Three new layered Co-Ca phosphonates are reported, namely, [CoCa(notpH 2 )(H 2 O) 2 ]X·nH 2 O (CoCa-X·nH 2 O; X = Cl -, NO 3 -, PF 6 -), where notpH 6 is 1,4,7-triazacyclononane-1,4,7triyltris(methylenephosphonic acid) [C 9 H 18 N 3 (PO 3 H 2 ) 3 ]. The layer topology of these compounds are identical to that of [CoCa(notpH 2 )(H 2 O) 2 ]ClO 4 ·nH 2 O (CoCa-ClO 4 ·nH 2 O). The most significant difference lies in the counter-anions, which not only have different size and shape but also show different capabilities towards hydrogen bonding. Consequently, the number of lattice water molecules and the hydrogen-bond networks be- [a]