A 3.6 nm Ti52-Oxo Nanocluster with Precise Atomic Structure

Supporting Information for: A 3.6 nm Ti52-Oxo Nanocluster with Precise Atomic Structure Wei-Hui Fang, Lei Zhang* and Jian Zhang* State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China. Corresponding Author *E-mail: LZhang@fjirsm.ac.cn; zhj@fjirsm.ac.cn Content Materials and Instrumentation.... S2 Figure S1 The EDS spectrum of compound COM-1.... S4 Figure S2 The EDS spectrum of compound COM-2.... S4 Figure S3 The EDS spectrum of compound COM-3.... S4 Figure S4 The IR spectrum of COM-1.... S5 Figure S5 The IR spectrum of COM-2.... S5 Figure S6 The IR spectrum of COM-3.... S5 Figure S7 The TGA curve of COM-1.... S6 Figure S8 The TGA curve of COM-3.... S6 Figure S9 The PXRD of the simulated and experimental patterns of COM-1.... S6 Figure S10 The PXRD of the simulated and experimental patterns of COM-3.... S7 Figure S11 ORTEP of COM-1 (left) and only the metal oxide core (right).... S7 Figure S12 ORTEP of COM-2 (left) and only the metal oxide core (right).... S7 Figure S13 ORTEP of COM-3 (left) and only the metal oxide core (right).... S8 Table S1 Bond valence sum (BVS) analysis [a] for COMs.... S8 Table S2 Selected bond lengths (Å) for COMs.... S11 Figure S14 The packing view of COM-1 along with the [100], [010], and [001] direction... S15 Figure S15 The Ti 17 structural comparison between literature 4 and COM-2 herein.... S15 Figure S16 The packing view of COM-2 along with the [100], [010], and [001] direction.... S15 Figure S17 The packing view of COM-3 along with the [100], [010], and [001] direction.... S16 Figure S18 Comparisons of the reported Ti 34 (top left), Ti 42 (top right) and Ti 52 herein (bottom).... S16 Figure S19 Representation of the assembly of the boat-like Ti 26 moiety in COM-3.... S16 Figure S20 The linear fit of the H 2 generation of COM-1.... S17 Figure S21 The linear fit of the H 2 generation of COM-3.... S17 Figure S22 Recycling water-splitting H 2 evolution tests under UV-visible light illumination on COM-1.... S17 Figure S23 FTIR of recycled COM-1.... S18 Figure S24 FTIR of recycled COM-3.... S18 Figure S25 TEM (left) and High-resolution TEM (right) micrographs of COM-3.... S18 Figure S26 Diffuse reflectance spectra of COM-1 and COM-3..... S18 Figure S27 ESI-MS spectra of the synthetic reactions for COM-1 (black), COM-2 (red) and COM-3 (blue)... S19 Figure S28 ESI-MS spectra of the synthetic reaction for COM-1 (red) and toluene solution of pure crystals of COM-1 (black)..... S19 Figure S29 ESI-MS spectra of the synthetic reaction for COM-3 (red) and toluene solution of pure crystals of COM-3 (black)..... S20 Figure S30 ESI-MS spectrum of toluene solution of pure crystals of COM-3..... S20 Figure S31 Chemical stability tests of COM-1, including the photos and PXRD patterns of samples treated in different conditions..... S20 Figure S32 Chemical stability tests of COM-3, including the photos and PXRD patterns of samples treated in different conditions..... S21 References... S21 S1

Experimental Section Materials and Instrumentation. The energy dispersive spectroscopy (EDS) analyses of single crystals were performed on a JEOL JSM6700F field-emission scanning electron microscope equipped with a Oxford INCA system. Elemental analysis was measured on a Vario MICRO Elemental Analyzer instrument. IR spectra (KBr pellets) were recorded on an ABB Bomem MB102 spectrometer over a range 400-4000 cm -1. The thermogravimetric analyses (TGA) were performed on a Mettler Toledo TGA/SDTA 851e analyzer in air atmosphere with a heating rate of 10 o C/min from 30 o C to 600 o C. Powder X-ray diffraction (PXRD) data were collected on a Rigaku Mini Flex II diffractometer using CuKα radiation (λ = 1.54056 Å) under ambient conditions. The UV diffuse reflection data were recorded at room temperature using a powder sample with BaSO 4 as a standard (100% reflectance) on a PerkinElmer Lamda-950 UV spectrophotometer and scanned at 200-800 nm. The absorption data are calculated from the Kubelka-Munk function, (F(R) = (1-R) 2 /2R), 1 where R representing the reflectance. Transmission electron microscopy (TEM) images and high-resolution transmission electron microscopy (HRTEM) images were obtained on a Tecnai G2 F20 field emission transmission electron microscope at an accelerating voltage of 200 kv. The powder sample was dispersed in ethanol and a drop of the slurry was placed onto a TEM grid. ESI-MS was carried out on Impact II UHR-TOF (Bruker). Chemicals and Materials All reagents were purchased commercially and used without further purification. Tetraisopropoxytitanium and 1,2-benzenedicarboxylic acid were purchased from Adamas-beta, while isopropanol, propionic acid were acquired from Sinopharm Chemical Reagent Beijing. Synthesis of Ti 6(μ 3-O) 4(BDC) 2(PA) 2(OiPr) 10 (COM-1) A mixture of tetraisopropoxytitanium (0.92 ml, 3.0 mmol), 1,2-benzenedicarboxylic acid (0.166 mg, 1.0 mmol), propionic acid (0.50 ml, 0.69 mmol) and isopropanol (10 ml) was sealed in a 20 ml vial and transferred to a preheated oven at 80 o C for 3 days. When cooled to room temperature, colorless crystals of COM-1 were obtained (yield: 70% based on Ti(OiPr) 4). The crystals are rinsed with isopropanol and preserved under a sealed and dry environment. Synthesis of Ti 17(μ 2-O) 2(μ 3-O) 18(μ 4-O) 2(PA) 8(OiPr) 16 (COM-2) A mixture of tetraisopropoxytitanium (0.92 ml, 3.0 mmol), propionic acid (0.50 ml, 0.69 mmol) and isopropanol (10 ml) was sealed in a 20 ml vial and transferred to a preheated oven at 80 o C for 3 days. When cooled to room temperature, colorless crystals of COM-2 were obtained (yield: 7% based on Ti(OiPr) 4). The crystals are rinsed with isopropanol and preserved under a sealed and dry environment. Synthesis of Ti 52(μ 2-OH) 2(μ 2-O) 16(μ 3-O) 48(μ 4-O) 8(PA) 34(OiPr) 28 (COM-3) A mixture of tetraisopropoxytitanium (0.92 ml, 3.0 mmol), propionic acid (0.50 ml, 0.69 mmol) and isopropanol (5 ml) was sealed in a 20 ml vial and transferred to a preheated oven at 80 o C for 4 days. When cooled to room temperature, colorless crystals of COM-3 were obtained (yield: 30% based on Ti(OiPr) 4). The crystals are rinsed with isopropanol and preserved under a sealed and dry environment. S2

