The incidence of kryptoracemic crystallization in [CoIII(tren)XY]+ compounds: The case of cis-[CoIII(tren)Cl2]Cl·H2O European Journal of Chemistry 11 (4) (2020) 314-318 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2020 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. http://dx.doi.org/10.5155/eurjchem.11.4.314-318.2022 European Journal of Chemistry View Journal Online View Article Online The incidence of kryptoracemic crystallization in [CoIII(tren)XY]+ compounds: The case of cis-[CoIII(tren)Cl2]Cl·H2O Mina Mikhael 1, Mary Hanna 1, Evana Halaka 1, Ivan Bernal 1,2 and Roger Lalancette 1,* 1 Carl A. Olson Memorial Laboratories, Department of Chemistry, Rutgers University, 73 Warren St., Newark, NJ, 07102 USA mtm205@scarletmail.rutgers.edu (M.M.), mh1164@scarletmail.rutgers.edu (M.H.), enh26@scarletmail.rutgers.edu (E.H.), rogerlal@newark.rutgers.edu (R.L.) 2 Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, 2050 Johannesburg, ZA, South Africa bernalibg@gmail.com (I.B.) * Corresponding author at: Carl A. Olson Memorial Laboratories, Department of Chemistry, Rutgers University, 73 Warren St., Newark, NJ, 07102 USA. e-mail: rogerlal@newark.rutgers.edu (R. Lalancette). 10.5155/eurjchem.11.4.314-318.2022 Received: 11 August 2020 Received in revised form: 09 October 2020 Accepted: 10 October 2020 Published online: 31 December 2020 Printed: 31 December 2020 We are evaluating the proposition that compounds with pronounced tendencies to crystallize as kryptoracemates contain molecular fragments responsible for such a property. Why Sohncke space groups display such a tendency is not currently known, but one such fragment is the [tris(2-aminoethyl)amine-N,N',N'',N'''] ligand when attached to cobalt(III). Therefore, proceeding to test the concept further, we examined the title compound and found a previously unknown kryptoracemic species, described in what follows. It seems then that the prescription has some merit and should be examined further inasmuch as guidelines for the occurrence of kryptoracemic crystallization are scant, if any exist. Crystal data for C6H20Cl3CoN4O: monoclinic, space group P21 (no. 4), a = 7.6672(3) Å, b = 15.7153(5) Å, c = 10.7170(4) Å, β = 92.964(2)°, V = 1289.59(8) Å3, Z = 4, T = 100(2) K, μ(CuKα) = 16.026 mm-1, Dcalc = 1.697 g/cm3, 13406 reflections measured (8.26° ≤ 2Θ ≤ 133.402°), 3976 unique (Rint = 0.0300, Rsigma = 0.0519) which were used in all calculations. The final R1 was 0.0220 (I > 2σ(I)) and wR2 was 0.0459 (all data). Flack parameter Kryptoracemates Metal compounds Molecular overlays Molecular conformations Tris(2-aminoethylamine) ligand Cite this: Eur. J. Chem. 2020, 11(4), 314-318 Journal website: www.eurjchem.com 1. Introduction In 1995 [1], a new mode of crystallization was described, which was labeled “kryptoracemic crystallization”, alluding to the fact that a racemic pair was “hidden or buried” (in a krypt) in a Sohncke space group. In time, additional examples were added to the list of crystals in that class, as example IKERUL02 [2], and in the appearance of two reviews [3,4] recording examples of coordination compounds, organometallic, and organic species. Pertinent additional comments can be found in reference [5]. Interested readers are encouraged to peruse sources [1-5] to get an idea of the classes of compounds under- going such crystallization modes, and of the variety of examples within those classes. In the past, we have explored the concept that various recognizable factors may influence kryptoracemic and related modes of crystallization of chemical species, using a rather broad approach, and while concentrating on just species of composition [CoN4(XY)], where N4 is any combination of amines occupying four sites of an octahedral Co(III) cation, we found many examples [3,5]. Here, we limit ourselves to [CoIII(tren)(X)(Y)]·[counter-anions, if any] to produce krypto- racemates, given that X and Y are monodentate ligands and tren = tris-(2-aminoethyl)amine. From the vantage point of our previous experiences, we have begun to discern certain patterns which may be useful, as orderly guides, in predicting crystallization pathways - a very desirable goal, if for no other reason than there are few, if any, orderly guides available now. Some very useful, but somewhat dated references are, for example, the monographs by Bernstein [6] and by Jacques, Collet & Wilen [7], which we recommend for those beginning inquiries of their own. Some attempts, limited to predicting crystallization modes by analogy to cases where it does occur, have been made previously, with limited but encouraging results in NIXGIK [8] and FILGIQ [9]. 2. Experimental 2.1. Materials The chemicals used are all available from Sigma-Aldrich and were used without further purification. 2.2. Synthetic procedure and crystal growth The synthesis of the title compound began with the preparation of the precursor [CoIII(tren)(NO2)2]Cl. This came ABSTRACT RESEARCH ARTICLE KEYWORDS http://dx.doi.org/10.5155/eurjchem.11.4.314-318.2022 http://www.eurjchem.com/ http://dx.doi.org/10.5155/eurjchem.11.4.314-318.2022 mailto:mtm205@scarletmail.rutgers.edu mailto:mh1164@scarletmail.rutgers.edu mailto:enh26@scarletmail.rutgers.edu mailto:rogerlal@newark.rutgers.edu mailto:bernalibg@gmail.com mailto:rogerlal@newark.rutgers.edu http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.11.4.314-318.2022&domain=pdf&date_stamp=2020-12-31 Mikhael et al. / European Journal of Chemistry 11 (4) (2020) 314-318 315 2020 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.11.4.314-318.2022 Table 1. Crystal data and structure refinement for cis-[CoIII(tren)Cl2]Cl·H2O. Empirical formula C6H18Cl2CoN4, Cl, H2O Formula weight 329.54 Temperature (K) 100(2) Crystal system Monoclinic Space group P21 a (Å) 7.6672(3) b (Å) 15.7153(5) c (Å) 10.7170(4) β (°) 92.964(2) Volume (Å3) 1289.59(8) Z 4 ρcalc (g/cm3) 1.697 μ (mm-1) 16.026 F(000) 680.0 Crystal size (mm3) 0.279 × 0.254 × 0.232 Radiation CuKα (λ = 1.54178 Å) 2Θ range for data collection (°) 8.26 to 133.402 Index ranges -8 ≤ h ≤ 9, -18 ≤ k ≤ 18, -12 ≤ l ≤ 12 Reflections collected 13406 Independent reflections 3976 [Rint = 0.0300, Rsigma = 0.0519] Data/restraints/parameters 3976/1/320 Goodness-of-fit on F2 0.888 Absorption correction Numerical Tmin, Tmax 0.054, 0.243 Final R indexes [I≥2σ (I)] R1 = 0.0220, wR2 = 0.0455 Final R indexes [all data] R1 = 0.0235, wR2 = 0.0459 (sin θ/λ)max (Å−1) 0.596 Largest diff. peak/hole (e Å-3) 0.37/-0.24 Flack parameter -0.004(3) H-atom treatment Treated by a mixture of independent and constrained refinement Computer programs SAINT [11], APEX2 [12], SADABS [13], SHELXL [14], DIAMOND [15] CCDC number 1978094 Figure 1. The two cations, chloride anions, and waters of crystallization as observed in cis-[CoIII(tren)Cl2]Cl·H2O. from the process of Uprety et al., 2018 [10]. 