| Summary: | A new series of tin(II) complexes (<b>1</b>, <b>2</b>, <b>4</b>, and <b>5</b>) were successfully synthesized by employing hydroxy functionalized pyridine ligands, specifically 2-hydroxypyridine (hpH), 8-hydroxyquinoline (hqH), and 10-hydroxybenzo[h]quinoline (hbqH) as stabilizing ligands. Complexes [Sn(μ-κ<sup>2</sup>ON-OC<sub>5</sub>H<sub>4</sub>N)(N{SiMe<sub>3</sub>}<sub>2</sub>)]<sub>2</sub> (<b>1</b>) and [Sn<sub>4</sub>(μ-κ<sup>2</sup>ON-OC<sub>5</sub>H<sub>4</sub>N)<sub>6</sub>(κ<sup>1</sup>O-OC<sub>5</sub>H<sub>4</sub>N)<sub>2</sub>] (<b>2</b>) are the first structurally characterized examples of tin(II) oxypyridinato complexes exhibiting {Sn<sub>2</sub>(OCN)<sub>2</sub>} heterocyclic cores. As part of our study, <sup>1</sup>H DOSY NMR experiments were undertaken using an external calibration curve (ECC) approach, with temperature-independent normalized diffusion coefficients, to determine the nature of oligomerisation of <b>2</b> in solution. An experimentally determined diffusion coefficient (298 K) of 6.87 × 10<sup>−10</sup> m<sup>2</sup> s<sup>−1</sup> corresponds to a hydrodynamic radius of Ca. 4.95 Å. This is consistent with the observation of an averaged hydrodynamic radii and equilibria between dimeric [Sn{hp}<sub>2</sub>]<sub>2</sub> and tetrameric [Sn{hp}<sub>2</sub>]<sub>4</sub> species at 298 K. Testing this hypothesis, <sup>1</sup>H DOSY NMR experiments were undertaken at regular intervals between 298 K–348 K and show a clear change in the calculated hydrodynamic radii form 4.95 Å (298 K) to 4.35 Å (348 K) consistent with a tetramer ⇄ dimer equilibria which lies towards the dimeric species at higher temperatures. Using these data, thermodynamic parameters for the equilibrium (ΔH° = 70.4 (±9.22) kJ mol<sup>−1</sup>, ΔS° = 259 (±29.5) J K<sup>−1</sup> mol<sup>−1</sup> and ΔG°<sub>298</sub> = −6.97 (±12.7) kJ mol<sup>−1</sup>) were calculated. In the course of our studies, the Sn(II) oxo cluster, [Sn<sub>6</sub>(m<sup>3</sup>-O)<sub>6</sub>(OR)<sub>4</sub>:{Sn<sup>(II)</sup>(OR)<sub>2</sub>}<sub>2</sub>] (<b>3</b>) (R = C<sub>5</sub>H<sub>4</sub>N) was serendipitously isolated, and its molecular structure was determined by single-crystal X-ray diffraction analysis. However, attempts to characterise the complex by multinuclear NMR spectroscopy were thwarted by solubility issues, and attempts to synthesise <b>3</b> on a larger scale were unsuccessful. In contrast to the oligomeric structures observed for <b>1</b> and <b>2</b>, single-crystal X-ray diffraction studies unambiguously establish the monomeric 4-coordinate solid-state structures of [Sn(κ<sup>2</sup>ON-OC<sub>9</sub>H<sub>6</sub>N)<sub>2</sub>)] (<b>4</b>) and [Sn(κ<sup>2</sup>ON-OC<sub>13</sub>H<sub>8</sub>N)<sub>2</sub>)] (<b>5</b>).
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