General Methods for X-ray Crystallography. Crystallographic data of COM-1 were collected on a Mercury single crystal diffractometer equipped with graphite-monochromatic Mo Kα radiation (λ = 0.71073 Å). While crystallographic data of COM-2 and COM-3 were collected on Supernova single crystal diffractometer equipped with graphite-monochromatic Cu Kα radiation (λ = 1.54178 Å) at room temperature. The structures were solved with direct methods using SHELXS-97 2 and refined with the full-matrix least-squares technique based on F 2 using the SHELXL-97. 3 Non-hydrogen atoms were refined anisotropically, and all hydrogen atoms bond C were generated geometrically. Crystal data for COM-1: C 52H 88O 26Ti 6, M = 1416.44, triclinic, a = 10.649(10) Å, b = 12.774(12) Å, c = 13.552(13) Å, α = 95.684(4) o, β = 101.803(15) o, γ = 100.819(17) o, V = 1754(3) Å 3, T = 293(2) K, space group P-1, Z = 1. 20118 reflections measured, 7953 independent reflections (R int = 0.0481). The final R 1 values were 0.0746 (I > 2σ(I)). The final wr(f 2 ) values were 0.2122 (I > 2σ(I)). The final R 1 values were 0.1174 (all data). The final wr(f 2 ) values was 0.2410 (all data). The goodness of fit on F 2 was 1.094. Crystal data for COM-2: C 72H 152O 54Ti 17, M = 2695.73, triclinic, a = 13.5955(5) Å, b = 17.6692(6) Å, c = 27.3364(6) Å, α = 101.765(2) o, β = 98.045(2) o, γ = 108.369(3) o, V = 5952.1(3) Å 3, T = 293(2) K, space group P-1, Z = 2. 42637 reflections measured, 22468 independent reflections (R int = 0.0589). The final R 1 values were 0.0644 (I > 2σ(I)). The final wr(f 2 ) values were 0.1742 (I > 2σ(I)). The final R 1 values were 0.0892 (all data). The final wr(f 2 ) values was 0.2096 (all data). The goodness of fit on F 2 was 1.008. Crystal data for COM-3: C 186H 368O 170Ti 52, M = 7815.6, triclinic, a = 16.9162(11) Å, b = 19.2495(6) Å, c = 28.6275(13) Å, α = 102.673(3) o, β = 103.063(5) o, γ = 102.052(4) o, V = 8525.8(7) Å 3, T = 293(2) K, space group P-1, Z = 1. 23398 reflections measured, 10260 independent reflections (R int = 0.0672). The final R 1 values were 0.0778 (I > 2σ(I)). The final wr(f 2 ) values were 0.2011 (I > 2σ(I)). The final R 1 values were 0.1039 (all data). The final wr(f 2 ) values was 0.2183 (all data). The goodness of fit on F 2 was 1.25. Photocatalytic H 2 generation Photocatalytic hydrogen production tests were carried out in a pyrex reaction cell connected to a closed gas circulation and evacuation system (Perfect Light Company Labsolar-III (AG)). 20 mg photocatalyst loaded with 33 μl 1.0 wt% H 2PtCl 6 was dispersed into an aqueous methanol solution (100 ml, 10%) in a closed gas circulation system. The suspension was degassed thoroughly and then irradiated by a 300W Xe lamp. The evolved hydrogen was detected by online GC (FULI; TDX-01 column, TCD, Ar Carrier). The composition of these three Ti-oxo clusters were further characterized by the combination of energy-dispersive X-ray spectroscopy (EDS) (Supplementary Figs S1-S3) and IR spectroscopy (Supplementary Figs S4-S6). The thermogravimetric analysis (TGA) confirmed that COM-1 and COM-3 could be stable up to about 200 C (Supplementary Figs S7-S8). COM-1 underwent two stages of weight loss for the presence of the BDC ligands, while COM-3 exhibited overall one-step weight loss. The peak positions of simulated and experimental powder X-ray diffraction (PXRD) patterns were in good agreement with each other, indicating the good purity of the crystalline samples (Supplementary Figs S9 and S10). Their detailed structure information was determined by single-crystal X-ray diffraction analysis (Supplementary Figs S11-S13). The valence states of the titanium ions were confirmed by bond valence sum (BVS) calculations (Table S1). S3

