Extreme Molecular Orientations in a Dimorphic System: Polar/Centric and Polar/Polar Cogrowth Crystal Architectures

Abstract

4-Pyrrolidinopyridyl)bis(acetylacetonato)zinc(II) forms perfectly polar as well as centrosymmetric crystal structures depending sensitively on the solvent and the rate of crystallization. Semiempirical computational modeling of molecular clusters, incorporating solvation effects, highlights the delicate balance of energetics involved in the solvent polarity preference of the extreme structures. A suitable choice of solvents provides crystals exhibiting an unusual cogrowth of polar/centric as well as polar/polar domains. This material provides a vivid illustration of the subtle nature of supramolecular assembly leading to extreme organizational motifs and opens up possibilities of realizing novel multidomain architectures in crystals.Organization of molecules in crystals results from a complex, often subtle interplay of intermolecular interactions, making accurate ab initio prediction of crystal structures a very difficult proposition. 1 The problem is considerably compounded in the case of polymorphic structures where, even under apparently identical conditions as in concomitant polymorphs, 2 the same molecule organizes in different crystalline assemblies. Particularly intriguing would be the case of polymorphs that manifest grossly different packing motifs. Such a situation could, in principle, be encountered in the context of centrosymmetric and noncentrosymmetric polymorphic structures of dipolar molecules, the latter being of potential interest in quadratic nonlinear optical applications. 3 Although several instances of such polymorphism are known, 4 noncentrosymmetric lattices often involve small deviations from a centrosymmetric organization, 5 leading to descriptions such as "approximately centrosymmetric". 4 Optimal molecular orientations for applications such as phase-matched second harmonic generation (SHG) or electrooptic effect call for specific design strategies. 6,7 A case that merits special attention is the formation of perfectly polar molecular assemblies 8 wherein every molecular dipole makes exactly 0°angle with respect to a specific crystallographic direction. This would be the opposite extreme of the commonly encountered centrosymmetric formation, 9 which by analogy can be described as constituted of "perfectly antiparallel" molecular dipoles with equal numbers making 0 and 180°a ngles with respect to specific crystallographic directions. Perfectly polar crystals are ideal candidates for molecular ferroelectric, piezoelectric, or pyroelectric materials as well as for electrooptic applications. Strategies such as cocrystallization, 7 salt formation, 10 and host-guest complexation 11 have been developed for achieving polar molecular assemblies. We have reported "self-poling" in a single component metal-organic system leading to perfectly polar molecular organization. 12 In the general context of supramolecular assembly and polymorphism in particular, it would be of considerable interest if a molecule was to form centrosymmetric as well as perfectly polar lattices. We report here such a scenario...

Novel zinc complexes with acetyloacetonate, imidazole and thiolate ligands: Crystal structure of a zinc complex of relevance to farnesyl transferase

“…The hydrogen-bonding interaction NHÁ Á ÁO between the molecules of 2 changes the ideally parallel alignment of molecules described in the previously studied zinc acetylacetonates with additional N-ligands [22,23,29] into a slightly zigzagged chain (Fig. 3b).…”

“…2b. There are two possible geometries of penta-coordinated zinc acetylacetonates: a distorted trigonal bipyramid or screw'-shaped, and square-pyramidal [21][22][23]29]. Contrary to the most of previously described geometries of penta-coordinated zinc acetyloacetonates, which are best approximated as a distorted trigonal bipyramid [21][22][23], Zn(II) in 2 has square-pyramidal coordination (Fig.…”

“…Zinc ion is surrounded by two O atoms from a chelating acetyloacetonate, N atom from isopropylimidazole and S from tritert-butoxysilanethiolate in a distorted tetrahedral geometry (Fig. 2a) with typical bonds lengths [12,14,[21][22][23]. Additionally one of the tert-butoxy groups approaches the zinc ion opposite to one of the acetylacetonate oxygens at a distance of approximately 2.95 Å.…”

Investigation of an Unusual Crystal Habit of Hydrochlorothiazide Reveals Large Polar Enantiopure Domains and a Possible Crystal Nucleation Mechanism

“…Monte-Carlo simulations suggest that the formation of monodomain polar crystals is unfeasible,w hile the growth of opposite polar domains within polar single crystals is very likely during crystal nucleation in order to reduce the net electric polarity of the growing crystals. [27] Although this molecule is not chiral, it crystallizes in both centrosymmetric (C2/c)and non-centrosymmetric polar (Fdd2) forms.Bipyramidal crystals of the polar form could be split along the (010) cleavage plane to reveal two domains of equivalent size but opposite polarity.T he calculated dipole moment of ZNPPA( B3LYP/6-31G(d,p)) is 10.0 D, aligned along the c axis of this space group,resulting in the net cancellation of crystal polarity in Figure 5b. Different orientations of unit-cell dipole moments in twinned polar crystals that exhibit conjoined growth and where the dipole moments of opposite twin domains mutuallyc ancel:a)Opposite polarity orientation in R and S wings of HCT twin crystal determined in this study;b )Observed antiparallel orientation of electric polarity in aZNPPA twin crystal.…”

Growing Molecular Crystals on Inorganic Crystals: Polar Structure Induced by Noncentrosymmetric Templates

“…Figure 3 shows the SEM images of ZNPPA crystals formed on the surface of K 2 SO 4 and NaBrO 3 crystals (see the http://www.wiley-vch.de/contents/jc_2002/2008/z704031_s.pdf for the images of other crystals); the morphologies of the dominant crystals, 1 and 2 in the respective cases, are highlighted. Dimorph 2 is often found to occur19 as co‐growth crystals 18. Some of the dominant template faces on which growth occurs are: KDP (100); K 2 SO 4 (0$\bar 1$ 1); Ba(BrO 3 ) 2 ⋅H 2 O (11$\bar 1$ ); KBrO 3 (001); NaBrO 3 [tetrahedral (111), cuboid ($\bar 1$ 00)].…”