7.267 g of NaNO2 was added to a solution of 11.992 g of CoCl2·6H2O in 10 mL deionized water in a 100 mL side-arm flask. To this solution, 4.4 mL of 32% HCl and 7.5 mL tris-(2-aminoethyl)amine (tren) in 10 mL deionized water were added and placed in an ice bath until the solution was ice-cold. Then air was pulled through the solution for 2 hours to oxidize the cobalt(II) to cobalt(III). A yellow-brown product was observed. The product was collec- ted by suction filtration and recrystallized from a minimum amount of warm water (enough to dissolve the crystallized product); the crystals were then collected by suction filtration and dried. This product was then used to synthesize, cis- [CoIII(tren)Cl2]Cl·H2O, again following Uprety et al.’s process, 2018 [10]. 7.056 g of the above precursor were dissolved in the minimum amount of deionized H2O in a 100 mL beaker and 50 mL of 30% HCl were added to it. The solution was heated on a hot water bath all the way to dryness. The precipitate was dissolved in a minimum amount of warm deionized water. After leaving this solution to crystallize, it was isolated by vacuum filtration and washed with cold deionized water. Crystals appeared to be purple in color. Note that our product molecular formula is different from that described in Uprety’s paper [10]; our complex has H2O of crystallization instead of hydroxonium chloride, H7O3+Cl-. 2.3. X-ray diffraction study, solution and refinement of the data A crystal of compound cis-[CoIII(tren)Cl2]Cl·H2O was mounted on a Bruker APEXII X-ray diffractometer using graphite-monochromated CuKα (λ = 1.54178 Å) radiation, oriented, and data were collected using ω and φ scans. After data collection at 100 K using an Oxford Cryostream, the crystal was brought to 296 K and reoriented. The cell was essentially the same, except for slight changes due to increased temperature. Data processing, Lorentz-polarization, and face- indexed numerical absorption corrections were performed using SAINT, APEX, and SADABS computer programs [11-13]. The structure was solved by direct methods and refined by full- matrix least-squares methods on F2, using the SHELXTL V6.14 program package (Figure 1) [14]. All non-hydrogen atoms were refined with anisotropic displacement parameters; the H atoms of the nitrogen atoms and the oxygen atoms were refined positionally. For cis-[CoIII(tren)Cl2]Cl·H2O, the structural and refinement parameters and the CCDC deposition number can be found in Table 1. 316 Mikhael et al. / European Journal of Chemistry 11 (4) (2020) 314-318 2020 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.11.4.314-318.2022 Table 2. Bond lengths for cis-[CoIII(tren)Cl2]Cl·H2O. Atom Atom Length (Å) Atom Atom Length (Å) Atom Atom Length (Å) Co1 N4 1.939(3) Co2 Cl3 2.2459(10) N5 C9 1.499(5) Co1 N3 1.940(3) Co2 Cl4 2.2833(11) N5 C8 1.512(5) Co1 N1 1.944(3) N4 C6 1.499(5) C2 N2 1.495(5) Co1 N2 1.973(3) N3 C4 1.482(5) C2 C1 1.513(5) Co1 Cl2 2.2771(11) N8 C12 1.499(5) N7 C10 