Lanthanides, lanterns, and lone pairs: computational studies of inorganic complexes
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Abstract
Computational work was performed to support several synthetic projects in the Doerrer lab. The new luminescent cerium complexes [K(THF)6][Ce(OC4F9)4(THF)2] (20) and [K(THF)2][Ce(pinF)2(THF)3] (22) were structurally optimized in the gas phase, and their uncommonly blue-shifted absorption spectra were simulated by TD-DFT. Electronic structure analysis elucidated the 4f→5d transitions responsible for the absorption peaks, showing the involvement of the fluorinated alkoxide ligands in the composition of the donor orbitals.
The [pinF]2− ligand was also coordinated to Sn(II) and Sn(IV). The structures of the new compounds [K]2[Sn(pinF)2] (31) and [K]2[Sn(pinF)3] (32) were optimized by DFT and their electronic structures examined, revealing a sterically exposed lone pair in the case of 31, and for 32 showing that its unusually twisted six-coordinate geometry (azimuthal angle ~30°) is maintained in the absence of counterions.
Metal-metal interactions were investigated in the diamagnetic lantern compounds [PtM(SOCR)4(OH2)] (R = CH3, M = Mg (1), Zn (56); R = C6H5, M = Mg (2), Ca (3), Zn (4)). 195Pt NMR spectra calculated for these lanterns and the precursor ion [Pt(SAc)4]2− (42) demonstrate the electronic effect of coordinating these Lewis acidic metals to the electron-rich Pt(II) center. Canonical and NBO analyses show that the {PtZn} lanterns 41 and 56 possess dative bonds between Pt and Zn, while Ca and Mg feature purely ionic interactions with Pt.
A new class of heterobimetallic lantern complexes of the form [PtM(pipCOS)4(py)] (M = Mn (43), Co (44), Ni (45), and Zn (46)) were synthesized. These species exhibit strong absorption in the visible range that was investigated by DFT. Structural and electronic analyses reveal donation from the lone pair on the piperidine N atom into the delocalized ligand system in the ground state, indicating the potential for LMCT to occur upon excitation.
A new bidentate ligand, a condensed thioamide, was bound to a Pt(II) center in the complexes [Pt(ctaPhMe)2] (57) and [Pt(ctaPhMe)2]2− (59). DFT analysis of these and the hypothetical ion [Pt(ctaPhMe)2]− (58) showed that reduction occurs on the ligands themselves, with the added electron density concentrated on carbon atoms in the ring, and that the doubly reduced species exists in the high-spin state.