Research and Teaching: D8 QUEST ECO – The ECOlogical and ECOnomical Solution

Crystallography is becoming a popular topic in the undergraduate curriculum. The technique demonstrates that the molecular structure is three-dimensional (3D), unlike the 2D illustrations shown in the classrooms and available in the text books. Crystallography explains ideas such as bond strength, atomic radius, and chemical structure, for various types of bonds including simple covalent bonds, Jahn-Teller distortions, and hydrogen bonding motifs, in a clear and definitive manner that is not seen in other methods. There is a need for versatile and inexpensive solutions to develop X-ray crystallography laboratories at the organizations that have been unable to provide support to these laboratories. This article deals with the Bruker D8 QUEST ECO instrument which is not expensive, leaves only a small environmental footprint, and can be flexibly adapted for original and creative science (Figure 1).

D8 QUEST ECO with PHOTON 50 detector.

Figure 1. D8 QUEST ECO with PHOTON 50 detector.

A Full Featured System — Shutterless Mode Built-In

The D8 QUEST ECO is a 3-circle goniometer. It has an innovative CMOS-based PHOTON 50 detector and a sealed-tube X-ray source (Figure 2), housed in a full-sized safety and radiation enclosure. It eliminates the need for external cooling of the X-ray source, as it possesses a 1000 W closed-cycle X-ray generator, avoiding expensive and high-maintenance water chillers in the laboratory.

Sensitive PHOTON 50 detector with 50 cm2 active area.

Figure 2. Sensitive PHOTON 50 detector with 50 cm2 active area.

The molybdenum X-ray tube is provided with TRIUMPH graphite monochromator to maximize the intensity at the crystal. To examine absolute configurations in light-atom structures the device has a copper X-ray tube. The latest CMOS technology is used with the PHOTON 50 detector to enable exacting and efficient collection of data. This 50 x 100 mm2 sensor is two times larger than the usual CCD sensors, but is half of the sensor used in the PHOTON 100 detector. The PHOTON 50 works in a shutterless mode, meaning no extra time is needed for processing the frames, allowing data collections to be completed in shorter time periods. This enables the device to be used in a teaching laboratories so that many experiments can be taught during one lab period. The instrument is also helpful for research labs, and can replace obsolete instruments including imaging plate systems, first-generation CCDs, and four-axis diffractometers with scintillation point detectors.

The Versatile Solution

High resolution data collections are enabled for both molybdenum and copper radiation, through the use of full 2-theta swing of the goni¬ometer. Both large and small unit cells can be viewed, as the detector distance can be adjusted between 35 to 180 mm.

The features of the D8 QUEST ECO are:

  • No external chillers required, as it is an air-cooled instrument
  • Full-safety enclosure, meeting the latest standards
  • Long life of sealed tube ensured, as the tube is operated at 1000 W
  • Full range of motion in 2-theta, phi and omega, fixed-chi goniometer
  • Large sensor area of 5 x 10 cm2 with taper-less 1:1 imaging devoid of blind areas
  • High detective collection efficiency (DCE) provides excel¬lent data in shortened time period
  • High sensitivity for better signal-to-noise ratios
  • Air-cooling reduces energy consumption and noise generation
  • No dead-time, as shutterless data acquisition helps in fast data acquisition
  • Low power operation enables prolonged lifetime and high reliability
  • 3-year warranty

Results

A wide range of samples can be handled using the D8 QUEST ECO, including known samples from a teaching laboratory, or new sample prepared in a research laboratory for the first time. To illustrate this point further, experiments were conducted by employing the D8 QUEST ECO and a standard D8 QUEST. The two instruments had fixed-chi goniometers and molybdenum-sealed tube sources. The experiments involved identical data collection techniques and X-ray exposures. For crystallography, the APEX3 suite was utilized to control the instruments, refine the structures and to generate reports. Data was collected using the shutterless feature of the detectors.

Aspirin

Aspirin can be readily synthesized in an organic chemical laboratory. It is usually purified by crystallization to provide crystals appropriate for structure determination. By employing XPRESSO technology and the D8 QUEST ECO (Table 1), an experiment can be conducted in only two steps: crystal alignment in the instrument; and feeding in the proposed chemical formula. The instrument determines the best data collection values, reduces data collection, and solves and refines the structure. In this instance, multiple sets of data were collected in only 11 minutes. Shutterless data collection, aided by the PHOTON 50 detector, removes detector overheads, shortens data collection time, and allows easy completion of the experiment in a teaching laboratory. Additionally the data can be provided before solution and refinement, enabling them to fully learn about the experiment. The D8 QUEST ECO allows complete hands-on control, in addition to automation through XPRESSO. Figure 3 displays PHOTON 50 images obtained from data collection for aspirin, and Figure 4 shows the structure of aspirin measured with D8 QUEST ECO.