Figure S1 The EDS spectrum of compound COM-1. Figure S2 The EDS spectrum of compound COM-2. Figure S3 The EDS spectrum of compound COM-3. S4

Figure S4 The IR spectrum of COM-1. Figure S5 The IR spectrum of COM-2. Figure S6 The IR spectrum of COM-3. S5

Figure S7 The TGA curve of COM-1. Figure S8 The TGA curve of COM-3. Figure S9 The PXRD of the simulated and experimental patterns of COM-1. S6

Figure S10 The PXRD of the simulated and experimental patterns of COM-3. Figure S11 ORTEP of COM-1 (left) and only the metal oxide core (right). Hydrogen atoms omitted for clarity. Thermal ellipsoids displayed at 30% probability. All of the six titanium atoms are 6-coordinated by oxygen atoms to form distorted octahedral geometries. Four μ 3-O atoms bridge these Ti atoms into a ribbon-like {Ti 6(μ 3-O) 4} structure. The up and down faces of the {Ti 6} cluster in COM-1 are occupied by two BDC ligands in (κ 1 -κ 1 -κ 1 -κ 1 )-μ 4-coordination mode, and the peripheral coordinate environments are fulfilled by a couple of propionic acid molecules and 10 isopropoxy groups. The diameter of this {Ti 6} cluster core is about 0.9 nm (taking off the ionic radius of two Ti 4+ ions). Figure S12 ORTEP of COM-2 (left) and only the metal oxide core (right). Hydrogen atoms omitted for clarity. Thermal ellipsoids displayed at 30% probability. The 17 titanium atoms in COM-2 are linked by 2 μ 2-oxo bridges, 18 μ 3-oxo bridges and 2 μ 4-oxo bridges to form a {Ti 17(μ 2-O) 2(μ 3-O) 18(μ 4-O) 2} cluster, whose structure can be seemed as a {Ti 6}-{Ti 4}-{Ti 6} sandwich decorated by an extra titanium centre. Therefore, the diameter of the cluster core of COM-2 is similar as that of COM-1, whilst the thickness is about three times higher. Of the 17 titanium atoms, 16 are 6-coordinated in distorted octahedral environments and only one is 5-coordinated to give S7

distorted square pyramidal geometry. Such sandwich type structure of COM-2 differs significantly from those formerly reported spherical {Ti 17} clusters composited of a {Ti 12} Keggin-unit plus four 5-coordinated titanium centers (Supplementary Figs S15 and S16). Figure S13 ORTEP of COM-3 (left) and only the metal oxide core (right). Hydrogen atoms omitted for clarity. Thermal ellipsoids displayed at 30% probability. Table S1 Bond valence sum (BVS) analysis [a] for COMs. COM-1 1 4.156 Ti1-O13 1.120 d=1.773(2) Ti1-O1 0.864 d=1.869(3) Ti1-O2 0.638 d=1.981(3) Ti1-O4 0.570 d=2.023(3) Ti1-O6 0.513 d=2.062(3) Ti1-O2 0.451 d=2.110(3) Ti1 4.057 Ti1-O24 0.902 d=1.853(4) Ti1-O11 0.825 d=1.886(3) Ti1-O2 0.817 d=1.890(3) Ti1-O18 0.613 d=1.996(3) Ti1-O4 0.502 d=2.070(3) Ti1-O9 0.398 d=2.156(4) Ti4 4.086 Ti4-O52 1.053 d=1.796(4) Ti4-O12 0.945 d=1.836(3) Ti4-O9 0.848 d=1.876(3) Ti4-O11 0.709 d=1.942(3) Ti2 4.196 Ti2-O9 1.099 d=1.780(3) Ti2-O2 0.902 d=1.853(3) Ti2-O12 0.711 d=1.941(3) Ti2-O1 0.517 d=2.059(3) Ti2-O5 0.483 d=2.084(3) Ti2-O8 0.482 d=2.085(4) COM-2 Ti2 4.178 Ti2-O28 0.960 d=1.830(3) Ti2-O8 0.898 d=1.855(3) Ti2-O2 0.741 d=1.926(3) Ti2-O5 0.723 d=1.935(3) Ti2-O31 0.530 d=2.050(4) Ti2-O13 0.327 d=2.229(4) Ti5 4.120 Ti5-O28 1.030 d=1.804(3) Ti5-O15 0.874 d=1.865(3) Ti5-O20 0.850 d=1.875(3) Ti5-O49 0.556 d=2.032(4) Ti3 4.238 Ti3-O11 1.123 d=1.772(3) Ti3-O10 1.073 d=1.789(4) Ti3-O7 0.573 d=2.021(4) Ti3-O1 0.534 d=2.047(3) Ti3-O3 0.499 d=2.072(4) Ti3-O12 0.435 d=2.123(3) Ti3 4.188 Ti3-O29 1.090 d=1.783(4) Ti3-O16 0.741 d=1.926(3) Ti3-O14 0.658 d=1.970(3) Ti3-O7 0.652 d=1.973(4) Ti3-O11 0.607 d=2.000(3) Ti3-O1 0.440 d=2.119(3) Ti6 4.188 Ti6-O44 1.114 d=1.775(4) Ti6-O13 0.810 d=1.893(3) Ti6-O12 0.689 d=1.953(4) Ti6-O8 0.558 d=2.031(3) S8

