STRUCTURE TOPOLOGY AND HYDROGEN BONDING IN MARTHOZITE, Cu2+[(UO2)3(SeO3)2O2](H2O)8, A COMPARISON WITH GUILLEMINITE, Ba[(UO2)3(SeO3)2O2](H2O)3
Bibliographic record
Abstract
The crystal structure of marthozite, Cu 2+ [(UO 2 ) 3 (SeO 3 ) 2 O 2 ] (H 2 O) 8 , a 6.9879(4), b 16.4537(10), c 17.2229(10) A, V 1980.2(3) A 3 , Pbn 2 1 , Z = 4, D calc = 4.37 g/cm 3 , has been solved by direct methods and refined to an R index of 5.7% for 4364 observed (| F o | > 4σ F ) reflections collected with a four-circle diffractometer fitted with Mo K α X-radiation and a CCD detector. There are three unique U sites, each occupied by U 6+ with two short U –O uranyl bonds (1.76–1.82 A) and coordination numbers of [8], [7] and [7], respectively. There are two unique Se sites, each occupied by Se 4+ and coordinated by three O atoms ( Se –O ≈ 1.70 A), forming a triangular pyramid with Se at the apex, indicative of stereoactive lone-pair behavior in Se 4+ . There is one Cu site, occupied by Cu 2+ in octahedral coordination by four (H 2 O) groups ( Cu –H 2 O ≈ 2.0 A) and two O atoms ( Cu –O ≈ 2.4 A). The structural unit is a sheet of composition [(UO 2 ) 3 (SeO 3 ) 2 O 2 ], comprised of chains of edge-sharing (Uϕ n ) polyhedra extending along [100] that are cross-linked in the [001] direction by (SeO 3 ) groups; this sheet is topologically identical to the structural unit in guilleminite, Ba [(UO 2 ) 3 (SeO 3 ) 2 O 2 ] (H 2 O) 3 . Adjacent sheets are linked through interstitial Cu 2+ cations via Cu 2+ –O apical bonds and via H bonds that involve both (H 2 O) groups bonded to Cu 2+ and interstitial (H 2 O) groups not bonded to any cation. The principal differences between marthozite and guilleminite involve the interlayer species. In guilleminite, the Ba atom is centrally positioned with respect to the chain of (UO n ) polyhedra, whereas in marthozite, the Cu 2+ atom is located off the pseudo-mirror plane of the chain of (UO n ) polyhedra. This differential positioning of the interstitial cations results in an intersheet separation in marthozite that is nearly 1 A greater than that in guilleminite, despite the fact that Ba (in guilleminite) is much larger than Cu 2+ (in marthozite). The H-bond arrangement in marthozite is very different from that in guilleminite. In marthozite, there are eight unique interlayer (H 2 O) groups; four of these (H 2 O) groups bond directly to Cu 2+ and four are held in the structure solely by H bonds. In guilleminite, there are two unique interlayer (H 2 O) groups, both of which bond to the interlayer Ba atoms.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".