**2. Results and Discussion**

### *2.1. Synthesis and Structural Studies*

Reaction of H4TBC[4] with MnCl2·6H2O, H2bd (1,4-butanediol), [NH4]ClO4, and NEt3 in a mixture of CH3CN and dmf, followed by vapour diffusion of diethyl ether into the mother liquor, afforded single crystals suitable for X-ray diffraction of formula [MnIII8MnII4(<sup>μ</sup>4-O)2(μ3-OH)6(μ-OH)4(μ-Cl)2(TBC[4])4(dmf)8(H2O)4(CH3CN)2]·2dmf·6CH3CN (**1**, Figure 2, please also see Appendix A). The crystals were found to be in a triclinic cell, and structure solution was carried out in the space group *P*-1, with the asymmetric unit (ASU) comprising half of the cluster (Mn1–Mn6, Figure 3). Before moving to the structural description of **1**, it is interesting to note that inspection of Figure 2 shows that 1,4-butanediol is not incorporated in the prevailing structure. Our original intention was to form a heteroleptic TBC[4]-diol cage, and although 1,4-butanediol is not incorporated, its presence in the reaction mixture is required for **1** to form. Indeed, analogous experiments in the absence of diol result in the formation of the well-known TBC[4]-supported [MnIII2MnII2] cluster topology shown in Figure 1B; this particular cluster can be isolated quantitatively in under 1 h, further indicating that the diol plays a crucial role in the formation of **1**.

**Figure 2.** Partial single crystal X-ray structure of **1**. Colour code: MnIII—purple; MnII—pale blue; O—red; C—grey; Cl—green; ligated dmf—orange sphere. *<sup>t</sup>*Bu groups, hydrogen atoms, solvent of crystallization and atoms other than oxygen of ligated dmf are omitted for clarity.

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**Figure 3.** Partial single crystal X-ray structure of **1** showing the asymmetric unit with selected labels shown. Colour code: MnIII—purple; MnII—pale blue; O—red; C—grey; Cl—green; dmf—orange. *<sup>t</sup>*Bu groups, hydrogen atoms, and solvent of crystallization omitted for clarity. Two s.e. atoms (O12 and O13) are included in order to show the octahedral coordination sphere around Mn4.

The central metal–oxygen core of **1** describes a near-planar, mixed-valent [MnIII6MnII4(<sup>μ</sup>4-O)2(μ3-OH)6(μ-OH)4(Cl)2] sheet-like structure (Figures 2 and 4). The MnIII ions in **1** (Mn1, Mn2, Mn4, and symmetry equivalent, s.e.) are easily distinguished through the presence of coparallel Jahn-Teller (JT) axes, oriented approximately 40◦ from the plane of the metal ions. The two Cl ions (Cl1 and s.e.) bridge between neighbouring MnII ions (Mn3-Cl-Mn5 and s.e., 86.21◦). Mn1 (and s.e.) is bound in a TBC[4] lower-rim tetraphenolato pocket (Mn1-O1-4, with bond distances in the range of 1.882(2)–1.973(2) Å), with its distorted octahedral geometry completed by a ligated dmf molecule residing within the TBC[4] cavity (Mn1–O18, 2.271(3) Å), and a μ3-OH (Mn1–O9, 2.216(2) Å) that also bridges Mn2 and Mn3 (Mn2–O9, 1.931(2) Å and Mn3–O9, 2.209(3) Å). The remaining MnIII ion (Mn6 and s.e.) is also bound within a TBC[4] lower-rim tetraphenolato pocket (Mn6-O5-8, with bond distances in the range of 1.930(2)–1.948(2) Å) sitting above/below the [Mn10] plane (Figure 2), bonded to Mn2 and Mn4 (and s.e.) through a <sup>μ</sup>4-O2- ion (Mn6–O13, 2.144(2) Å). Each of these O-atoms is H-bonded to a bridging hydroxide in the [Mn10] plane (O···O, 2.643–2.870 Å).

**Figure 4.** The near-planar, mixed-valent [MnIII6MnII4(<sup>μ</sup>4-O)2(μ3-OH)6(μ-OH)4(Cl)2] sheet-like structure at the core of complex **1**. Colour code: MnIII—purple; MnII—pale blue; O – red; Cl—green; dmf—orange. Carbon, nitrogen and hydrogen atoms, as well as solvent of crystallization omitted for clarity.

Interestingly, Mn6 (and s.e.) is formally five-coordinate and in square-pyramidal geometry (Figure 3), with the CH3CN molecule occupying the TBC[4] cavity and interacting with the Ph rings through CH···<sup>π</sup> interactions. We have observed such behaviour in other TBC[4]-supported Mn cages [25], and this is also reminiscent of the host-guest chemistry found in the CH3CN solvate of TBC[4] (Figure 1a) [12]. The preference of the TBC[4] ligands to host MnIII ions over MnII ions in **1** is entirely consistent with our previously published empirical binding rules for this ligand [17].

One of the goals behind our use of C[*n*]s in cluster synthesis is to isolate or 'dilute' these species in the solid state. This has been achieved efficiently in the formation of **1**, with TBC[4]s protecting the cluster core (Figure 5). The closest intermolecular interactions found between s.e. of **1** in the extended structure occur between Cl ions at a Cl···Cl distance of ~3.3 Å, and between dmf molecules at an N···O distance of ~3.6 Å, directing chains of [Mn12] cages along the *a*-axis of the cell. Inspection of Figure 5 and comparison with Figure 1A shows similar assembly behaviours despite the fact that the overall shape of **1** is markedly different to that of the parent H4TBC[4]. The 'coating' of **1** with [MnIIITBC[4]]− capping moieties results in head-to-head packing dominated by the calixarenes. This is another common structural trend that is emerging as this work progresses, another example being that trigonal planar enneanuclear [CuII9] clusters adapt to display similar packing behaviour in sheets, even though the clusters are unable to form the typical bi-layers. Interestingly, the metal–oxygen core present in **1** (Figure 4) is reminiscent of a portion of the Brucite ([Mg(OH)2]) lattice, and is similar to that observed in [Mn6–12] "rods" built with the tripodal alcohol ligands H3thme (1,1,1-tris(hydroxymethyl)ethane) and H3tmp (1,1,1-tris(hydroxymethyl)propane) [26], and to the [MnIII6MnII4] "planar discs" built with the ligands 2-amino-2-methyl-1,3-propanediol (ampH2) and 2-amino-2-ethyl-1,3-propanediol (aepH2) [27].

**Figure 5.** Extended structure of **1** looking down the *a*-axis. Packing of neighbouring clusters is dominated by TBC[4]s, which mimic head-to-head dimer assembly akin to that shown for the CH3CN solvate of H4TBC[4] in Figure 1a [12]. Colour code: MnIII—purple polyhedra; MnII—pale blue polyhedra; O—red; C—grey; hydrogen atoms, solvent of crystallization and ligated solvent omitted for clarity.