Ti4-O7 0.531 d=2.049(3) Ti7 4.140 Ti7-O26 1.108 d=1.777(4) Ti7-O3 0.788 d=1.903(4) Ti7-O7 0.755 d=1.919(3) Ti7-O19 0.572 d=2.022(4) Ti7-O1 0.468 d=2.096(3) Ti7-O12 0.449 d=2.111(4) Ti10 4.066 Ti10-O24 1.064 d=1.792(3) Ti10-O16 0.890 d=1.858(3) Ti10-O20 0.763 d=1.915(3) Ti10-O38 0.533 d=2.048(4) Ti10-O45 0.487 d=2.081(4) Ti10-O39 0.328 d=2.227(4) Ti13 4.222 Ti13-O37 1.182 d=1.753(4) Ti13-O6 0.776 d=1.909(4) Ti13-O9 0.759 d=1.917(3) Ti13-O21 0.640 d=1.980(4) Ti13-O42 0.474 d=2.091(4) Ti13-O4 0.390 d=2.163(3) Ti16 4.220 Ti16-O34 1.093 d=1.782(4) Ti16-O33 1.084 d=1.785(5) Ti16-O18 0.562 d=2.028(4) Ti16-O41 0.520 d=2.057(5) Ti16-O21 0.487 d=2.081(4) Ti16-O4 0.473 d=2.092(3) Ti1 4.167 Ti1-O37 1.053 d=1.796(9) Ti1-O47 0.905 d=1.852(9) Ti1-O8 0.817 d=1.890(10) Ti1-O21 0.780 d=1.907(9) Ti1-O38 0.613 d=1.996(12) Ti4 3.842 Ti4-O25 0.753 d=1.920(9) Ti4-O55 0.590 d=2.010(10) Ti4-O16 0.564 d=2.027(10) Ti4-O24 0.550 d=2.036(10) Ti4-O42 0.536 d=2.046(12) Ti4-O2 0.435 d=2.123(10) Ti4-O10 0.414 d=2.141(9) Ti7 3.898 Ti7-O44 1.139 d=1.767(11) Ti7-O58 0.613 d=1.996(11) Ti5-O36 0.507 d=2.066(4) Ti5-O35 0.302 d=2.258(4) Ti8 4.182 Ti8-O22 1.108 d=1.777(4) Ti8-O5 0.834 d=1.882(3) Ti8-O4 0.660 d=1.969(4) Ti8-O2 0.578 d=2.018(3) Ti8-O43 0.544 d=2.040(4) Ti8-O6 0.458 d=2.104(4) Ti11 4.222 Ti11-O46 1.108 d=1.777(4) Ti11-O35 0.780 d=1.907(4) Ti11-O17 0.763 d=1.915(4) Ti11-O47 0.527 d=2.052(4) Ti11-O15 0.526 d=2.053(3) Ti11-O10 0.519 d=2.058(4) Ti14 4.194 Ti14-O40 1.061 d=1.793(4) Ti14-O13 0.837 d=1.881(3) Ti14-O6 0.823 d=1.887(4) Ti14-O30 0.502 d=2.070(4) Ti14-O5 0.499 d=2.072(4) Ti14-O48 0.472 d=2.093(4) Ti17 4.131 Ti17-O53 1.126 d=1.771(4) Ti17-O35 0.853 d=1.874(4) Ti17-O39 0.837 d=1.881(4) Ti17-O51 0.489 d=2.080(4) Ti17-O54 0.477 d=2.089(4) Ti17-O20 0.350 d=2.203(3) COM-3 Ti2 4.302 Ti2-O29 1.225 d=1.740(10) Ti2-O1 0.860 d=1.871(10) Ti2-O34 0.656 d=1.971(10) Ti2-O37 0.620 d=1.992(10) Ti2-O20 0.570 d=2.023(12) Ti2-O3 0.372 d=2.181(11) Ti5 4.105 Ti5-O26 1.033 d=1.803(11) Ti5-O31 0.920 d=1.846(9) Ti5-O8 0.823 d=1.887(9) Ti5-O21 0.755 d=1.919(9) Ti5-O85 0.575 d=2.020(13) Ti8 4.136 Ti8-O17 1.163 d=1.759(11) Ti8-O6 0.709 d=1.942(10) Ti6-O3 0.528 d=2.051(3) Ti6-O23 0.489 d=2.080(4) Ti9 4.235 Ti9-O15 0.803 d=1.896(3) Ti9-O8 0.780 d=1.907(3) Ti9-O1 0.741 d=1.926(3) Ti9-O10 0.719 d=1.937(3) Ti9-O3 0.625 d=1.989(3) Ti9-O27 0.567 d=2.025(4) Ti12 4.175 Ti12-O50 1.058 d=1.794(4) Ti12-O39 0.788 d=1.903(4) Ti12-O17 0.780 d=1.907(3) Ti12-O16 0.524 d=2.054(3) Ti12-O14 0.523 d=2.055(4) Ti12-O32 0.502 d=2.070(4) Ti15 4.112 Ti15-O25 1.099 d=1.780(4) Ti15-O14 0.733 d=1.930(3) Ti15-O10 0.656 d=1.971(4) Ti15-O17 0.638 d=1.981(4) Ti15-O19 0.513 d=2.062(4) Ti15-O1 0.473 d=2.092(3) Ti3 4.211 Ti3-O28 1.231 d=1.738(10) Ti3-O7 0.715 d=1.939(10) Ti3-O25 0.687 d=1.954(10) Ti3-O47 0.625 d=1.989(10) Ti3-O11 0.540 d=2.043(13) Ti3-O2 0.413 d=2.142(9) Ti6 4.206 Ti6-O13 1.129 d=1.770(10) Ti6-O31 0.721 d=1.936(9) Ti6-O4 0.667 d=1.965(10) Ti6-O25 0.656 d=1.971(10) Ti6-O22 0.568 d=2.024(11) Ti6-O10 0.464 d=2.099(10) Ti9 4.067 Ti9-O16 0.995 d=1.817(9) Ti9-O35 0.735 d=1.929(10) S9

Ti7-O35 0.564 d=2.027(10) Ti7-O53 0.561 d=2.029(10) Ti7-O50 0.513 d=2.062(12) Ti7-O40 0.509 d=2.065(10) Ti10 4.232 Ti10-O54 0.893 d=1.857(10) Ti10-O40 0.843 d=1.878(10) Ti10-O35 0.661 d=1.968(11) Ti10-O83 0.627 d=1.988(11) Ti10-O40 0.611 d=1.997(10) Ti10-O58 0.597 d=2.006(11) Ti13 4.198 Ti13-O75 1.195 d=1.749(10) Ti13-O24 0.819 d=1.889(10) Ti13-O30 0.620 d=1.992(12) Ti13-O47 0.610 d=1.998(9) Ti13-O71 0.499 d=2.072(11) Ti13-O2 0.455 d=2.106(10) Ti16 4.323 Ti16-O56 1.053 d=1.796(12) Ti16-O12 0.803 d=1.896(10) Ti16-O15 0.725 d=1.934(11) Ti16-O3 0.704 d=1.945(10) Ti16-O23 0.578 d=2.018(13) Ti16-O1 0.460 d=2.102(11) Ti19 4.079 Ti19-O5 1.117 d=1.774(12) Ti19-O1 0.771 d=1.911(10) Ti19-O18 0.767 d=1.913(12) Ti19-O45 0.553 d=2.034(13) Ti19-O27 0.493 d=2.077(12) Ti19-O12 0.377 d=2.176(12) Ti22 4.351 Ti22-O15 0.912 d=1.849(11) Ti22-O14 0.843 d=1.878(10) Ti22-O9 0.711 d=1.941(10) Ti22-O67 0.702 d=1.946(14) Ti22-O6 0.603 d=2.002(10) Ti22-O70 0.579 d=2.017(13) Ti25 4.203 Ti25-O84 1.079 d=1.787(11) Ti25-O13 0.867 d=1.868(11) Ti25-O28 0.788 d=1.903(10) Ti25-O59 0.552 d=2.035(10) Ti25-O49 0.478 d=2.088(14) Ti25-O41 0.440 d=2.119(12) Ti8-O26 0.656 d=1.971(10) Ti8-O34 0.647 d=1.976(9) Ti8-O63 0.550 d=2.036(14) Ti8-O9 0.410 d=2.145(10) Ti11 3.935 Ti11-O34 0.797 d=1.899(9) Ti11-O48 0.640 d=1.980(10) Ti11-O81 0.625 d=1.989(10) Ti11-O32 0.550 d=2.036(14) Ti11-O15 0.536 d=2.046(10) Ti11-O9 0.447 d=2.113(10) Ti11-O3 0.340 d=2.214(11) Ti14 4.283 Ti14-O46 1.105 d=1.778(12) Ti14-O44 0.790 d=1.902(10) Ti14-O10 0.713 d=1.940(10) Ti14-O4 0.576 d=2.019(10) Ti14-O16 0.555 d=2.033(9) Ti14-O19 0.543 d=2.041(14) Ti17 4.247 Ti17-O59 1.033 d=1.803(10) Ti17-O4 0.821 d=1.888(11) Ti17-O53 0.814 d=1.891(10) Ti17-O80 0.654 d=1.972(11) Ti17-O82 0.528 d=2.051(11) Ti17-O78 0.396 d=2.158(15) Ti20 4.494 Ti20-O36 1.087 d=1.784(12) Ti20-O55 0.922 d=1.845(10) Ti20-O81 0.767 d=1.913(10) Ti20-O24 0.727 d=1.933(10) Ti20-O48 0.663 d=1.967(9) Ti20-O8 0.328 d=2.228(9) Ti23 3.986 Ti23-O68 1.039 d=1.801(15) Ti23-O77 0.902 d=1.853(10) Ti23-O55 0.694 d=1.950(10) Ti23-O65 0.509 d=2.065(12) Ti23-O10 0.451 d=2.110(10) Ti23-O31 0.391 d=2.162(9) Ti26 4.247 Ti26-O39 1.248 d=1.733(15) Ti26-O12 0.850 d=1.875(11) Ti26-O14 0.806 d=1.895(11) Ti26-O79 0.491 d=2.078(14) Ti26-O43 0.470 d=2.094(14) Ti26-O18 0.381 d=2.172(12) Ti9-O2 0.681 d=1.957(10) Ti9-O7 0.632 d=1.985(9) Ti9-O72 0.527 d=2.052(12) Ti9-O69 0.498 d=2.073(11) Ti12 4.373 Ti12-O54 1.221 d=1.741(10) Ti12-O53 0.774 d=1.910(10) Ti12-O7 0.739 d=1.927(10) Ti12-O57 0.607 d=2.000(12) Ti12-O62 0.540 d=2.043(14) Ti12-O59 0.493 d=2.077(11) Ti15 4.346 Ti15-O66 1.202 d=1.747(12) Ti15-O48 0.797 d=1.899(10) Ti15-O75 0.784 d=1.905(10) Ti15-O3 0.579 d=2.017(10) Ti15-O74 0.514 d=2.061(12) Ti15-O37 0.469 d=2.095(10) Ti18 4.539 Ti18-O61 1.251 d=1.732(14) Ti18-O77 1.084 d=1.785(10) Ti18-O81 0.733 d=1.930(10) Ti18-O76 0.600 d=2.004(15) Ti18-O26 0.444 d=2.115(10) Ti18-O9 0.426 d=2.131(10) Ti21 4.161 Ti21-O60 1.076 d=1.788(12) Ti21-O17 0.817 d=1.890(11) Ti21-O29 0.776 d=1.909(10) Ti21-O64 0.526 d=2.053(14) Ti21-O52 0.498 d=2.073(13) Ti21-O21 0.469 d=2.095(9) Ti24 4.533 Ti24-O33 1.300 d=1.718(13) Ti24-O18 0.922 d=1.845(12) Ti24-O6 0.825 d=1.886(10) Ti24-O73 0.592 d=2.009(13) Ti24-O51 0.526 d=2.053(15) Ti24-O14 0.368 d=2.185(11) [a] Vi =ΣSij = Σexp[(r1-rij)/B], where r0 is the length of a single bond (here r1=1.815 for Ti iv -O), r1 is the bond length between atoms i and j; B is a constant, the universal parameter ~0.37 Å; Sij is the valence of a bond between atoms i and j; Vi is the sum of all bond valences of the bonds formed by a given atom i. S10

