Building-block approach to the discovery of Na8Mn2(Ge2Se6)2: A polar chalcogenide exhibiting promising harmonic generation signals with a high laser-induced damage threshold

•The building block approach has been utilized to prepare Na8Mn2(Ge2Se6)2 at 750 °C.•The polar structure of Na8Mn2(Ge2Se6)2 features the ethane-like [Ge2Se6]6- unit.•Na8Mn2(Ge2Se6)2 is a paramagnetic semiconductor with an optical bandgap of 1.95 eV.•The compound displays modest second-harmonic and s...

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