Spectrally-resolved third-harmonic generation and the fundamental role of O–H⋯Cl hydrogen bonding in O_h, T_d-cobalt(ii) tetraphenylmethane-based coordination polymers

Abstract

The reaction of a phosphonate-diester tetraphenylmethane-based tecton, tetrakis[4-(diethoxyphosphoryl)phenyl]methane, (L) with cobalt(ii) chloride afforded a centrosymmetric coordination polymer (CP), [L·2Co(HO)·2CoCl], 2-Cl, possessing simultaneously octahedral (O) and tetrahedral (T) metal centers. This material served as a model compound for the demonstration of factors influencing the spectral dependence of one of the nonlinear optical (NLO) phenomena, the third-harmonic generation (THG). The spectrally-resolved THG (SR-THG) measurements in the range from 1125 to 1750 nm revealed that a maximum of THG response is obtained when the fundamental beam is around 1300 nm. The SR-THG study was combined with an analysis of the self-absorption effects of pumping and of third-harmonic radiation; based on these results, we put forward a hypothesis that the THG action spectrum is influenced more by the ability of the material to self-absorb the third harmonic rather than by the extent of self-absorption of the pumping radiation. Apart from investigations of NLO properties, we have explored coordination and particularly the supramolecular interactions that build up the 2-Cl CP. Despite the tetrahedral, spatial shape of the ligand L, CP 2-Cl has a two-dimensional net. The structure was found to be strongly supported by O-HCl hydrogen bonds, since each CoCl complex anion is an acceptor of eight of such interactions within a distorted square grid layer of cobalt(ii) ions. While coordination and hydrogen-bonded nets are both featuring the sql topology when treated separately, the consideration of both of them as topological paths yields a trinodal 4,4,6-connected net, described by the point symbol (4·8)(4·6)(4·6·8). SR-THG and structural studies of 2-Cl have been also supported by far- and mid-infrared spectroscopy, UV-Vis-NIR solid state absorption analysis, thermogravimetry and preliminary magnetic characterization.

Second‐Harmonic and Terahertz Generation in a Prussian‐Blue Analogue

“…In the HT phase, and over the scanned spectral range, we measured χ HT ,RbMnFe (2) ≈ 0.03 ± 0.01 pm V –1 . This value is very close to the one previously published for this sample and it indicates that two‐photon absorption, which has been considered by previous authors in second‐ and third‐harmonic generation experiments, is likely negligible in our sample , , . However, in the LT phase, χ xvz (2) presents clear dispersion.…”

“…This value is very close to the one previously published for this sample and it indicates that two-photon absorption, which has been considered by previous authors in second-and third-harmonic generation experiments, is likely negligible in our sample. [7,19,20] However, in the LT phase, xvz (2) presents clear dispersion. Below 1.2 μm, it rapidly increases, and at 1.1 μm, it is ca.…”

Benzyl Dihydrazone versus Thiosemicarbazone Schiff Base: Effects on the Supramolecular Arrangement of Cobalt Thiocyanate Complexes and the Generation of CoN6 and CoN4S2 Coordination Spheres

“…As a result, the structure 5 is an interesting example of the rare group of mixed‐geometry cobalt coordination compounds, in which the Co centers exist in both octahedral and tetrahedral forms. The simultaneous presence of both of those coordination polyhedra is observed for ligands that cannot be deprotonated such as N‐heterocyclic bases and phosphonate diesters…”

Multifunctional DyIII Enantiomeric Pairs Showing Enhanced Photoluminescences and Third-Harmonic Generation Responses through the Coordination Role of Homochiral Tridentate N,N,N-Pincer Ligands

“…The SHG response is only observed for noncentrosymmetric crystalline materials . In contrast, the THG process does not have a symmetry constraint of molecular structures . Theoretically, it can occur in any crystalline material with or without inversion symmetry.…”