Table 1. Experiment performed on Aspirin using D8 QUEST ECO and D8 QUEST.

Aspirin D8 QUEST ECO D8 QUEST
Crystal size [mm3] 0.30 x 0.40 x 0.80 0.30 x 0.40 x 0.80
Generator power 1000 W 1500 W
Detector size 50 x 100 mm2 100 x 100 mm2
No. frames 688 688
Data collection XPRESSO XPRESSO
Experiment 1 s / ½° 1 s / ½°
Time 11.4 min 11.4 min
Resolution 0.84 Å 0.84 Å
Redundancy 2.94 6.33
Completeness 97.9 % 99.1
Rint 2.29 % 2.37 %
R1 (obs. refl.) 4.02 % 3.76 %
wR2 (all data) 10.69 % 9.92 %

PHOTON 50 images from data collection for aspirin. Each image covers 64° at 4cm crystal-detector distance.

Figure 3. PHOTON 50 images from data collection for aspirin. Each image covers 64° at 4cm crystal-detector distance.

Structure of aspirin determined with D8 QUEST ECO.

Figure 4. Structure of aspirin determined with D8 QUEST ECO.

Ni(imidazole) Complex

Nickel imidazole complexes are studied for their magnetic properties. Some complexes show zero-field splitting, which depends on the distortions seen in a 3D hydrogen bonding network (Figure 5). Hexakis(1-methyl-imidazole)nickel(II) chloride dihydrate has been the subject of two crystallographic research studies (Figure 6). One of them used an Enraf-Nonius CAD4 diffractometer, and the other a Siemens P4 diffractometer (Table 2). D8 QUEST ECO was employed to re-analyze the structure of this compound. Additionally the structure was examined, using a D8 QUEST fitted with a PHOTON 100 detector. The results obtained from the CMOS APS detectors were compared with those obtained from the earlier research, which utilized point detectors.

Table 2. Experiment performed on Ni(imidazole) complex using D8 QUEST ECO, D8 QUEST, Siemens P4 diffractometer and an Enraf-Nonius CAD4 diffractometer

Ni complex D8 QUEST ECO D8 QUEST Siemens P4 Enraf-Nonius CAD4
Crystal size [mm3] 0.30 x 0.35 x 0.56 0.30 x 0.35 x 0.56 0.15 x 1.0 x 1.1 0.23 x 0.25 x 0.25
Generator power 1000 W 1500 W
Detector size 50 x 100 mm2 100 x 100 mm2 Serial detector Serial detector
No. frames 915 672 n/a n/a
Experiment 1 s / 1° 1 s / 1°
Time 15.3 min 11.2 min hours hours
Resolution 0.75 A 0.75 A 0.70 A 0.84 A
Redundancy 8.169 8.815 1.286 1.054
Completeness 99.8 % 99.6
Rint 5.03 % 4.32 % 5.00 % 1.2 %

PHOTON 50 images from data collection for Ni(imidazole) complex. Each image covers 64° at 4cm crystal-detector distance.

Figure 5. PHOTON 50 images from data collection for Ni(imidazole) complex. Each image covers 64° at 4cm crystal-detector distance.

Structure of hexakis(1-methyl-imidazole)nickel(II) chloride dihydrate, determined with D8 QUEST ECO (Hydrogens of Ni cation deleted for clarity).

Figure 6. Structure of hexakis(1-methyl-imidazole)nickel(II) chloride dihydrate, determined with D8 QUEST ECO (Hydrogens of Ni cation deleted for clarity).

Although the time needed to complete the earlier experiments has not been reported, it is possible that they took one day or more to complete. Only 15 minutes was required for data collection, when shutterless data collection and PHOTON detectors were used. Considerable improvement was seen in quality measures R1 and wR2, and Rint value was identical, even when measured reflections were six times more.

Conclusion

The D8 QUEST ECO is an economical research-grade device, and since it is air-cooled it can be operated at two-thirds of the power of a traditional sealed-tube model, while yielding ideal results. The active area is 5 x 10 cm2, and the PHOTON 50 detector’s CMOS sensor allows compact strategies, shortening the time needed to conduct experiments, and improving laboratory throughput. The examples illustrated in the article show that the experiments can be performed efficiently and quickly. With the advanced APEX3 software, the instrument provides quick learning for a beginner, and at the same time it is also ideal for an expert crystallographer since it possesses all the necessary tools and capabilities. The XPRESSO plug-in allows a complete experiment to be fully performed, right from indexing until the final report, through the centering of the crystal and feeding of a chemical formula – an ideal scenario for an undergraduate laboratory. The D8 QUEST ECO can serve a laboratory looking for an economical instrument as its first system, or a laboratory aiming for capacity expansion.

This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.

For more information on this source, please visit Bruker AXS Inc.

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