. 2022 Jul 19;25(8):104763. doi: 10.1016/j.isci.2022.104763

Table 2.

The averaged distance between ion ( $M$ ) and the oxygen atoms of water molecules in the first hydration shell ( ${\bar{r}}_{M - O}$ ) and coordination number (CN) observed via experiments, effective ionic radii (EIR) and CN, and the differences between ${\bar{r}}_{M - O}$ and EIR for alkali earth metal ions

Ion ( $M)$	${\bar{r}}_{M - O}$ (Å)	CN	EIR (Å) (Shannon, 1976)	CN (Shannon, 1976)	${\bar{r}}_{M - O} - E I R$ (Å)	Method
Ra²⁺	2.87 ± 0.06 (This study)	9.2 ± 1.9 (This study)	1.48	8	1.39	EXAFS
Ba²⁺	2.79 ± 0.02 (Yamaguchi et al., 2021)	8.0 ± 1.9 (Yamaguchi et al., 2021)	1.42	8	1.37	EXAFS
Sr²⁺	2.64 ± 0.01 (Yokoyama, 1995)	8.1 ± 0.1 (Yokoyama, 1995)	1.26	8	1.38	XRD and ND
Ca²⁺	2.40 ± 0.04 (Yokoyama, 1995)	6.3 ± 0.7 (Yokoyama, 1995)	1.00	6	1.40	XRD and ND
Mg²⁺	2.09 ± 0.04 (Yokoyama, 1995)	6.0 ± 0.1 (Yokoyama, 1995)	0.72	6	1.37	XRD

XRD and ND means X-ray diffraction and neutron diffraction, respectively. The values of Sr²⁺, Ca²⁺, and Mg²⁺ reported in the literature (Yokoyama, 1995) were average of the reported values in literature (Ohtaki and Radnai, 1993; Persson et al., 1995).