1.501(5) Co1 Cl1 2.2783(11) N1 C5 1.489(5) C4 C3 1.516(5) Co2 N5 1.946(3) N1 C1 1.494(5) C10 C9 1.530(5) Co2 N8 1.948(3) N1 C3 1.514(4) C6 C5 1.525(5) Co2 N7 1.951(4) N6 C7 1.477(5) C12 C11 1.521(5) Co2 N6 1.956(3) N5 C11 1.496(5) C8 C7 1.503(6) Table 3. Bond angles for cis-[CoIII(tren)Cl2]Cl·H2O. Atom Atom Atom Angle (°) Atom Atom Atom Angle (°) Atom Atom Atom Angle (°) N4 Co1 N3 93.80(15) N7 Co2 N6 94.42(15) C11 N5 C9 111.9(3) N4 Co1 N1 84.71(14) N5 Co2 Cl3 174.06(11) C11 N5 C8 111.9(3) N3 Co1 N1 87.92(14) N8 Co2 Cl3 93.83(10) C9 N5 C8 109.6(3) N4 Co1 N2 170.59(15) N7 Co2 Cl3 92.50(11) C11 N5 Co2 106.4(2) N3 Co1 N2 90.27(15) N6 Co2 Cl3 87.81(10) C9 N5 Co2 107.0(2) N1 Co1 N2 86.97(14) N5 Co2 Cl4 93.73(10) C8 N5 Co2 109.8(2) N4 Co1 Cl2 92.01(10) N8 Co2 Cl4 88.09(11) N2 C2 C1 109.6(3) N3 Co1 Cl2 86.84(10) N7 Co2 Cl4 87.16(11) C2 N2 Co1 110.4(2) N1 Co1 Cl2 173.62(10) N6 Co2 Cl4 178.42(11) C10 N7 Co2 111.4(3) N2 Co1 Cl2 96.68(11) Cl3 Co2 Cl4 92.12(4) N3 C4 C3 107.7(3) N4 Co1 Cl1 89.10(11) C6 N4 Co1 112.9(2) N7 C10 C9 109.1(3) N3 Co1 Cl1 176.57(11) C4 N3 Co1 110.9(3) N4 C6 C5 109.5(3) N1 Co1 Cl1 94.17(10) C12 N8 Co2 110.9(2) N8 C12 C11 109.2(3) N2 Co1 Cl1 87.13(11) C5 N1 C1 110.7(3) N1 C1 C2 109.2(3) Cl2 Co1 Cl1 91.24(4) C5 N1 C3 108.6(3) N5 C11 C12 109.3(3) N5 Co2 N8 87.42(13) C1 N1 C3 112.8(3) C7 C8 N5 110.9(3) N5 Co2 N7 86.75(14) C5 N1 Co1 108.1(2) N5 C9 C10 108.5(3) N8 Co2 N7 172.22(15) C1 N1 Co1 108.0(2) N1 C5 C6 108.1(3) N5 Co2 N6 86.37(14) C3 N1 Co1 108.5(2) N6 C7 C8 107.1(3) N8 Co2 N6 90.34(15) C7 N6 Co2 110.8(3) N1 C3 C4 110.8(3) Figure 2. Center of mass is at the intersection of the dotted lines. The center of mass is located at 0.2453, 0.2416, 0.2333. The bond lengths, bond angles, and hydrogen bonding values are summarized in Tables 2-4. Figures were drawn using the graphics program DIAMOND [15]. In this article, six-letter acronyms used by CSD [16], such as IKERUL, are provided for the convenience of the interested reader who wishes to further examine the data provided here. Thus, access to the CSD entry will be automatic. 3. Results and discussion A view of the contents of the asymmetric unit in cis- [CoIII(tren)Cl2]Cl·H2O is given in Figure 1. Figure 2 depicts the packing of two pairs of the cations alone. Their center of mass is located at 0.2453, 0.2416, 0.2233 (see further, Figure 3). Note that in the polar space group, P21, the y-coordinate of the origin is arbitrary, and must be fixed. The fact that there is a pseudo-inversion center relating the cations does not limit that relationship to them alone. The entire unit cell, depicted in Figure 3, also demonstrates that such a relationship exists for the overall contents of the lattice. In fact, the lattice, as a whole, is closer to a true inversion center of a higher symmetry supergroup. Note in that regard that the Flack parameter (Table 1) assures that the space group belongs in the Sohncke class. Using an overlay technique, Figure 4 illustrates the stereo- chemical difference(s) between the cations present in an overlay of the cations in cis-[CoIII(tren)Cl2]Cl·H2O. For compa- rison, Figure 5 depicts a comparable overlay for the cations in IKERUL02, which was one of the earliest kryptoracemates described [1,2]. Inasmuch as it is difficult to observe