in easiness of movement of molecules and occurrence of reaction. So the melting is essentially important for the reaction. In other words, even an enough heat is given, reaction may occur. Thus, the methodology proposed in this study is not limited to grinding and/or direct heating, even if enough energy may be added to the reaction molecules. Addition of such as microwave, ultrasound is next candidates for the heat sources.