A molecular model for the Ge(100) buckled dimer.

The 'buckled dimer' defines the key properties of silicon and germanium(100) semiconductor surfaces and governs their behaviour during passivation, functionalization and device fabrication. Each dimer combines a Lewis-acidic 'down' atom with a Lewis-basic 'up' atom, creating a polarized motif that is difficult to isolate or to quantify. Accordingly, their atomically resolved chemistry remains challenging to interrogate. Here we show that structural constraint can translate this surface motif into a molecular system. A calix[4]pyrrolato ligand enforces a unique cis-bent geometry in a dinuclear Ge(II) complex, generating a polarized Ge-Ge unit that emulates the ambiphilic character of a Ge(100) buckled dimer. Structural analysis, quantitative Lewis acidity/basicity measurements and solution-phase reactivity reveal pronounced surface-like features, but clear divergence from conventional digermenes. The rigid geometry creates spatially separated, exceptionally strong Lewis acidic and basic sites that govern distinct reactivity patterns. Accordingly, this work establishes constrained main-group complexes as molecular surrogates for interrogating solid-vacuum interface chemistry in solution.