Table S2 Selected bond lengths (Å) for COMs. COM-1 Ti(1)-O(1) 1.869(3) Ti(2)-O(5) 2.084(3) Ti(1)-O(13) 1.773(2) Ti(2)-O(8) 2.085(4) Ti(1)-O(2) 2.110(3) Ti(2)-O(9) 1.780(3) Ti(1)-O(2)#1 1.981(3) Ti(3)-O(1) 2.047(3) Ti(1)-O(4)#1 2.023(3) Ti(3)-O(10) 1.789(4) Ti(1)-O(6) 2.062(3) Ti(3)-O(11) 1.772(3) Ti(2)-O(1) 2.059(3) Ti(3)-O(12) 2.123(3) Ti(2)-O(12) 1.941(3) Ti(3)-O(3)#1 2.072(4) Ti(2)-O(2) 1.853(3) Ti(3)-O(7) 2.021(4) Symmetry transformations used to generate equivalent atoms: #1 -x+1,-y,-z. COM-2 Ti(1)-O(24) 1.853(4) Ti(9)-O(3) 1.989(3) Ti(1)-O(11) 1.886(3) Ti(9)-O(8) 1.907(3) Ti(1)-O(18) 1.996(3) Ti(10)-O(16) 1.858(3) Ti(1)-O(2) 1.890(3) Ti(10)-O(20) 1.915(3) Ti(1)-O(4) 2.070(3) Ti(10)-O(24) 1.792(3) Ti(1)-O(9) 2.156(4) Ti(10)-O(38) 2.048(4) Ti(2)-O(13) 2.229(4) Ti(10)-O(39) 2.227(4) Ti(2)-O(2) 1.926(3) Ti(10)-O(45) 2.081(4) Ti(2)-O(28) 1.830(3) Ti(11)-O(10) 2.058(4) Ti(2)-O(31) 2.050(4) Ti(11)-O(15) 2.053(3) Ti(2)-O(5) 1.935(3) Ti(11)-O(17) 1.915(4) Ti(2)-O(8) 1.855(3) Ti(11)-O(35) 1.907(4) Ti(3)-O(1) 2.119(3) Ti(11)-O(46) 1.777(4) Ti(3)-O(11) 2.000(3) Ti(11)-O(47) 2.052(4) Ti(3)-O(14) 1.970(3) Ti(12)-O(14) 2.055(4) Ti(3)-O(16) 1.926(3) Ti(12)-O(16) 2.054(3) Ti(3)-O(29) 1.783(4) Ti(12)-O(17) 1.907(3) Ti(3)-O(7) 1.973(4) Ti(12)-O(32) 2.070(4) Ti(4)-O(11) 1.942(3) Ti(12)-O(39) 1.903(4) Ti(4)-O(12) 1.836(3) Ti(12)-O(50) 1.794(4) Ti(4)-O(52) 1.796(4) Ti(13)-O(21) 1.980(4) Ti(4)-O(7) 2.049(3) Ti(13)-O(37) 1.753(4) Ti(4)-O(9) 1.876(3) Ti(13)-O(4) 2.163(3) Ti(5)-O(15) 1.865(3) Ti(13)-O(42) 2.091(4) Ti(5)-O(20) 1.875(3) Ti(13)-O(6) 1.909(4) S11

Ti(5)-O(28) 1.804(3) Ti(13)-O(9) 1.917(3) Ti(5)-O(35) 2.258(4) Ti(14)-O(13) 1.881(3) Ti(5)-O(36) 2.066(4) Ti(14)-O(30) 2.070(4) Ti(5)-O(49) 2.032(4) Ti(14)-O(40) 1.793(4) Ti(6)-O(12) 1.953(4) Ti(14)-O(48) 2.093(4) Ti(6)-O(13) 1.893(3) Ti(14)-O(5) 2.072(4) Ti(6)-O(23) 2.080(4) Ti(14)-O(6) 1.887(4) Ti(6)-O(3) 2.051(3) Ti(15)-O(1) 2.092(3) Ti(6)-O(44) 1.775(4) Ti(15)-O(10) 1.971(4) Ti(6)-O(8) 2.031(3) Ti(15)-O(14) 1.930(3) Ti(7)-O(1) 2.096(3) Ti(15)-O(17) 1.981(4) Ti(7)-O(12) 2.111(4) Ti(15)-O(19) 2.062(4) Ti(7)-O(19) 2.022(4) Ti(15)-O(25) 1.780(4) Ti(7)-O(26) 1.777(4) Ti(16)-O(18) 2.028(4) Ti(7)-O(3) 1.903(4) Ti(16)-O(21) 2.081(4) Ti(7)-O(7) 1.919(3) Ti(16)-O(33) 1.785(5) Ti(8)-O(2) 2.018(3) Ti(16)-O(34) 1.782(4) Ti(8)-O(22) 1.777(4) Ti(16)-O(4) 2.092(3) Ti(8)-O(4) 1.969(4) Ti(16)-O(41) 2.057(5) Ti(8)-O(43) 2.040(4) Ti(17)-O(20) 2.203(3) Ti(8)-O(5) 1.882(3) Ti(17)-O(35) 1.874(4) Ti(8)-O(6) 2.104(4) Ti(17)-O(39) 1.881(4) Ti(9)-O(1) 1.926(3) Ti(17)-O(51) 2.080(4) Ti(9)-O(10) 1.937(3) Ti(17)-O(53) 1.771(4) Ti(9)-O(15) 1.896(3) Ti(17)-O(54) 2.089(4) Ti(9)-O(27) 2.025(4) COM-3 Ti(1)-O(21) 1.907(9) Ti(14)-O(10) 1.940(10) Ti(1)-O(37) 1.796(9) Ti(14)-O(16) 2.033(9) Ti(1)-O(38) 1.996(12) Ti(14)-O(19) 2.041(14) Ti(1)-O(47) 1.852(9) Ti(14)-O(4) 2.019(10) Ti(1)-O(8) 1.890(10) Ti(14)-O(44) 1.902(10) Ti(2)-O(1) 1.871(10) Ti(14)-O(46) 1.778(12) Ti(2)-O(20) 2.023(12) Ti(15)-O(3) 2.017(10) Ti(2)-O(29) 1.740(10) Ti(15)-O(37) 2.095(10) Ti(2)-O(3) 2.181(11) Ti(15)-O(48) 1.899(10) Ti(2)-O(34) 1.971(10) Ti(15)-O(66) 1.747(12) Ti(2)-O(37) 1.992(10) Ti(15)-O(74) 2.061(12) S12

Ti(3)-O(11) 2.043(13) Ti(15)-O(75) 1.905(10) Ti(3)-O(2) 2.142(9) Ti(16)-O(1) 2.102(11) Ti(3)-O(25) 1.954(10) Ti(16)-O(12) 1.896(10) Ti(3)-O(28) 1.738(10) Ti(16)-O(15) 1.934(11) Ti(3)-O(47) 1.989(10) Ti(16)-O(23) 2.018(13) Ti(3)-O(7) 1.939(10) Ti(16)-O(3) 1.945(10) Ti(4)-O(10) 2.141(9) Ti(16)-O(56) 1.796(12) Ti(4)-O(16) 2.027(10) Ti(17)-O(4) 1.888(11) Ti(4)-O(2) 2.123(10) Ti(17)-O(53) 1.891(10) Ti(4)-O(24) 2.036(10) Ti(17)-O(59) 1.803(10) Ti(4)-O(25) 1.920(9) Ti(17)-O(78) 2.158(15) Ti(4)-O(42) 2.046(12) Ti(17)-O(80) 1.972(11) Ti(4)-O(55) 2.010(10) Ti(17)-O(82) 2.051(11) Ti(5)-O(21) 1.919(9) Ti(18)-O(26) 2.115(10) Ti(5)-O(26) 1.803(11) Ti(18)-O(61) 1.732(14) Ti(5)-O(31) 1.846(9) Ti(18)-O(76) 2.004(15) Ti(5)-O(8) 1.887(9) Ti(18)-O(77) 1.785(10) Ti(5)-O(85) 2.020(13) Ti(18)-O(81) 1.930(10) Ti(6)-O(10) 2.099(10) Ti(18)-O(9) 2.131(10) Ti(6)-O(13) 1.770(10) Ti(19)-O(1) 1.911(10) Ti(6)-O(22) 2.024(11) Ti(19)-O(12) 2.176(12) Ti(6)-O(25) 1.971(10) Ti(19)-O(18) 1.913(12) Ti(6)-O(31) 1.936(9) Ti(19)-O(27) 2.077(12) Ti(6)-O(4) 1.965(10) Ti(19)-O(45) 2.034(13) Ti(7)-O(35) 2.027(10) Ti(19)-O(5) 1.774(12) Ti(7)-O(40) 2.065(10) Ti(20)-O(24) 1.933(10) Ti(7)-O(44) 1.767(11) Ti(20)-O(36) 1.784(12) Ti(7)-O(50) 2.062(12) Ti(20)-O(48) 1.967(9) Ti(7)-O(53) 2.029(10) Ti(20)-O(55) 1.845(10) Ti(7)-O(58)#1 1.996(11) Ti(20)-O(8) 2.228(9) Ti(8)-O(17) 1.759(11) Ti(20)-O(81) 1.913(10) Ti(8)-O(26) 1.971(10) Ti(21)-O(17) 1.890(11) Ti(8)-O(34) 1.976(9) Ti(21)-O(21) 2.095(9) Ti(8)-O(6) 1.942(10) Ti(21)-O(29) 1.909(10) Ti(8)-O(63) 2.036(14) Ti(21)-O(52) 2.073(13) Ti(8)-O(9) 2.145(10) Ti(21)-O(60) 1.788(12) Ti(9)-O(16) 1.817(9) Ti(21)-O(64) 2.053(14) Ti(9)-O(2) 1.957(10) Ti(22)-O(14) 1.878(10) Ti(9)-O(35) 1.929(10) Ti(22)-O(15) 1.849(11) S13

