Segregation of tetracarbon units in low‐energy tetracarbindane structures: Major differences from their aluminum and gallium analogs

Abstract

The structures and energetics of the tetracarbindanes C4Inn−4Men (n = 6‐14) have been determined by density functional theory. In contrast to their aluminum and gallium analogs, the lowest energy tetracarbindanes typically have all four carbon atoms segregated into a single C4 unit. Thus, linear C4 units resembling butadiene are found in the lowest energy C4Inn−4Men structures. In addition, some higher energy tetracarbindane structures have a structural feature not found in any of the corresponding tetracarbalanes and tetracarbagallanes, namely closed trapezoidal C4 units resembling cyclobutene. Such trapezoidal C4 units bind to the Inn−4 subcluster with the CC edge bonding to a single indium atoms as an olefin‐metal or 3‐center 2‐electron bond. These differences may be attributed to the larger size of indium atoms (1.42 Å covalent radius) relative to gallium atoms (1.22 Å covalent radius).