| Summary: | We have explored the suitability of an <i>O,N,N</i>−donor Schiff base (H<sub>2</sub>SB) for obtaining dinuclear complexes with heavy metal ions such as Cu<sup>2+</sup>, Zn<sup>2+</sup>, Ni<sup>2+</sup>, and Co<sup>2+</sup> (borderline acids) as well as Pd<sup>2+</sup> and Cd<sup>2+</sup> (soft acids). Spectroscopic studies demonstrated that the complexation of H<sub>2</sub>SB and Cu<sup>2+</sup>, Zn<sup>2+</sup>, Ni<sup>2+</sup>, Co<sup>2+</sup>, Pd<sup>2+</sup>, and Cd<sup>2+</sup> occurred at a 1:1 stoichiometry. We have found two square planar centers with Pd-N-Pd angles of 93.08(11)° and a Pd−Pd distance of 3.0102(4) Å in Pd<sub>2</sub>(SB)<sub>2</sub>·Me<sub>2</sub>CO. This Pd−Pd distance is 30% shorter than the sum of the van der Waals radii, which is in accordance with a strong palladophilic interaction. Fluorescence studies on H<sub>2</sub>SB-M<sup>2+</sup> interaction showed that H<sub>2</sub>SB can detect Cu<sup>2+</sup> ions in a sample matrix containing various metal ions (hard, soft, or borderline acids) without interference. Determination of binding constants showed that H<sub>2</sub>SB has a greater affinity for borderline acids than for soft acids.
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