Ti(9)-O(69) 2.073(11) Ti(22)-O(6) 2.002(10) Ti(9)-O(7) 1.985(9) Ti(22)-O(67) 1.946(14) Ti(9)-O(72) 2.052(12) Ti(22)-O(70) 2.017(13) Ti(10)-O(35) 1.968(11) Ti(22)-O(9) 1.941(10) Ti(10)-O(40) 1.878(10) Ti(23)-O(10) 2.110(10) Ti(10)-O(40)#1 1.997(10) Ti(23)-O(31) 2.162(9) Ti(10)-O(54) 1.857(10) Ti(23)-O(55) 1.950(10) Ti(10)-O(58) 2.006(11) Ti(23)-O(65) 2.065(12) Ti(10)-O(83) 1.988(11) Ti(23)-O(68) 1.801(15) Ti(11)-O(15) 2.046(10) Ti(23)-O(77) 1.853(10) Ti(11)-O(3) 2.214(11) Ti(24)-O(14) 2.185(11) Ti(11)-O(32) 2.036(14) Ti(24)-O(18) 1.845(12) Ti(11)-O(34) 1.899(9) Ti(24)-O(33) 1.718(13) Ti(11)-O(48) 1.980(10) Ti(24)-O(51) 2.053(15) Ti(11)-O(81) 1.989(10) Ti(24)-O(6) 1.886(10) Ti(11)-O(9) 2.113(10) Ti(24)-O(73) 2.009(13) Ti(12)-O(53) 1.910(10) Ti(25)-O(13) 1.868(11) Ti(12)-O(54) 1.741(10) Ti(25)-O(28) 1.903(10) Ti(12)-O(57) 2.000(12) Ti(25)-O(41) 2.119(12) Ti(12)-O(59) 2.077(11) Ti(25)-O(49) 2.088(14) Ti(12)-O(62) 2.043(14) Ti(25)-O(59) 2.035(10) Ti(12)-O(7) 1.927(10) Ti(25)-O(84) 1.787(11) Ti(13)-O(2) 2.106(10) Ti(26)-O(12) 1.875(11) Ti(13)-O(24) 1.889(10) Ti(26)-O(14) 1.895(11) Ti(13)-O(30) 1.992(12) Ti(26)-O(18) 2.172(12) Ti(13)-O(47) 1.998(9) Ti(26)-O(39) 1.733(15) Ti(13)-O(71) 2.072(11) Ti(26)-O(43) 2.094(14) Ti(13)-O(75) 1.749(10) Ti(26)-O(79) 2.078(14) Symmetry transformations used to generate equivalent atoms: #1 -x,-y,-z+1. S14

Figure S14 The packing view of COM-1 along with the [100], [010], and [001] direction. The shortest inter-cluster separation (Ti Ti distance) is 8.83 Å. Figure S15 The Ti 17 structural comparison between literature 4 and COM-2 herein. Figure S16 The packing view of COM-2 along with the [100], [010], and [001] direction. The shortest inter-cluster separation (Ti Ti distance) is 8.38 Å. S15

Figure S17 The packing view of COM-3 along with the [100], [010], and [001] direction. The shortest inter-cluster separation (Ti Ti distance) is 7.49 Å. Figure S18 Comparisons of the reported Ti34 (top left), Ti42 (top right) and Ti52 herein (bottom). Figure S19 Representation of the assembly of the boat-like Ti26 moiety in COM-3. Color code: green Ti; pink μ-o; red μ3-o; yellow μ4-o. The {Ti@Ti5} subunits are emphasized in blue. S16

Figure S20 The linear fit of the H 2 generation of COM-1. Figure S21 The linear fit of the H 2 generation of COM-3. Figure S22 Recycling water-splitting H 2 evolution tests under UV-visible light illumination on COM-1. S17

Figure S23 FTIR of recycled COM-1. Figure S24 FTIR of recycled COM-3. Figure S25 TEM (left) and High-resolution TEM (right) micrographs of COM-3. The crystalline spots represent similar sizes as the Ti 52 cluster in COM-3. S18

Figure S26 Diffuse reflectance spectra of COM-1 and COM-3. Insert displays the photos of COM-1 and COM-3 crystals. Figure S27 ESI-MS spectra of the synthetic reactions for COM-1 (black), COM-2 (red) and COM-3 (blue). Samples were diluted by methanol and immediately injected into the MS instrument. Figure S28 ESI-MS spectra of the synthetic reaction for COM-1 (red) and toluene solution of pure crystals of COM-1 (black). Samples were diluted by methanol and immediately injected into the MS instrument. S19

Figure S29 ESI-MS spectra of the synthetic reaction for COM-3 (red) and toluene solution of pure crystals of COM-3 (black). Samples were diluted by methanol and immediately injected into the MS instrument. Figure S30 ESI-MS spectrum of toluene solution of pure crystals of COM-3. Samples were diluted by methanol and immediately injected into the MS instrument. Figure S31 Chemical stability tests of COM-1, including the photos and PXRD patterns of samples treated in different conditions. Simulated PXRD pattern of COM-1 has also been illustrated for comparison. S20

Figure S32 Chemical stability tests of COM-3, including the photos and PXRD patterns of samples treated in different conditions. Simulated PXRD pattern of COM-3 has also been illustrated for comparison. References (1) W. W. Wendlandt; H. G. Hecht Reflectance Spectroscopy; Interscience: New York, 1966. (2) Sheldrick, G. M. SHELXS97, Program for Crystal Structure Solution (University of Göttingen, Göttingen, Germany, 1997). (3) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refinement (University of Göttingen, Göttingen, Germany, 1997).. (4) Steunou, N.; Kickelbick, G.; Boubekeur, K.; Sanchez, C. J. Chem. Soc., Dalton Trans. 1999, 3653. S21