Key indicators: single-crystal X-ray study; T = 150 K; mean (Co-O) = 0.003 Å; R factor = 0.035; wR factor = 0.103; data-to-parameter ratio = 12.2.Single crystals of Co 3 (PO 4 ) 2 Á4H 2 O, tricobalt(II) bis[orthophosphate(V)] tetrahydrate, were obtained under hydrothermal conditions. The title compound is isotypic with its zinc analogue Zn 3 (PO 4 ) 2 Á4H 2 O (mineral name hopeite) and contains two independent Co 2+ cations. One Co 2+ cation exhibits a slightly distorted tetrahedral coordination, while the second, located on a mirror plane, has a distorted octahedral coordination environment. The tetrahedrally coordinated Co 2+ is bonded to four O atoms of four PO 4 3À anions, whereas the six-coordinate Co 2+ is cis-bonded to two phosphate groups and to four O atoms of four water molecules (two of which are located on mirror planes), forming a framework structure. In addition, hydrogen bonds of the type O-HÁ Á ÁO are present throughout the crystal structure. Related literatureBesides crystals of the title compound, crystals of (2000). The structure of the isotypic mineral hopeite was first described by Liebau (1965). ExperimentalCrystal data

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Single crystals of Co3(PO4)2·H2O, tricobalt(II) bis­[ortho­phosphate(V)] monohydrate, were obtained under hydro­thermal conditions. The compound is the second polymorph of this composition and is isotypic with its zinc analogue, Zn3(PO4)2·H2O. Three independent Co2+ cations are bridged by two independent orthophosphate anions. Two of the metal cations exhibit a distorted tetra­hedral coordination while the third exhibits a considerably distorted [5 + 1] octa­hedral coordination environment with one very long Co—O distance of 2.416 (3) Å. The former cations are bonded to four different phosphate anions, and the latter cation is bonded to four anions (one of which is bidentate) and one water mol­ecule, leading to a framework structure. Additional hydrogen bonds of the type O—H⋯O stabilize this arrangement.

BackgroundPrevious studies have reported that higher serum uric acid (SUA) levels are associated with higher bone mineral density (BMD) in men and postmenopausal women, and lower risk of fragility fracture in men. However, whether this association is also present in patients with rheumatoid arthritis (RA) has not yet been investigated.ObjectivesTo examine the association of SUA levels with BMD and osteoporosis in postmenopausal women with RA.MethodsWe retrospectively evaluated 447 postmenopausal female RA patients (mean age 61.1 years) who underwent measurement of L1–4, femoral neck, and total hip BMD using dual energy X-ray absorptiometry, in addition to SUA levels at a university rheumatology centre in South Korea between 2004 and 2017. Osteoporosis was defined as a T-score of ≤−2.5 according to the World Health Organisation classification.ResultsThe median (interquartile range) SUV level was 4 (3.3–4.8) mg/dL. The mean (±SD) L1–4, femoral neck, and total hip BMD were 0.93±0.16 g/cm2, 0.75±0.12 g/cm2, and 0.81±0.12 g/cm2, respectively, and the frequencies of osteoporosis in the spine, hip, and either site were 25.6%, 15.9%, and 32.5%, respectively. SUA levels were positively correlated with L1–4 (ρ=0.102, p=0.032), femoral neck (ρ=0.123, p=0.01), and total hip BMD values (ρ=0.146, p=0.002) and body mass index (ρ=0.231, p<0.001), and negatively correlated with glomerular filtration rate (ρ=−0.363, p<0.001) in Spearman correlation analysis. In multivariable linear regression models adjusted for confounding factors, SUA levels showed a significant positive association with femoral neck BMD (β=0.0099, p=0.015) and total hip BMD (β=0.0118, p=0.01) but not with L1–4 BMD (β=0.0086, p=0.159) as shown in table 1. In addition, multivariable logistic analysis revealed that the third (OR=0.44, p=0.038) and fourth SUA quartiles (OR=0.37, p=0.021) were associated with lower risk of hip osteoporosis, as compared with the first SUA quartile. However, this association was not observed in lumbar spine osteoporosis.Abstract AB1000 – Table 1Linear regression models evaluating the association between serum uric acid levels and bone mineral density in postmenopausal women with rheumatoid arthritisIndependent variablesDependent variablesUnivariable modelMultivariable model Unstandardized β (SE)p-value*Unstandardized β (SE)p-value Serum uric acid, mg/dLFemoral neck BMD0.0125 (0.0045)0.0060.0099 (0.004)0.015Serum uric acid, mg/dLTotal hip BMD0.0138 (0.0048)0.0040.0118 (0.0045)0.01Serum uric acid, mg/dLL1–4 BMD0.0127 (0.0063)0.0440.0086 (0.0061)0.159*Estimated using stepwise multivariable linear regression models adjusting for age, BMI, DAS28-ESR, cumulative GCs dose, disease duration and eGFRConclusionsHigher SUA levels were associated with a reduced risk of low BMD and osteoporosis at hip in postmenopausal women with RA, but no significant association between SUA levels and lumbar spine BMD was found. Our data suggests that uric acid may act as a protective factor against hip bone loss in RA patients.Disclosure of InterestNone declared