Barium complexes ligated by bulky boryloxides [OBR
2]
− (where R=CH(SiMe
3)
2, 2,4,6-
iPr
3-C
6H
2 or 2,4,6-(CF
3)
3-C
6H
2), siloxide [OSi(SiMe
3)
3]
−, and/or phenoxide [O-2,6-Ph
2-C
6H
3]
−, have been prepared. A diversity of coordination patterns is observed in the solid state for both homoleptic and heteroleptic complexes, with coordination numbers ranging between 2 and 4. The identity of the bridging ligand in heteroleptic dimers [Ba(μ
2-X
1)(X
2)]
2 depends largely on the given pair of ligands X
1 and X
2. Experimentally, the propensity to fill the bridging position increases according to [OB{CH(SiMe
3)
2}
2)]
−<[N(SiMe
3)
2]
−<[OSi(SiMe
3)
3]
−<[O(2,6-Ph
2-C
6H
3)]
−<[OB(2,4,6-
iPr
3-C
6H
2)
2]
−. This trend is the overall expression of 3 properties: steric constraints, electronic density and σ- and π-donating capability of the negatively charged atom, and ability to generate Ba ⋅ ⋅ ⋅ F, Ba ⋅ ⋅ ⋅ C(π) or Ba ⋅ ⋅ ⋅ H−C secondary interactions. The comparison of the structural motifs in the complexes [Ae{μ
2-N(SiMe
3)
2}(OB{CH(SiMe
3)
2}
2)]
2 (Ae = Mg, Ca, Sr and Ba) suggest that these observations may be extended to all alkaline earths. DFT calculations highlight the largely prevailing ionic character of ligand-Ae bonding in all compounds. The ionic character of the Ae-ligand bond encourages bridging coordination, whereas the number of bridging ligands is controlled by steric factors. DFT computations also indicate that in [Ba(μ
2-X
1)(X
2)]
2 heteroleptic dimers, ligand predilection for bridging vs. terminal positions is dictated by the ability to establish secondary interactions between the metals and the ligands.
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