Can Serendipity Still Hold Any Surprises in the Coordination Chemistry of Mixed-Donor Macrocyclic Ligands? The Case Study of Pyridine-Containing 12-Membered Macrocycles and Platinum Group Metal Ions PdII, PtII, and RhIII

Abstract

This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L¹-L³ towards Platinum Group metal ions Pd^II, Pt^II, and Rh^III. The reactions between the chloride salts of these metal ions and the three ligands in MeCN/H₂O or MeOH/H₂O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and ¹H- and ¹³C-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L¹)Cl]₂[Pd₂Cl₆], [Pt(L¹)Cl](BF₄), [Rh(L¹)Cl₂](PF₆), and [Rh(L³)Cl₂](BF₄)·MeCN shows the coordinated macrocyclic ligands adopting a folded conformation, and occupying four coordination sites of a distorted square-based pyramidal and octahedral coordination environment for the Pd^II/Pt^II, and Rh^III complexes, respectively. The remaining coordination site(s) are occupied by chlorido ligands. The reaction of L₃ with PtCl₂ in MeCN/H₂O gave by serendipity the complex [Pt(L³)(m-1,3-MeCONH)PtCl(MeCN)](BF₄)₂·H₂O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) Å and feature one square-planar and one octahedral coordination environment. Density Functional Theory (DFT) calculations, which utilize the broken symmetry approach (DFT-BS), indicate a singlet d⁸-d⁸ Pt^II-Pt^II ground-state nature for this compound, rather than the alleged d⁹-d⁷ Pt^I-Pt^III mixed-valence character reported for related dinuclear Pt-complexes.

Keywords: DFT-Calculations; Rhodium; macrocyclic ligands; palladium; platinum.

Figure 1

Pyridine-based macrocyclic ligands are considered in this study.

Figure 2

View of the [Pd(L¹)Cl]⁺ complex cation in [Pd(L¹)Cl]₂[Pd₂Cl₆] with the numbering scheme adopted. Displacement ellipsoids are drawn at a 30% probability level. H-atoms are omitted for clarity. Selected bond distances (Å): Pd1-N1 2.013(3), Pd1-S1 2.3062(10), Pd1-S2 2.2915(10), Pd1-Cl1 2.2984(11), Pd1-O1 2.654(3); angles (°): N1-Pd1-S1 86.52(9), N1-Pd1-S2 86.17(9), N1-Pd1-Cl1 179.14(9), N1-Pd1-O1 89.5(1), S1-Pd1-S2 162.32(4), S1-Pd1-Cl1 94.34(4), S1-Pd1-O1 81.69(6), S2-Pd1-Cl1 92.99(4), S2-Pd1-O1 82.17(6), O1-Pd1-Cl1 90.57(6).

Figure 3

View of the [Pt(L¹)Cl]⁺ complex cation in [Pt(L¹)Cl](BF₄) with the numbering scheme adopted. Displacement ellipsoids are drawn at a 30% probability level. H-atoms are omitted for clarity. Selected bond distances (Å): Pt1-N1 2.010(4), Pt1-S1 2.2753(14), Pt1-S2 2.2804(14), Pt1-Cl1 2.3008(15), Pt1-O1 2.752(4); angles (°): N1-Pt1-S1 86.48(14), N1-Pt1-S2 86.95(14), N1-Pt1-Cl1 178.99(13), N1-Pt1-O1 89.5(2), S1-Pt1-S2 163.59(6), S1-Pt1-Cl1 92.76(6), S1-P1-O1 82.71(9), S2-Pt1-Cl1 93.61(6), S2-P1-O1 82.21(9), O1-Pt1-Cl1 89.80(9).

