HKUST-1
HKUST-1, which is also called MOF-199, is a material in the class of metal-organic frameworks. Metal-organic frameworks are crystalline materials, in which metals are linked by ligands to form repeating coordination motives extending in three dimensions. The HKUST-1 framework is build up of dimeric metal units, which are connected by benzene-1,3,5-tricarboxylate linker molecules. The paddlewheel unit is the commonly used structural motiv to describe the coordination environment of the metal centers and also called secondary building unit of the HKUST-1 structure. The paddlewheel is build up of four benzene-1,3,5-tricarboxylate linkers molecules, which bridge two metal centers. One water molecules is coordinated to each of the two metal centers at the axial position of the paddlewheel unit in the hydrated state, which is usually found if the material is handled in air. After an activation process, these water molecules can be removed and the coordination site at the metal atoms is left unoccupied. This unoccupied coordination site is called coordinatively unsaturated site and can be accessed by other molecules.
Structural analogs
Monometallic HKUST-1 analogs
Cu2+ was used as metal center in the first synthesized HKUST-1 material, but the HKUST-1 structure was also obtained with other metals. The oxidation state of most used metals is +II, which results in a neutral overall framework. In the case of trivalent metals, the overall framework is positively charged and requires anions to compensate the charge and guarantee charge neutrality.| Metal center and oxidation state | Year of first publication | Alternative name | Citation |
| Cu2+ | 1999 | Cu3BTC2 CuBTC | |
| Mo2+ | 2006 | TUDMOF-1 | |
| Fe2+/3+ | 2007 | ||
| Cr2+ | 2010 | ||
| Ni2+ | 2011 | ||
| Zn2+ | 2011 | ||
| Ru2+/3+ | 2011 | ||
| Mn2+ | 2012 | ||
| Fe2+ | 2012 | ||
| Co2+ | 2012 | ||
| Fe3+ | 2014 | ||
| Ru2+ | 2016 | ||
| Fe2+ | 2019 |
Mixed-metal HKUST-1 analogs
In addition to monometallic HKUST-1 analogs, several mixed-metal HKUST-1 materials were synthesized, in which two metals are incorporated into the framework structure at crystallographically equivalent positions. The incorporation of two metals can be achieved by using both metals for the synthesis or by using post-synthetic metal-exchange. For the post-synthetic metal exchange, a monometallic HKUST-1 material is synthesized in the first step. Subsequently, this monometallic HKUST-1 is suspended in a solution containing the second metal, which results in an exchange of metal centers in the framework leading to a mixed-metal HKUST-1.| Metal centers and oxidation states | Metal ratios | Synthesis method | Citation |
| Cu2+ / Zn2+ | 0.99 : 0.01 | Direct synthesis | |
| Cu2+ / Zn2+ | 0.99 : 0.01 0.97 : 0.03 0.95 : 0.05 0.90 : 0.10 0.79 : 0.21 | Direct synthesis | |
| Cu2+ / Zn2+ | 0.95 : 0.05 0.90 : 0.10 | Direct synthesis ball milling | |
| Cu2+ / Ni2+ | 0.70 : 0.30 0.50 : 0.50 0.20 : 0.80 | Direct synthesis | |
| Cu2+ / Ru3+ | 0.92 : 0.08 | Direct synthesis | |
| Cu2+ / Ag+ | not reported | Post-synthetic metal-exchange | |
| Cu2+ / Mn2+ | 0.94 : 0.06 | Post-synthetic metal-exchange | |
| Cu2+ / Fe2+ | 0.86 : 0.14 | Post-synthetic metal-exchange | |
| Cu2+ / Co2+ | 0.74 : 0.26 | Post-synthetic metal-exchange | |
| Cu2+ / Pd2+ | 0.91 : 0.09 0.86 : 0.14 0.80 : 0.20 | Direct synthesis | |
| Cu2+ / Pd2+ | 0.81 : 0.19 0.59 : 0.41 | Direct synthesis | |
| Ru2+/3+ / Rh2+ | 0.95 : 0.05 0.89 : 0.11 0.79 : 0.21 0.47 : 0.53 0.24 : 0.76 0.03 : 0.97 | Direct synthesis | |
| Cu2+ / Fe3+ | 0.69 : 0.31 | Direct synthesis | |
| Cu2+ / Zn2+ / Mo6+ | 0.80 : 0.15 : 0.05 0.70 : 0.15 : 0.15 0.55 : 0.15 : 0.30 | Direct synthesis ball milling |