differences in superimposed 3D objects when depicted in 2D, we illustrate their difference by the torsional angles of their respective Tren ligands in Table 5. While there is a very close racemic relationship between the first two sets, the last pair is very far from that, given that there is no inversion of sign. Thus, effectively, they differ from being a racemic pair by 77.86°. Mikhael et al. / European Journal of Chemistry 11 (4) (2020) 314-318 317 2020 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.11.4.314-318.2022 Table 4. H-bonding interactions in cis-[CoIII(tren)Cl2]Cl·H2O. D-H…A D-H (Å) H…A (Å) D…A (Å) ∠ D-H…A (°) N4-H6…O2i 0.83(4) 2.17(5) 2.977(5) 163(4) N4-H5…Cl3 0.92(5) 2.42(4) 3.263(3) 152(4) N3-H4…Cl6ii 1.00(4) 2.40(4) 3.307(3) 150(3) N3-H3…O2i 0.83(4) 2.12(5) 2.901(5) 156(4) N8-H12…Cl6iii 0.92(4) 2.54(4) 3.380(3) 154(3) N8-H11…Cl2 0.88(4) 2.56(4) 3.413(3) 165(4) N6-H8…Cl2 0.87(4) 2.70(4) 3.426(4) 143(4) N6-H7…Cl5ii 1.00(4) 2.24(4) 3.231(4) 169(3) N2-H2…Cl1 0.83(4) 2.54(4) 2.938(4) 110(3) N2-H1…Cl6ii 0.86(4) 2.40(4) 3.244(4) 170(4) N7-H10…Cl5ii 0.76(4) 2.61(5) 3.302(4) 153(4) N7-H9…O1ii 0.96(4) 2.38(4) 3.223(6) 146(3) O1-H13…Cl1 0.93(7) 2.24(7) 3.164(3) 175(6) O1-H14…Cl5ii 1.01(6) 2.42(7) 3.401(4) 164(5) O2-H15…Cl5ii 0.77(5) 2.40(5) 3.160(3) 167(5) O2-H16…Cl6iv 0.77(5) 2.33(5) 3.088(3) 172(5) Symmetry codes: i = x, y, z+1; ii = -x+1, y-1/2, -z+1; iii = x-1, y, z+1; iv = x-1, y, z. Table 5. Torsional angles of tren observed for cations 1 and 2. Atoms Angle (°) Atoms Angle (°) N1-C1-C2-N2 -41.28 N5-C8-C7-N6 41.28 N1-C3-C4-N3 41.43 N5-C11-C12-N8 -40.10 N1-C5-C6-N4 38.30 N5-C9-C10-N7 39.56 Figure 3. Packing diagram of the unit cell for cis-[CoIII(tren)Cl2]Cl·H2O. The center of mass located at 0.5028, 0.4915, 0.5072 is a pseudo-inversion center which is remarkably close to ½, ½, ½. Dotted lines have been omitted to avoid cluttering. This diagram displays the characteristic kryptoracemic packing described previously [1-5]; e.g., the center of mass is expected to be near a special position of a centrosymmetric supergroup. Figure 4. Overlay of cation 2 onto cation 1. The differences appear tiny and it is difficult to separate the images of chemically related atoms, except for some of the hydrogen atoms. Figure 5. The stereochemical differences between the cations present in IKERUL02, which was one of the earliest kryptoracemates described [2]. 318 Mikhael et al. / European Journal of Chemistry 11 (4) (2020) 314-318 2020 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.11.4.314-318.2022 4. Conclusions We began with the premise that experimentally observed examples of interesting modes of crystallization of a given substance may be used as clues for which other related species may crystallize likewise [8]; and having the example of IKERUL02 [2] as a guide, we tested that premise with cis- [CoIII(tren)Cl2]Cl·H2O. It is encouraging that both are krypto- racemates, as attested by the Flack parameter test, see Table 1. How far this concept may be extended can only be ascertained by experiments, which we are currently examining with the tren derivatives of 3d metals, using variations of the mono- dentate ligands at the fifth and sixth positions, as well as variations of the charge-compensating anions. Acknowledgements