Figure 4

Partial view along the [−1,1,0] direction of the packing of [Pt(L¹)Cl]⁺ cations in [Pt(L¹)Cl](BF₄). Only H atoms involved in the relevant H-bonds are shown for clarity. Dimers of the complex cation featuring C-H···O and C-H···Cl bonds [H10Bⁱ···Cl1 2.89, C10ⁱ···Cl1 3.751(7) Å, C10ⁱ-H10Bⁱ···Cl1 146°, H11Bⁱ···O1 2.43, C11ⁱ···O1 3.397(9)Å, C11ⁱ-H11Bⁱ···O1 167°] are held together by weak Pt1ⁱ···Sⁱⁱ [Pt1ⁱ···S2ⁱⁱ 3.625(2) Å] contacts and C-H···Cl H-bonds [H12Aⁱⁱ···Cl1ⁱ 2.88, C12ⁱⁱ···Cl1ⁱ 3.533(6) Å, C12ⁱⁱ-H12Aⁱⁱ···Cl1ⁱ 124°] to form chains which run along the [001] direction. Symmetry codes: i = 1 − x, 1 − y, −z; ii = x, y, −1 + z.

Figure 5

View of the [Rh(L¹)Cl₂]⁺ complex cation in [Rh(L¹)Cl₂](PF₆) with the numbering scheme adopted. Displacement ellipsoids are drawn at a 30% probability level. H-atoms are omitted for clarity. Selected bond distances (Å): Rh1-N1 2.015(3), Rh1-O1 2.088(2), Rh1-S1 2.2851(10), Rh1-S2 2.3056(10), Rh1-Cl1 2.3318(11), Rh1-Cl2 2.3001(10); angles (°): N1-Rh1-O1 89.92(11), N1-Rh1-S1 87.20(8), N1-Rh1-S2 86.48(8), N1-Rh1-Cl1 177.55(9), N1-Rh1-Cl2 89.96(9), S1-Rh1-O1 86.60(7), S1-Rh1-Cl1 91.94(4), S1-Rh1-Cl2 92.57(4), S1-Rh1-S2 170.23(3), S2-Rh1-O1 85.96(7), S2-Rh1-Cl1 94.07(4), S2-Rh1-Cl2 94.86(4), O1-Rh1-Cl1 87.74(8), O1-Rh1-Cl2 179.16(7), Cl1-Rh1-Cl2 92.37(4).

Figure 6

Partial view along the [100] direction of [Rh(L¹)Cl₂]⁺ complex cations joined head to tail via C-H···Cl bonds to form zig-zag chains running along the [010] direction in [Rh(L¹)Cl₂](PF₆). Only H atoms involved in the relevant H-bonds are shown for clarity. Cl1···H7Aⁱ 2.66, Cl1···C7ⁱ 3.567(4) Å, Cl1-H7Aⁱ···C7ⁱ 157°. Symmetry code: i = −x, −½ + y, 3/2 − z.

Figure 7

A view of the [Pt(L³)(μ-1,3-MeCONH)PtCl(MeCN)]²⁺ cation in [Pt(L³)(μ-1,3-MeCONH)PtCl(MeCN)](BF₄)₂·H₂O with labelling scheme adopted. Displacement ellipsoids are drawn at a 30% probability level. H-atoms are omitted for clarity reasons. Selected bond distances (Å): Pt1-N3 1.971(4); Pt1-N4 1.981(4), Pt1-Cl1 2.3433 (11), Pt1-Pt2 2.5798(3), Pt2-N1 2.006(3), Pt2-O1 2.018(3), Pt2-N2 2.237(3), Pt2-S1 2.2926(10), Pt2-S2 2.3067(10), N4-C13 1.274(5), O1-C13 1.290(4); and angles (°): N3-Pt1-N4 176.46(15), N3-Pt1-Cl1 89.16(11), N3-Pt1-Pt2 98.39(11), N4-Pt1-Pt2 83.11(11), Cl1-Pt1-Pt2 172.44(3), N1-Pt2-O1 177.98(12), N1-Pt2-N2 91.81(13), O1-Pt2-N2 86.92(12), N1-Pt2-S1 87.28(9), O1-Pt2-S1 91.09(9), N2-Pt2-S1 87.27(9), N1-Pt2-S2 86.61(9), O1-Pt2-S2 94.86(9), N2-Pt2-S2 86.02(9), S1-Pt2-S2 170.77(4), N1-Pt2-Pt1 94.45(9), O1-Pt2-Pt1 86.86(8), N2-Pt2-Pt1 173.64(10), S1-Pt2-Pt1 94.19(3), S2-Pt2-Pt1 93.17(3).

