Pt–Mg, Pt–Ca, and Pt–Zn Lantern Complexes and Metal-Only Donor–Acceptor Interactions

Abstract

Pt-based heterobimetallic lantern complexes of the form [PtM(SOCR)(L)] have been shown previously to form intermolecular metallophilic interactions and engage in antiferromagnetic coupling between lanterns having M atoms with open shell configurations. In order to understand better the influence of the carboxylate bridge and terminal ligand on the electronic structure, as well as the metal-metal interactions within each lantern unit, a series of diamagnetic lantern complexes, [PtMg(SAc)(OH)] (1), [PtMg(tba)(OH)] (2), [PtCa(tba)(OH)] (3), [PtZn(tba)(OH)] (4), and a mononuclear control (PhP)[Pt(SAc)] (5) have been synthesized. Crystallographic data show close Pt-M contacts enforced by the lantern structure in each dinuclear case. Pt-NMR spectroscopy of 1-4, (PhP)[Pt(SAc)] (5), and several previously reported lanterns revealed a strong chemical shift dependence on the identity of the second metal (M), mild influence by the thiocarboxylate ligand (SOCR; R = CH (thioacetate, SAc), CH (thiobenzoate, tba)), and modest influence from the terminal ligand (L). Fluorescence spectroscopy has provided evidence for a Pt···Zn metallophilic interaction in [PtZn(SAc)(OH)], and computational studies demonstrate significant dative character. In all of 1-4, the short Pt-M distances suggest that metal-only Lewis donor (Pt)-Lewis acceptor (M) interactions could be present. DFT and NBO calculations, however, show that only the Zn examples have appreciable covalent character, whereas the Mg and Ca complexes are much more ionic.

Imposing high-symmetry and tuneable geometry on lanthanide centres with chelating Pt and Pd metalloligands

“…The platinum atom is shifted slightly out of plane either towards (for the S1 4 plane) or away from (for the S1a 4 plane) the gadolinium centre by 0.086 Å and 0.038 Å, respectively. These out of plane shifts are slightly larger than those observed in the related heterobimetallic lantern complexes, 39 – 43 and significantly larger than for the non-coordinated metalloligand in which the platinum sits exactly in the S 4 plane. 39 …”

“…the Ln( iii ) ion, was recently evidenced in the heterobimetallic lantern complexes based on the alkaline earth metals using 195 Pt NMR, thereby demonstrating the Lewis-basic behaviour of the platinum centre. 39 The minimization of the off-diagonal terms in the Hamiltonian (1) is again found upon going from 1Y 0.98 Gd 0.02 ′ to the higher symmetry 2Y 0.98 Gd 0.02 ′ species. Albeit a direct comparison is hampered by our failure in determining the sixth order off-diagonal parameters for 1Y 0.98 Gd 0.02 ′ , we note that the values of B +44 and B –46 for 2Y 0.98 Gd 0.02 ′ are found to be equal to zero within error, supporting the notion that the point group symmetry in the 2Ln′ compounds is D 4d to a very good approximation.…”

“…Direct addition of [PPh 4 ]Cl to aqueous solutions containing [Ln{Pt(SAc) 4 } 2 ] – precipitates the non-coordinated metalloligand as golden-yellow crystals of formulation [PPh 4 ] 2 [Pt(SAc) 4 ]·4.5H 2 O, 39 preventing direct preparation of the [PPh 4 ] + salts. However, facilitated by the reasonable solubility of the near-amorphous crude [N n Pr 4 ][Ln{Pt(SAc) 4 } 2 ] salts in polar organic solvents like acetonitrile, nitromethane, and acetone, golden quadratic single crystals of [PPh 4 ][Ln{Pt(SAc) 4 } 2 ] ( 2Ln ) could instead be obtained in high yields by the metathesis reaction of crude [N n Pr 4 ][Ln{Pt(SAc) 4 } 2 ] and [PPh 4 ]Cl in MeNO 2 ( Scheme 1 ).…”

“…The platinum( ii ) complexes [Pt II (SC(O)R) 4 ] 2– (R = Me (thioacetate), Ph (thiobenzoate)) have previously been reported on their own (for R = Me), 39 and as constituent units of a family of heterobimetallic lantern complexes of formulation [Pt II M II (SC(O)R) 4 (solv) n ] (M = Mg, Ca, Fe, Co, Ni, Zn; solv = solvent molecules), 39 – 42 A[Pt II M II (SC(O)Me) 4 (NCS)] (A = [Na(15-crown-5)], [Na(12-crown-4) 2 ]; M = Mn, Co, Ni, Zn), 43 and [Pt II Cr III (SC(O)Ph) 4 (NCS)] n . 43 In the bimetallic lantern compounds, the soft Lewis acidity of platinum( ii ) allows for selective coordination by the soft sulphur donors, while the harder Lewis acids, that is the divalent n s and 3d metal ions, are selectively coordinated by the oxygen atoms of the thiocarboxylates.…”

Au3-to-Ag3coordinate-covalent bonding and other supramolecular interactions with covalent bonding strength

“…Tz)] 3 , blue regions) during the stacking process and quite small formation energies of $3 kcal mol À1 . Notwithstanding the small magnitude of each constituent force, the overall dimer-of-trimer stabilization magnitude of $65 kcal mol À1 herein is even stronger than those in literature precedents of largely undisputed intermolecular covalent bonds, such as those in d 1 -d 1 or d 9 -d 9 ground-state single bonds, 3 P g or 3 S u + excited-state single bonds in the Hg 2 excimer, or singlet (or triplet) p-stacked pyrene 2 sandwiched excimersall of which attain D e values in the #50 kcal mol À1 range 41,[46][47][48][49][50][51]. The stabilization herein is likewise $2Â higher than that in the claimed polar-covalent bonding reported recently in a heterobimetallic Au 2 CuIm 2 Pz complex (D e ¼ $35-40 kcal mol À1 ).…”