NLO Properties of Unidirectional Lengthening [Pt3(CO)3(μ2-CO)3]n2− Clusters: A TDDFT Study

The first and second hyperpolarizability of three platinum carbonyl cluster dianions [Pt3(CO)3(μ2-CO)3]n2− (n = 1, 2, 3) have been studied at B3LYP level of density functional theory. The structures of the dianions are made up of parallel tri-platinum carbonyl [Pt3(CO)3(μ2-CO)3]2− plane layers, which are stacked up vertically by Pt–Pt bonds inter layers presenting a growing length along the stacking direction as n enlarging, and forming cluster wires with a little torsion when n ≥ 3. All of the three dianions possess moderately large β and γ components and the results present a strengthening sign of the NLO response along the stacked up direction, as the cluster lengthening. Based on the results, it is determined that n = 2 and 3 is the start point of the exhibition of the unidirectional characters along lengthening direction of the second and third NLO response, respectively, of this kind of clusters. For the further knowledge of the NLO response mechanism, the electronic properties and the excited spectra have also been studied.