A Molecular Model for the Ge(100) Buckled Dimer

Silicon and germanium (100) surfaces underpin modern semiconductor technologies, yet their atomic-scale reactivity remains difficult to access experimentally due to the need for sophisticated surface analytical techniques. Their defining structural element, the buckled dimer (BD), comprises a Lewis-acidic "down" atom and a Lewis-basic "up" atom, but a faithful molecular analogue has remained elusive. Here we report a dinuclear Ge(II) complex supported by a calix[4]pyrrolato ligand that enforces a rigid cis-bent geometry closely mirroring the Ge(100) BD. Single-crystal X-ray diffraction and solution-phase reactivity studies reveal distinct surface-like behaviour—including Lewis base coordination, chalcogen binding, and selective [2+2] alkyne cycloaddition—while diverging sharply from the reactivity of conventional, unconstrained digermenes. Quantitative scaling of Lewis acidity and basicity positions the two Ge centres among the strongest molecular Lewis acids and bases, providing the first numerical benchmark for Ge(100) ambiphilicity and highlighting an overlooked aspect of semiconductor surface chemistry. The observed substrate selectivities are rationalized by the rigid BD geometry, offering new molecular-level perspectives on Ge(100) surface passivation and functionalization. Together, these findings demonstrate how structural constraint can translate the elusive chemistry of solid–vacuum interfaces into isolable, quantifiable molecular systems.