 along the b-axis. Along the c-axis, the BF4- links the [Co(NH3)6]3+ cations as well. Additional [Co(NH3)6]3+ cations are not shown because the component species are diminished in size excessively.
Figure 1 The packing of (A) in projection down the c-axis, slightly canted so as to clearly reveal the presence of both the BF4- and SiF62- ions, both of which are ordered. All figures in this report were generated using the program DIAMOND [12].
Figure 2 All three ions lie at positions with symmetry -43m and the BF4- and SiF62- anions have only partial, but orderly, occupancies at the sites shown above. One fluorine from the BF4- at the lower left-hand was selected, and the entire anion removed; likewise, we then destroyed the SiF62- anion at upper right. The procedure can be reversed with analogous results.
Figure 3 Another view of the contents of the lattice of [Co(NH3)6](BF4)(SiF6). The cations sit at an inversion center; therefore, the BF4- and SiF62- anions extend the columns of the cobalt cations in all directions, shown here along the b- and c-axes, only. However, the overall (3D) packing diagram is so complex that additional components would merely clutter the figure.
In Figure 4, we describe the environment around the unique cation in the asymmetric unit of the orthorhombic space group Pnma, at 100K.
Figure 4 The cation sits at an inversion center as is obvious from the labeling system. It is heavily hydrogen bonded by the fluoride counteranions, which also hydrogen bond the waters of hydration. Many bonds to the amine hydrogen atoms were omitted to avoid unnecessary cluttering. The complexity of the packing in these crystals is shown in Figure 5, below.
Figure 5 F1, F2, F3 and the waters (O1) link rows of cations along the b-axis, while the F3 anions link adjacent rows in this projection down the a-axis as well; note also that there is an inversion center located halfway between the pair of waters at the center of the diagram. Therefore, the structure consists of layers such as the two depicted above.
This structure has the BF4- anions linked together through the agency of the ammonium cation, which in turn is H-bonded to one of the Cl ions in the lattice joining alternating rows, as displayed below in Figure 6.
Figure 6 Packing in the structure of (C), showing the multiple H bonds in this network. Note that the function of the ammonium cations (N3) is linking strings of tetrafluoroborate anions, which in turn stitch together strings of [cobalt cations + Cl- ] fragments.
Figure 7 In this case, the packing differs from that of the BF4- because of the additional waters of hydration that act as bridges between ammonium cations (N14) and –NH3 ligands to the cobalts. Additionally, three-water clusters link fluosilicates to the cobalt cations via ammonium cations.
The complexity of the hydrogen-bonded network in both (C) and (D) is such that an effort in displaying all those interactions in a single picture simply leads to figures so cluttered that they defeat the purpose of conveying a description of the overall network. Thus, the figures were designed to show examples of all types of hydrogen-bonded interactions present in each. Hopefully, we succeeded in so doing.
Table 1 X-Ray structural parameters for (A), (B), (C), and (D).
90., 90., 90.
90., 90., 120.
90., 97.635(1), 90.
No. of params.
Computer programs: Bruker (2009) SAINT, APEX, SADABS, Sheldrick (2015) SHELXL, Putz & Brandenburg (2019) DIAMOND.
We are still surprised that the simple trifluoride was not isolated before, since in reality, the use of Teflon-ware for chemistry of fluorides is very old and some chemistry was done earlier using glassware coated with waxes. It simply took the current procedure (see Experimental) for the crystals to form from a stoichiometric solution of the relevant ions by starting with the iodide salt of the cobalt hexamine and adding AgF to precipitate the AgI salt. Starting with the trichloride salt of cobalt hexamine is not advantageous because of the greater solubility of AgCl. Note the desirability of darkness while working with silver!
The unexpectedly isolated double salt of SiF62- and BF4- with [Co(NH3)]3+ was described in the section on X-ray crystallography. An interesting and important result of our analysis is that the ratio of Si:B, obtained by crystallographically refining the occupancies of those anionic species produced a number very close to that present in Pyrex glass; namely, the composition of both Corning 7740 and Schott 8830 is given as 80.6% SiO2; 12.6% B2O3; 4.2% Na2O, 2.2% Al2O3; other traces, constitute only ca. 0.4%. To us, it is remarkable that we were able to determine its composition, by X-ray diffraction analysis of (A), especially since we were unaware of the composition of those crystals. The resulting co-crystal is unusual since the Si:B ratio is approximately 4:1. Thus, a study of the phase diagram of such a system would be interesting because of the possibility that there may be other well-defined crystalline phases with Si:B ratios such as 3:1, 2:1, etc. This would be especially so if those phases resulted in well-behaved, orderly co-crystals, given the importance of co-crystallization to the pharmaceutical industry [13].
We have prepared and examined the structures of (NH4)[Co(NH3)6](BF4)(2Cl), (C) and (NH4)[Co(NH3)6]2(SiF6)3(Cl) · 3H2O, (D) while attempting to prepare, initially [Co(NH3)6]F3 [B], and preparing instead the double salt, (A). In both cases we failed and, instead, isolated the double salts (C) and (D) - an unexpected bonus because it opens up an interesting area of phase diagrams and double salts analyses, which may be useful in a clearer understanding of that aspect of crystallization phenomena, which is still largely empirical in nature, as perusal of Bernstein’s [13] monograph illustrates.
We acknowledge the National Science Foundation for NSF-CRIF Grant No. 0443538 for part of the purchase of the X-ray diffractometer.
Figure S1: ORTEP for [Co(NH3)6](BF4)(SiF6), (A): Ellipsoids are drawn at 40% probability level.
Figure S2: ORTEP for [Co(NH3)6](F3) · 2H2O, (B): Ellipsoids are drawn at 40% probability level.
Figure S3: ORTEP of (NH4)[Co(NH3)6](BF4)(2Cl), (C): Ellipsoids are drawn at 40% probability level.
Figure S4: ORTEP of (NH4)[Co(NH3)6]2(SiF6)3(Cl) · 3H2O, (D): Ellipsoids are drawn at 30% probability level.
Sandra Mikhael, Maria Shawky, Gulraiz Hashmi are undergraduate students who prepared the complexes under direct supervision of RAL. IB and RAL wrote the manuscript.
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Inorganic Chemistry Structural Database (ICSD) - FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbHHermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Gimenez-Huguet M. Single crystal X-ray studies of chromium(III) and cobalt(III) hexammine halides. Thesis, Lafayette, IN: Purdue University; 1961.
Shevchenko YN, Davidenko NK, Yatsimirskii KB. Thermal dissociation of hexamminocobalt(II)- and hexamminochromium(III) fluorides. Zh Neorg Khim. 1975; 20: 406-412.
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Bruker. SADABS. 2016, Bruker AXS Inc., Madison, WI.
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Putz H, Brandenburg K. DIAMOND Version 4.4.1. 2017. GbR, Kreuzherrenstr. 102, 53227 Bonn, Germany.
Bernstein J. Polymorphism in Molecular Crystals. New York: Oxford, Clarendon Press; 2002.Various Artists
Man of Somebody’s Dreams: A Tribute to Chris Gaffney
(Yep Roc)
US: 26 May 2009
UK: 25 May 2009
I didn’t really know who Chris Gaffney was beyond a much-mentioned obscurity I