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Caption : figure s1. powder x-ray diffraction pattern of alloy sc<sub>10</sub>pt<sub>61</sub>b<sub>29</sub> (in at.%) annealed at 780 ºc: upper row of hkl labels corresponds to sc<sub>5</sub>pt<sub>24</sub>b<sub>12</sub>, space group <i>im</i>-3, <i>a</i>=10.21112(9) å; middle row stands for pt<sub>3</sub>b<sub>2</sub>, space group <i>cmcm</i>, <i>a</i>=3.3671(1) å, <i>b</i>=5.7962(2) å, <i>c</i>=4.0565(2) å; lower row represents the phase scpt<sub>3</sub>b<sub>x</sub>, space group <i>pm</i>-3<i>m</i>, <i>a</i>=4.0235(4) å. the excluded region contains a small peak from sample holder.

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Caption : figure s2. polyhedral representation of ce<sub>4</sub>pt<sub>12</sub>sn<sub>25</sub> structure showing [sn<sub>12</sub>] (gold) and [sn<sub>12</sub>pt<sub>6</sub>] (blue) cages capturing sn and ce, respectively (a). linkage of [ptsn<sub>6</sub>] trigonal prisms. for clarity, a half of the unit cell along b is shown (b).

File Name : figure_s3_revised.tif

Caption : figure s3. ellipsoidal model of the sc<sub>5</sub>pt<sub>24</sub>b<sub>12</sub> crystal structure (a) and coordination polyhedra of atoms: sc1 (b), sc2 (c), pt1 (d), pt2 (e) and b1 (f). thermal ellipsoids represent 99.99% probability level.

File Name : figure_s4_revised.tif

Caption : figure s4. ellipsoidal model of the sc<sub>4.9</sub>pt<sub>24</sub>b<sub>12</sub> crystal structure (a) and coordination polyhedra of atoms: sc1 (b), sc2 (c), pt1 (d), pt2 (e) and b1 (f). thermal ellipsoids represent 99.99% probability level.

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Caption : figure s5. polyhedral representation of the yb<sub>3</sub>rh<sub>4</sub>sn<sub>13</sub> structure showing [sn<sub>12</sub>] (gold) and [sn<sub>12</sub>rh<sub>4</sub>] (blue) cages capturing sn and yb, respectively. (a). linkage of [rhsn<sub>6</sub>] trigonal prisms in yb<sub>3</sub>rh<sub>4</sub>sn<sub>13</sub>. for clarity, a half of the unit cell along b is shown (b).

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Caption : figure s6. arrangements of sc-filled [pt<sub>12</sub>] and yb-filled [sn<sub>12</sub>] cubooctahedra in sc<sub>5</sub>pt<sub>24</sub>b<sub>12</sub> (a) and yb<sub>3</sub>rh<sub>4</sub>sn<sub>13</sub> (b) structures respectively.

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Caption : figure s7. arrangements of [fep<sub>6</sub>] octahedra (a) and p<sub>12</sub> icosahedra around la atom (b) in the lafe<sub>4</sub>p<sub>12</sub> structure.

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Caption : figure s8. group-subgroup relationships for the yb<sub>3</sub>rh<sub>4</sub>sn<sub>13</sub> and sc<sub>5</sub>rh<sub>24</sub>b<sub>12</sub> structures.

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Caption : figure s9. distribution of electron localization function in sc<sub>5</sub>pt<sub>24</sub>b<sub>12</sub> in the plane (100) (a). sections of calculated electron localization function in the planes within the [sc2pt<sub>12</sub>b<sub>6</sub>] polyhedron containing the chemical bonds: sc2-pt1, sc2-pt2 and the bonds between platinum atoms (b); sc2-b1, pt1-b1 and pt2-b1 (c). sections of calculated electron localization function visualizing platinum-boron interactions in [bpt<sub>6</sub>] trigonal prism (d).