Figure 8

Partial view of complex cations interacting with BF₄⁻ anions and H₂O molecules to form chains extending along the [001] direction in [Pt(L³)(μ-1,3-MeCONH)PtCl(MeCN)](BF₄)₂·H₂O. H-atoms not involved in H-interactions were omitted for clarity. N2H···OW 2.04(4), N2···OW 2.910(6) Å, N2-H···OW 174(4)°, F8···HW2 2.02(5), OW···F8 2.775(7) Å, OW-HW2···F8 145(4)°, F7···H11B 2.62, C11···F7 3.43(7) Å, C11-H11B···F7 141°, F8···H14A 2.48, C14···F8 3.283(5) Å, C14-H14A···F8 141°, F5···HW1 2.45(6), OW···F5 2.970(6) Å, OW-HW1···F5 119(6)°, F4···H16Bⁱ 2.59, C16ⁱ···F4 3.52(7) Å, C16ⁱ-H16Bⁱ···F4 161°. Symmetry code: i = x, y, 1 + z.

Figure 9

2D view of the number of structurally characterized diplatinum-based fragments formally belonging to dⁿ-dⁿ and mixed-valence dⁿ-d^m discrete binuclear complexes (n, n = 6, 7, 8, 9; n, m = 6, 8; 7, 8; and 7, 9) against the coordination number displayed by the platinum ions.

Figure 10

View of the [Rh(L³)Cl₂]⁺ complex cation in [Rh(L³)Cl₂](BF₄)·MeCN with the numbering scheme adopted. Displacement ellipsoids are drawn at a 30% probability level. H-atoms are omitted for clarity. Selected bond distances (Å): Rh1-N1 2.018(5), Rh1-N2 2.047(5), Rh1-S1 2.3124(15), Rh1-S2 2.3010(15), Rh1-Cl1 2.3511(15), Rh1-Cl2 2.3515(14); angles (°): N1-Rh1-N2 91.72(19), N1-Rh1-S1 86.99(15), N1-Rh1-S2 87.20(15), N1-Rh1-Cl1 178.94(14), N1-Rh1-Cl2 88.24(14), S1-Rh1-N2 87.20(15), S1-Rh1-Cl1 93.31(6), S1-Rh1-Cl2 92.94(6), S1-Rh1-S2 171.78(5), S2-Rh1-N2 87.17(15), S2-Rh1-Cl1 92.40(6), S2-Rh1-Cl2 92.68(6), N2-Rh1-Cl1 87.29(14), N2-Rh1-Cl2 179.84(17), Cl1-Rh1-Cl2 92.76(5).

Figure 11

(a) Partial view of head-to-head interacting [Rh(L³)Cl₂]⁺ complex cations in [Rh(L³)Cl₂](BF₄)·MeCN to form chains running along the [100] direction: N2-H2···Cl2ⁱ 2.45 Å, N2···Cl2ⁱ 3.235(5) Å, N2-H2···Cl2ⁱ 142°; (b) partial view along the [101] direction of an undulated sheet lying in the (101) plane and formed by weak soft-soft interactions between [Rh(L³)Cl₂]⁺ complex cations: Cl2···S2ⁱⁱ 3.478(2), Cl2···S1ⁱⁱⁱ 3.483(2) Å. Symmetry codes: i = −1 + x, y, z; ii = ½ + x, ½ − y, ½ + z; iii = ½ + x, ½ − y, − ½ + z; iv = 1 + x, y, z.

Figure 12

Frontier KS-MO isosurfaces calculated at the optimized geometry in its singlet ground-state for [Pt(L³)(μ-1,3-MeCONH)PtCl(MeCN)]²⁺ (top) and for [Pt₂(tfepma)₂Cl₄] (bottom) in the gas phase; hydrogen atoms omitted for clarity; cutoff value = 0.05 |e|.