We acknowledge the National Science Foundation for NSF- CRIF Grant No. 0443538 for part of the purchase of the X-ray diffractometer. Supporting information CCDC-1978094 contains the supplementary crystallo- graphic data for this paper. These data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/, or by e- mailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033. Disclosure statement Conflict of interest: The authors have declared that no competing interests exist. Author contributions: Mina Mikhael, Mary Hanna, and Evana Halaka are undergraduate students who prepared the complexes under the direct supervision of Roger Lalancette. Ivan Bernal and Roger Lalancette wrote the manuscript. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. ORCID Mina Mikhael http://orcid.org/0000-0002-6630-7553 Mary Hanna http://orcid.org/0000-0001-7124-3702 Evana Halaka http://orcid.org/0000-0001-8565-3892 Ivan Bernal http://orcid.org/0000-0002-8168-5907 Roger Lalancette http://orcid.org/0000-0002-3470-532X References [1]. Bernal, I. The American Crystallographic Association Annual Meeting, Abstract 4a. 1. e, Montreal, Quebec, Canada, 1995. [2]. Saha, M. K.; Fronczek, F. R.; Rees, L. H.; Bernal, I. Inorg. Chem. Commun. 2003, 6, 983-988. [3]. Bernal, I.; Watkins, S. F. Acta Cryst. C 2015, 71, 216-221. [4]. Fabian, L.; Brock, C. P. Acta Cryst. B 2010, 66, 94-103. [5]. Bernal, I.; Lalancette, R. A. C. R. Chimie 2015, 18, 929-934. [6]. Bernstein, J. Polymorphism in Molecular Crystals, New York: Oxford University Press, 2002. [7]. Jacques, J.; Collet, A.; Wilen S. Enantiomers, Racemates and Resolutions, New York: John Wiley & Sons, 1981. [8]. Bernal, I.; Cai, J.; Massoud, S. S.; Watkins, S. F.; Fronczek, F. R. J. Coord. Chem. 1996, 38(1-2), 165-181. [9]. Cai, J.; Myrczek, J.; Chun. H.; Bernal, I. J. Chem. Soc., Dalton. Trans. 1998, 24, 4155-4160. [10]. Uprety, B.; Arderne, C.; Bernal, I. Eur. J. Inorg. Chem. 2018, 47, 5058- 5067. [11]. Bruker (2008). SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. [12]. Bruker (2009). APEX2. Bruker AXS Inc., Madison, Wisconsin, USA. [13]. Sheldrick, G. M. SADABS. University of Gottingen, Germany, 1996. [14]. Sheldrick, G. M. Acta Cryst. C 2015, 71, 3-8. [15]. Diamond - Crystal and Molecular Structure Visualization, Crystal Impact - H. Putz and K. Brandenburg GbR, Kreuzherrenstr. 102, 53227 Bonn, Germany [16]. Groom, C. R.; Bruno, I. J.; Lightfoot, M. P.; Ward, S. C. Acta Cryst. B 2016, 72, 171-179. Copyright © 2020 by Authors. This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at http://www.eurjchem.com/index.php/eurjchem/pages/view/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). https://www.ccdc.cam.ac.uk/structures/ mailto:data_request@ccdc.cam.ac.uk http://orcid.org/0000-0002-6630-7553 http://orcid.org/0000-0001-7124-3702 http://orcid.org/0000-0001-8565-3892 http://orcid.org/0000-0002-8168-5907 http://orcid.org/0000-0002-3470-532X http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Materials 2.2. Synthetic procedure and crystal growth 2.3. X-ray diffraction study, solution and refinement of the data 3. Results and discussion 4. Conclusions Acknowledgements Supporting information Disclosure statement ORCID References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: