In an attempt to add ligands to the sixth (axial) position of vanadyl bis-acetylacetonate: A unique tetranuclear vanadyl species European Journal of Chemistry 14 (4) (2023) 494-498 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2023 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. https://dx.doi.org/10.5155/eurjchem.14.4.494-498.2485 European Journal of Chemistry View Journal Online View Article Online In an attempt to add ligands to the sixth (axial) position of vanadyl bis-acetylacetonate: A unique tetranuclear vanadyl species 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 2 Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, 2050 Johannesburg, South Africa * 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.14.4.494-498.2485 Received: 23 October 2023 Received in revised form: 20 November 2023 Accepted: 01 December 2023 Published online: 31 December 2023 Printed: 31 December 2023 We have explored the interaction of [(acac)2V=O] (acac = acetylacetone) with a series of potential ligands which were chosen because of their expected ability to attach themselves onto its sixth (axial) position. Furthermore, some of the species chosen were expected to have the capability of linking pairs of [(acac)2V=O] molecules, thus creating magnetically coupled substances whose behavior would be interesting to document by magnetic as well as structural methods. Some of the synthetic results were surprising in that unexpected products were obtained which we had not envisioned; specifically, herein we describe a tetranuclear vanadyl cluster (Crystal data for C38H51N4O17ClV4: orthorhombic, space group Pca21 (no. 29), a = 26.4698(3) Å, b = 13.5167(2) Å, c = 12.7659(2) Å, V = 4567.44(11) Å3, Z = 4, μ(CuKα) = 7.842 mm-1, Dcalc = 1.53 g/cm3, 41277 reflections measured (6.538° ≤ 2Θ ≤ 137.892°), 7841 unique (Rint = 0.0428, Rsigma = 0.0421) which were used in all calculations; the final R1 was 0.0675 (I > 2σ(I)) and wR2 was 0.1641 (all data)), which is unusual in several aspects of its composition as well as its stereochemistry. Axial adducts Bridging vanadyls 1,3-Diazine ligands Vanadyl acetylacetonate Tetra-nuclear vanadyl compounds 5- and 6-Coordinated vanadyl species Cite this: Eur. J. Chem. 2023, 14(4), 494-498 Journal website: www.eurjchem.com 1. Introduction In the past [1-3], we have described studies of [(acac)2V=O] acting as a substrate for donor ligands capable of attacking the vanadium moiety via the sixth position. In [1], we documented the magnetic and spectroscopic consequences of such interac- tions for both solids and solutions and suggested that those results could be used as quantitative gauges of the electron- donor acceptor characteristics of such systems. Moreover, it is clear that the subject could be vast since (a) the acac ligands could be modified in an orderly fashion while retaining the potential donor skeleton constant; (b) the ligands could be retained while changing the potential donor; and (c) the solvent can play a role (being able to compete with the potential donor), as in the case of, e.g., pyridine. In the process of carrying out a series of such studies, we discovered tiny black crystals, which are the subject of this report. 2. Experimental 2.1. Preparation of bis-acetylacetonato-chlorido- hydroxydo-tetravanadyl(IV) complex (I) 0.500 g (1.89 mmoles) of vanadyl(acac)2 (C10H14O5V) and 0.600 g (7.5 mmoles) of pyrimidine (1,3-diazine) (C4H4N2) (3.97:1 mole ratio of the 1,3-diazine ligand to vanadyl) and 0.5 mL of 12 M HCl were added to 45 mL of toluene in a sealed glass pressure cell and heated at 130 °C in a silicone oil bath for 1.5 hours with stirring. The mixture was allowed to cool slowly, filtered through a sintered glass funnel, and the filtrate was transferred to three 20 mL vials, whose openings were sealed with parafilm through which was poked a number of small holes. The solutions were allowed to evaporate slowly. After 3- 4 days, a small number of black crystals of a vanadyl complex was formed containing four vanadiums, six acac ligands, two 1,3-diazine molecules bridging, a chloride anion and a hyd- roxide counter anion (which is bridging two of the vanadyls), having composition C38H51ClN4O17V4, which showed totally unexpected compositional and structural features, as described in what follows. Interestingly, in preparation, the addition of 12 M HCl led to the removal of one acac ligand per vanadyl(acac)2 (1,3-diazine) fragment and replaced these with one chloride and one OH– ion, to take care of the charge compensation; the OH– counter anion bridges the two central vanadyl moieties. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.14.4.494-498.2485 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.14.4.494-498.2485 mailto:rogerlal@newark.rutgers.edu http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.14.4.494-498.2485&domain=pdf&date_stamp=2023-12-31 Bernal and Lalancette / European Journal of Chemistry 14 (4) (2023) 494-498 495 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.4.494-498.2485 Table 1. Crystal data and structure refinement for compound I. Empirical formula C38H51N4O17ClV4 Formula weight (g/mol) 1075.03 Temperature (K) 100(2) Crystal system Orthorhombic Space group Pca21 a, (Å) 26.4698(3) b, (Å) 13.5167(2) c, (Å) 12.7659(2) Volume (Å3) 4567.44(11) Z 4 ρcalc (g/cm3) 1.53 μ (mm-1) 7.842 F(000) 2208.0 Crystal size (mm3) 0.21 × 0.144 × 0.127 Radiation CuKα (λ = 1.54178) 2Θ range for data collection (°) 6.538 to 137.892 Index ranges -30 ≤ h ≤ 31, -15 ≤ k ≤ 14, -14 ≤ l ≤ 15 Reflections collected 41277 Independent reflections 7841 [Rint = 0.0428, Rsigma = 0.0421] Data/restraints/parameters 7841/13/590 Goodness-of-fit on F2 1.062 Final R indexes [I≥2σ (I)] R1 = 0.0675, wR2 = 0.1512 Final R indexes [all data] R1 = 0.0854, wR2 = 0.1641 Largest diff. peak/hole (e.Å-3) 3.23/-1.28 Flack parameter 0.51(2) CCDC no. 2201346 Programs SAINT, APEX, SADABS [4-6], SHELXL [8], DIAMOND [11]. Figure 1. The tetra-nuclear species incorporates two vanadyls, each with 2 acac ligands, and has a 1,3-diazine in the sixth position. The two central vanadyl moieties, which have only one acac ligand each, are joined to the 'outer' vanadyl fragments via 1,3-diazine linkers. Finally, V3 is bonded exclusively by a Cl– counter anion, while V3 and V4 are bridged by the unique OH– (O17). Furthermore, a) no oxidation-reduction reaction was found, and b) HCl merely causes displacement of the acac ligands from the possible dimer, and the resulting fragments are linked to form the tetramer. 2.2. X-ray diffraction data collection and processing A suitable crystal was mounted on a Bruker-AXS SMART APEXII CCD diffractometer at 100(1) K. Cell dimensions and intensities were collected with CuKα radiation (λ = 1.54178 Å). Data processing, Lorentz polarization, and face-indexed numerical absorption corrections were performed using SAINT, APEX and SADABS computer programs [4-6]. The structure was solved by direct methods and refined by full-matrix least squares on F2, using the SHELXTL V6.14 program package [7- 9]. Non-H atoms were refined anisotropically. All H atoms were found on electron density difference maps; the methyl H atoms were placed in ideal staggered positions with C-H distances of 0.98 Å and Uiso(H) = 1.5Ueq(C); the methine Hs were placed in geometrically idealized positions and constrained to ride on their parent C atoms with C-H distances of 0.95 Å and Uiso(H) = 1.2Ueq(C). The crystal data, intensity data collection, and structure refinement details are summarized in Table 1. The X- ray data for I have been deposited in CCDC #2201346 [10]. 3. Results and discussion The molecule consists of two terminal fragments [(acac)2- V=O] whose sixth position (per vanadyl moiety) is filled with 1,3-diazine, as shown below in Figure 1. These two fragments are joined by an asymmetric species consisting of a dinuclear vanadyl cation moiety bridged by a hydroxide (O17) (for more details, see Figure 2); however, the two aforementioned fragments differ in that only V3 has a dangling Cl counter anion. Figure 2 shows the central vanadyl cations with the bridging hydroxide and the single terminal chloride anion. The distances in structure (I) are the following: V3-Cl1 = 2.284(4) Å, V3-O17 = 2.141(8) and V4-O17 = 1.731(8) Å. The distance of V-OH can be compared with 1.968 and 1.959 Å found in the literature [12]. The V-Cl distance from the literature ranges from 2.275 to 2.3031 Å [13]; the V-Cl distance in a bridging Cl (between two vanadyls) is 2.470-2.490 Å [14]. The selected bond distances and angles are given in Table 2. 496 Bernal and Lalancette / European Journal of Chemistry 14 (4) (2023) 494-498 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.4.494-498.2485 Table 2. Selected bond distances (Å) and angles (o) for compound I. Atom Atom Length (Å) Atom Atom Length (Å) V3 Cl1 2.284(4) V2 O9 2.010(9) V3 O17 2.141(8) V2 O10 1.972(8) V4 O17 1.731(8) V2 N4 2.452(12) V1 O1 1.602(10) V3 O11 1.665(10) V1 O2 1.990(9) V3 O12 2.044(10) V1 O3 2.012(10) V3 O13 1.956(9) V1 O4 1.985(9) V3 N3 2.077(11) V1 O5 2.027(9) V4 O14 1.602(12) V1 N1 2.477(11) V4 O15 1.981(10) V2 O6 1.592(9) V4 O16 1.967(9) V2 O7 1.994(9) V4 N2 2.225(11) V2 O8 1.977(11) Atom Atom Atom Angle (°) Atom Atom Atom Angle (°) O1 V1 O2 101.0(4) O10 V2 O9 89.0(3) O1 V1 O3 98.5(4) O10 V2 N4 79.6(4) O1 V1 O4 103.5(5) O17 V3 Cl1 82.1(2) O1 V1 O5 100.7(5) O11 V3 Cl1 90.2(4) O1 V1 N1 177.5(5) O11 V3 O17 169.8(4) O2 V1 O3 90.2(4) O11 V3 O12 99.2(5) O2 V1 O5 158.3(4) O11 V3 O13 96.8(4) O2 V1 N1 78.8(4) O11 V3 N3 93.7(4) O3 V1 O5 86.8(4) O12 V3 Cl1 168.3(4) O3 V1 N1 79.0(4) O12 V3 O17 87.6(4) O4 V1 O2 86.0(4) O12 V3 N3 82.8(4) O4 V1 O3 157.9(4) O13 V3 Cl1 97.9(3) O4 V1 O5 88.8(4) O13 V3 O17 91.0(4) O4 V1 N1 79.0(4) O13 V3 O12 88.0(4) O5 V1 N1 79.5(4) O13 V3 N3 167.0(4) O6 V2 O7 100.9(4) N3 V3 Cl1 89.7(3) O6 V2 O8 100.2(5) N3 V3 O17 79.5(4) O6 V2 O9 101.4(5) O17 V4 O15 148.2(4) O6 V2 O10 100.9(4) O17 V4 O16 93.3(4) O6 V2 N4 179.4(5) O17 V4 N2 89.9(4) O7 V2 O9 84.5(4) O14 V4 O17 112.8(5) O7 V2 N4 78.5(4) O14 V4 O15 98.3(6) O8 V2 O7 90.3(4) O14 V4 O16 100.9(5) O8 V2 O9 158.4(4) O14 V4 N2 89.1(5) O8 V2 N4 80.0(4) O15 V4 N2 83.6(4) O9 V2 N4 78.5(4) O16 V4 O15 87.3(4) O10 V2 O7 158.0(4) O16 V4 N2 167.4(4) O10 V2 O8 88.0(4) Figure 2. A view of the molecular species with labels for the geometrical factors which form part of the discussion that follows. Figure 3. ADAHUI [15] as drawn from the data in the CIF document in the CSD [10]. The 'bare' carbon atoms do not contain substituents because they are disordered CF3 fragments. Despite the disorder, it is an excellent model for what we envision as the process described above. Bernal and Lalancette / European Journal of Chemistry 14 (4) (2023) 494-498 497 2023 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.14.4.494-498.2485 Complex (I) may have been obtained as follows: 1,3-diazine attaches itself to the axial position of each of the two [(acac)2V=O] molecules (such attachments are illustrated elsewhere [1,3,15]), thereby forming a dimer in which the μ2 bridge is the 1,3-diazine, a particularly effective model being that of ADAHUI [15], which, for the convenience of the readers, we have redrawn as Figure 3, below; (b) as for the bridging hydroxide, these are ubiquitous in CCDC [16-18], as examples. 4. Conclusions The process by which (I) is formed is obviously very complex, involving several displacement and formation steps; our above suggestion is likely to be simplistic, but it is a reasonable description of the process of its formation based on known synthetic and structural studies of vanadyl (see refs. [1] and [3], and references therein). Meanwhile, we are attempting to trap intermediates, such as those suggested above, in an effort to unravel the process of formation of this unique species. Currently we are hindered in making magnetic or any other measurements by the lack of enough material, which, as mentioned above, consisted of only a few, very obviously (black) different, well-defined crystals. Recently, it has been pointed out [19], and references therein], that there are cases in which the selection of the space group is not straightforward because molecules containing flexible fragments pack better if they undergo relatively small torsional motions that lead to conformational disorder, for example, in [Co(en)3]I3·H2O [19], which had previously [21] been assigned the space group Pbca, and most recently proven to be a case of kryptoracemic crystallization in which the en ligands’ torsional angles required to be enantiomorphic pairs fail to do so. A detailed analysis of this problem is given in [20], where it was shown that lowering the space group from Pbca to one of its subgroups, Pca21, still resulted in an unacceptable chemical model, while further lowering the symmetry to that of P212121 completely cleared the problems encountered previ- ously [20]. Here, we refrain from describing these problems in more detail because they are long and complex and require additional illustrative figures already available in [19], to which the interested readers are directed. When collecting the data set described here, we solved the structure in the P1 space group and submitted the results to the PLATON program [21], resulting in a recommendation of Pbca as the correct space group, which we accepted. However, refinement in that space group resulted in another totally unacceptable model; therefore, we resorted to the previously successful procedure of changing the space group to Pca21, (an acceptable subgroup of Pbca), producing the model described in Figure 1. The bottom line is that the newly proposed model must make chemical sense and will do so if the appropriate space group is chosen, which, in this case, is Pca21. With respect to the Flack parameter [0.51(2)], it is not surprising that PLATON [21] suggests that the space group is Pbca, which we have demonstrated above to be incorrect. The core of the cluster in Figure 2 (and the graphical abstract) suggests that if the bridge were symmetrical (for example, two chlorides or two hydroxides), the resulting fragment would approximately have an inversion center. Additionally, Figure 1, which shows the entire molecule, shares the same charac- teristics. Therefore, the X-ray scattering power of such an “asymmetric” unit would skew the statistical distribution of x- rays such that the overall lattice would resemble that of a higher symmetry space group, such as suggested by PLATON, which recommended the use of Pbca. We have observed this situation on two different occasions in our own work: the above- mentioned [Co(en)3]I3·H2O [19], and in our article describing previous work with a Co(III) complex with L and D leucinato as ligands where the (L:D) ratios of the ligands were not (1:1) [22]. Acknowledgements The authors acknowledge support by NSF-CRIF Grant No. 0443538 for part of the purchase of the X-ray diffractometer. We thank Dr. Evrim Arslan for helping to prepare the complex. Supporting information CCDC-2201346 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/ data_request/cif, 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. CCDC compound codes: AQAPEP [13]; DECYEQ [14]; ADAHUI [15]; EZEPAA [16]; HOFYAE [17]; PASFIY [18]; ENCOIH [20]. Disclosure statement Conflict of interest: The authors have declared that there are no competing interests. Ethical approval: All ethical guidelines have been adhered to. CRediT authorship contribution statement Conceptualization: Roger Lalancette, Ivan Bernal; Methodology: Roger Lalancette, Ivan Bernal; Software: Roger Lalancette, Ivan Bernal; Validation: Roger Lalancette, Ivan Bernal; Formal Analysis: Roger Lalancette, Ivan Bernal; Investigation: Roger Lalancette, Ivan Bernal; Resources: Roger Lalancette, Ivan Bernal; Data Curation: Roger Lalancette, Ivan Bernal; Writing - Original Draft: Roger Lalancette, Ivan Bernal; Writing - Review and Editing: Roger Lalancette, Ivan Bernal; Visualization: Roger Lalancette, Ivan Bernal; Supervision: Roger Lalancette; Project Administration: Roger Lalancette, Ivan Bernal. Funding We acknowledge the National Science Foundation for NSF-CRIF Grant No. 0443538 for part of the purchase of the X-ray diffractometer. ORCID and Email Ivan Bernal bernalibg@gmail.com https://orcid.org/0000-0002-8168-5907 Roger Lalancette roger.lalancette@gmail.com rogerlal@newark.rutgers.edu https://orcid.org/0000-0002-3470-532X References [1]. Bernal, I.; Rieger, P. H. Solvent effects on the optical and electron spin resonance spectra of vanadyl acetylacetonate. Inorg. Chem. 1963, 2, 256–260. [2]. Arslan, E.; Lalancette, R. A.; Bernal, I. An unexpected and unusual V(5+)10 cluster containing oxygen bridges as well as six bidentate acetylacetonates. Struct. Chem. 2020, 31, 1217–1222. [3]. Arslan, E.; Bernal, I.; Lalancette, R. Vanadyl(acetylacetonate)2 mediated hydrolytic splitting of 1,3,5-triazine in a solution of toluene at 130 °C: The crystal structure of its axial formamide adduct. Eur. J. Chem. 2022, 13, 168–171. [4]. Bruker (2009). SAINT, Version 7.23a. Bruker AXS Inc., Madison, Wisconsin, USA. [5]. Bruker (2009). APEX2, Version 2.0–2. Bruker AXS Inc., Madison, Wisconsin, USA. [6]. Bruker (2009). 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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). 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. Preparation of bis-acetylacetonato-chlorido-hydroxydo-tetravanadyl(IV) complex (I) 2.2. X-ray diffraction data collection and processing 3. Results and discussion 4. Conclusions Acknowledgements Supporting information Disclosure statement CRediT authorship contribution statement Funding ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: