The rapidly growing number of luminescent coordination polymers (CPs) and metal-organic frameworks (MOFs) illustrates high interest as well as accessibility of such materials. The interplay between inorganic and organic components in these materials offers a large number of viable luminescence processes. The enormous variability of available ligand-metal combinations opens the possibility of creating luminescence "by design", based on a proper understanding of the processes involved. Together with the multifunctionality of MOFs (e.g. porosity) further options like sensing become accessible. This tutorial review covers the main luminescence processes and focuses especially on metal-based luminescence of coordination polymers and MOFs.

This feature article focuses on tuning options of photoluminescence properties of lanthanide containing Metal-Organic Frameworks (MOFs) and Dense Frameworks by selection of an appropriate set of metal ions together with suitable ligands. In addition to lanthanide-only systems, frameworks with main group and transition metal ions that are heterometallic or co-doped with variable lanthanide content offer excellent tuning options for luminescence. The MOF feature porosity enables further applications such as sensors for a large number of chemical analytes by selective influences on the luminescence upon contact. The application of functional thin films marks the most recent development of this amazingly growing field, involving processing and structuring.

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Janus type Water-Splitting Catalysts have attracted highest attention as a tool of choice for solar to fuel conversion. AISI Ni 42 steel was upon harsh anodization converted in a bifunctional electrocatalyst. Oxygen evolution reaction-(OER) and hydrogen evolution reaction (HER) are highly efficiently and steadfast catalyzed at pH 7, 13, 14, 14.6 (OER) respectively at pH 0, 1, 13, 14, 14.6 (HER). The current density taken from long-term OER measurements in pH 7 buffer solution upon the electro activated steel at 491 mV overpotential (η) was around 4 times higher (4 mA/cm 2 ) in comparison with recently developed OER electrocatalysts. The very strong voltagecurrent behavior of the catalyst shown in OER polarization experiments at both pH 7 and at pH 13 were even superior to those known for IrO 2 -RuO 2 . No degradation of the catalyst was detected even when conditions close to standard industrial operations were applied to the catalyst. A stable Ni-, Fe-oxide based passivating layer sufficiently protected the bare metal for further oxidation. Quantitative charge to oxygen-(OER) and charge to hydrogen (HER) conversion was confirmed. High resolution XPS spectra showed that most likely γ−NiO(OH) and FeO(OH) are the catalytic active OER and NiO is the catalytic active HER species.

Homoleptic frameworks of the formula 3 N [Sr 1Àx Eu x (Im) 2 ] (1) (x = 0.01-1.0; Im À = imidazolate anion, C 3 H 3 N 2 À ) are hybrid materials that exhibit an intensive green luminescence. Tuning of both emission wavelength and quantum yield is achieved by europium/strontium substitution so that a QE of 80% is reached at a Eu content of 5%. Even 100% pure europium imidazolate still shows 60% absolute quantum efficiency. Substitution of Sr/Eu shows that doping with metal cations can also be utilized for coordination compounds to optimize materials properties. The emission is finely tuneable in the region 495-508 nm via variation of the europium content. The series of frameworks 3 N [Sr 1Àx Eu x (Im) 2 ] presents dense MOFs with the highest quantum yields reported for MOFs so far.Framework and MOF chemistry 1 have attracted attention, as interesting properties were reported like conductivity, 2 catalytic effects, 3 luminescence 4 and porosity. 5 They are mainly known for oxygen coordinating ligands, mostly metal carboxylates 6 which include the alkaline earth and 4f elements. 7 Because of the oxophilicity of lanthanides oxygen-free multi-dimensional coordination networks are rarely found except for a few rare earth imidazolates and triazolates. 8 Among transition metals the imidazole ring system is of exceptional interest together with several 3d metals as they adopt zeolite structures (ZIFs) 9 that can be used for sorption and gas separation. Different from many solid state phosphors, coordination compounds can exhibit luminescence by metal ions although they contain 100% luminescence centres. 10 An expected quenching by concentration is suppressed by ligand shielding. They are furthermore interesting luminescent hybrid materials, as emission can be achieved either via a fluorescence of the ligand system 11 or the metal centres, mainly by the use of lanthanides. 4 The excitation can benefit from antenna effects, viz. the ligand system is excited primarily followed by a transfer of the energy to the luminescence centres. 12 However there are only little coordination compounds for which effective emission characterized by high quantum efficiencies has been reported. 4,11,13 Mostly, no quantum yields were determined, although luminescence becomes important for MOFs concerning sensoring and lighting from UV to near IR. 14,15 We now report a series of homoleptic imidazolate frameworks containing divalent strontium and europium that shows an exceptional combination of properties: an effective luminescence with the highest quantum yield reported for coordination polymers today, together with multiple excitation options including excitation maxima at the applicationally important wavelengths 370 and 460 nm (for Hg and blue LED excitation). The emission can be finely tuned in the region 495-508 nm (blue-green to green) via variation of the Eu content (Fig. 1). Furthermore a low quenching by concentration is observed, combined to a high thermal stability of the frameworks up to 530 1C. (1) are obtained by reactions of t...