Supramolecular cis-“Bis(Chelation)” of [M(CN)6]3− (M = CrIII, FeIII, CoIII) by Phloroglucinol (H3PG)

Abstract

Studies on molecular co-crystal type materials are important in the design and preparation of easy-to-absorb drugs, non-centrosymmetric, and chiral crystals for optical performance, liquid crystals, or plastic phases. From a fundamental point of view, such studies also provide useful information on various supramolecular synthons and molecular ordering, including metric parameters, molecular matching, energetical hierarchy, and combinatorial potential, appealing to the rational design of functional materials through structure–properties–application schemes. Co-crystal salts involving anionic d-metallate coordination complexes are moderately explored (compared to the generality of co-crystals), and in this context, we present a new series of isomorphous co-crystalline salts (PPh4)3[M(CN)6](H3PG)2·2MeCN (M = Cr, 1; Fe, 2; Co 3; H3PG = phloroglucinol, 1,3,5-trihydroxobenzene). In this study, 1–3 were characterized experimentally using SC XRD, Hirshfeld analysis, ESI-MS spectrometry, vibrational IR and Raman, 57Fe Mössbauer, electronic absorption UV-Vis-NIR, and photoluminescence spectroscopies, and theoretically with density functional theory calculations. The two-dimensional square grid-like hydrogen-bond {[M(CN)6]3–;(H3PG)2}¥ network features original {[M(CN)6]3–;(H3PG)4} supramolecular cis-bis(chelate) motifs involving: (i) two double cyclic hydrogen bond synthons M(-CN×××HO-)2Ar, {[M(CN)6]3–;H2PGH}, between cis-oriented cyanido ligands of [M(CN)6]3– and resorcinol-like face of H3PG, and (ii) two single hydrogen bonds M-CN×××HO-Ar, {[M(CN)6]3–;HPGH2}, involving the remaining two cyanide ligands. The occurrence of the above tectonic motif is discussed with regard to the relevant data existing in the CCDC database, including the multisite H-bond binding of [M(CN)6]3– by organic species, mononuclear coordination complexes, and polynuclear complexes. The physicochemical and computational characterization discloses notable spectral modifications under the regime of an extended hydrogen bond network.

Nonlinear and Emissive {[MIII(CN)6]3–···Polyresorcinol} (M = Fe, Co, Cr) Cocrystals Exhibiting an Ultralow Frequency Raman Response

“…700 nm for FeTriRB , ca . 700 nm for FeH 3 PG , and only ca . 580 nm for K 3 [Fe(CN) 6 ], and not present for PPh 4 [Fe(CN) 6 ]·7H 2 O salt (Figure ).…”

“…In the same order, an increase in the extent of the π-electron system across the molecule can be noted, which facilitates the possibility of the aforementioned intra-CT interactions within L leading to overall stronger orbital interactions and finally stronger total interactions between L and [M(CN) 6 ] 3− . Moreover, in the MTriRB and MH 3 PG molecular clusters, topologically identical single linear D contacts can be noted, characterized by interaction energies ranging from 52,61,62 LF-Raman scattering spectra for all the presented materials exhibit numerous symmetrical LF-Raman peaks (Figures 4 and S24) with a few peaks in the sub-THz region: 25 cm −1 (0.75 THz) for FeDiR, 31 cm −1 (0.93 THz) for CoDiR, 22 cm −1 (0.66 THz) for CrDiR, 18 cm −1 (0.54 THz) for CrTriRB as well as FeTriRB, and 24 cm −1 (0.72 THz) for CoTriRB. A noteworthy observation is that the lowest Raman peak for the Co(III) based compounds is shifted to higher energy by 6 cm −1 compared to the other analogs.…”

“…The most elegant ones are “intuitive” ( e.g. , expected based on the results of our previous studies involving phloroglucinol H 3 PG coformer) supramolecular cis -bis(chelate)-like {[M(CN) 6 ] 3– ;­( H 2 L) 2 ­( H L) 2 } or tris(chelate)-like {[M(CN) 6 ] 3– ;­( H 2 L) 3 } fragments. In the current work, they are composed of the cyclic, either frontal or side {[M(CN) 6 ] 3– ;­( H 2 L)}, synthons, involving phenolic groups attached to the same resorcinol-like ring of an L molecule or the different rings of one L, respectively.…”

“…50 Then, following the works of Desiraju and Paul on multicomponent topological CT-colored resorcinol (1,3-dihydroxybenzene) based systems 29 and the pioneering works of Oshio and co-workers on phloroglucinol-conditioned (H 3 PG, 1,3,5-trihydroxybenzene) spin-crossover cyanidobridged square Co 2 Fe 2 complexes, 51 we explored further possible schemes of noncovalent interactions between multiple hydrogen bond donor H 3 PG (Scheme 1) and mononuclear 52 and polynuclear 53 − ;-HPGH 2 }, involving the remaining two cyanide ligands (Figure 1). 52 Spectroscopic and computational descriptions revealed notable strength of the underlying interactions. While the local symmetry of the {[M(CN) 6 ] 3− ;(H 3 PG) 4 } motif might be approached with the chiral C 2 point group, interesting from the standpoint of the noncentrosymmetric and enantiopure resolution, regrettably, the centrosymmetric C2/c space group was observed for these crystals.…”

“…46−50 Notably, our studies introduced the first instances of binary core−shell crystals based on anion-π interactions. 50 Then, following the works of Desiraju and Paul on multicomponent topological CT-colored resorcinol (1,3-dihydroxybenzene) based systems 29 and the pioneering works of Oshio and co-workers on phloroglucinol-conditioned (H 3 PG, 1,3,5-trihydroxybenzene) spin-crossover cyanidobridged square Co 2 Fe 2 complexes, 51 we explored further possible schemes of noncovalent interactions between multiple hydrogen bond donor H 3 PG (Scheme 1) and mononuclear 52 and polynuclear 53 − ;-HPGH 2 }, involving the remaining two cyanide ligands (Figure 1). 52 Spectroscopic and computational descriptions revealed notable strength of the underlying interactions.…”